e-binder for 2013 CEETEP workshop 123

Additional Resources on this DVD amp Internet relevant to Build a Better Wall

VIDEOS mdashin the folder on this DVD 3 VIDEOS_Earthquake amp Tsunami

gt DEMO_Build a Better Wall_Butlermov and the clip VIIDEO_Building_design-Narrated_USGSmov

DEMO available on the Internet httpwwwiriseduhqprogramseducation_and_outreachvideosM

ANIMATIONS mdashare in the folder 2 ANIMATIONS_Earthquake amp Tsunami gt Structural Design amp EQ Damage

INTERNET LINKSUSGS has video demonstrations of this activity are available from httpsicariuswrusgsgovwoodenbuildings

Design a bridge add structural elements then set off an earthquake Interactive program allows you to design the Bay Bridgeand then destroy it with an earthquake Select bridge types seismic safety features and earthquake type httpeduwebcomportfoliobridgetoclassroomengineeringforhtml

Make a QuakemdashEarthquake Simulator Add quake-proofing technology to a building then subject is to increasing magnitude earthquakes httptlcdiscoverycomconvergencequakesinteractivesmakeaquakehtml

ActivitymdashBuild a Better WallDesigning structural elements for earthquake-hazard mitigation through building strength Learn about shear strengthldquoTeacher Background ReadingmdashBuilding Engineeringrdquo can be found on last page of this activity

This activity is from Unit 4 Can Buildings Be Made Safer of the five-part ldquoSeismic Sleuthsrdquo earthquake guide published by AGUFEMA (httpwwwfemagov

libraryviewRecorddoid=3558) Unit 4 is ldquodesigned to allow students to construct an understanding of how buildings respond to earthquakes Lessons on building design and how earthquake forces act on various designs provide students with information on how to build earthquake resistant structures Students then apply this knowledge by constructing testing devices and testing their designs This unit is critical for developing studentsrsquo understanding of why buildings collapse and what can be done to make buildings saferrdquo

Science Standards

Systemsbull Inquirybull Science Technology amp Societybull Forces amp Motionbull Energy amp Matter Transformation bull amp ConservationPredictability amp Feedbackbull

124

A G U F E M A 233 S E I S M I C S L E U T H S

42

Structural ReinforcementThe Better Building

RA T I ONA L EStudents will learn how diagonal braces shear walls and rigidconnections strengthen a structure to carry forces resulting fromearthquake shaking

FOC US QUES T I ONSHow may the structure of a building be reinforced to make it betterable to withstand earthquake shaking

OBJ EC T I V ES

Students will

1 Recognize some of the structural elements of a building

2 Describe how the horizontal and vertical structural elementscarry the horizontal and vertical loads of a building

3 Describe how diagonal braces shear walls and rigidconnections provide paths for the horizontal load resultingfrom an earthquake

4 Observe how added structural elements strengthen a model wallto withstand shaking TEACHING CLUES AND CUES

M A T ERI A L SFor the teacher Materials for one model wall

Jumbo craft sticks areavailable at craft andhobby stores They arelarger than ice cream

Master 42a Building a Model Wall

21 jumbo craft sticks about 15 cm x 2 cm x 2 mm thick

sticks about the size of tonguedepressors

Electric drill with 316 bit

Goggles for eye protection

1 piece of thin wood (about 2 mm thick) 45 cm x 6 cm (about18 in x 2 in)

You may want to buildthis model and the onein Lesson 43 at thesame time andintroduce them

1 piece of sturdy wood (2 x 6) for a base about 45 cm (18 in)long

16 machine bolts 10 x 24 about 2 cm long (75 in)

16 machine screw nuts 10 x 24

32 washers 8

both in the same class period Thiswould allow two groups to beactively engaged with the modelsof the same time

MATERIALSTeacher for one model wall

104857710485771048577 104857710485771048577 104857710485771048577104857710485771048577 104857710485771048577104857710485771048577 104857710485771048577i1048577k1048577 1048577104857710485771048577104857710485771048577 104857710485775 10485771048577 x 104857710485771048577 x 1048577 10485771048577 10485771048577hi1048577k 104857710485771048577i1048577k1048577 1048577104857710485771048577104857710485771048577 10485771048577he 1048577ize 104857710485771048577 1048577104857710485771048577ng1048577e dep1048577e104857710485771048577104857710485771048577

104857710485771048577 10485771048577e1048577104857710485771048577i1048577 d1048577i10485771048577 wi10485771048577h 3104857710485776rdquo 1048577i10485771048577

104857710485771048577 104857710485771048577gg1048577e1048577 1048577104857710485771048577 eye p10485771048577104857710485771048577e104857710485771048577i10485771048577n

104857710485771048577 10485771048577 pie1048577e 104857710485771048577 10485771048577hin w1048577104857710485771048577d (1048577104857710485771048577104857710485771048577 1048577 10485771048577 10485771048577hi1048577k) 45 10485771048577 x 6 10485771048577 (1048577104857710485771048577104857710485771048577 104857710485778 in x 1048577 in)

104857710485771048577 10485771048577 pie1048577e 104857710485771048577 10485771048577104857710485771048577dy w1048577104857710485771048577d (1048577 x 6) 1048577104857710485771048577 1048577104857710485771048577e 1048577104857710485771048577104857710485771048577 45 10485771048577 (104857710485778 in) 104857710485771048577ng

