The Biggest Factors in Deciding Bridge Design

Many factors go into deciding on the best design for a bridge.

Designing a bridge is a serious undertaking. Depending on what it will be used for, you must consider safety, durability and functionality. The requirements for each of these will vary with the landscape around the bridge, the bridge size and how long it is meant to last. For every bridge, there are some basic characteristics that describe how the bridge is made.

Bridge Span

Span refers to how many sections the bridge itself will be in and the space between supporting structures. A continuous span means the entire bridge is in one piece. Simple spans are built in sections that split over the weight bearing braces or columns. Cantilever spans project beyond supporting structures and are supported only at one end.

It is important to consider how long the bridge must be, and whether or not it will be hinged.

Travel Surface Configuration

This refers to where the bridge traffic will be relative to the structure itself. With a deck truss, traffic moves over the entire bridge structure. In a pony truss, traffic goes between two parallel structures that have no cross bracing within the top structure section. A through truss allows traffic to move through one large structure that is cross braced both above and below the traffic.

Bridge Form

The form of a bridge is basically its overall shape. Beam bridges are horizontal structures that support traffic by resisting bending, Typically made of metal or concrete. Arch bridges get their support from an upward curving arch shape that provides support either above or below the bridge's traffic. In addition to dictating traffic surface configuration, truss is also a type of bridge form. Trusses are actually made of several smaller parts.

Building Material

The material used to build a bridge will generally be metal, concrete, wood or stone. The type of material will depend on safety and functionality needs, as well as aesthetic preferences.

Surrounding Landscape

The type of landscape the bridge rests upon and travels through will dictate the terms of many other building aspects. Soil conditions, weather and environmental concerns must all be considered when designing the bridge.

References

• PGH Bridges: Bridge Basics
• Ohio Department of Transportation: Bridge Terms Definitions
• NIreland.com: Bridge Design

Resources

• 42 Explore: Bridge Building