An optimum retrofit strategy for moment resisting frames with nonlinear viscous dampers for seismic applications

The dynamic response of a multi-story steel moment resisting frame (MRF) equipped with fluid viscous (VS) dampers and subjected to seismic loads is investigated numerically. The structure is retrofitted with two fluid VS dampers per story in its middle bay. Its dynamic response is analyzed when retrofitted with linear and nonlinear VS dampers. Two performance indices are developed in order to evaluate by means of a simple procedure the adequacy of each retrofitting option. The different options are evaluated and an optimum design is selected. The main objective of this numerical research is to build a simple methodology leading to an optimum retrofitting option with nonlinear fluid VS dampers. A secondary objective of the study is to compare the structure response retrofitted with linear and nonlinear VS dampers and finding an optimum retrofit strategy attending to two performance indices that are developed. The seismic behavior of a six-story steel structure is analyzed and it is found that the maximum force experienced by the dampers in the nonlinear case may be reduced in more than a 35% in comparison with the linear retrofitting case with a similar structural seismic performance. (C) 2003 Elsevier Science Ltd. All rights reserved.