104857710485771048577 104857710485776 104857710485771048577hine 1048577104857710485771048577104857710485771048577 104857710485770 x 10485774 1048577104857710485771048577104857710485771048577 1048577 10485771048577104857710485771048577ng (75 in)

104857710485771048577 104857710485776 104857710485771048577hine 104857710485771048577ew n1048577104857710485771048577 104857710485770 x 10485774

104857710485771048577 10485771048577 w10485771048577he10485771048577 8

104857710485771048577 7 10485771048577104857710485771048577 w1048577104857710485771048577d 104857710485771048577ew1048577 104857710485771048577 1048577 pie1048577e1048577 1048577104857710485771048577104857710485771048577ing e10485771048577h 1048577pp104857710485771048577x i1048577104857710485771048577e1048577y 10485775 10485771048577 (104857710485770 in) 104857710485771048577ng

Reinforcing elements for one wall

104857710485771048577 10485771048577 pie1048577e 104857710485771048577 10485771048577hin w1048577104857710485771048577d (1048577104857710485771048577104857710485771048577 10485771048577 10485771048577hi1048577k 1048577104857710485771048577he 104857710485771048577104857710485771048577 104857710485771048577i1048577k1048577) 10485770 10485771048577 x 1048577 10485771048577

104857710485771048577 10485771048577 pie1048577e 104857710485771048577 1048577igh10485771048577weigh10485771048577 104857710485771048577d10485771048577104857710485771048577d 1048577104857710485771048577104857710485771048577104857710485775 10485771048577 x 104857710485775 10485771048577 (1048577 1048577i10485771048577104857710485771048577e 1048577e10485771048577 10485771048577h1048577n 6 in 1048577q104857710485771048577e)

104857710485771048577 8 10485771048577104857710485771048577 p1048577pe1048577 1048577104857710485771048577p1048577 1048577104857710485771048577 10485771048577104857710485771048577en w1048577104857710485771048577d1048577nd 104857710485771048577d10485771048577104857710485771048577d

For each small group

104857710485771048577 1048577ne 1048577e10485771048577 104857710485771048577 10485771048577he 1048577104857710485771048577ve 10485771048577pp1048577ie1048577 i1048577 10485771048577hey 10485771048577ee10485771048577h 10485771048577i1048577ding 1048577 104857710485771048577de1048577 w104857710485771048577

104857710485771048577 1048577ne 104857710485771048577py 104857710485771048577 M1048577104857710485771048577e1048577 410485771048577 L104857710485771048577d P104857710485771048577h1048577W104857710485771048577k1048577hee10485771048577

104857710485771048577 Pen1048577 1048577nd pen1048577i10485771048577

Watch video lecture on the next page

e-binder for 2013 CEETEP workshop 125A G U F E M A 234 S E I S M I C S L E U T H S

7 small wood screws VOCABULARYreinforcing elements for one wall

2 pieces of string each approximately 25 cm (10 in) long

Braces or Bracingstructural elements builtinto a wall to addstrength These may be1 piece of thin wood (about as thick as the craft sticks) 20 cm x

2 cm (about 8 in x 1 in)

1 piece of lightweight cardboard about 15 cm x 15 cm (a littleless than 6 in square)

8 small paper clamps to fasten wood and cardboard

for each small group

One set of the above supplies if they are each building a modelwall

One copy of Master 42b Load Paths Worksheet

Pens and pencils

P ROC EDURETeacher Preparation

Assemble the model wall following the diagram on Master 42aBuilding a Model Wall and try it out before class Be sure the boltsare just tight enough to hold the structure upright when no force isapplied

A Introduction

Tell students that this lesson is designed to demonstrate how thestructural elements of a wall carry forces The activity deals withthree structural elements that carry the lateral shear forces causedby ground shaking during an earthquake diagonal bracing shearwalls and rigid connections It is designed around an apparatuscalled the model wall Remind the students that this is a modeldesigned to demonstrate only certain characteristics of real walls

B Lesson Development

1 Show students the model and tell them that it represents part ofthe frame of a building Describe the components of the wall andask them ldquoWhat holds this wall uprdquo The answer is in theinteraction of the vertical and horizontal elements but try to keepthe students focused on discovery since in this activity they willsee the architectural principles demonstrated Explain to studentsthat what they refer to as weight will be called the force of gravityin this lesson

2 Now ask students to predict what would happen if you quicklypushed the base of the wall simulating an earthquake Remind themthat an earthquake may cause ground shaking in many directionsbut for now we are modeling shaking in one direction only

3 Divide the class into the same seismic engineering teams (SETs)as for Lesson 1 and give each group one copy of Master 42b LoadPaths Worksheet Invite students to take turns investigating themodelrsquos response in their small groups

made of various materials andconnected to the building and eachother in various ways Their abilityto withstand stress depends on thecharacteristics of the materials andhow they are connectedLead the sum of vertical forces(gravity) and horizontal forces(shear forces) acting on the massof a structure The overall load isfurther broken down into the loadsof the various parts of the buildingDifferent parts of a building aredesigned and constructed to carrydifferent loadsLead path the path a load or forcetakes through the structuralelements of a buildingRigid connections connectionsthat do not permit any motion ofthe structural elements relative toeach otherShear force force that actshorizontally (laterally) on a wallThese forces can be caused byearthquakes and by wind amongother things Different parts of awall experience different shearforcesShear walls walls added to astructure to carry horizontal (shear)forces These are usually solidelements and are not necessarilydesigned to carry the structurersquosvertical loadStructural elements or structuralfeatures a general term for all theessential non-decorative parts of abuilding that contribute structuralstrength These include the wallsvertical column supports horizontalbeams connectors and braces

