Bidirectional-resistant ductile end diaphragms for straight steel bridges

Ductile end diaphragms can be used both in retrofit and new design of bridges superstructures to mitigate seismic damage in other substructure and superstructure members. They have been introduced in the latest AASHTO Guide Specifications as a structural system that can be used to resist transverse earthquake effects. Here, the ductile end diaphragm concept developed for straight bridges is expanded to make it able to resist bidirectional earthquake excitations. Buckling restrained braces (BRBs) are used as the ductile fuses. Two bidirectionally-acting end diaphragm configurations (EDS-1 and EDS-2) are proposed and analytically investigated to seek the best geometrical layout to maximize the dissipated hysteretic energy. Closed form solutions are presented for practical design purposes. Strength, stiffness, and drift characteristics of the proposed configurations are quantified with an emphasis on hysteretic energy dissipation. Numerical results show that the generic bridge geometry, bidirectional loading, and the loading ratio, have a pronounced effect on the end diaphragm's inelastic behavior. In specific circumstances, each of the diaphragm concepts considered exhibit better seismic response, depending on the aspects of response that are deemed preferable in specific applications.