Behaviour and seismic design of stiffeners for steel bridge tower legs and piers

Abstract

Thin-walled steel box columns have wide applications in piers of urban highway bridges, and in the towers of suspension and cable-stayed bridges. Currently, in practice, the stiffeners for tower legs and steel box pier columns are flat plates, all having the same cross sections and equally spaced from each other and from outside walls. With the constraint due to the adjacent walls, and with the stiffeners, especially the middle stiffeners, being not stiff and strong enough to form nodal lines due to yielding during cyclic loading, the middle portion of the stiffened plate tends to have the largest out-of-plane deformation. A new and more efficient concept for design of longitudinal stiffeners is proposed in this paper - to invest more stiffening material in the middle stiffeners instead of making all stiffeners to have the same cross section. In addition, based on the studies summarized here, we propose to use sections other than flat plates as stiffeners. We studied the effects of stiffeners cross sections and stiffener spacing on the local and overall buckling as well as the resulting stiffness and cyclic ductility of the steel box pier and steel tower legs. Our investigations showed that using stiffeners with an angle, plate or pipe welded to the traditional flat plate stiffener can improve the performance of the stiffened plate considerably - delay local buckling and increase cyclic ductility of the stiffened plate. Some of the new stiffener geometries we studied and recommended can very efficiently be used in seismic retrofit of the steel box piers and tower legs of elevated freeways and major cable-supported suspension and cable-stayed bridge towers.