Mechanism Based Assessment of Damaged Building's Residual Capacity

Abstract eng:
Seismic behavior of damaged buildings may be expressed as a function of their REsidual Capacity (REC). The residual capacity RECSa is defined as the minimum spectral acceleration (at the period Teq of the equivalent SDOF) corresponding to building collapse. When referring to peak ground acceleration ag as damaging intensity parameter, RECag is defined as the minimum anchoring peak ground acceleration such as to determine building collapse. For a given spectral shape, RECag corresponds to RECSa scaled by the spectral amplification factor for Teq. RECSa and RECag, generally indicated as REC, lower with increasing damage level in buildings; hence REC may be very useful in estimating the post-seismic building safety. In a recent work [1] it has been shown how it is possible to derive REC (RECSa and RECag) through Pushover Analyses (PA), where a suitable modification of plastic hinges for damaged elements is applied. The applicability of PA for damaged structures is verified in [2] by comparison of the PA results with those on nonlinear time-history analyses. On the other hand, it is unrealistic that in the aftermath of an earthquake, when the assessment of building safety has to be performed in an emergency situation, there would be time for the execution of detailed nonlinear analyses. Acknowledging the need for easier and faster evaluation tools, in [3] a simplified MEChanism based method (MEC) for evaluating the building REC was preliminary tested. The present work extends the comparison of the results (in terms of REC), that could be obtained by PA and MEC analyses, considering a number of Reinforced Concrete (RC) frames building typologies. Moreover, by adopting the MEC approach, the possible variation of REC as a function of seismic demand is investigated. The simplified method can be used to explore the possible ranges of REC variation for RC building classes considering the anticipated mechanism formation after an earthquake; in addition, it could be used in the post-seismic phase for estimating the REC of damaged buildings having undergone identifiable plastic mechanisms and for fast assessment of damage-dependent collapse fragility curves.

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