Simplified Methods For The Analysis Of Non-classical Damping Of Isolated Bridges

There are two main ways for earthquake response analysis, i.e response spectrum method and time history method. The former, based on real modal theory and proposed earlier than the latter, is mostly used for elastic analysis, however, the latter can be used for non-linear analysis. The vital defect of time history analysis lies in it's sensitive to earthquake input, so analysis results may vary greatly among different inputs. Isolated bridges are relatively special, mostly for the damping characteristic of different parts aren't equal, which leads to non-classical damping problem. Engineering practice should consider the effect of non-classical damping, but this hampers the application of simple method, such as response spectrum analysis. Therefore, this paper introduced the main methods for dynamic response analysis of non-classical damped structure, then studied the effect of non-classical damping of isolated bridges by approximate decoupling method, and studied how to analysis the earthquake response of isolated bridges in a simple way, the main contents of this study include:1. The effect of non-classical damping of isolated bridges and applicability of approximate decoupling method.Approximate decoupling method neglects the off-diagonal terms of damping matrix, thus avoids the coupling problem. According to this concept, this paper studied the effect of non-classical damping and applicability of approximate decoupling method by changing bridge type, equivalent damping coefficient and earthquake input. On the basis of above study, this paper drew some conclusions: the effect of non-classical damping vary among bridge type, damping coefficient and earthquake input, firstly, regular model shows less sensitive to non-classical damping, compared with irregular ones; secondly, all models shows the decoupling error rises greatly if damping coefficient increases; thirdly, for regular model, different earthquake inputs don't lead to evident decoupling error, but as far as irregular models are concerned, the relative displacement between beam and pier is much more sensitive to earthquake inputs.