Civil & Environmental Engineering Design

Civil & Environmental Civil & Environmental Engineering DesignEngineering Design

Prof. Michael Chajes, ChairProf. Michael Chajes, ChairDepart. of Civil & Env. EngineeringDepart. of Civil & Env. Engineering

Photo by Doug Baker

Webster’s Definition of DesignWebster’s Definition of Design

“to create, fashion, execute, or construct according to plan,” and “to devise for a specific function or end.”

Webster’s Definition of DesignWebster’s Definition of Design

“to create, fashion, execute, or construct according to plan,” and “to devise for a specific function or end.”

Design ConstraintsDesign Constraints

SafePE code of ethics states: “Engineers, in the fulfillment of their professional duties, shall hold paramount the safety, health, and welfare of the public.”

FunctionalEconomicAesthetically pleasing

No one solution!

Design ExampleDesign Example

Design a shelf for you dorm room

Wood 1” x 8” x 6’

Wall

Design ExampleDesign Example

Design a shelf for you dorm room

Tension Strut

Design ExampleDesign Example

Design a shelf for you dorm room

Compression Strut

Design Tension StrutDesign Tension StrutMode of Failure: FractureMode of Failure: Fracture

8”

6”

10”

LOADSW books = 50 lbs/ftW total = 6 x 50 = 300 lbsEach strut (2 total) = 150 lbsFactor of safety = 2W books/strut = 300 lbs

F=ma, a=0, F=0Vertical direction0 = - 300 lbs + (3/5) F strutF strut = (300) x (5/3)

F strut = 500 lbs

F strut

W books/strut

F shelfFree BodyDiagram

8”

6”

10” STRUT SIZEStress = Force/AreaUse steel rodsStress Ultimate = 36,000 lb/inArea = Force/Stress = 300/36,000

Area required = 0.008 in

2

2

1/8” diameter rod

A = r = d / 40.008 = d / 4d = 0.10 in.1/8 = 0.125 in.

2 2

2

Design Tension StrutDesign Tension StrutMode of Failure: FractureMode of Failure: Fracture

8”

6”

10”

LOADSW books = 50 lbs/ftW total = 6 x 50 = 300 lbsEach strut (2 total) = 150 lbsFactor of safety = 2W books/strut = 300 lbs

F=ma, a=0, F=0Vertical direction0 = - 300 lbs + (3/5) F strutF strut = (300) x (5/3)

F strut = 500 lbs

F strut

W books/strut

F shelfFree BodyDiagram

Design Compression StrutDesign Compression StrutMode of Failure: FractureMode of Failure: Fracture

8”

6”

10”

1/8” diameter rod

STRUT SIZEStress = Force/AreaUse metal rodsStress Ultimate = 36,000 lb/inArea = Force/Stress = 300/36,000

Area required = 0.008 in

2

2

Design Compression StrutDesign Compression StrutMode of Failure: FractureMode of Failure: Fracture

A = r = d / 40.008 = d / 4d = 0.10 in.1/8 = 0.125 in.

2 2

2

8”

6”

10”

steel rod

Design Compression StrutDesign Compression StrutAnother Mode of Failure: ?Another Mode of Failure: ?

P

P

8”

6”

10”

Design Compression StrutDesign Compression StrutMode of Failure: Mode of Failure: BucklingBuckling

Euler Buckling Formula

Pcr = EI / L

Pcr = Buckling loadE = Material stiffnessI = Moment of inertiaL = Length

Pcr = 500 lbsE = 29,000,000 lb/inI rod = r / 4L = 10 in.

22

Pcr

Pcr

4

2

8”

6”

10”

Design Compression StrutDesign Compression StrutMode of Failure: BucklingMode of Failure: Buckling

Strut Size

Pcr = EI / L

500=()(29,000,000)(r / 4)/(10 )

r = 0.12, d = 0.24, 1/4 = 0.25 in.

22

Pcr

Pcr

4

1/4” diameter rod

2 2

8”

6”

10”

Strut Design SummaryStrut Design Summary

1/4” diameter rod Stability *

6”

10”

1/8” diameter rod Strength

1/8” diameter rod Strength *

What did we not consider (failure modes, design criteria)?

Bridge DesignBridge Design

Case Study:Case Study:The New Indian River Inlet BridgeThe New Indian River Inlet Bridge

http://travel.yahoo.com/p-travelguide-577578-map_of_delaware-i

Bridge Location

ExistingIndian River Inlet Bridge

Reason for Replacement: Scour

Scour holes greater than 30 m deep

Specificationsfor the New Bridge

Because the piers of the Because the piers of the existing Indian River existing Indian River Inlet bridge are in the Inlet bridge are in the tidal inlet, scour has tidal inlet, scour has become a serious become a serious problem problem

A new bridge will be A new bridge will be built by 2010 to replace built by 2010 to replace the existing bridgethe existing bridge

The bridge span will be The bridge span will be over 900 ft. in order to over 900 ft. in order to span the inletspan the inlet

http://www.deldot.gov/static/projects/indian_river_bridge/replacement.shtml

Preliminary DesignPreliminary Design

Courtesy of FIGG Engineering GroupCourtesy of FIGG Engineering Group

Preliminary DesignPreliminary Design

Courtesy of FIGG Engineering GroupCourtesy of FIGG Engineering Group

Preliminary DesignPreliminary Design

Courtesy of FIGG Engineering GroupCourtesy of FIGG Engineering Group

Design Constraints/DecisionsDesign Constraints/Decisions

How many can you list?How many can you list?

Design Constraints/DecisionsDesign Constraints/Decisions

Location of bridgeLocation of bridgeSpan of bridgeSpan of bridgeNumber of lanesNumber of lanesAlignment of roadwayAlignment of roadwayType of bridgeType of bridgeBridge aestheticsBridge aestheticsType of foundationType of foundationScour protectionScour protectionEnvironmental impactEnvironmental impactMaterials to be usedMaterials to be usedLoadings to considerLoadings to considerSize of membersSize of members

How will it be constructedHow will it be constructedHow will it be inspectedHow will it be inspectedHow will it be maintainedHow will it be maintainedHow will it be financedHow will it be financed

West Point Bridge Design West Point Bridge Design ProgramProgram

http://bridgecontest.usma.edu

Designing a BreakwaterDesigning a Breakwater

Protecting a Bridge with a Breakwater

Sandbar

Waves

Bridge Roadway

Elevation View

1

30

Bridge Roadway

Pier

3.5 in.

2.25 in. 8 in.

4.5 in.

Plan View

Sandbar

Brick

Water Surface

12 in.

Breakwater

26 in.

QuestionsQuestions