Response of multi-span bridges subjected to seismic excitation

Multiple support excitation (MSE) during earthquakes is a significant hazard for structures with large distances between ground support points. Typically this applies to long-span bridges, with Eurocode 8 recommending that bridges longer than 600m are assessed under the effects of MSE. Much research has been carried out on modelling long span bridges with MSE both numerically and analytically, however very few experimental programmes have successful investigated the effect of MSE on bridges. In addition, previous analytical work has suggested that for shorter multi-span bridges (less than 200m) MSE can also have an effect on the overall bridge response which is at odds with the recommendations in Eurocode 8. This paper summarises the results of a series of tests at Bristol University looking at the effect of MSE on bridges. To generate the different input motions at each of the bridge piers a set of five parallel single axis shaking tables have been used to shake a variety of different bridge configurations. These tests have confirmed that, even for short multi-span bridges, MSE can have a significant effect on the bridge response and that the response of some piers may be underestimated if only synchronous ground motion is assumed.