Effect of unreinforced masonry infills on seismic performance of reinforced concrete frame-shear wall buildings

Reinforced concrete (RC) shear wall buildings with unreinforced masonry (URM) infilled moment frames are common in India and neighboring countries. This study assesses the influence of the URM infills on their seismic performance. Fully infilled, open first-storied, and bare frame versions of a 25-story shear wall building are considered. Multiple stripe analysis is conducted at five return periods to estimate their performance. Fragility functions for the collapse prevention limit state, which is based on seven engineering demand parameter exceedance thresholds, are generated and compared. The presence of infills (full or partial) is observed to have an overall positive effect on the performance of the RC frame-shear wall buildings. The performance of the open first-story building was comparable to that of the fully infilled building. The ratio of story shear carried by the moment frames and shear walls is studied at all return periods to understand the variation in frame shear wall interaction with increased damage for each building. In the case of buildings with infills, the frames carry a higher proportion of story shear at lower return periods. For all three buildings, the fraction of story shear carried by moment frames increases along the height of the building.     

汶川地震作用下约束砌体房屋的抗震能力分析

为验证约束砌体结构的抗震性能,取4栋7层砌体房屋为例进行非线性地震反应分析。4栋房屋中2栋(代号为A1、A2)选自汶川地震影响区的约束砌体房屋,另2栋(代号为B1、B2)为虚拟无筋(或非约束)砌体房屋,除了无任何约束作用的构造措施之外,其他都分别和A1、A2相同。分析中选取汶川地震中基岩和土层场地的共20条地震动作为地震输入。基于分析结果,做了两方面的比较:约束砌体结构房屋地震反应特征和汶川大地震现场调查所见的对比和约束砌体房屋和无筋砌体房屋地震性状的对比。主要结论有:①计算得到的约束砌体房屋在大地震下的震害特征和实际地震相当吻合,结构分析所用的计算模型、恢复力模型和参数取值的可靠性得到验证;②和无筋(或非约束)砌体房屋相比,约束砌体房屋使砌体结构的抗震强度和延性大为改善,具有很好的抗倒塌能力。     

Seismic performance evaluation of reinforced concrete hilly buildings under sequence of earthquakes

The present study investigates the effect of earthquake sequences on the response of reinforced concrete hilly buildings having typical configurations, that is, stepback and split-foundation, with three different story ratios. A set of 30 as-recorded mainshock-aftershock sequence of earthquake ground motions is considered for this study. Mainshock acceleration time histories are scaled at two distinct intensity levels to obtain the mainshock-damaged building. These mainshock-damaged hilly buildings are then subjected to aftershocks. A comparative study is performed for various response quantities, such as peak interstory drift ratio, peak floor acceleration, and peak roof displacement of undamaged and mainshock-damaged buildings under aftershocks. Further, fragility analysis is carried out to study the effect of aftershocks on undamaged and mainshock-damaged hilly buildings. Subsequently, component-wise seismic loss estimation due to damage in the non-structural and structural components is performed. It is concluded from the study that the building components that contribute maximum to the expected repair cost ratio vary with respect to the intensity of the aftershocks. Also, the estimated seismic loss is higher in mainshock-damaged split-foundation buildings in comparison to stepback buildings.     

