INVESTIGATION OF THE SEISMIC POUNDING EFFECT ON TORSIONAL RESPONSE OF HIGHWAY BRIDGES

This paper using an analytical approach investigates the effect of seismic pounding on torsional response of highway bridges by an emphasis on the variation of skewness angle. The occurrence of seismic pounding is limited to the case which a deck collides with abutments, and other casewhich the deck possibly collides with adjacent decks is not considered in this study. A simple analytical model with three degrees of freedom (3DOF model) accounting the skewness angle of the highway bridge is presented to measure the rotational motion of the deck caused by collision of the deck with abutments. It is assumed that the deck behaves rigidly in its own plane and columns remain linear during the ground excitation and, moreover, the soil-structure interaction is ignored due to the stiffness assumption of soil around the base of columns and behind abutments. The collision between the deck and abutments is limited to some candidate contact points placed between them. To simulate impact forces at these points the nonlinear viscoelastic contact model is employed. As a numerical example, a sample bridge is analyzed subjected to seven pairs of accelerograms recorded on stiff soil and the variation of stiffness eccentricity, skewness angle and width of expansion joints. Particularly, it can be inferred that in skewed highway bridges larger impact forces are transmitted to the deck through acute corners but no obtuse corners. Also, the results of the parametric study indicate that in highway bridges tending to the symmetry the seismic pounding amplifies the torsional response when the skewness angle and the width of expansion joint are increased. However in the asymmetric cases the seismic pounding is more influential for medium values of skewness angles ( =30°) and small values of the width of expansion joint (gap=5cm~10cm).

Keywords:

highway bridges , skewness angle , seismic pounding , non-linear viscoelasticcontact model , torsional response