Evaluation of pushover procedures for the seismic design of buildings

Student: Dario Pietra
Supervisors: Dr Rui Pinho


A number of recent studies raised doubts on the effectiveness of conventional pushover methods, whereby a constant incremental force vector is applied to the structure, in estimating the seismic demand/capacity of framed buildings subjected to earthquake action. The latter motivated the recent development of the so-called Adaptive Pushover methods whereby the loading vector is updated at each analysis step, considering one or more response modes, reflecting in this way the effects that damage progression have on the response characteristics of structures subjected to increasing loading levels. Within such adaptive framework, the application of a displacement incremental loading vector becomes not only feasible but also possibly advantageous since it seems to lead to superior response predictions, with little or no additional modelling/analysis effort, with respect to conventional pushover procedures. In this work, a parametric study, whereby the accuracy of the Displacement-based Adaptive Pushover algorithm (DAP) in predicting the seismic response of 3-, 9- and 20-storey high steel buildings responding in the inelastic range is presented. A large set of natural records is used in the dynamic analyses that are carried out for comparison. The performance of the adaptive procedures is evaluated in terms of prediction of the main structural response parameters of interest (interstorey drifts, shears and overturning moments). Results, expressed as absolute values of these design parameters as well as their ratio between static- and dynamic-analysis values, are compared with those provided by conventional pushover schemes. Results show that DAP, compared with non-adaptive procedures, represents an alternative simpler procedure (involving a single pushover analysis) that allows predicting the response shape of high-rise steel buildings with an accuracy that is at least as good as that obtained with more complex multiple-pushover procedures.

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