Nonlinear methods of seismic analysis have been gaining acceptance by practicing engineers as a useful way of assessing and improving the seismic performance of structures in which the nonlinear behavior of components of the structural model is captured in great detail. For the nonlinear components of moment-resisting framed structures, ASCE 41 uses plastic rotation as the parameter for defining the acceptance criteria. Since plastic rotation is the key to the seismic damage assessment of moment-resisting frames, the method to calculate this quantity must be understood completely. However, engineers often rely on the output of plastic rotations from seismic structural analysis software packages for the assessment, but the actual analysis in achieving such plastic rotation quantities usually lie within a so-called black box. Many of these seismic analysis software packages use one algorithm for performing material nonlinearity analysis and use another algorithm for performing geometric nonlinearity analysis. It can be shown that running an algorithm considering material nonlinearity by itself will produce reasonably accurate results using most structural analysis software packages. Moreover, separately running an algorithm considering geometric nonlinearity also can produce accurate results. However, when material nonlinearity is combined with geometric nonlinearity in an analysis, accurate results nor even stable solutions may not be possible. The coupling effect between the two nonlinearities can be significant and needs to be verified through some analytical means. Yet, the verification process is difficult because a robust analytical framework for calculating plastic rotation is currently unavailable and urgently needed.
Citation: Computational Methods in Earthquake Engineering
Publisher Info: Springer, GX Dordrecht, -1
Pub Type: Book Chapters