ABSTRACT
ABSTRACT: The existing Poplar Street Interchange at I-55/I-64 in downtown St. Louis, MO adjoins the approach viaduct to the Poplar Street Mississippi River Bridge. A major seismic retrofit initiative was completed on the approach viaduct within the last 15 years. The ramps were not part of the retrofit project and are currently being replaced. The eastbound approach viaduct will also be widened to accommodate an additional lane. A design response spectrum was developed through the use of site specific probabilistic rock accelerations in conjunction with at-depth analysis of ground motion. Using the refined spectrum it was demonstrated, without time-consuming modeling, that the widening and new ramps would not appreciably affect the existing viaduct structure and associated retrofit details. Design of the new ramps for the seismic hazard was also greatly simplified. The refined seismic spectrum ultimately translated into time savings during a compressed design schedule and reduced structure costs.
