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 of bridge 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 a distance Due to gravity, all loads have a downward force (weight) All bridges can be classified into the following basic types based on how they carry 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 what is going on. They serve no structural purpose.
The top rods are pushed together in compression The bottom rods are pulled apart in tension
Tension/Compression - Beam Photo: Todd Wilson
Tension/Compression - Truss As a beam gets taller and taller, it becomes 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
Photo: Todd Wilson Truss Type - Bowstring
Photo: Todd Wilson Truss Type - Lenticular
Photo: Todd Wilson Truss Type - Pratt
Truss Type - Double Intersection Pratt Photo: Todd Wilson
Photo: Todd Wilson Truss Type - Baltimore
Photo: Todd Wilson Truss Type - Parker
Truss Type - Pennsylvania Photo: Todd Wilson
Photo: Todd Wilson Truss Type - Warren
Photo: Todd Wilson Truss Type - Warren
Photo: Todd Wilson Truss Type - Warren
Photo: Todd Wilson Truss Type - Warren
Truss Type - Double Intersection Warren Photo: Todd Wilson
Truss Type - Warren Quadrangular Photo: Todd Wilson
Photo: Todd Wilson Truss Type - K
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 projected past the end of a support - the projected anchor spans A subsequent beam or truss is connected to the projected spans - the suspended span
Photo: Todd Wilson Configuration - Simple
Configuration - Simple Photo: Todd Wilson
Photo: Todd Wilson Configuration - Continuous
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 of structure 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
Suspension Photo: Todd Wilson
Cantilever Through Truss
Photo: Todd Wilson Cantilever Deck Truss
Cantilever Through Truss & Arch Photo: Todd Wilson
Through Arch Photo: Todd Wilson
Photo: Todd Wilson Tied Arch
Materials Steel Weathering Galvanized Iron Wire Rope Wood Concrete Reinforced Concrete Masonry (stone)
More Design Considerations 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 handicapped accessible 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.com Todd.Wilson@dmjmharris.com