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1.
Recent major earthquakes around the world have evidenced that research in earthquake engineering must be directed to the vulnerability assessment of existing constructions lacking appropriate seismic resisting characteristics. Their retrofit or replacement should be made in order to reduce vulnerability, and consequent risk, to currently accepted levels. In this work, the efficiency of ductile steel eccentrically-braced systems in the seismic retrofitting of existing reinforced concrete (RC) buildings is studied. The retrofit technique studied consists in a bracing system with an energy dissipation device, designed to dissipate energy by shear deformation. The numerical model was calibrated with cyclic test results on a full-scale structure. The models used for the RC frame and masonry represent their real behavior and influence in the global structural response. The steel bracing system was modeled with strut rigid elements. The model for the energy dissipater device reproduces rigorously the behavior of the shear-link observed in the cyclic tests, namely in terms of shear, drift and energy dissipation. With the calibrated numerical model, a series of non-linear dynamic analyses were performed, for different earthquake input motions, intending to study: the influence of the retrofitting system in the response of bare and infilled structures; the influence of the location and strength of the retrofitting system.  相似文献   

2.
A refined probabilistic assessment of seismic demands and fracture capacity of welded column splice (WCS) connections in welded steel moment resisting frames (WSMRFs) is presented. Seismic demand assessment is performed through cloud-based nonlinear time history analysis (NLTHA) for two case-study structures, i.e., a 4- and a 20- story WSMRFs. Results from NLTHA are used to derive fracture fragility of WCS connections. To this aim, the study investigates (1) optimal ground-motion intensity measures for conditioning probabilistic seismic demand models in terms of global (i.e., maximum inter-story drift ratio) and local (i.e., peak tensile stress in the flange of WCSs) engineering demand parameters of WSMRFs; (2) the effect of ground-motion vertical components on the longitudinal flange stress of WCS connections and their resulting fracture fragility; and (3) the effect of WCS capacity uncertainties on the fracture fragility estimates of those connections. For the latter case, an advanced finite element fracture mechanics-based approach proposed by the authors is employed to capture aleatory and epistemic uncertainties affecting fracture capacities. The focus is on pre-Northridge WCS connections featuring partial joint penetration and brittle materials, making them highly vulnerable to seismic fracture. Fracture fragility results for the case-study structures are compared and discussed, highlighting the importance of the considered issues on fragility estimates, particularly in the case of high-rise structures. Findings from the study contribute shedding some light on the influence of seismic demand and capacity uncertainties on the assessment of fracture fragility of WCS connections. These findings can guide similar performance-based assessment exercises for WSMRFs to inform, for instance, the planning and design of retrofitting strategies for those vulnerable connections.  相似文献   

3.
针对既有的C类框架学校建筑提高一度抗震设防的加固目标,从地震作用计算、结构抗震验算和抗震构造措施等方面详细分析了其中的加固难点,指出了应用传统抗震加固方法的一些不足之处,探讨了应用消能减震技术进行结构提高一度抗震设防加固的可行性;并以某C类框架学校建筑加固工程为实例,从减震控制效果分析、弹塑性变形验算、消能部件影响评价、抗震构造措施核查4个方面论证了消能减震加固方法的有效性和可操作性。结果表明,消能减震技术在C类框架学校建筑抗震加固中具有一定的应用优势,不但能有效控制结构的地震响应,而且依据减震效果可以适当降低结构的抗震构造要求。因此,只要通过合理的消能减震加固设计,再辅以额外的局部加强处理,完全可以实现C类框架学校建筑提高一度抗震设防的加固目标需求。  相似文献   