MOVIE Robert Butler demonstrates and discusses the building model Touch to playVideo not linked See previous page for location of video clip as QuickTime movie

126

A G U F E M A 235 S E I S M I C S L E U T H S

TEACHING CLUES AND CUESThis activity is designedas a demonstration oras a group activity Ifyou decide to haveeach

group build a model wall you willneed more materials

Encourage students tochoose roles within theirSETs and later reporttheir results by role with

the technician reporting the datathe engineer describing thecalculations the scientist explainingthe relationships and thecoordinator facilitating

Students may try bothpushing the structuredirectly and moving thetable Shaking the table

a Instruct one student in each group to push at the bottom of themodel from the lower right or left side (When pushed just fastenough the model should collapse at the first floor only) Askstudents why the other floors didnrsquot collapse (The first floorcollapsed because it was too weak to transfer enough horizontalforce to move the upper stories It could not transfer the shakingto the upper stories)

b Direct studentsrsquo attention to the load path diagrams on Master42b and explain that pushing the base of the building is equivalentto applying force horizontally to the upper stories A force appliedhorizontally to any floor of a building is called the shear force onthat floor Shear forces can be caused by the ground shaking of anearthquake as well as by high winds Invite students to carefullyapply horizontal forces at different points on the model tosimulate earthquake shaking (Earthquakes affect buildings atground level)

4 Ask students how they could add structural elements to create apath for the load to follow to the ground when strong forces actupon the structure Help the students discover the effect of adding ashear wall diagonal bracing and rigid connections using stringcardboard extra wood and clamps as in the diagrams on themaster On each of the three diagrams provided have students drawa force arrow (a vector) and trace the path the force takes to theground

5 Challenge students to design and build three differentarrangements of the six structural elements depicted on theworksheet Each time they modify the design they must modify thediagram to show the new load path Check each structure anddiagram until you are sure that students understand the conceptsWhen a structure is well reinforced you should be able to push onthe upper story and slide the whole structure without any of thewalls failing

6 Either have the groups discuss the questions on the master withone student recording each grouprsquos response or ask individualstudents to write responses to specific questions After all thegroups finish the questions have a reporter for each SET presentits response to one of the questions Allow the class to come tosome consensus on their responses to that question then proceedto another group until all the questions have been discussed

C ConclusionAs a closing activity challenge a volunteer to remove an element(a craft stick) that according to the load path diagram is notcarrying any load Have the student unbolt one end of that elementand push the reinforced structure to see if it holds It will if theload path is correct

Finally help the students connect the behavior of their model wallsto their mental images of real buildings during an earthquakeEmphasize that the back and forth horizontal component (orshearing) of ground shaking is the force most damaging to buildingsBuildings are primarily designed to carry the downward pull of

on which the structure rests wouldsimulate the transfer of energy fromthe ground to the building

e-binder for 2013 CEETEP workshop 127

A G U F E M A 236 S E I S M I C S L E U T H S

gravity but to withstand earthquake shaking they need to be able towithstand sideways or horizontal pushes and pulls

A DA P T A T I ONS A ND EX T ENS I ONS1 Challenge students to find the minimum number of diagonalbraces shear walls or rigid connections that will ensure horizontalstability in their models

2 Invite students to design construct and test other structuralelements that could make buildings earthquake-resistant such assquare rigid connections Some might try putting wheels or sleds onthe bottom of their buildings

3 If you have some very interested students you may give themaccess to all your building supplies and challenge them to design andconstruct larger structures Ask students to consider how they coulddesign a building so that the ground shaking does not transfer to thebuilding There are new technologies that allow the ground tomove but not the building One of these is called base isolationHave students research this topic in periodicals (See UnitResources)

128

M A S T E R P A G E Building a Model Wall

A G U F E M A 238 S E I S M I C S L E U T H S

42a

1 Stack 21 craft sticks one on top of the other Wrap a rubber band around the center to hold themtogether Using a 316 in bit carefully drill a hole through all the sticks at once 1 cm from the end of thestack Drill slowly to avoid cracking the wood

2 Select the thinner of the two large pieces of wood (45 cm x 6 cm) Drill a 316 in hole 1 cm from one endand 1 cm from the edge Measure the distance between the holes drilled in the craft sticks and space threemore 316 in holes at that distance 1 cm from the edge so that a total of four holes are drilled (seeillustration)

3 Use the small wood screws to mount this piece of wood on the base (the 2 x 6) fastening at the bottomand in the center Leave the pre-drilled holes sticking up far enough above the top to accept the drilled craftsticks

4 Using the bolts washers and nuts assemble the craft sticks to build a model wall

5 Experiment with tightening bolts and washers until they are just tight enough for the wall to stand on itsown

e-binder for 2013 CEETEP workshop 129

M A S T E R P A G E Load Paths Worksheet

A G U F E M A 240 S E I S M I C S L E U T H S

42bName__________________________________________________________

Date____________________

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first______________________________________________________________

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structuralfailure_________________________________________________________________________________________________________________________________________________________________

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

130

M A S T E R P A G E

A G U F E M A 241 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

e-binder for 2013 CEETEP workshop 131

M A S T E R P A G E

A G U F E M A 242 S E I S M I C S L E U T H S

C Summary

1 What is a load path

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

3 How many additional elements did you need to add

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

4 Why doesnrsquot the force take some path other than the one you diagrammed

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

132

M A S T E R P A G E Load Paths Worksheet (key)

