Envelope‐based pushover analysis procedure for the approximate seismic response analysis of buildings

Abstract

SUMMARY An envelope‐based pushover analysis procedure is presented that assumes that the seismic demand for each response parameter is controlled by a predominant system failure mode that may vary according to the ground motion. To be able to simulate the most important system failure modes, several pushover analyses need to be performed, as in a modal pushover analysis procedure, whereas the total seismic demand is determined by enveloping the results associated with each pushover analysis. The demand for the most common system failure mode resulting from the ‘first‐mode’ pushover analysis is obtained by response history analysis for the equivalent ‘modal‐based’ SDOF model, whereas demand for other failure modes is based on the ‘failure‐based’ SDOF models. This makes the envelope‐based pushover analysis procedure equivalent to the N2 method provided that it involves only ‘first‐mode’ pushover analysis and response history analysis of the corresponding ‘modal‐based’ SDOF model. It is shown that the accuracy of the approximate 16th, 50th and 84th percentile response expressed in terms of IDA curves does not decrease with the height of the building or with the intensity of ground motion. This is because the estimates of the roof displacement and the maximum storey drift due to individual ground motions were predicted with a sufficient degree of accuracy for almost all the ground motions from the analysed sets. Copyright © 2013 John Wiley & Sons, Ltd.

Concept of Risk-Based Seismic Design of Buildings Using Methods of Nonlinear Analysis

“…For brevity, the detailed description of these pushover-based methods is omitted in this paper. However, an overview of recently introduced envelope-based pushover analysis procedure [27] is given in the following subsection. This procedure involves nonlinear response history analysis for equivalent single-degreeof-freedom models, which correspond to pushover analyses based on invariant force vectors associated with the first three vibration modes.…”

“…However, for some ground motions from a set, the system failure modes observed in the response history analysis cannot be simulated by the 'first-mode' pushover analysis. For this reason, the modal-based SDOF model becomes inaccurate in order to estimate the collapse fragility [27]. This awareness is not new.…”

“…They concluded that the 'first-mode' SDOF models can estimate the median roof displacement to a useful degree of accuracy, whereas this may not be true in the case when the roof displacement is estimated for an individual ground motion. This inability of the modal-based SDOF model motivated Brozovič and Dolšek [27] to perform a detailed study in order to better understand when the 'first-mode' SDOF model provides inaccurate estimates of global response of structures. They came to an interesting conclusion, that for particular ground motions, the 'first-mode' SDOF model always provides sufficiently accurate estimate of global response of buildings regardless how tall the building is, whereas for some other ground motions, the response of build-ings based on the 'first-mode' SDOF model cannot be simulated with useful degree of accuracy even for buildings having only four stories.…”

“…An emphasis is given on the envelope-based pushover analysis procedure [27], which was recently developed, and assumes that the seismic demand for each response parameter is controlled by a predominant system failure mode that may vary according to the ground motion and intensity level. The concept of the risk-based design procedure as foreseen in the project is then explained.…”

Risk-Based Design Check for Collapse Safety Using Few Ground Motions

“…There are several other reasons why the characteristic value of collapse intensity is selected at low percentile of collapse intensities. For example, (i) uncertainties associated with the seismic hazard are controllable at lower intensity levels, (ii) scale factors of ground motions are more likely in the range which still allow unbiased estimates of seismic demand, (iii) the accuracy of simplified methods to provide approximate collapse intensities is greater for those ground motions which cause the collapse of buildings at low intensities [16] and (iv) it is well known that the intensities which have the largest contribution to the collapse risk occur in the lower half of the collapse fragility function, e.g. [12].…”