4.
This paper presents the results of a parametric study of self-centering seismic retrofit schemes for reinforced concrete (RC) frame buildings. The self-centering retrofit system features flag-shaped hysteresis and minimal residual deformation. For comparison purpose,an alternate seismic retrofit scheme that uses a bilinear-hysteresis retrofit system such as buckling-restrained braces (BRB) is also considered in this paper. The parametric study was carried out in a single-degree-of-freedom (SDOF) system framework since a multi-story building structure may be idealized as an equivalent SDOF system and investigation of the performance of this equivalent SDOF system can provide insight into the seismic response of the multi-story building. A peak-oriented hysteresis model which can consider the strength and stiffness degradation is used to describe the hysteretic behavior of RC structures. The parametric study involves two key parameters -the strength ratio and elastic stiffness ratio between the seismic retrofit system and the original RC frame. An ensemble of 172 earthquake ground motion records scaled to the design basis earthquake in California with a probability of exceedance of 10% in 50 years was constructed for the simulation-based parametric study. The effectiveness of the two seismic retrofit schemes considered in this study is evaluated in terms of peak displacement ratio,peak acceleration ratio,energy dissipation demand ratio and residual displacement ratio between the SDOF systems with and without retrofit. It is found from this parametric study that RC structures retrofitted with the self-centering retrofit scheme (SCRS) can achieve a seismic performance level comparable to the bilinear-hysteresis retrofit scheme (BHRS) in terms of peak displacement and energy dissipation demand ratio while having negligible residual displacement after earthquake.  相似文献   

5.
钢筋混凝土框架中震可修标准及简化抗震设计方法   总被引：4，自引：1，他引：4  
本文对国际上主要建筑抗震设计规范中钢筋混凝土框架可修水准的层间位移角限值进行了比较,讨论了国内的一些相关研究结果,结合中国抗震规范确定钢筋混凝土框架中震可修层间位移角限值和屋顶侧移率限值分别为1/150和1/200。采用安全系数的抗震设计表达、论述了对应于结构层间位移角基于承载力的简化抗震设计方法。最后用实例按反应谱分析和弹性时程分析验证了钢筋混凝土框架中震可修层间位移角限值的有效控制作用,初步确定了简化抗震设计方法中梁柱构件的抗震安全系数并分析了提高目前结构抗震安全度的措施。  相似文献   

6.
针对目前RC框架结构地震易损性分析中整体损伤模型研究的薄弱性以及广泛采用的层间位移角方法不能准确反应结构在地震作用下损伤机理的现状,本文基于现有损伤模型的对比分析,提出了一种较准确反映地震破坏机理同时便于应用的最大变形和滞回耗能非线性组合的双参数损伤模型。以8层RC框架结构为例,进行50条地震波作用下的结构增量动力分析,分别绘制了变形和能量2种单参数模型以及牛荻涛模型和本文模型两种双参数模型的结构损伤曲线与易损性曲线,并进行了模型的对比分析和检验评估。分析结果表明:仅以层间位移角作为结构整体损伤指标会高估结构的抗倒塌性能,仅以能量作为结构整体损伤指标会低估结构损伤的超越概率。本文模型能较好地平衡最大变形和累积损伤对结构损伤的影响程度。  相似文献   

7.
由于承重结构构件分布不均匀,导致高层建筑框架承重构件间的距离不相等。在地震时,这种不规则分布可能引起加速度共振效应,从而导致建筑失稳。为此,以地震动强度、地震动速度峰值、最大层间位移角为参数指标,分析高层建筑的极限状态,提出基于增量动力地震易损性分析的高层结构抗震加固研究。以某实际工程为试验对象,运用ABAQUS软件构造高层建筑框架结构三维模型,选取多条地震波以及符合场地条件的地震动记录进行验证,绘制地震易损性曲线。结果表明:在高层建筑框架结构中安装阻尼器,可增强结构中各构件的承载力,改善高层建筑抗震性能;增加钢板厚度可提高结构抗震水平,降低极限状态下框架结构IO、LS与CP的超越概率;提高混凝土强度,可改善框架结构抗倒塌性能。高层结构完成抗震加固后,抗震能力由0.91提升至1.01。由此证明,以增量动力分析得到的结构易损性为基础,对建筑易损性较大的地方进行加固、完善,能够改善高层建筑框架结构地震易损性,减少地震灾害损失。  相似文献   

8.
Nowadays, one of the most important methodologies to reduce the destructive effects of severe earthquakes on structures is the use of energy dissipation devices (EDDs). In this paper, a new configuration of special truss moment frame (STMF) systems including EDDs is theoretically proposed to improve their seismic performance. Such an improvement is achieved by provision of bending performance in these frames. For this purpose, the devices called buckling resistant braces (BRBs) are located at the side of beam‐column connections as the top and bottom members of truss‐girders. In this context, a five‐bay nine‐story STMF is designed using the damage and energy concepts recently proposed in the literature. To show the effectiveness of the proposed system with respect to the similar recently presented STMFs, this frame is then subjected to non‐linear static and non‐linear time‐history analyses under several ground motion records in order to survey on its seismic performance. Subsequently, such engineering demand parameters as lateral displacement, inter‐story drift ratio, overturning moment and shearing forces of stories, residual deformations and maximum time‐history displacement at roof level, as well as the process of plastic hinges formation are investigated. The results show the effectiveness of proposed configuration of EDDs used to improve the seismic safety of STMFs. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

