physics
posted by Rebecca .
What is a cross sectional area of a bridge and does it affect the length of a bridge?

Generally, first the length of a bridge is determined, and the cross section of the bridge is designed such that it will resist the bending moments, shear forces, and axial forces(if any) exerted on the bridge supporting member.
The longer the span (i.e. length between supports), the higher is the bending moments, so the cross section has to be deeper (taller). To support the increased shear forces or axial forces, the cross sectional area has to be increased.
In addition, the bridge members have to be braced laterally to prevent buckling, a failure that can occur before relatively slender beams are fully stressed.
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