NONLINEAR DYNAMIC ANALYSIS PROCEDURE WITH LIMITED NUMBER OF ANALYSES AND SCALING

Abstract

Incremental dynamic analysis (IDA) is the most frequently used non-linear dynamic analysis procedure for seismic fragility assessment. Nevertheless, its implementation involves complications such as heavy computational burden and potential bias in the results due to excessive scaling of the ground motion records. Cloud Analysis is an alternative nonlinear dynamic analysis procedure based on the structural response to as-recorded ground motions. Cloud Analysis does not suffer from the above-mentioned complications for IDA; however, it may lead to results that reveal too much sensitivity to the choice of the ground motion records. A novel hybrid nonlinear dynamic analysis procedure referred to as “Cloud to IDA” exploits the predictive capacity provided by Cloud Analysis to perform Incremental Dynamic Analysis (IDA) in a very efficient manner and with very little amount of scaling --without any loss of accuracy with respect to IDA. The procedure adopts as a systemic damage measure the critical demand to capacity ratio (DCR). This facilitates to a great extent identification of the intensity values at the onset of the limit state (where DCR is equal to unity by definition) and thereby the implementation of the IDA procedure. Cloud to IDA procedure is applied to the transverse perimeter frame of an older seven-storey reinforced concrete building in Van Nuys, US. This frame is modeled in OpenSees with fiber sections considering flexural-shearaxial interactions and bar slip due to fixed-end rotations. The proposed Cloud to IDA leads to results that are identical to IDA, when the same set of records are used. All of this is possible with a number of analyses that is sensibly lower with respect to IDA.