9.
This paper presents a new type of structural bracing intended for seismic retrofitting use in framed structures. This special composite brace,termed glass-fiber-reinforced-polymer(GFRP)-tube-confined-concrete composite brace,is comprised of concrete confined by a GFRP tube and an inner steel core for energy dissipation.Together with a contribution from the GFRP-tube confined concrete,the composite brace shows a substantially increased stiffness to control story drift, which is often a preferred feature in seismic retrofitting.An analysis model is established and implemented in a general finite element analysis program-OpenSees,for simulating the load-displacement behavior of the composite brace.Using this model,a parametric study of the hysteretic behavior(energy dissipation,stiffness,ductility and strength)of the composite brace was conducted under static cyclic loading and it was found that the area ratio of steel core to concrete has the greatest influence among all the parameters considered.To demonstrate the application of the composite brace in seismic retrofitting, a three-story nonductile reinforced concrete(RC)frame structure was retrofitted with the composite braces.Pushover analysis and nonlinear time-history analyses of the retrofitted RC frame structure was performed by employing a suite of 20 strong ground motion earthquake records.The analysis results show that the composite braces can effectively reduce the peak seismic responses of the RC frame structure without significantly increasing the base shear demand.  相似文献   

10.
为提高斜交网格结构的抗震性能，提出一种双防线可恢复性能斜交网格结构。双防线可恢复性能斜交网格结构采用剪切耗能段和特定梁端塑形铰进行集中耗能，使主体结构构件保持弹性。剪切耗能段不承受和传递重力荷载，易在震后修复或更换，使建筑可迅速恢复功能。为实现目标耗能机制，对等效能量塑形设计法进行改进以适用于可恢复性能斜交网格结构，并进行结构设计举例。采用OpenSees软件对所设计结构建立详细的有限元计算模型，进行非线性动力时程分析，以验证双防线耗能机制并评估抗震性能。分析结果表明:（1）小震、中震和大震下的结构顶部位移角分别为0.28%、0.8%和1.7%，与性能设计目标基本相同；（2）中震时剪切耗能段屈服，特定梁端未出现塑性铰；（3）大震时，特定梁端出现塑性铰以增加结构耗能能力，剪切耗能段屈服且处于延性范围内。因此新型可恢复性能斜交网格结构具有有效的双防线耗能机制，在中震后可迅速修复，在大震中可保持延性，实现"中震可修，大震不倒"的性能目标。  相似文献   

11.
This paper presents a new FRP retrofi tting scheme to strengthen local beam-column joints in reinforced concrete(RC) frames.The new retrofi tting scheme was proposed following a preliminary study of four different existing retrofi tting schemes.A numerical simulation was conducted to evaluate the effectiveness of FRP-strengthened reinforced concrete frames by bridging behavior of local joints to the whole structure.Local confi nement effects due to varying retrofi tting schemes in the joints were simulated in the frame model.The seismic behavior factor was used to evaluate the seismic performance of the strengthened RC frames.The results demonstrated that the new proposed retrofi tting scheme was robust and promising,and fi nite element analysis appropriately captured the strength and global ductility of the frame due to upgrading of the local joints.  相似文献   

12.
Passive structural control techniques are generally used as seismic rehabilitation and retrofit methodologies for existing structures. A poorly explored and exciting opportunity within structural seismic control research is represented by the possibility to design new structural forms and configurations, such as slender buildings, without compromising the structural performance through an integrated design approach. In this paper, with reference to viscous dampers, an integrated seismic design procedure of the elastic stiffness resources and viscoelastic properties of a dissipative bracing‐damper system is proposed and developed to ensure a seismic design performance, within the displacement‐based seismic design, explicitly taking into account the dynamic behaviour both of the structural and control systems. The optimal integrated seismic design is defined as the combination of the variables that minimizes a suitable index, representing an optimized objective function. Numerical examples of the proposed integrated cost‐effectiveness seismic design approach both on an equivalent SDOF system and a proportionally damped MDOF integrated system are developed defining the design variables, which minimize the cost index. Validation of the effectiveness of the proposed integrated design procedure is carried out by evaluating the average displacement of the time‐history responses to seven unscaled acceleration records selected according to EC8 provisions. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

