On structural damage processes of storm and earthquake-induced low-cycle fatigue

Abstract eng:
This paper specializes recent concepts of structural damage evaluation to design of structures under earthquake respectively storm actions. Thereto, the paradigm that structures fail by passing of their damage evolution over an ultimate bound, is extended to both mentioned excitation. The work first adopts the necessity of additional protection aims, beyond failure safety, in the framework of performance-Based Engineering. Concentrating then on quasi-static approximations of time-dependent structural processes, e.g. pushover concepts in earthquake engineering, the manuscript simplifies non-linear time-history analyses by nonlinear quasi-static design tools. This time-independent concept is connected with low-cycle fatigue failure, focusing now on RC structures. The entire treatment will be embedded into a finite element (FE) environment, and the tangential stiffness matrix KT then is identified as the most general assemblage of structural damage information: Its spectra of eigenvalues λi or of natural frequencies ωi serve to derive damage indicators Di, applied to quasi-static approximations of structural seismic as well as wind damage problems. Because of det KT = 0 denoting structural failure, such damage indices range from the virgin situation Di=0 up to their failure values Di=1. They thus correspond well with FEMA-proposals on Performance-Based Seismic Design. Finally, the developed concept is checked by re-analysis of two experimentally investigated RC frames and by the damage simulation of a natural draft cooling tower.

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