配筋混凝土砌块砌体小高层框支结构抗震研究

论述了与配筋混凝土砌块砌体小高层框支结构相关的剪力墙及房屋抗震设计和性能的研究进展概况，介绍了其需要重点研究的几个方面，促进其在抗震设计中广泛地应用。     

Seismic fragility assessment of a tall reinforced concrete chimney

In China, a considerable proportion of reinforced concrete (RC) industrial chimneys in operation was designed and constructed in accordance with less rigorous outdated seismic criteria during the end of 19th and early 20th century. However, few research works have been reported till date on a realistic overall assessment of the seismic performance of these existing aging RC chimney structures. Therefore, in this study, fragilities of existing RC chimney were studied. For this purpose, an existing 240 m tall RC chimney was selected and structurally modeled with a lumped mass beam (stick) model by means of the OpenSees analysis program. In order to capture the uncertainties in ground motion realizations, a series of 21 ground motions are selected from the Next Generation Attenuation database as the input motions. To develop the analytical fragility curves, nonlinear incremental dynamic analysis of the studied RC chimney was then carried out using the selected input motions, which were normalized to different excitation levels. The section curvature ductility ratio was considered as the damage index. Based on material strain and sectional analysis, four limit states (LSs) were defined for five damage state. The seismic responses of the all sections were utilized to evaluate the likelihood of exceeding the LSs. Then the peak ground acceleration (PGA)‐based seismic fragility curves of the structure were constructed assuming a lognormal distribution. Finally, under the light of these fragility curves, the damage risks in existing RC chimney were discussed. The analytical results indicated that for design level earthquake of PGA = 0.1 g (g is the gravitational acceleration) and the maximum considered earthquake of PGA = 0.22 g, the probabilities of exceeding the light damage state were around 1.5% and 44%, respectively, while the exceedance probabilities corresponding to moderate, extensive and complete damage states were approximately zero in both cases. On the other hand, fragility analysis revealed that the RC chimney structure had considerable ductility capacity and was capable to withstand a strong earthquake with some structural damages. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic collapse assessment of reinforced concrete moment frames using endurance time analysis

In this paper, seismic collapse of reinforced concrete moment frames is assessed using endurance time (ET) analysis. A set of 30 frames that incorporate deterioration of concrete components is used for this assessment. Application of ET method for collapse assessment of structures is explained, and its accuracy for this purpose is evaluated by comparing its results with incremental dynamic analysis results. Input motions for ET analysis are generated based on ASCE7‐05 design spectrum, and also accelerograms used for incremental dynamic analysis are spectrally matched to the same spectrum. Distribution of different engineering demand parameters over frames height and their values at collapse occurrence are compared for two methods. Results show that spectral accelerations in which collapse occurs in both analyses are very similar for most of the frames, and ET method can appropriately predict the collapse mechanisms of the structures especially for taller frames. Accuracy of ET method in collapse assessment of reinforced concrete moment frames is satisfactory, and this method can be used as a good estimator for study of collapse mechanisms with much less computational effort. Copyright © 2014 John Wiley & Sons, Ltd.     

Lifetime seismic performance assessment for chloride-corroded reinforced concrete buildings

The main aim of this paper was to build an estimating procedure based on the static nonlinear analysis (pushover analysis) such that structural engineers can evaluate the seismic performance of a deteriorating reinforced concrete (RC) building. For engineers' convenience, this paper suggests the probabilistic deterioration prediction model and the visual estimation of deterioration degree to evaluate corrosion-induced weight loss of reinforcing steel bars. In addition, flexural and shear capacity models for a corroded column or beam are proposed and verified by full-scale corroded beam specimens, allowing engineers to simulate its nonlinear mechanical behaviour. This paper incorporates these mechanical models of corroded members into the static nonlinear analysis to construct a procedure for assessing the seismic performance of a deteriorating RC building. An elementary school at Lanyu Island, Taitung, Taiwan, is used as an example and its lifetime seismic performance is identified utilising the proposed approach.     

底部框剪配筋砌块砌体房屋弹塑性地震反应的数值模拟

在总结底部框剪砖房和配筋砌块砌体的抗震性能研究成果的基础上,对底部框剪上部配筋砌块砌体结构的抗震特性进行了初步研究。采用层间剪切模型和三折线骨架曲线恢复力模型,分别按6、7、8度区的多遇烈度、基本烈度和罕遇烈度,输入ElCentro地震波,模拟此类房屋的线性和非线性地震反应。通过分析加速度和位移地震反应,恢复力和层间位移角的变化,考察了该结构的抗震性能和抗震能力。结果表明:底部两层框剪上部六层配筋砌块砌体结构(高25.5m)可用于8度地震区,这种结构的底部框剪层是薄弱部位;应提高框剪层的水平地震剪力设计值,增强延性设计,提高抗倒塌能力。     

配筋混凝土砌块砌体剪力墙位移延性的数值分析

针对设计规范计算方法的不足,探讨了数值计算方法在配筋混凝土砌块砌体剪力墙位移延性计算中的应用问题,给出了详细的计算步骤,并编写程序进行了配筋混凝土砌块砌体剪力墙位移延性系数计算.研究结果表明,采用数值计算方法,能较好地解决配筋混凝土砌块砌体剪力墙延性简化计算存在的问题,其适应性更强,便于工程应用.     

