Cyclic testing of ductile end diaphragms for slab-on-girder steel bridges

Ductile end diaphragms have been proposed as seismic retrofit strategy to protect the substructures of existing steel slab-on-girder bridges from damage during earthquakes. This paper presents the results from an experimental program to investigate the adequacy of some proposed details. Cyclic tests on full-size girder specimens having the proposed ductile diaphragms demonstrate that these can possess adequate initial elastic stiffness, strength, and capacity to dissipate hysteretic energy in the intended manner. The specimens developed a rotational capacity of 0.2 rad when energy dissipation devices of the TADAS (Triangular-plate Added Damping And Stiffness) type were used, and link distortion angles of 0.08 to 0.11 rad when eccentrically braced frame and shear panel systems were in place, corresponding to average ductilities of 8 to 10 before failure. Better performance of the eccentrically braced frame system would have been possible had lateral support been provided at the ductile link. However, ductile end diaphragms having bolted connections suffered significant slippage, leading to pinched hysteretic curves. Tests show that welding significantly improves the seismic behavior of these ductile systems. Specimens with nominal channel diaphragms and those without any diaphragm dissipated significantly less hysteretic energy, and suffered bolt rupture, buckling of the web stiffeners, and fracture of the stiffeners welds at large drifts.