A G U F E M A 244 S E I S M I C S L E U T H S

42b

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first The first floor

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structural failure The first floor has to carry all the load to the upper stories It transfersforces to move the upper stories

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

e-binder for 2013 CEETEP workshop 133

M A S T E R P A G E

A G U F E M A 245 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

e-binder for 2013 CEETEP workshop 125A G U F E M A 234 S E I S M I C S L E U T H S

7 small wood screws VOCABULARYreinforcing elements for one wall

2 pieces of string each approximately 25 cm (10 in) long

Braces or Bracingstructural elements builtinto a wall to addstrength These may be1 piece of thin wood (about as thick as the craft sticks) 20 cm x

2 cm (about 8 in x 1 in)

1 piece of lightweight cardboard about 15 cm x 15 cm (a littleless than 6 in square)

8 small paper clamps to fasten wood and cardboard

for each small group

One set of the above supplies if they are each building a modelwall

One copy of Master 42b Load Paths Worksheet

Pens and pencils

P ROC EDURETeacher Preparation

Assemble the model wall following the diagram on Master 42aBuilding a Model Wall and try it out before class Be sure the boltsare just tight enough to hold the structure upright when no force isapplied

A Introduction

Tell students that this lesson is designed to demonstrate how thestructural elements of a wall carry forces The activity deals withthree structural elements that carry the lateral shear forces causedby ground shaking during an earthquake diagonal bracing shearwalls and rigid connections It is designed around an apparatuscalled the model wall Remind the students that this is a modeldesigned to demonstrate only certain characteristics of real walls

B Lesson Development

1 Show students the model and tell them that it represents part ofthe frame of a building Describe the components of the wall andask them ldquoWhat holds this wall uprdquo The answer is in theinteraction of the vertical and horizontal elements but try to keepthe students focused on discovery since in this activity they willsee the architectural principles demonstrated Explain to studentsthat what they refer to as weight will be called the force of gravityin this lesson

2 Now ask students to predict what would happen if you quicklypushed the base of the wall simulating an earthquake Remind themthat an earthquake may cause ground shaking in many directionsbut for now we are modeling shaking in one direction only

3 Divide the class into the same seismic engineering teams (SETs)as for Lesson 1 and give each group one copy of Master 42b LoadPaths Worksheet Invite students to take turns investigating themodelrsquos response in their small groups

made of various materials andconnected to the building and eachother in various ways Their abilityto withstand stress depends on thecharacteristics of the materials andhow they are connectedLead the sum of vertical forces(gravity) and horizontal forces(shear forces) acting on the massof a structure The overall load isfurther broken down into the loadsof the various parts of the buildingDifferent parts of a building aredesigned and constructed to carrydifferent loadsLead path the path a load or forcetakes through the structuralelements of a buildingRigid connections connectionsthat do not permit any motion ofthe structural elements relative toeach otherShear force force that actshorizontally (laterally) on a wallThese forces can be caused byearthquakes and by wind amongother things Different parts of awall experience different shearforcesShear walls walls added to astructure to carry horizontal (shear)forces These are usually solidelements and are not necessarilydesigned to carry the structurersquosvertical loadStructural elements or structuralfeatures a general term for all theessential non-decorative parts of abuilding that contribute structuralstrength These include the wallsvertical column supports horizontalbeams connectors and braces

MOVIE Robert Butler demonstrates and discusses the building model Touch to playVideo not linked See previous page for location of video clip as QuickTime movie

126

A G U F E M A 235 S E I S M I C S L E U T H S

TEACHING CLUES AND CUESThis activity is designedas a demonstration oras a group activity Ifyou decide to haveeach

group build a model wall you willneed more materials

Encourage students tochoose roles within theirSETs and later reporttheir results by role with

the technician reporting the datathe engineer describing thecalculations the scientist explainingthe relationships and thecoordinator facilitating

Students may try bothpushing the structuredirectly and moving thetable Shaking the table

a Instruct one student in each group to push at the bottom of themodel from the lower right or left side (When pushed just fastenough the model should collapse at the first floor only) Askstudents why the other floors didnrsquot collapse (The first floorcollapsed because it was too weak to transfer enough horizontalforce to move the upper stories It could not transfer the shakingto the upper stories)

b Direct studentsrsquo attention to the load path diagrams on Master42b and explain that pushing the base of the building is equivalentto applying force horizontally to the upper stories A force appliedhorizontally to any floor of a building is called the shear force onthat floor Shear forces can be caused by the ground shaking of anearthquake as well as by high winds Invite students to carefullyapply horizontal forces at different points on the model tosimulate earthquake shaking (Earthquakes affect buildings atground level)

4 Ask students how they could add structural elements to create apath for the load to follow to the ground when strong forces actupon the structure Help the students discover the effect of adding ashear wall diagonal bracing and rigid connections using stringcardboard extra wood and clamps as in the diagrams on themaster On each of the three diagrams provided have students drawa force arrow (a vector) and trace the path the force takes to theground

5 Challenge students to design and build three differentarrangements of the six structural elements depicted on theworksheet Each time they modify the design they must modify thediagram to show the new load path Check each structure anddiagram until you are sure that students understand the conceptsWhen a structure is well reinforced you should be able to push onthe upper story and slide the whole structure without any of thewalls failing