配筋混凝土砌块砌体框支剪力墙模型房屋抗震性能试验研究

为研究配筋混凝土砌块砌体框支剪力墙房屋的抗震性能,通过对一幢按1/4缩尺比例建造的配筋混凝土砌块砌体框支剪力墙模型房屋进行子结构拟动力地震反应试验,研究了在各种加速度峰值地震作用下,这种结构体系的动力反应、破坏机理和倒塌机制,分析了试验模型的水平承载能力和破坏形态。试验结果表明,随着输入地震波的加速度峰值的增大,这种结构体系的地震反应由弹性阶段过渡到塑性阶段,最后底部框剪层承载力下降而临近倒塌;结构薄弱层在底部框剪层,最终破坏形态为剪切型;框架托梁与上部配筋混凝土砌块砌体剪力墙组成整体性能较好的组合深梁。这种结构体系应用于7度抗震设防区,具有较好的抗震性能。     

Fundamental period of infilled reinforced concrete frame structures

The fundamental period of vibration appears to be one of the most critical parameters for the seismic design and assessment of structures. In the present paper, the results of a large-scale analytical investigation on the parameters that affect the fundamental period of reinforced concrete structures are presented. The influence of the number of storeys, the number of spans, the span length, the infill wall panel stiffness and the percentage of openings within the infill panel on the fundamental period of infilled RC frames was investigated. Based on these results, a regression analysis is applied in order to propose a new empirical equation for the estimation of the fundamental period. The derived equation is shown to have better predictive power compared with equations available in the literature.     

钢筋混凝土-砖砌体组合墙抗震性能

以往的研究表明,钢筋混凝土-砖砌体组合墙是一种抗震性能好、造价低的优良结构形式。本研究通过22片不同高宽比、不同竖向压应力、不同竖向配筋率和不同水平配筋率的钢筋混凝土-砖砌体组合墙的抗震性能研究,并通过国内其它65片类似墙体的分析,对这种墙体在竖向和水平荷载作用下的破坏特征、墙体的正截面承载力、斜截面承载力及抗震性能进行了分析研究,给出了墙体抗震承载力计算公式,可为该类房屋的设计提供参考。     

Seismic assessment of concrete buildings reinforced with shape memory alloy materials in different stories

Shape memory alloy (SMA) is a unique material with many beneficial characteristics such as superelasticity and excellent resistance against corrosion. However, the high expenses related to the material costs and difficulties associated with implementation of SMAs in reinforced concrete (RC) structures may limit their usage. To decrease the costs related to SMA installation, this paper investigates the seismic performance of RC moment‐resisting frames with the intention of specifying the optimal stories for SMA utilization. To this end, RC frames with 3, 5, 7, and 9 stories are modeled and various cases are considered for SMA locations in different story levels. For each building, 4 different cases are considered including a frame with regular steel reinforcement (Steel), a frame with SMAs in all story levels (full SMA), and 2 remaining cases consist of frames with SMAs in bottom and middle story levels only. In the first part, nonlinear dynamic time history analyses are conducted to evaluate the base shear, roof displacement, interstory, and residual drift demands of the structures using 10 ground‐motion records. In the second part, the incremental dynamic analysis is employed to assess the entire range of structural dynamic behavior. By using the generated data from incremental dynamic analysis procedure, fragility evaluation is conducted on multiple limit states to provide a comprehensive performance assessment for each case. The results indicate that frames with SMA in their lower story levels performed similar to frames equipped with SMA in all story levels. However, the fragility assessments show the better performance of frames with SMA in their bottom stories versus other cases. On this basis, the costs associated with SMA fabrication could be reduced noticeably (nearly two‐thirds) without sacrificing the overall performance of the frame and its post‐earthquake serviceability.     

