Calculating the Impact of Partial Warp Restraint on Steel Girder Elastic Buckling Strength

The impact of warp-restraint devices on girder elastic buckling strength has typically been estimated by assuming no warp restraint or total warp restraint at both ends of the girders. However, neither of these conditions is typically present in steel bridge construction. In a typical steel bridge, even one with warp restraining devices, two ends of any given girder segment will be restrained to different degrees by a warp restraining device at the abutment or pier and by any adjacent segments in the span of the bridge.

Previous research has shown the large impact warp restraint has on girder elastic buckling strength. In particular, large scale buckling tests at the University of Texas at Austin Ferguson Structural Engineering Laboratory with subsequent computational studies, and an energy solution proposed by Trahair have resulted in methods to analytically estimate the increase in buckling strength. However, these methods have not been applied to continuous girders where the end restraints on the critical span may differ and include warp restraining devices. This paper investigates these conditions using a series of parametric studies with a previously validated finite element model and proposes a method to account for the increase in elastic buckling strength due to a split pipe warp restraining devices at the abutments and intermediate piers of continuous span girders.

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