Pre-Schematic Considerations MASTERrichardson.eng.ua.edu/Former_Courses/CE_331_fa07/...Pre-schematic Considerations Deflections and Drift What to look for • Long spans adjacent to

PrePre--schematicschematicConsiderationsConsiderations

WhoWho

WhereWhere

WhatWhat


Who, What & WhereWho, What & Where

WhoWho are the users?are the users?

ChurchChurch

SchoolSchool

ManufacturersManufacturers

ResearchersResearchers



WhatWhat is the purpose?is the purpose?

FellowshipFellowship

TeachingTeaching

ManufacturingManufacturing

ProductionProduction



Location, Location, Location, LocationLocation, Location



Where is the project locatedWhere is the project located??

Building CodeBuilding Code

Environmental ForcesEnvironmental Forces

Construction PracticesConstruction Practices


Limitation of DiscussionLimitation of Discussion

Use Use Educational, Educational, Administrative and Administrative and Assembly spaceAssembly space

StructureStructureStructural Steel with typical Structural Steel with typical and long span components up and long span components up to approximately 3 floorsto approximately 3 floors


Building LoadsBuilding Loads

Forces Forces experienced experienced

by by structuresstructures


Building LoadsBuilding LoadsSTRUCTURESTRUCTURE

LIVE LOADSLIVE LOADS

OCCUPANCYOCCUPANCYAND USEAND USE

ROOFROOFLOADSLOADS

UNIFORMUNIFORMLOADSLOADS

CONCENTRATEDCONCENTRATEDLOADSLOADS

SPECIALSPECIALEQUIPMENTEQUIPMENT

ENVIRONMENTALENVIRONMENTALLOADSLOADS

WINDWINDLOADSLOADS

EARTHQUAKEEARTHQUAKELOADSLOADS

FLOODFLOODLOADSLOADS

SNOWSNOWLOADSLOADS

THERMALTHERMALLOADSLOADS

EARTHEARTHPRESSURESPRESSURES

SELFSELF--WEIGHTWEIGHT

STRUCTURALSTRUCTURALFRAMINGFRAMING

MEPMEPEQUIPMENTEQUIPMENT

ARCHITECTURALARCHITECTURALFINISHES &FINISHES &CLADDINGCLADDING


“…“…. loads produced by the . loads produced by the use and occupancy of the buildinguse and occupancy of the building…”…”

Live LoadsLive Loads



7575RetailRetail100100Stairs & ExitsStairs & Exits

4040ClassroomsClassrooms5050AdministrativeAdministrative

150150LibrariesLibraries(stack rooms)(stack rooms)

6060LibrariesLibraries(reading rooms)(reading rooms)

4040Parking DecksParking Decks100100Dinning Rooms & Dinning Rooms & RestaurantsRestaurants

100100Corridors & LobbiesCorridors & Lobbies4040CatwalksCatwalks

5050Projection & Control RoomsProjection & Control Rooms125125Stages and PlatformsStages and Platforms

100100AssemblyAssembly(movable seats)(movable seats)

6060Assembly & TheatersAssembly & Theaters(fixed seats)(fixed seats)

LiveLiveLoadLoad

Occupancy or Occupancy or UseUse

LiveLiveLoadLoad

Occupancy or Occupancy or UseUse


Live Loads are ReducibleLive Loads are Reducible

•• Reduction reflects the statistical Reduction reflects the statistical probability that a floor will be probability that a floor will be fully loaded at any one time.fully loaded at any one time.

•• Reduction based on occupancy, Reduction based on occupancy, structural component and floor structural component and floor area being supported by area being supported by component.component.

•• Most floor joist or floor beams Most floor joist or floor beams do not see a reduction.do not see a reduction.