13.
Improving seismic performance is one of the critical objectives in earthquake engineering. With the development of economy and society, reparability and fast resilience of a structure are becoming increasingly important. Reinforced concrete (RC) frame structure is prone to soft story mechanism. As a result, deformation and damage are so concentrated that reparability is severely hampered. Rocking wall provides an available approach for deformation control in RC frame by introducing a continuous component along the height. Previous researches mostly focus on seismic responses of rocking wall frame structures, while damage mode and reparability have not been investigated in detail. In this study, a novel infilled rocking wall frame (IRWF) structure is proposed. A half‐scaled IRWF model was designed according to Chinese seismic design code. The model was subjected to cyclic pushover testing up to structure drift ratio of 1/50 (amplitude 1/50), and its reparability was evaluated thereafter. Retrofit was implemented by wrapping steel plates and installing friction dampers. The retrofitted model was further loaded up to amplitude 1/30. The IRWF model showed excellent reparability and satisfactory seismic performance on deformation control, damage mode, hysteresis behavior, and beam‐to‐column joint rotation. After retrofitting, capacity of the model was improved by 11% with limited crack distribution. The model did not degrade until amplitude 1/30, due to shear failure in frame beams. The retrofit procedure was proved effective, and reparability of the IRWF model was demonstrated. Seismic resilience tends to be achieved in the proposed system.  相似文献   

14.
In the seismic retrofit of existing masonry constructions, global interventions are often needed to inhibit the onset of local mechanisms and to engage the whole building box-like structural behaviour. Such interventions are represented by perimeter ties and roof and floor diaphragms. This paper considers the roof diaphragm strengthening solution and investigates the use of stud connections securing the roof thin-folded shell to the perimeter walls. Stud connections serve the dual purpose of collecting and transferring the out-of-plane inertia forces of the masonry walls to the roof diaphragm, as well as transferring the diaphragm reaction forces to the shear walls. Specific detailing of the stud connection and the adoption of an improved lime-mortar overlay on the top of the masonry walls are proposed to improve the connection strength; without such improvements, the connection capacity would be jeopardised by the reduced shear resistance of the masonry wall due to the absence of significant vertical confining action at the roof level. The intervention entirely changes the behaviour of the connection and significantly reduces shear stresses on the masonry wall. The structural behaviour of the connection is analysed and discussed. Emphasis is made on the conceptual design of laboratory and in-field test procedures and testing frames in order to replicate the boundary conditions in real applications. In-situ tests may help during the design of the roof thin-folded shell system and allow for the efficiency assessment of the connections prior to the final intervention, thereby proving the actual feasibility of the retrofit solution.  相似文献   

15.
Building structures damaged by a seismic event may be exposed to the risk of aftershocks or another event within a certain period. In this paper, the seismic assessment of damaged piloti‐type RC buildings was carried out to evaluate probabilistic retrofitting effects under successive earthquakes. First, a framework to evaluate the effectiveness of retrofitting was proposed, and then the proposed methodology was demonstrated with a structure retrofitted with buckling‐restrained braces (BRBs). For consideration of realistic successive earthquakes, past records measured at the same station were combined. Within the framework, a series of nonlinear time history analyses were performed for an as‐is model subjected to single earthquake, a damaged model subjected to successive earthquakes, and a damaged model retrofitted with BRBs subjected to successive earthquakes. In addition, fragility analysis was systematically applied in the framework for evaluation of effectiveness of the retrofitting strategy. The proposed framework was capable of quantifying the influence of successive earthquakes and evaluating the effectiveness of BRB retrofitting by considering the severity of the first earthquake damage and the hysteresis behavior of the retrofit element. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

16.
为研究核心筒抗震性能水准及其指标限值,完成了3个核心筒拟静力试验,记录了损伤过程及对应的层间位移角。在现有核心筒研究成果及国内外规范的基础上,将核心筒的抗震性能水准划分为4个等级,并给出了相应的宏观描述。通过总结相关试验研究结果,发现《建筑抗震设计规范》(GB50011-2010)对层间位移角限制过于严格,考虑到结构带裂缝工作,层间位移角限制过严会增加建筑成本,并导致结构自重增加而不利于抗震,故建议适当放宽核心筒的层间位移角限值,分别给出框架-核心筒及筒中筒结构最大层间位移角建议值。  相似文献   

