Displacement Based Analysis of Steel Girder Bridges with Ductile End Cross Frames

Steel bridge superstructures will not necessarily remain elastic during transverse earthquake excitation unless designed to do so. Unlike in structural concrete bridges, it is possible to use components in the superstructure of steel girder bridges to reduce the transverse seismic forces. Recent experimental and analytical investigations showed that ductile end cross frames are effective in reducing the transverse seismic demand. The primary objective of this paper is to describe a displacement based analysis procedure for the design of ductile end cross frames. The displacement based capacity-demand spectrum analysis procedure used for the design of seismically isolated bridges is adapted for the design of bridges with ductile end cross frames. The bi-linear properties of the end cross frames are defined by the properties of the ductile braces and transverse stiffness of the girders. In order to minimize the transverse girder stiffness and maximize the allowable drift in the ends of the girders they are designed with no shear studs in the regions directly above the supports, and bearings which can accommodate relatively large rotations. Minimum and maximum bi-linear properties are used during analysis of a bridge with ductil