Capacity design principles and ductile end-diaphragms to seismically retrofit slab-on-girder steel bridges having vulnerable substructures

Steel bridges are frequently supported by seismically vulnerable substructures, as demonstrated by recent earthquakes. Current practice generally consists of seismically retrofitting these non-ductile substructures; this can be, in many cases, a rather costly operation. In order to recognize the benefits granted by the presence of a steel superstructure, an innovative seismic retrofit strategy using ductile steel bridge end-diaphragms has been developed. By replacing the steel diaphragms over abutments and piers with specially designed ductile diaphragms (such as shear panels, eccentrically braced frames and TADAS devices) calibrated to yield before the strength of the substructure is reached, the substructure can be protected and need not be retrofitted, resulting in considerable savings.