Design of Seismic Restrainers for In-Span Hinges

A reinforced concrete, box-girder bridge will collapse during an earthquake if the relative displacement between adjacent frames at an in-span expansion joint exceeds the available seat width. To identify factors that most affect these relative displacements, 216 nonlinear response-history analyses were conducted for various frame, abutment, and restrainer properties, as well as for four ground motions. The researchers considered only longitudinal motion of straight bridges without skew, and the ground motions were assumed to be coherent. Maximum relative joint displacements were sensitive to the stiffnesses of adjacent frames, the frames' effective periods, and the restrainer properties. The relative displacement between the frames and abutment seats was sensitive to the overall stiffness and weight of the bridge. Based on the results of the parametric study, new design procedures are proposed for designing in-span seismic restrainers and abutment seats. Examples illustrate both procedures. Compared with existing design methods, the proposed methods result in restrainer designs that are more consistent with the results of nonlinear analysis.