Seismic Design and Performance of Ductile End-Diaphragms in Slab-on-Girder Steel Bridges with Flexible Substructure

Abstract

Conventionally, in the conceptual seismic design of bridges, absorption of earthquake energy is provided through plastic deformation in the main components of the bridge, such as columns and walls. In recent decades, ductile end-diaphragms have been proposed as one of the passive control systems to reduce the inelastic deformation in the substructure of steel bridges by transferring the majority of seismic energy dissipation to diaphragm inelastic deformations under ground motion in the transverse direction. The proper operation of these systems with stiff substructures has been already demonstrated in several numerical and experimental studies, but the need for separate studies about their design and performance in steel bridges with flexible substructures is quite tangible. In this article, first, the generalized single-degree-of-freedom (SDOF) dimensionless relations of single-span and continuous three-span bridges located on flexible piers are developed. Then, using some assumptions, the relations are extended to the inelastic range. Different forms of ductility imposed on bridges equipped with ductile end-diaphragms, including global, support, diaphragm, and damper ductility, are identified. Moreover, using simplified analyses, a new step-by-step design method is proposed, and the accuracy of the results is verified using nonlinear time-history analyses for some numerical examples. The simultaneous role of the substructure stiffness and deck flexural stiffness and the contribution of girder stiffness in the design and evaluation of ductile diaphragms are examined. Results indicate that increasing flexibility of the substructure may result in superstructure damage like yielding of the girders or impractical required damper components. Although the main focus of this article is on the design of ductile end-diaphragms, because of the subject generality, the concepts can be extended to slab-on-girder steel bridges equipped with other yielding devices.