Seismic behavior of bidirectional-resistant ductile end diaphragms with buckling restrained braces in straight steel bridges

The ductile end diaphragm concept developed for regular (i.e., straight) slab-on-girder or deck-truss steel bridge superstructures is expanded to make it applicable to bidirectional earthquake excitation. Buckling restrained braces (BRBs) are used as the ductile fuses. Two retrofit schemes (Retrofit Scheme-1 and Retrofit Scheme-2) are investigated to seek the best geometrical layout to maximize the dissipated hysteretic energy of the ductile diaphragms with BRB end diaphragms. Closed form solutions are presented for practical design purposes. Behavioral characteristics (strength, stiffness, and drift) of the proposed retrofit schemes for end diaphragms are quantified with an emphasis on hysteretic energy dissipation. Results from selected numerical examples show that the generic bridge geometry, bidirectional loading, and the loading ratio (or the assumed combination rule), have a pronounced effect on the end diaphragm's inelastic behavior. Volumetric hysteretic energy dissipation is used to compare the effectiveness of the proposed retrofit schemes under several loading cases. These indicate that, in most cases, Retrofit Scheme-1 is superior to Retrofit Scheme-2 and may exhibit better seismic response.