多层砌体房屋的抗震鉴定方法

通过利用砖砌体墙片的抗震试验结果 ,结合房屋的动力特性实测 ,提出了如何判断墙体震害等级的准则和方法 ,经实践 ,此法较客观地评估了多层砖房的抗震能力     

砖混建筑现浇混凝土梁常见裂缝的原因及预防

总结了目前砖砌体建筑中现浇混凝土梁中存在的多种裂缝特点 ,分析了其产生的各种原因 ,提出了有效防治措施 ,指出引起建筑物混凝土梁产生裂缝的原因是多方面的 ,应综合分析     

钢筋混凝土框格单元结构受力性能影响因素分析

为研究填充块材和外围构件对钢筋混凝土框格单元结构受力性能的影响,对4个框格单元和2个空框格结构进行1/2比例模型加载试验。结果表明,开裂前填充砌体与钢筋混凝土框格粘着为一体共同抵抗外力,开裂后结构转化为砌体压杆抗力机制。外围构件弯曲刚度对结构抗裂能力及极限承载能力均有显著影响。提高填充块材抗压强度时结构极限承载能力显著提高。当填充块材抗压强度及弹性模量较低时,钢筋混凝土框格单元结构的变形能力很好。     

浅析钢筋混凝土结构的非线性问题

介绍了钢筋混凝土结构非线性分析的意义及非线性主要包括的问题，探讨了钢筋混凝土结构有限元分析的特点与国内外研究现状，最后提出了钢筋混凝土结构有限元分析的发展趋势和研究方向。     

Verification of performance criteria using shake table testing for the vulnerability assessment of reinforced concrete buildings

Shake table experiments are conducted to support the selection of performance criteria and to verify the inelastic modeling approach for developing the fragility functions of reinforced concrete buildings. Two frames representing the lateral force‐resisting system of a preseismic code building are tested under the effect of an earthquake record with increasing severity. Shear failure is detected in columns at a PGA of 1.28g before other failure modes, which was effectively predicted by the fiber‐based numerical model, performance criteria, and shear supply approaches adopted for vulnerability assessment. Five buildings, ranging from 2 to 40 stories, are then assessed under the effect of far‐field and near‐source earthquake records, considering the experimentally verified modeling approach and shear failure prediction models that account for flexural ductility and shear‐axial force interaction. The impact of considering shear response on the vulnerability assessment results is considerable, particularly for the lower‐height wall structures when subjected to the near‐source earthquake scenario. Higher modes dominate the behavior of wall structures, principally under the latter seismic scenario, and shift their response to shear‐controlled. Therefore, seismic scenario‐structure‐based performance criteria are adopted for developing a range of analytically derived, experimentally verified fragility functions for the earthquake loss estimation of buildings with different characteristics.     

Reliability-based service life assessment for deteriorating reinforced concrete buildings considering the effect of cumulative damage

Most engineering systems used in maintenance strategies must consider deterioration and seismic structural damage. To identify the effects of deterioration and earthquakes simultaneously on structural performance, this study applies an integral simulation method. Compared with that of previous studies, the feature of the proposed method is its analysis of the time-dependent structural capacity of a deteriorating reinforced concrete (RC) building and the simulation of life-cycle earthquake events within a specified service period, while considering cumulative damage induced by deterioration and earthquakes. In addition, the proposed assessment method is applied to derive the reliability-based service life of a deteriorating RC building located in a region with high seismic hazard. Briefly, for deteriorating RC buildings, the proposed reliability-based service life assessment method provides useful information related to maintenance based on both serviceability and safety.     

Life cycle cost assessment of masonry structures

The objective of this study is to propose a life cycle cost (LCC) model able to assess the structural performance of masonry structures. For this purpose the proposed LCC model is used for assessing the structural behaviour of one unreinforced and three retrofitted masonry structures derived following three retrofit scenarios that are suitable for strengthening this type of structures. According to the proposed LCC model the exceedance probabilities required, are calculated by means of fragility analysis (FA). In particular, FA is applied to the unreinforced and retrofitted masonry structures and the limit-states' exceedance frequencies are obtained by convolving fragilities with hazard curve. Life-cycle cost analysis models are recognised as suitable for assessing the structural performance, especially when the structure is expected to be functional for a long period of time. For the needs of the study, linear time history analyses are performed over a large database of natural records.