Towards a Practice-Oriented Strategy To Include Losses in the Seismic Assessment of RC Frame Buildings

Abstract eng:
One of the main objectives of Performance-Based Earthquake Engineering (PBEE) is to allow for the direct analysis of a set of decision variables characterizing the response of a structure located in a specific site. Among these decision variables, loss metrics are particularly important due to their direct connection to the decisions related with retrofitting needs and postearthquake reparability issues. Despite the recognized importance of these decision variables (DV) for stakeholder information and to develop adequate mitigation strategies, their inclusion in current seismic assessment frameworks for RC frame buildings is still limited when assessing the performance of both new and older structures. Conversely, most of the assessments are based on engineering demand parameters (EDPs) such as interstorey drifts or component deformations, which are used as benchmarks to classify the damage states and the overall performance of a building. However, the information provided by EDPs is insufficient to support adequate decision-making by stakeholders, mostly because they do not provide objective estimates for the potential post-earthquake reparability needs and for the respective losses/costs they may involve. In some cases, the importance of losses and repair costs might even be larger than that of the probability of collapse of the building when exposed to a given scenario. As an example, for lower seismic hazard levels, a structure may present inadequate damage accumulation which may lead to excessive repair needs or even to the decision of replacing it by a new structure, while exhibiting a low probability of collapse. With this in mind, the present paper analyses how decision variables can be included in the assessment of the expected losses or of loss-based limit states in RC frame buildings. Specifically, the derivation of simplified analytical tools is addressed, since they provide expressions that are simple to apply and allow for a widespread use of PBEE methods within the technical community. Moreover, such analytical expressions do not require extensive knowledge on probabilistic analysis or the use of numerical integration procedures. Methodologies to include loss estimates into standard intensity-based assessments and in limit state compliance criteria for the evaluation of the mean annual frequency of exceedance are developed in the paper. A first approximation is analysed using a storey-based loss assessment approach to verify how to analytically estimate the losses based on the demand results obtained from an intensity-based assessment. An analytical function is fitted to EDP-DV datasets available in the literature and an expression is proposed to compute the expected value of the losses using the distribution of the interstorey drifts evaluated at a stripe of ground motions (intensity-based assessment). Secondly, a new set of limit state conditions is analysed using the referred analytical storey-based loss assessment approach combined with incremental dynamic analysis and scalar loss variables.

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