•• Girders and beams Girders and beams –– maximum maximum reduction is 40%reduction is 40%

•• Columns Columns –– maximum reduction maximum reduction is 60%is 60%



Consider designing with Consider designing with

Unreduced live loads Unreduced live loads

or or

More than code required live loadsMore than code required live loads



Environmental LoadsEnvironmental Loads•• Snow Snow •• WindWind•• FloodingFlooding•• SeismicSeismic


Snow LoadsSnow Loads

Low ImpactLow Impact

ImpactImpact•• Snow drifts and slidingSnow drifts and sliding

snowsnow

Structural considerationsStructural considerations•• Local near parapetsLocal near parapets•• Mechanical EquipmentMechanical Equipment•• MultiMulti--tiered roofstiered roofs

Cost implicationsCost implications•• Some increased memberSome increased member

sizessizes



Moderate ImpactModerate Impact

ImpactImpact•• Snow weight over entire Snow weight over entire

structurestructure

Structural considerationsStructural considerations•• Entire roofEntire roof

Cost implicationsCost implications•• Most Structural membersMost Structural members

will require increased sizeswill require increased sizes



Severe ImpactSevere ImpactImpactImpact•• Snow weight over entireSnow weight over entire

structure structure

Structural considerationsStructural considerations•• Entire roofEntire roof

Cost implicationsCost implications•• Increased decking gaugeIncreased decking gauge•• Reduction of memberReduction of member

spacingspacing•• Significant increase in Significant increase in

member sizesmember sizes


Wind LoadsWind Loads

90 - 100

100 - 110

110 - 120

120 - 130

130 - 140

140 - 150

150 - 160

Design Peak Gust Hurricane WindSpeeds (mph) in Open Terrain




ImpactImpact•• Typically limited to Typically limited to

buildings lateral systembuildings lateral system

Structural considerationsStructural considerations•• Slight increase in bracingSlight increase in bracing

and foundationsand foundations

Cost implicationsCost implications•• Some increased Some increased

member sizesmember sizes




ImpactImpact•• Entire building includingEntire building includingexterior claddingexterior cladding

Structural considerationsStructural considerations•• Roof decking and Roof decking and

attachmentsattachments•• Drag strutsDrag struts•• Increased foundationIncreased foundationsizessizes

Cost implicationsCost implications•• Significant over entireSignificant over entire

building including claddingbuilding including cladding•• Stringent component Stringent component

attachment requirementsattachment requirementsSevere ImpactSevere Impact


Flood LoadsFlood Loads

Low AreasLow Areas

RiversRivers

Coastal RegionsCoastal Regions

ConsiderationsConsiderations

•• BreakBreak--away wallsaway walls

•• Crawl space flowCrawl space flow--throughthrough

•• Limitation of inhabitable spaceLimitation of inhabitable space

•• Foundation scourFoundation scour


Seismic LoadsSeismic Loads



Severe ImpactSevere Impact

ImpactImpact•• Wide building expansion Wide building expansion

jointsjoints

•• Loads on building increaseLoads on building increaseexponentiallyexponentially

•• Attachments of all buildingAttachments of all buildingcomponentscomponents

•• Anchorage of MEP Anchorage of MEP equipment and building equipment and building fixturesfixtures


Seismic LoadsSeismic Loads

LowLow

ModerateModerate

SevereSevere

Cost ImplicationsCost Implications•• Moderate and severe Moderate and severe

regions often see regions often see significant cost increasessignificant cost increases


BEST PLACE TO BUILD A BUILDINGBEST PLACE TO BUILD A BUILDING



Dead LoadsDead Loads

•• Weight of structureWeight of structure

•• Mechanical equipmentMechanical equipment

•• FinishesFinishes


Dead LoadDead Load

EngineersEngineers

Design must Design must hold it uphold it up


Dead LoadDead Load

Special finishes and featuresSpecial finishes and featuresBaptisteriesBaptisteries


Dead LoadDead Load


CatwalksCatwalks


Dead LoadDead Load


CatwalksCatwalks

PlatformsPlatforms


Dead LoadDead Load


CatwalksCatwalks

PlatformsPlatforms

Drywall soffits and special glazingDrywall soffits and special glazing


Deflections and DriftDeflections and Drift

Framing DeflectionFraming Deflection

Serviceability, Serviceability, not a strength not a strength

issueissue



““Structural Structural systems and systems and

members thereof members thereof shall be designed shall be designed to have adequate to have adequate stiffness to limit stiffness to limit deflections and deflections and

lateral drift.lateral drift.””