17.
This study describes the seismic performance of an existing five storey reinforced concrete building which represents the typical properties of low-rise non-ductile buildings in Turkey. The effectiveness of shear walls and the steel bracings in retrofitting the building was examined through nonlinear static and dynamic analyses. By using the nonlinear static analysis, retrofitted buildings seismic performances under lateral seismic load were compared with each other. Moreover, the performance points and response levels of the existing and retrofitting cases were determined by way of the capacity-spectrum method described in ATC-40 (1996). For the nonlinear dynamic analysis the records were selected torepresent wide ranges of duration and frequency content. Considering the change in the stiffness and the energy dissipation capacities, the performance of the existing and retrofitted buildings were evaluated in terms of story drifts and damage states. It was found that each earthquake record exhibited its own peculiarities, dictated by frequency content, duration, sequence of peaks and their amplitude. The seismic performance of retrofitted buildings resulted in lower displacements and higher energy dissipation capacity depending mainly on the properties of the ground motions and the retrofitting strategies. Moreover, severe structural damage (irreparable or collapse) was observed for the existing building. However, buildings with retrofit alternatives exhibited lower damage levels changing from no damage to irreparable damage states.  相似文献   

18.
为研究钢框架内填竖缝RC墙结构（Steel frame with slit RC wall,简称"SRCW"）在不同地震水平下的性态指标,结合我国现行抗震规范,对已完成的8榀SRCW试验数据进行了统计分析,基于修正的Park-Ang模型及损伤指数与性态指标的对应关系,提出了以层间位移角表征的SRCW结构的性态指标矩阵。分析结果表明:SRCW结构在显著屈服和倒塌时的层间位移角均值分别为0.63%和2.36%。SRCW结构在正常使用、基本完好、轻微破坏、中等破坏、严重破坏和倒塌状态下的层间位移角限值分别为1/170、1/130、1/100、1/70、1/50和1/40,研究成果可为SRCW结构开展基于性态的抗震设计及地震易损性分析提供参考。  相似文献   

19.
非线性黏滞阻尼减震结构基于位移的设计方法   总被引：1，自引：0，他引：1  
结合我国抗震设计规范,提出非线性黏滞阻尼减震结构基于位移的设计方法.根据减震结构的特点,将其性能划分为使用良好、人身安全和防止倒塌3个水平,并用层间位移角限值予以量化;以简化的方法计算非线性黏滞阻尼器的等效阻尼比.在此基础上将结构转化为等效单自由度体系,利用基于位移的设计方法对非线性黏滞阻尼减震结构进行设计,通过算例,介绍用该方法对框架结构进行非线性黏滞阻尼减震设计的设计过程.实例分析表明,提出的非线性黏滞阻尼减震结构基于位移的设计方法是可行的,并且与时程分析得出的平均结果吻合较好,而且该方法简单实用,便于操作,能够控制减震结构在不同强度水准地震作用下的性能.  相似文献   

20.
The seismic vulnerability of old multi‐storey reinforced concrete (R.C.) buildings reinforced with substandard details is assessed as a function of interstorey drift demand imposed by the design earthquake while considering brittle termination of elastic response of the critical members of the structure due to a premature shear failure. Interstorey drift demand is related to column and wall translational stiffnesses which are expressed through analytical derivations in terms of the floor area ratios of gravity and lateral load bearing members in the critical floor. Interstorey drift capacity is related to the available transverse reinforcement and the axial load ratio of the vertical members. The significance of the area ratio of vertical members in the typical floor as an index of vulnerability is explored with reference to the limitations in the value of axial load ratio used in R.C. design in order to secure ductile flexural behavior, and also with reference to the stability index of gravity load bearing members. Interstorey Drift Spectra are derived for the existing R.C. buildings suitable for rapid seismic vulnerability screening but also as a guide for rehabilitation of the existing structures. Lightly reinforced or substandard reinforced concrete buildings that reportedly collapsed during previous earthquakes are used as example case studies in order to calibrate the proposed methodology. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

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