Collapse safety margin and seismic loss assessment of RC frames with equal material cost

Abstract

SummaryWith the premise of equal material cost, a collapse safety margin-based collapse resistance optimization strategy for passively controlled reinforced concrete (RC) frames is proposed based on seismic fragility analysis, collapse safety margin analysis, and seismic hazard loss assessment.The efficiency of introducing buckling restrained braces or lead-rubber bearings on the performance of RC frames is studied by so-called collapse margin ratio (CMR) suggested by FEMA P695 and the modified rigidity-to-gravity ratio (RGR). The proposed strategy is developed from the case study on 4 low-rise and medium-rise RC frames and then verified on a high-rise RC frame. The study indicates that lead-rubber bearings can cause a significant improvement at all damage levels. The contribution of buckling restrained braces to structural stiffness and collapse resistance can be maximized when they are located in potential weak stories determined through inelastic time history analysis. CMR exhibits a better linear relation with the minimum modified RGR. Increasing the equivalent story lateral stiffness and the minimum modified RGR simultaneously can give rise to a significant improvement in seismic capacity, especially CMR. Base isolation is proved to be desirable not only for improving the collapse safety margin of RC frames significantly but also for reducing seismic hazard loss. KEYWORDSbuckling restrained brace, collapse safety margin, equal material cost, lead-rubber bearing, optimization, seismic loss 1 | INTRODUCTION Earthquake-induced damage or even collapse in building structures can cause substantial economic loss or even casualties. As is well-known, earthquakes are typically rare and random probabilistic events. It is much of importance for building structures, especially for essential buildings, for example, hospitals, tall buildings, and communication center to possess adequate collapse resistance in case of these accidental events.[1]As one of quantified indexes for structural collapse resistance, the collapse margin ratio (called CMR hereafter) suggested in the Federal Emergency Management Agency (FEMA) P695 report [2] can quantify the relative margin between the performance of structures under rare-level earthquakes and that of structures under earthquakes causing the probability of collapse of 50%. CMR is determined based on collapse fragility analysis that arises from the incremental dynamic analysis method. [3] CMR is dependent on many factors, for example, structural height, component span, strength deterioration, stiffness degradation, and uncertainty of ground motions. Some investigations have been carried out in this aspect. [4][5][6] Liel et al. [7] compared the collapse safety margin of ductile structures and nonductile structures. They observed that ductile structures would be able to resist stronger earthquake because they can experience substantial inelastic deformation before collapse. Manie et al. [8] used CMR to assess the collapse safety margin of low-rise plan-asymmetric with different plan e...

Estimation of Aleatory Randomness by Sa(T1)-Based Intensity Measures in Fragility Analysis of Reinforced Concrete Frame Structures

“…Two typical 4-and 8-story RC frame structures with seismic design [36,37] according to the current Chinese Code for Seismic Design of Building [38] are selected as the analysis cases, as shown in Fig. 1.…”

“…The frame beams and columns are made of C40 concrete, and the longitudinal reinforcement is HRB335. The detailed dimensions and reinforcement information of frame beams and columns can be found in Wang [36] and He et al [37].…”

“…Table 2 summarizes some transverse and longitudinal vibration periods of the two RC frames. More detailed modeling information can be obtained referring to Wang [36] and He et al [37].…”

Seismic Performance Evaluation of Special RC Frames with Gravity Steel Columns under the Base Level

“…. IDA procedure recommended by FEMA P695 involves performing a series of nonlinear dynamic time-history analyses using 22 pairs of ground motion records [35]. Individual ground motions are scaled to increasing intensities until the structural model reaches a global collapse point.…”

بررسی عملکرد فروریزش لرزه‌یی ساختمان های بتنی کوتاه مرتبه‌ی نامنظم در پلان با رفتار نرم پیچشی در چارچوب Fema-P695

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