Wabash Bridge Competition

Bridge Engineering

Todd Wilson, B.S., E.I.T.Traffic Engineer - DMJM Harris

In 1904, the Wabash Bridge opened to carry the Wabash-Pittsburg Terminal Railroad over the Monongahela River. In

1948, the bridge was removed. The piers still remain.

Now it is up to you to design a pedestrian bridge or structure to bring new life to the old abandoned bridge piers.

Overview

• Definitions• Engineering

– Forces– Type– Configuration– Form

• Classification Challenge• Other Design Considerations

Definitions

• Abutment - support at beginning or end ofbridge integrated with the ground

• Pier - intermediate support• Span - the bridge between two supports• Girder - a tall, narrow beam• Support Structure - the part of the bridge

that carries the load

Engineering - Classification of Forces

• Function of bridge: to carry a load across adistance

• Due to gravity, all loads have a downwardforce (weight)

• All bridges can be classified into thefollowing basic types based on how theycarry the weight:– Compression– Tension– Tension/Compression (Both)

Compression Bridges

• Compression is the “push” force• Compression causes an object to get shorter• Stone and concrete are strong in

compression

Compression Bridges - Arch• A bridge that supports a weight in compression is

an arch bridge• The circular arc in compression supports the road• The arch can be below the road or above the road

Compression Bridge - Arch

Photo: Todd Wilson

Tension Bridges

• Tension is a “pull” force• Tension causes an object to get longer• Wire rope and chains are strong in tension

Tension Bridge - Suspension• A suspension bridge features a long cable strung

over towers and anchored on both sides• Smaller cables are hung from the main cables and

connect to the road deck• The cables in tension support the road

Tension Bridge - Suspension

Photo: Todd Wilson

Tension Bridge - Cable Stayed• A cable stayed bridge features cables that connect

directly from a tower to the road• The cables in tension support the road

Tension Bridge - Cable Stayed

Photo: Todd Wilson

Tension/Compression Bridge

• A beam bends under the weight of a load• When the beam bends, the top half is in

compression and the bottom half is in tension• The taller the beam, the stronger it is

A Beam Bridge…

Now let’s add vertical rods to help you see whatis going on. They serve no structural purpose.

The top rods are pushed together incompression

The bottom rods are pulled apart in tension

Tension/Compression - BeamPhoto: Todd Wilson

Tension/Compression - Truss

•As a beam gets taller and taller, itbecomes too costly and too heavy

•Solution: build a truss•Trusses have the same function as

beams, but are composed of triangles

Tension/Compression - Truss– Top composed of thick beams (compression)– Bottom composed of thin eye-bar chains (tension)

Photo: Todd Wilson

Truss Types

• Bowstring• Lenticular• Pratt• Double Intersection

Pratt (Whipple)• Baltimore• Parker

• Pennsylvania• Warren• Double Intersection

Warren• Warren Quadrangular

(Lattice)• K Truss

Truss Type - Bowstring

Photo: Todd Wilson

Truss Type - Lenticular

Photo: Todd Wilson

Truss Type - Pratt

Photo: Todd Wilson

Truss Type - Double Intersection Pratt

Photo: Todd Wilson

Truss Type - Baltimore

Photo: Todd Wilson

Truss Type - Parker

Photo: Todd Wilson

Truss Type - Pennsylvania

Photo: Todd Wilson

Truss Type - Warren

Photo: Todd Wilson

Truss Type - Warren

Photo: Todd Wilson

Truss Type - Warren

Photo: Todd Wilson

Truss Type - Warren

Photo: Todd Wilson

Truss Type - Double Intersection Warren

Photo: Todd Wilson

Truss Type - Warren Quadrangular

Photo: Todd Wilson

Truss Type - K

Photo: Todd Wilson

Tension/Compression Configurations

• Simple– Beam or truss rests on one support on each end

• Continuous– Beam or truss continues over at least one support

between the end supports• Cantilever

– One (or both) ends of a beam or truss are projectedpast the end of a support - the projected anchor spans

– A subsequent beam or truss is connected to theprojected spans - the suspended span

Configuration - Simple

Photo: Todd Wilson

Configuration - Simple

Photo: Todd Wilson

Configuration - ContinuousPhoto: Todd Wilson

Configuration - Continuous

Photo: Todd Wilson

Configuration - Cantilever

Photo: Todd Wilson

Configuration - Cantilever

Photo: Todd Wilson

Configuration - Cantilever

Photo: Todd Wilson

Bending - Simple• A simple bridge bends the most at the midpoint

between supports• Simple bridges are often thickest in center

Photo: Todd Wilson

Bending - Continuous• An intermediate support causes bending• A continuous structure becomes thicker over a pier

Photo: Todd Wilson

Bending - Cantilever• Each projected span bends over a pier• Weight of suspended span applies a weight to the

ends of the projected spans• This also causes bending• Cantilevers are thickest over pier to resist bending

Photo: Todd Wilson

Classification of Form

• Bridges are classified based on location ofstructure relative to the road (deck)– Deck: (structure beneath road)– Pony: (structure next to, but not above road)– Through: (structure above road)– Half Through (structure above and below road)

Classification of Form - Deck

Photo: Todd Wilson

Classification of Form - Pony

Photo: Todd Wilson

Classification of Form - Through

Photo: Todd Wilson

Classification of Form - Half Through

Photo: Todd Wilson

Classification Challenge

• For each bridge, try to classify it!• Use the following categories:

– Form: deck, pony, through, half through– Type: tension, compression, tension/compression– Style: arch, suspension, cable stayed, beam,

truss– Beam Configuration (if applicable): deck, pony,

through, half through• Note: Some bridges will be combinations of

styles we discussed

Cable Stayed

Photo: Todd Wilson

Simple Through Truss

Photo: Todd Wilson

Continuous Deck Girder (Beam)

Photo: Todd Wilson

SuspensionPhoto: Todd Wilson

Cantilever Through Truss

Cantilever Deck Truss

Photo: Todd Wilson

Cantilever Through Truss & Arch

Photo: Todd Wilson

Through ArchPhoto: Todd Wilson

Tied ArchPhoto: Todd Wilson

Materials

• Steel– Weathering– Galvanized

• Iron• Wire Rope• Wood• Concrete• Reinforced Concrete• Masonry (stone)

More Design Considerations

ß Impact on area– Traffic– Railroad– Pedestrian

• Implementability• Signage• Lighting

• Marketing• Maintenance• Security/Crime• Size• Liability (Lawsuits)• Clearance• Attractiveness

ADA Requirements

• Bridge or structure must be handicappedaccessible

• Maximum slope: 1 ft rise per 12 ft run• Maximum rise between landings: 2.5 ft• 5 ft x 5 ft landing required where ramp

changes direction• Handrails required:

– Rise greater than 0.5 ft.– Run greater than 6 ft.

Some Bridge Websites• www.pghbridges.com• www.venangoil.com/bridges.html• www.oldohiobridges.com• www.historicbridges.org• okbridges.wkinsler.com• www.iceandcoal.org/bridges/bridgefront.html• bridgehunter.com• www.bridgemeister.com• en.structurae.de/index.cfm• memory.loc.gov/ammem/collections/habs_haer/index.html

Bridge Design Software

• http://bridgecontest.usma.edu/• Free bridge designer software

Good Luck!!!

Questions?

alancatt@gmail.comTodd.Wilson@dmjmharris.com