Deflection LimitsDeflection Limits

I/120I/120GreenhousesGreenhouses

I/180I/180Farm buildingsFarm buildings

I/240I/240I/120I/120

Exterior walls and interior Exterior walls and interior partitions:partitions:

With brittle finishesWith brittle finishesWith flexible finishesWith flexible finishes

I/240I/240I/360I/360Floor MembersFloor Members

I/240I/240I/180I/180I/120I/120

I/360I/360I/240I/240I/180I/180

I/360I/360I/240I/240I/180I/180

Roof Members:Roof Members:Supporting plaster ceilingSupporting plaster ceilingSupporting nonSupporting non--plaster ceilingplaster ceilingNot supporting ceilingNot supporting ceiling

D + LD + LS or WS or WLLConstructionConstruction

IBC TABLE 1604.3IBC TABLE 1604.3

DEFLECTION LIMITSDEFLECTION LIMITS



What to look forWhat to look for•• Long spans adjacent to wallsLong spans adjacent to walls•• Detail for movement between structure,Detail for movement between structure,

cladding and finishescladding and finishes•• Long spans adjacent to windows and Long spans adjacent to windows and

brittle finishesbrittle finishes•• Walls with masonry veneerWalls with masonry veneer•• Tall wallsTall walls•• Flat roofsFlat roofs

PondingPonding –– the retention of water due tothe retention of water due tothe deflection of the roof framingthe deflection of the roof framing

•• Roofs with no free edge to drainRoofs with no free edge to drain


Building DriftBuilding Drift

““The movement of the top of the building The movement of the top of the building relative to the base of the building.relative to the base of the building.””


Building Expansion JointsBuilding Expansion Joints



Expansion Joint ConfigurationExpansion Joint Configuration

Overall length of buildingOverall length of building

Shape of buildingShape of building


Building Expansion JointsBuilding Expansion JointsOnce it is determined an expansion joint is requiredOnce it is determined an expansion joint is required

Factors of Joint WidthFactors of Joint Width

•• Temperature changeTemperature change

Generally very small, especiallyGenerally very small, especiallyif the structure is continuously if the structure is continuously heated or cooledheated or cooled





Generally very smallGenerally very small

•• Wind forcesWind forces

Less than one inch dependingLess than one inch dependingon lateral systemon lateral system





Generally very smallGenerally very small

•• Wind forcesWind forces

Less than one inch dependingLess than one inch dependingon lateral systemon lateral system

•• Seismic forcesSeismic forcesCan require large structural Can require large structural jointsjoints



Additional ConsiderationsAdditional Considerations

Location of lateral bracingLocation of lateral bracing

Stiffness of columnsStiffness of columns



Avoid them if possibleAvoid them if possible

ExpensiveExpensive

Special cladding and finish Special cladding and finish requiredrequired

MEP system can incur special MEP system can incur special detailingdetailing


Vibration Vibration


VibrationVibrationWhen do structural engineers worry about vibration?When do structural engineers worry about vibration?

Large open spaces with few usersLarge open spaces with few users•• MallsMalls

•• Large classroomsLarge classrooms

•• Fellowship hallsFellowship halls



Theatrical and exercise spaceTheatrical and exercise space

Rhythm of dancers, athletesRhythm of dancers, athletesand music can create unacceptableand music can create unacceptablelevels of vibration.levels of vibration.



