Effect of pounding and restrainers on seismic response of multiple-frame bridges

Pounding between adjacent frames in a multiple-frame bridge produces undesirable forces resulting in large displacements, local damage. and possible failure of column. bents. In this study, analytical models are used to examine the factors affecting the global response of a multiple-frame bridge due to pounding of adjacent frames. Parameter studies of one-sided and two-sided pounding are conducted to determine the effects of frame stiffness ratio, ground motion characteristics, frame yielding, and restrainers on the pounding response of bridge frames. It is determined that the most important parameters are the frame period ratio and the characteristic period of the ground motion. The amplification in the frame response due to one-sided pounding is most severe for cases with highly out-of-phase frames, in particular for short period structures. Two-sided pounding amplifies the stiff frame response, and reduces the flexible frame response. The addition of restrainers has a minor effect on the one-sided pounding response of highly out-of-phase frames. Current recommendations by Caltrans for limitations in frame period ratios to reduce the effects of pounding are evaluated through an example case.