6 Either have the groups discuss the questions on the master withone student recording each grouprsquos response or ask individualstudents to write responses to specific questions After all thegroups finish the questions have a reporter for each SET presentits response to one of the questions Allow the class to come tosome consensus on their responses to that question then proceedto another group until all the questions have been discussed

C ConclusionAs a closing activity challenge a volunteer to remove an element(a craft stick) that according to the load path diagram is notcarrying any load Have the student unbolt one end of that elementand push the reinforced structure to see if it holds It will if theload path is correct

Finally help the students connect the behavior of their model wallsto their mental images of real buildings during an earthquakeEmphasize that the back and forth horizontal component (orshearing) of ground shaking is the force most damaging to buildingsBuildings are primarily designed to carry the downward pull of

on which the structure rests wouldsimulate the transfer of energy fromthe ground to the building

e-binder for 2013 CEETEP workshop 127

A G U F E M A 236 S E I S M I C S L E U T H S

gravity but to withstand earthquake shaking they need to be able towithstand sideways or horizontal pushes and pulls

A DA P T A T I ONS A ND EX T ENS I ONS1 Challenge students to find the minimum number of diagonalbraces shear walls or rigid connections that will ensure horizontalstability in their models

2 Invite students to design construct and test other structuralelements that could make buildings earthquake-resistant such assquare rigid connections Some might try putting wheels or sleds onthe bottom of their buildings

3 If you have some very interested students you may give themaccess to all your building supplies and challenge them to design andconstruct larger structures Ask students to consider how they coulddesign a building so that the ground shaking does not transfer to thebuilding There are new technologies that allow the ground tomove but not the building One of these is called base isolationHave students research this topic in periodicals (See UnitResources)

128

M A S T E R P A G E Building a Model Wall

A G U F E M A 238 S E I S M I C S L E U T H S

42a

1 Stack 21 craft sticks one on top of the other Wrap a rubber band around the center to hold themtogether Using a 316 in bit carefully drill a hole through all the sticks at once 1 cm from the end of thestack Drill slowly to avoid cracking the wood

2 Select the thinner of the two large pieces of wood (45 cm x 6 cm) Drill a 316 in hole 1 cm from one endand 1 cm from the edge Measure the distance between the holes drilled in the craft sticks and space threemore 316 in holes at that distance 1 cm from the edge so that a total of four holes are drilled (seeillustration)

3 Use the small wood screws to mount this piece of wood on the base (the 2 x 6) fastening at the bottomand in the center Leave the pre-drilled holes sticking up far enough above the top to accept the drilled craftsticks

4 Using the bolts washers and nuts assemble the craft sticks to build a model wall

5 Experiment with tightening bolts and washers until they are just tight enough for the wall to stand on itsown

e-binder for 2013 CEETEP workshop 129

M A S T E R P A G E Load Paths Worksheet

A G U F E M A 240 S E I S M I C S L E U T H S

42bName__________________________________________________________

Date____________________

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first______________________________________________________________

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structuralfailure_________________________________________________________________________________________________________________________________________________________________

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

130

M A S T E R P A G E

A G U F E M A 241 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

e-binder for 2013 CEETEP workshop 131

M A S T E R P A G E

A G U F E M A 242 S E I S M I C S L E U T H S

C Summary

1 What is a load path

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

3 How many additional elements did you need to add

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

4 Why doesnrsquot the force take some path other than the one you diagrammed

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

132

M A S T E R P A G E Load Paths Worksheet (key)

A G U F E M A 244 S E I S M I C S L E U T H S

42b

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first The first floor

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structural failure The first floor has to carry all the load to the upper stories It transfersforces to move the upper stories

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

e-binder for 2013 CEETEP workshop 133

M A S T E R P A G E

A G U F E M A 245 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

126

A G U F E M A 235 S E I S M I C S L E U T H S

TEACHING CLUES AND CUESThis activity is designedas a demonstration oras a group activity Ifyou decide to haveeach

group build a model wall you willneed more materials

Encourage students tochoose roles within theirSETs and later reporttheir results by role with

the technician reporting the datathe engineer describing thecalculations the scientist explainingthe relationships and thecoordinator facilitating

Students may try bothpushing the structuredirectly and moving thetable Shaking the table

a Instruct one student in each group to push at the bottom of themodel from the lower right or left side (When pushed just fastenough the model should collapse at the first floor only) Askstudents why the other floors didnrsquot collapse (The first floorcollapsed because it was too weak to transfer enough horizontalforce to move the upper stories It could not transfer the shakingto the upper stories)

b Direct studentsrsquo attention to the load path diagrams on Master42b and explain that pushing the base of the building is equivalentto applying force horizontally to the upper stories A force appliedhorizontally to any floor of a building is called the shear force onthat floor Shear forces can be caused by the ground shaking of anearthquake as well as by high winds Invite students to carefullyapply horizontal forces at different points on the model tosimulate earthquake shaking (Earthquakes affect buildings atground level)

4 Ask students how they could add structural elements to create apath for the load to follow to the ground when strong forces actupon the structure Help the students discover the effect of adding ashear wall diagonal bracing and rigid connections using stringcardboard extra wood and clamps as in the diagrams on themaster On each of the three diagrams provided have students drawa force arrow (a vector) and trace the path the force takes to theground

5 Challenge students to design and build three differentarrangements of the six structural elements depicted on theworksheet Each time they modify the design they must modify thediagram to show the new load path Check each structure anddiagram until you are sure that students understand the conceptsWhen a structure is well reinforced you should be able to push onthe upper story and slide the whole structure without any of thewalls failing