Laboratory, healthcare imaging Laboratory, healthcare imaging and research spaceand research space

Specialized equipment may not work if Specialized equipment may not work if vibration limits are exceeded.vibration limits are exceeded.


VibrationVibrationWhat can minimize vibration worries?What can minimize vibration worries?

Stiffening the structureStiffening the structure

Increase mass of structureIncrease mass of structure


VibrationVibrationWhat can minimize vibration worries?What can minimize vibration worries?

Stiffening the structureStiffening the structure

Increase mass of structureIncrease mass of structure

Will add cost to minimizeWill add cost to minimize


AcousticsAcoustics

Structures do move. . .Structures do move. . .

Movement of steel results in Movement of steel results in creaking and poppingcreaking and popping

Most noticeable in large, Most noticeable in large, quiet placesquiet places


The GridThe Grid

Optimization of grid=

Savings to the Owner


The GridThe Grid

• Avoid grids that do not stack

• Avoid transfer girders

• Avoid irregular grids– Lose advantage of

repetitive fabrication– More beams required

to support offset conditions


The Optimal GridThe Optimal Grid

Optimal Bay Size: Length to width ratio of approximately 1.25 tOptimal Bay Size: Length to width ratio of approximately 1.25 to 1.50o 1.50


Preliminary Structural Preliminary Structural ComponentsComponents

BeamsBeams

Optimal Depth = Cost EffectiveOptimal Depth = Cost Effective

Depth (in) = Span (ft) / 2Depth (in) = Span (ft) / 2

Consult with structural engineer Consult with structural engineer if bay size is flexibleif bay size is flexible


Preliminary Structural Preliminary Structural ComponentsComponents

JoistJoist(typical for basic wind, snow and seismic regions)(typical for basic wind, snow and seismic regions)

Roof : 6Roof : 6’’ 00””

Floor: 2Floor: 2’’ 00”” to 3to 3’’ 00””

Depth (in) = Span (ft) *3/4Depth (in) = Span (ft) *3/4


Structural Steel DepthsStructural Steel DepthsAvailable Joist ProfilesAvailable Joist Profiles


Structural Steel DepthsStructural Steel DepthsTruss DepthsTruss Depths

Great for large loadsGreat for large loads

Great for long spansGreat for long spans

Can be designed and Can be designed and detailed to match detailed to match architectural preferencesarchitectural preferences

Avoid arches if possibleAvoid arches if possible

Very expensiveVery expensive


ColumnsColumns

TypesTypesPipesPipes

TubesTubes

Hollow Structural ShapesHollow Structural Shapes

Wide FlangesWide Flanges


ColumnsColumns

Cost Cost ––

Varies based on Varies based on marketmarket


ColumnsColumns

Wide flanges may be Wide flanges may be preferable in preferable in

multimulti--story constructionstory construction


Preliminary Column SizesPreliminary Column Sizes

Maximum 15Maximum 15’’ 00”” Floor HeightFloor Height

Table is approximate and provides for allowance for selection ofTable is approximate and provides for allowance for selection of optimal shape and size of columnoptimal shape and size of column

13 X 12 1/413 X 12 1/410 1/2 X 10 1/410 1/2 X 10 1/48 X 88 X 840 X 4040 X 4012 1/2 X 12 1/412 1/2 X 12 1/410 1/4 X 1010 1/4 X 106 X 66 X 630 X 4030 X 4010 1/4 X 10 1/410 1/4 X 10 1/48 X 88 X 86 X 66 X 630 X 3030 X 3010 1/4 X 10 1/410 1/4 X 10 1/48 X 88 X 86 X 66 X 620 X 4020 X 40

10 X 1010 X 106 X 66 X 65 X 55 X 520 X 3020 X 3010 X 1010 X 106 X 66 X 65 X 55 X 520 X 2020 X 20

332211Bay SpacingBay Spacing

Number of StoriesNumber of Stories


Lateral BracingLateral Bracing

Placement and LocationsPlacement and LocationsPreferred locations varies between Preferred locations varies between structural engineersstructural engineers

