Experimental Investigations of Dynamics of Queensborough Bridge

This paper presents results from the experimental investigations of the dynamic characteristics conducted on a long-span bridge in the Vancouver area, the Queensborough Bridge. This bridge is a key component of Canada's Highway 91, which leads through a highly populated area of the Fraser Delta. A major subduction zone is located off the coast of British Columbia and represents a significant risk of a possible megathrust earthquake with magnitude in the range of 8.5–9.0. The four lanes of the Queenborough Bridge were built to cross the North Arm of the Fraser River in 1960. These tests were part of an ongoing seismic retrofit program and were conducted to evaluate the bridge's dynamic response using an efficient technique to determine its fundamental dynamic characteristics from ambient vibration measurements. Although some results matched the expected behavior quite closely, others yielded additional insight into the dynamic response of the bridge. The results of soil-structure interaction at different locations along the bridge, which showed a close relationship between the lateral and vertical modes of vibration, presented rather valuable information for the retrofit efforts.