Moment‐Rotation Tests of Steel Bridge Girders

Abstract

Three transversely stiffened A572 Grade 50 steel girders were tested to obtain full moment‐rotation curves for use in the autostress design of continuous‐span bridge girders. The flange and web slendemess ratios were close to the limiting AASHTO values for transversely stiffened girders. The tests included a variety of conditions that affect rotation characteristics: (1) Symmetric and unsymmetric cross sections; (2) long and short spans; (3) relatively large and small amounts of initial out‐of‐flatness; and (4) relatively large shear stresses. Each specimen reached a maximum moment very close to its yield moment and then was able to sustain large plastic rotations as further deflections were imposed to obtain the unloading portion of the momentrotation curve. A simple equation was developed to represent a lower bound for the plastic rotation capacity of the specimens at various moment levels. Two alternative ways of utilizing ah effective plastic moment based on this equation in autostress design procedures are suggested.