Characteristics of combined loading demands on the piers of skewed bridges

Due to the correlation of natural vibration modes of skewed bridges, and the multi-directional nature of the earthquake ground motions; piers of skewed bridges would be subjected to combined axial, flexural and torsional loadings. The characteristic of combined loading of the piers depends upon several parameters including the strong ground motion characteristics and the structural system type. In this research seismic performance of a group of torsion sensitive skewed bridges with three different pier-deck connections is studied. Skew angles vary from 0° to 60°. Seismic performance of the bridges is investigated conducting bidirectional nonlinear time history analysis in OpenSees. Considering the effect of different pier-deck connection types, combined loading demand on the skewed piers is compared with those on the straight piers. On the basis of results, for both pinned and fixed piers, ductility demand increases with the skew angle. Opposed to pinned piers, fixed piers are subjected to combined torsional-flexural loadings, and the torsional demand increases with an increase in the skew angle. The value of torsional demand on fixed piers is limited to one half of cracking torque of the section (Tcr/2). Concerning to the collapse prevention criteria, 30 degree skew angle is found to be a threshold skew angle. For bridges with skew angles greater than 30 degree, applying monolithic pier-deck connections is more sensible.