Tension members

Tension members are the simplest steel members because tension straightens a member instead of buckling it. Ties in roof trusses, bracing rods, hangers in suspension bridges and bottom chords of trusses all work in tension. The design question is which of several possible failures comes first.

There are three limit states. Yielding of the gross section causes excessive elongation; its strength is the gross area times fy divided by γm0. Rupture of the net section happens at the bolt holes, where area is reduced; its strength uses the net area and fu with the larger factor γm1, and a factor that reflects stress concentration. Block shear is a tearing failure where a chunk of plate tears out along a shear plane and a tension plane around a bolt group. The design strength is the least of the three.

Net area depends on the hole pattern. For a chain of holes across the plate, subtract each hole. For staggered holes, a zig-zag path may be critical, and each inclined segment adds back s²/(4g), where s is the stagger and g the gauge. Angles connected by one leg suffer shear lag, because the outstanding leg is not fully effective near the connection, so codes reduce their rupture strength. Slenderness limits prevent sagging and vibration of long tension members, and members that can reverse into compression under wind must also be checked as struts.