6 Either have the groups discuss the questions on the master withone student recording each grouprsquos response or ask individualstudents to write responses to specific questions After all thegroups finish the questions have a reporter for each SET presentits response to one of the questions Allow the class to come tosome consensus on their responses to that question then proceedto another group until all the questions have been discussed

C ConclusionAs a closing activity challenge a volunteer to remove an element(a craft stick) that according to the load path diagram is notcarrying any load Have the student unbolt one end of that elementand push the reinforced structure to see if it holds It will if theload path is correct

Finally help the students connect the behavior of their model wallsto their mental images of real buildings during an earthquakeEmphasize that the back and forth horizontal component (orshearing) of ground shaking is the force most damaging to buildingsBuildings are primarily designed to carry the downward pull of

on which the structure rests wouldsimulate the transfer of energy fromthe ground to the building

e-binder for 2013 CEETEP workshop 127

A G U F E M A 236 S E I S M I C S L E U T H S

gravity but to withstand earthquake shaking they need to be able towithstand sideways or horizontal pushes and pulls

A DA P T A T I ONS A ND EX T ENS I ONS1 Challenge students to find the minimum number of diagonalbraces shear walls or rigid connections that will ensure horizontalstability in their models

2 Invite students to design construct and test other structuralelements that could make buildings earthquake-resistant such assquare rigid connections Some might try putting wheels or sleds onthe bottom of their buildings

3 If you have some very interested students you may give themaccess to all your building supplies and challenge them to design andconstruct larger structures Ask students to consider how they coulddesign a building so that the ground shaking does not transfer to thebuilding There are new technologies that allow the ground tomove but not the building One of these is called base isolationHave students research this topic in periodicals (See UnitResources)

128

M A S T E R P A G E Building a Model Wall

A G U F E M A 238 S E I S M I C S L E U T H S

42a

1 Stack 21 craft sticks one on top of the other Wrap a rubber band around the center to hold themtogether Using a 316 in bit carefully drill a hole through all the sticks at once 1 cm from the end of thestack Drill slowly to avoid cracking the wood

2 Select the thinner of the two large pieces of wood (45 cm x 6 cm) Drill a 316 in hole 1 cm from one endand 1 cm from the edge Measure the distance between the holes drilled in the craft sticks and space threemore 316 in holes at that distance 1 cm from the edge so that a total of four holes are drilled (seeillustration)

3 Use the small wood screws to mount this piece of wood on the base (the 2 x 6) fastening at the bottomand in the center Leave the pre-drilled holes sticking up far enough above the top to accept the drilled craftsticks

4 Using the bolts washers and nuts assemble the craft sticks to build a model wall

5 Experiment with tightening bolts and washers until they are just tight enough for the wall to stand on itsown

e-binder for 2013 CEETEP workshop 129

M A S T E R P A G E Load Paths Worksheet

A G U F E M A 240 S E I S M I C S L E U T H S

42bName__________________________________________________________

Date____________________

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first______________________________________________________________

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structuralfailure_________________________________________________________________________________________________________________________________________________________________

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

130

M A S T E R P A G E

A G U F E M A 241 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

e-binder for 2013 CEETEP workshop 131

M A S T E R P A G E

A G U F E M A 242 S E I S M I C S L E U T H S

C Summary

1 What is a load path

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

3 How many additional elements did you need to add

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

4 Why doesnrsquot the force take some path other than the one you diagrammed

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

132

M A S T E R P A G E Load Paths Worksheet (key)

A G U F E M A 244 S E I S M I C S L E U T H S

42b

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first The first floor

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structural failure The first floor has to carry all the load to the upper stories It transfersforces to move the upper stories

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

e-binder for 2013 CEETEP workshop 133

M A S T E R P A G E

A G U F E M A 245 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

e-binder for 2013 CEETEP workshop 127

A G U F E M A 236 S E I S M I C S L E U T H S

gravity but to withstand earthquake shaking they need to be able towithstand sideways or horizontal pushes and pulls

A DA P T A T I ONS A ND EX T ENS I ONS1 Challenge students to find the minimum number of diagonalbraces shear walls or rigid connections that will ensure horizontalstability in their models

2 Invite students to design construct and test other structuralelements that could make buildings earthquake-resistant such assquare rigid connections Some might try putting wheels or sleds onthe bottom of their buildings

3 If you have some very interested students you may give themaccess to all your building supplies and challenge them to design andconstruct larger structures Ask students to consider how they coulddesign a building so that the ground shaking does not transfer to thebuilding There are new technologies that allow the ground tomove but not the building One of these is called base isolationHave students research this topic in periodicals (See UnitResources)

128

M A S T E R P A G E Building a Model Wall

A G U F E M A 238 S E I S M I C S L E U T H S

42a

1 Stack 21 craft sticks one on top of the other Wrap a rubber band around the center to hold themtogether Using a 316 in bit carefully drill a hole through all the sticks at once 1 cm from the end of thestack Drill slowly to avoid cracking the wood

2 Select the thinner of the two large pieces of wood (45 cm x 6 cm) Drill a 316 in hole 1 cm from one endand 1 cm from the edge Measure the distance between the holes drilled in the craft sticks and space threemore 316 in holes at that distance 1 cm from the edge so that a total of four holes are drilled (seeillustration)

3 Use the small wood screws to mount this piece of wood on the base (the 2 x 6) fastening at the bottomand in the center Leave the pre-drilled holes sticking up far enough above the top to accept the drilled craftsticks

