Dynamic Behaviour of the Confederation Bridge Under Seismic Loads

The 12.9 km Confederation Bridge, crossing the Northumberland Strait in eastern Canada, is one of the longest reinforced concrete bridges in the world. In the design of the bridge, the seismic hazard for the bridge location was represented by a seismic design spectrum. This spectrum was derived by applying spectral amplification factors to the peak ground acceleration, velocity and displacement, corresponding to the design life of the bridge of 100 years. The design forces and displacements due to seismic loads were computed using the modal response spectrum method. This paper describes results from a study on the dynamic behaviour of the Confederation Bridge due to seismic loads. The seismic hazard for the bridge location was represented by a uniform hazard spectrum corresponding to the most recent seismic hazard models. For the purpose of the seismic analysis of the bridge, a finite element model was developed using 3-D beam elements. The model was calibrated using measured data of the bridge vibrations during a dynamic load test. Dynamic time-history analyses were conducted by applying seismic excitation motions corresponding to the seismic hazard of the location. The bending moments and the displacements obtained from the seismic analysis were compared with the design values. It was found that the seismic effects used in the design are quite representative of the seismic hazard of the bridge location. (A)