Seismic Analysis Of A Combined Suspension And Cable Stayed Bridge System

Abstract

This work presents the experimental and analytical evaluation of the Wheeling suspension bridge, a historic American landmark and the longest single span suspension system in the world for many years. The study was funded by the Federal Highway Administration and the West Virginia Department of Transportation to assess the condition of the structure and determine its response to selected seismic motions in order to recommend proper retrofit measures and possible strengthening of the bridge. The bridge is one of the few historic suspension bridges still in service in the U.S. The 307 m bridge deck is suspended by two main suspension cables assisted by diagonal stay cables. The stay cables are located within the end quarter spans, they pass over the saddles at each tower and are anchored into the main cable anchorages. The study includes in-situ testing of the cable system, validation of two- and three-dimensional finite element models to reflect the modal characteristics of the bridge, static analysis of the structure for code defined dead and live loads, and several seismic analyses using AASHTO seismic loads and historic earthquake data. The AASHTO seismic loads were modified to correspond to 10% probability of being exceeded in 100 years. The historic data were based on Mercalli intensity local earthquakes recorded in the early eighteenth century. Load rating indicated that none of the structural members are overstressed by the posted live load. The seismic analysis to AASHTO loads showed little damage that was confined to floor beams at the east tower. Analysis using historic earthquakes showed localized damage of floor beams and diagonal floor ties at the east tower and top chords of the stiffening truss at mid-span. The study concludes that the methodology can be applied to a wide range of cable suspension bridges.