Options IncludeOptions Include

•• Core of buildingCore of building

•• Perimeter of buildingPerimeter of building


Lateral BracingLateral BracingTypes ofTypes of BracesBraces



MaterialsMaterials•• MasonryMasonry

•• Concrete ShaftsConcrete Shafts

•• TiltTilt--up Panelsup Panels

•• Steel XSteel X--type Bracingtype Bracing

•• Steel FramesSteel Frames



Most Economical:Most Economical:

Typically steel XTypically steel X--type type BracingBracing

(Exception: load bearing (Exception: load bearing walls are present)walls are present)



ConsiderationsConsiderations•• Avoidance of openingsAvoidance of openings

•• Environmental LoadingsEnvironmental Loadings


FoundationsFoundations

Coastal RegionsCoastal RegionsAnticipate PilingAnticipate Piling

•• Near coastlineNear coastline

•• For heavily loaded foundationsFor heavily loaded foundations

•• Soils with anticipated Soils with anticipated settlementssettlements



Lowland AreasLowland AreasImproved swampland or filled valleysImproved swampland or filled valleys

•• Significant soil remediationSignificant soil remediation

•• Deep foundationsDeep foundations



Northern ClimatesNorthern Climates•• Bottoms: below the frost elevationBottoms: below the frost elevation

•• Sidewalks: stabilized to avoid frost heaveSidewalks: stabilized to avoid frost heave

•• Perimeter insulationPerimeter insulation



Mississippi GumboMississippi Gumbo•• Expansive clays shrink and swellExpansive clays shrink and swell

•• Combination of remedial solutions:Combination of remedial solutions:



Mississippi GumboMississippi Gumbo•• Expansive clays shrink and swellExpansive clays shrink and swell

•• Combination of remedial solutions:Combination of remedial solutions:

•• Soil remediationSoil remediation

•• Deep foundationsDeep foundations

•• Framed slabs over carton formsFramed slabs over carton forms

•• PostPost--tensioned slabstensioned slabs



BirminghamBirmingham•• Limestone geology presents Limestone geology presents

unique challengesunique challenges

•• Pinnacled limestonePinnacled limestone

•• Sinkhole activitySinkhole activity

•• Soft clay layer directly aboveSoft clay layer directly aboverockrock


Exterior CladdingExterior Cladding

Exterior CladdingExterior Cladding•• BrickBrick

•• Other cladding typesOther cladding types

•• Moderate and severe wind Moderate and severe wind regions and seismic regionsregions and seismic regions

•• Store fronts and curtain wallsStore fronts and curtain walls

•• Force protection systemsForce protection systems



BrickBrick

•• BIA provides BIA provides recommendations for backup recommendations for backup deflectiondeflection

•• Usually L / 600Usually L / 600

•• May require use of masonry or May require use of masonry or deeper studs to meet deeper studs to meet deflection requirements.deflection requirements.



Other Cladding TypesOther Cladding Types

•• Allowable deflection assumed Allowable deflection assumed to be per IBCto be per IBC

•• Usually L / 240 Usually L / 240

•• Consider limitation carefullyConsider limitation carefully•• 1515’’ wall would deflect wall would deflect ¾”¾”



Wind & Seismic RegionsWind & Seismic Regions

•• Anticipate stringent cladding Anticipate stringent cladding attachmentsattachments

•• Deeper backup systemsDeeper backup systems



Curtain WallsCurtain Walls

•• MultiMulti--story walls require eitherstory walls require eitherinternal or external supportinternal or external support

•• Cost and coordination often not Cost and coordination often not recognized until late in therecognized until late in theproject!project!


Documents

Pre-Schematic Considerations MASTERrichardson.eng.ua.edu/Former_Courses/CE_331_fa07/...Pre-schematic Considerations Deflections and Drift What to look for • Long spans adjacent to