DAMAGE TO CABLE-STAYED BRIDGE DURING 1988 SAGUENAY EARTHQUAKE .2. DYNAMIC ANALYSIS

The November 25, 1988, Saguenay earthquake (M(L) = 6.0) is the largest seismic event recorded in eastern Canada. The cable-stayed Shipshaw b ridge, which crosses the Saguenay river near Jonquiere, Quebec, suffer ed significant structural damage during the earthquake. One of four an chorage plates connecting the steel box girders to one abutment failed , apparently due to the ground shaking. This paper is the second of tw o companion papers describing the circumstances of the failure. This p aper deals with the dynamic analyses and testing of the bridge that we re performed to confirm the cause of failure. Free-vibration analyses were undertaken to determine the natural frequencies and mode shapes o f the bridge. These results were verified by field vibration measureme nts. A nonlinear dynamic model of the contact friction at the tie-rod assembly was derived. The model was incorporated in nonlinear time-ste p dynamic analyses using horizontal and vertical accelerograms recorde d near the site. The results of these analyses confirm the hypothesis that the Saguenay earthquake was the direct cause of failure.