Bridge Builder
Objective: Use the online Bridge Builder program to build bridges.
Wooden truss bridges were used as early as the 1500s, but the first metal one was completed in 1841. They are very strong and have been used for railroad bridges mainly because of the heavy loads that they can support. A truss, a rigid support structure that is made up of interlocking triangles, holds up the roadbed and is set between two piers. The triangle is used because it is the only shape that is inherently rigid.
Pros and Cons of Truss Bridges
Pros: Very strong; frequently used as a draw bridge or as an overpass for railroad trains
Cons: Difficult to construct; high maintenance; difficult to widen if necessary; generally not considered attractive
■ ■ Compression and Tension ■ ■ ■
Compression: As traffic pushes down on the roadway, compression acts on the upper horizontal members of the truss structure.
Tension: Tension acts on the bottom horizontal members of the truss structure. The forces of tension and compression are shared among the angled members.