4 Using the bolts washers and nuts assemble the craft sticks to build a model wall

5 Experiment with tightening bolts and washers until they are just tight enough for the wall to stand on itsown

e-binder for 2013 CEETEP workshop 129

M A S T E R P A G E Load Paths Worksheet

A G U F E M A 240 S E I S M I C S L E U T H S

42bName__________________________________________________________

Date____________________

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first______________________________________________________________

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structuralfailure_________________________________________________________________________________________________________________________________________________________________

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

130

M A S T E R P A G E

A G U F E M A 241 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

e-binder for 2013 CEETEP workshop 131

M A S T E R P A G E

A G U F E M A 242 S E I S M I C S L E U T H S

C Summary

1 What is a load path

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

3 How many additional elements did you need to add

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

4 Why doesnrsquot the force take some path other than the one you diagrammed

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

132

M A S T E R P A G E Load Paths Worksheet (key)

A G U F E M A 244 S E I S M I C S L E U T H S

42b

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first The first floor

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structural failure The first floor has to carry all the load to the upper stories It transfersforces to move the upper stories

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

e-binder for 2013 CEETEP workshop 133

M A S T E R P A G E

A G U F E M A 245 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

128

M A S T E R P A G E Building a Model Wall

A G U F E M A 238 S E I S M I C S L E U T H S

42a

1 Stack 21 craft sticks one on top of the other Wrap a rubber band around the center to hold themtogether Using a 316 in bit carefully drill a hole through all the sticks at once 1 cm from the end of thestack Drill slowly to avoid cracking the wood

2 Select the thinner of the two large pieces of wood (45 cm x 6 cm) Drill a 316 in hole 1 cm from one endand 1 cm from the edge Measure the distance between the holes drilled in the craft sticks and space threemore 316 in holes at that distance 1 cm from the edge so that a total of four holes are drilled (seeillustration)

3 Use the small wood screws to mount this piece of wood on the base (the 2 x 6) fastening at the bottomand in the center Leave the pre-drilled holes sticking up far enough above the top to accept the drilled craftsticks

4 Using the bolts washers and nuts assemble the craft sticks to build a model wall

5 Experiment with tightening bolts and washers until they are just tight enough for the wall to stand on itsown

e-binder for 2013 CEETEP workshop 129

M A S T E R P A G E Load Paths Worksheet

A G U F E M A 240 S E I S M I C S L E U T H S

42bName__________________________________________________________

Date____________________

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first______________________________________________________________

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structuralfailure_________________________________________________________________________________________________________________________________________________________________

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

130

M A S T E R P A G E

A G U F E M A 241 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

e-binder for 2013 CEETEP workshop 131

M A S T E R P A G E

A G U F E M A 242 S E I S M I C S L E U T H S

C Summary

1 What is a load path

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

3 How many additional elements did you need to add

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

4 Why doesnrsquot the force take some path other than the one you diagrammed

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

132

M A S T E R P A G E Load Paths Worksheet (key)

A G U F E M A 244 S E I S M I C S L E U T H S

42b

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first The first floor

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structural failure The first floor has to carry all the load to the upper stories It transfersforces to move the upper stories

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

e-binder for 2013 CEETEP workshop 133

M A S T E R P A G E

A G U F E M A 245 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

e-binder for 2013 CEETEP workshop 129

M A S T E R P A G E Load Paths Worksheet

A G U F E M A 240 S E I S M I C S L E U T H S

42bName__________________________________________________________

Date____________________

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first______________________________________________________________

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structuralfailure_________________________________________________________________________________________________________________________________________________________________

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

130

M A S T E R P A G E

A G U F E M A 241 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

e-binder for 2013 CEETEP workshop 131

M A S T E R P A G E

A G U F E M A 242 S E I S M I C S L E U T H S

C Summary

1 What is a load path

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

3 How many additional elements did you need to add

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

4 Why doesnrsquot the force take some path other than the one you diagrammed

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

132

M A S T E R P A G E Load Paths Worksheet (key)

A G U F E M A 244 S E I S M I C S L E U T H S

42b

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first The first floor

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structural failure The first floor has to carry all the load to the upper stories It transfersforces to move the upper stories

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

e-binder for 2013 CEETEP workshop 133

M A S T E R P A G E

A G U F E M A 245 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

130

M A S T E R P A G E

A G U F E M A 241 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

e-binder for 2013 CEETEP workshop 131

M A S T E R P A G E

A G U F E M A 242 S E I S M I C S L E U T H S

C Summary

1 What is a load path

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

3 How many additional elements did you need to add

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

4 Why doesnrsquot the force take some path other than the one you diagrammed

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

132

M A S T E R P A G E Load Paths Worksheet (key)

A G U F E M A 244 S E I S M I C S L E U T H S

42b

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first The first floor

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structural failure The first floor has to carry all the load to the upper stories It transfersforces to move the upper stories

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

e-binder for 2013 CEETEP workshop 133

M A S T E R P A G E

A G U F E M A 245 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

e-binder for 2013 CEETEP workshop 131

M A S T E R P A G E

A G U F E M A 242 S E I S M I C S L E U T H S

C Summary

1 What is a load path

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

3 How many additional elements did you need to add

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

4 Why doesnrsquot the force take some path other than the one you diagrammed

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

____________________________

132

M A S T E R P A G E Load Paths Worksheet (key)

A G U F E M A 244 S E I S M I C S L E U T H S

42b

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first The first floor

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structural failure The first floor has to carry all the load to the upper stories It transfersforces to move the upper stories

