INFLUENCES OF DAMPING PROPERTIES ON BRIDGE NONLINEAR SEISMIC RESPONSES

摘要

In the typical time history analysis of singledegree-of-freedom (SDOF) systems,a hypothesis of 5% elastic damping ratio is adopted,which is believed to be related to the initial stiffness though not clarified in most former researches. However,recent studies argued that the tangent stiffness based elastic damping is more logical and this may result in major differences of analysis results from the initial stiffness damping definition. In this paper,substantial nonlinear time history analyses of real bridges with elastic damping properties defined respectively with the initial stiffness and tangent stiffness are conducted to study the influence of damping properties on bridge nonlinear seismic responses. The results show that,tangent stiffness based elastic damping yields larger displacement demands than the initial stiffness based elastic damping hypothesis especially when the ductility factor is large,and is advised to be the preferable choice in the nonlinear time history analysis. The influences of damping ratio on displacement modification factor are considerable using the tangent stiffness based elastic damping hypothesis,implying that the traditional treatment of neglecting the damping factor in the displacement modification factor method is not always suitable considering the damping theory and value uncertainties. Simplified approaches to calculate SDOF nonlinear seismic demands with elastic damping ratio other than 5% are also discussed and some advices are proposed.