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

e-binder for 2013 CEETEP workshop 133

M A S T E R P A G E

A G U F E M A 245 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

132

M A S T E R P A G E Load Paths Worksheet (key)

A G U F E M A 244 S E I S M I C S L E U T H S

42b

A Failing Wall

Observe and explain how the wall fails when its base is shaken rapidly back and forth simulating the motionof a building hit by S waves during an earthquake Tighten all the nuts just enough to allow the joints tomove Sharply push the base a few centimeters horizontally (right or left)

1 What part of the wall fails first The first floor

2 Imagine how the horizontal force you applied to the base travels to the upper parts of the wall Whatcaused the first structural failure The first floor has to carry all the load to the upper stories It transfersforces to move the upper stories

B Load Paths with Additional Structural Elements

1 Pick up the two rigid connections one shear wall (cardboard) one solid diagonal brace and two pieces ofstring Add structural elements to your wall to provide paths for the horizontal forces or loads to travelthrough the wall Study the diagrams below to see how these structural elements provide load paths

Use arrows to show the load path on each diagram

e-binder for 2013 CEETEP workshop 133

M A S T E R P A G E

A G U F E M A 245 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

e-binder for 2013 CEETEP workshop 133

M A S T E R P A G E

A G U F E M A 245 S E I S M I C S L E U T H S

2 Put additional structural elements on your wall andpush the third level If the elements you addedprovided a load path to the base the base of the wallshould move If they do not the wall will failsomewhere When you discover a setup that worksdiagram it and sketch the load paths with arrows Haveyour instructor look it over before you continue

3 Design and build another set of additional structuralelements Sketch the load path here and have yourinstructor check it Be sure each member of the teamdesigns a set The base of the model wall should movewhen lateral force is applied to the top elements

4 Design and build a third set of additional structuralelements Use as few additional elements as possibleSketch the load path and have your instructor checkit Be sure each member of the team designs a setTest your load paths by removing elements not in thepath to see if the building will stand up to a force

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

134

M A S T E R P A G E

A G U F E M A 246 S E I S M I C S L E U T H S

C Summary

1 What is a load path

The path that the load (or force) follows through the structural elements of a building

2 Why must additional structural elements be added to a wall before it can carry horizontal forces

Normally buildings only have to support vertical force (gravity) When horizontal forces are applied as in

an earthquake additional elements are needed to carry them

3 How many additional elements did you need to add

Each joint needs only one additional structural element Only one joint on each floor needs to carry the

horizontal force in this model

4 Why doesnrsquot the force take some path other than the one you diagrammed

The diagram shows the places that are strong enough to carry the load If there were more than one place

the load (or force) would travel through both

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)

e-binder for 2013 CEETEP workshop 135

M A S T E R P A G E Teacher Background ReadingBuilding Engineering

A G U F E M A 232 S E I S M I C S L E U T H S

41a

During an earthquake a marked spot on the Earth might be seen to move erratically tracing out a randompath resembling that of a wandering insect ldquoGround motionrdquo is a literal description since the ground moves(generally for a distance measured only in centimeters) relative to its starting point The ground motion thatis important in determining the forces on a building is acceleration As the seismic waves move through theground the ground moves back and forth Acceleration is the rate at which ground movement changes itsspeed

Two other unit measures are directly related to acceleration Velocity measured in centimeters per secondrefers to the rate of the motion at a given instant Displacement measured in centimeters refers to thedistance an object is moved from its resting position If you move your hand back and forth rapidly in frontof your face it might experience a displacement of 20 to 30 centimeters in one second and its accelerationand velocity may be quite high but no damage will be done because the mass of your hand is low In a buildingwith a mass in the thousands of metric tons tremendous forces are required to produce the same motionThese forces are transmitted throughout the structure so if the movement repeats for some minutes thebuilding may shake to pieces

To overcome the effects of these forces engineers rely on a small number of components that can becombined to form a complete load path In the vertical plane three kinds of structural systems are used toresist lateral forces shear walls braced frames and moment-resistant or rigid frames In the horizontal planediaphragms (generally formed by the floor and roof planes of the building) or horizontal trusses are usedDiaphragms are designed to receive lateral force between the vertical resistance elements (shear walls orframes) Shear walls are solid walls designed to carry the force to the vertical resistance system In a simplebuilding with shear walls at each end ground motion enters the building and moves the floor diaphragms Thismovement is carried by the shear walls and transmitted back down through the building to the foundationBraced frames act in the same manner as shear walls but may not carry as much load depending on theirdesign Bracing generally takes the form of steel rolled sections (I-beams) circular bar sections (rods) ortubes Rigid frames rely on the capacity of joints to carry loads from columns to beams Because these jointsare highly stressed during movement the details of their construction are important As a last-resort strategyrigid frames use the energy absorption obtained by deformations of the structure before it ultimately fails

Architecturally rigid frames offer a certain advantage over shear walls or braced frames because they tend toprovide structures that are much less obstructed internally than shear wall structures This allows morefreedom in the design of accompanying architectural elements such as openings exterior walls partitionsand ceilings and in the placement of building contents such as furniture and loose equipment Neverthelessmoment-resistant frames require special construction and detailing and therefore are more expensive thanshear walls or braced frames

Note Adapted from FEMA 99 October 1990 Non-technical Explanation of the NEHRP Recommended Provisions

Diaphragm

Shear

MomentResistant

BracedFrame

(Touch here to return to intro page)