FREE VIBRATION ANALYSIS OF SHEAR WALLS WITH SHORT PIERS

The equations of the lateral deflection curve of the short pier shear wall under a lateral concentrated load at any level are derived by employing a continuous approach. Lateral flexibility matrixes for the dynamic analysis are also obtained by repeatedly calculating the lateral unit load on the wall at each level where a lumped mass located. Dynamic analyses are implemented for short pier shear walls with different parameters, called the integrative coefficient and the pier strength coefficient related to the dimensions of walls. The influences of two coefficients on the dynamic performances of the structure are studied. Results indicate that with the increase of the integrative coefficient, the periods of top two modes apparently decrease but the other periods of higher frequency modes show little variation when the pier strength coefficient remains constant. Similarly, if the integrative coefficient is constant, the top two periods of the free vibration decrease with the increase of the integrative coefficient but the other periods of higher frequency modes show less variation.

Seismic performance evaluation of hybrid coupled shear wall system with shear and flexural fuse-type steel coupling beams

Replaceable flexural and shear fuse-type coupling beams are used in hybrid coupled shear wall(HCSW)systems,enabling concrete buildings to be promptly recovered after severe earthquakes.This study aimed to analytically evaluate the seismic behavior of flexural and shear fuse beams situated in short-,medium-and high-rise RC buildings that have HCSWs.Three building groups hypothetically located in a high seismic hazard zone were studied.A series of 2D nonlinear time history analyses was accomplished in OpenSees,using the ground motion records scaled at the design basis earthquake level.It was found that the effectiveness of fuses in HCSWs depends on various factors such as size and scale of the building,allowable rotation value,inter-story drift ratio,residual drift quantity,energy dissipation value of the fuses,etc.The results show that shear fuses better meet the requirements of rotations and drifts.In contrast,flexural fuses dissipate more energy,but their sectional stiffness should increase to meet other requirements.It was concluded that adoption of proper fuses depends on the overall scale of the building and on how associated factors are considered.

A study on the seismic behavior of a retrofitted building based on nonlinear static and dynamic analyses

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 to represent 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.

Shaking table experimental study of recycled concrete frame-shear wall structures

In this study, four 1/5 scaled shaking table tests were conducted to investigate the seismic performance of recycled concrete frame-shear wall structures with different recycled aggregates replacement rates and concealed bracing detail. The four tested structures included one normal concrete model, one recycled coarse aggregate concrete model, and two recycled coarse and fi ne aggregate concrete models with or without concealed bracings inside the shear walls. The dynamic characteristics, dynamic response and failure mode of each model were compared and analyzed. Finite element models were also developed and nonlinear time-history response analysis was conducted. The test and analysis results show that the seismic performance of the recycled coarse aggregate concrete frame-shear wall structure is slightly worse than the normal concrete structure. The seismic resistance capacity of the recycled concrete frame-shear wall structure can be greatly improved by setting up concealed bracings inside the walls. With appropriate design, the recycled coarse aggregate concrete frame-shear wall structure and recycled concrete structure with concealed bracings inside the walls can be applied in buildings.

Lateral load-carrying capacity analyses of composite shear walls with double steel plates and filled concrete with binding bars

A method is developed to predict the lateral load-carrying capacity of composite shear walls with double steel plates and filled concrete with binding bars(SCBs). Nonlinear finite element models of SCBs were established by using the finite element tool, Abaqus. Tie constraints were used to connect the binding bars and the steel plates. Surface-to-surface contact provided by the Abaqus was used to simulate the interaction between the steel plate and the core concrete. The established models could predict the lateral load-carrying capacity of SCBs with a reasonable degree of accuracy. A calculation method was developed by superposition principle to predict the lateral load-carrying capacity of SCBs for the engineering application. The concrete confined by steel plates and binding bars is under multi-axial compression; therefore, its shear strength was calculated by using the Guo-Wang concrete failure criterion. The shear strength of the steel plates of SCBs was calculated by using the von Mises yielding criterion without considering buckling. Results of the developed method are in good agreement with the testing and finite element results.

DYNAMIC RESPONSE AND ENERGY DISSIPATION ANALYSIS OF THE WALL WITH HORIZONTAL SHORT KEYWAYS AND LOWRISE SHEARWALL

A new type of ductile lowrise shearwall with many short horizontalkeyways is proposed in this paper in order to improve the earthquake resistant behav-ior of ordinary lowrise shearwall.The behavior of this wall is studied through low-frequency cyclic loading test.Based on the test results,the paper puts forward thedifferent restoring force models for different lowrise shearwalls,and a program fortheir nonlinear dynamic analysis is worked out.Thr(?)h directly inputting earth-quake waves,the paper analyses the dynamic response and energy dissipation of 3types of lowrise shearwalls.The calculation results dem(?)strate that the newly de-vised ductile shearwall has good earthquake resistant behavior.

EXPERIMENTAL STUDY OF TENSILE CAPACITY OF CONCRETE IN RC SHEAR WALLS AFTER CRACKING

Through the test of 8 RC shear wall specimens and computer analysis ofstrains of steel bars with keyways in the specimens,the authors have studied the remains oftensile stress of concrete between cracks after concrete cracking and put forward a formulato calculate coefficient Ψ,the ununiform distribution factor of steel strain.This coefficientcan be used to modify the calculated steel strain in cracked zone,so as to make the resultsof using finite clement method to analyze shear walls more accurate.

Field measurements for calibration of simplified models of the stiffening effect of infill masonry walls in high-rise RC framed and shear-wall buildings

As a type of nonstructural component, infill walls play a significant role in the seismic behavior of high-rise buildings. However, the stiffness of the infill wall is generally either ignored or considered by simplified empirical criteria that lead to a period shortening. The difference can be greatly decreased by using a structural identification methodology. In this study, an ambient vibration test was performed on four on-site reinforced concrete high-rise buildings, and the design results were compared with the PKPM models using corresponding finite element(FE) models. A diagonal strut model was used to simulate the behavior of the infill wall, and the identified modal parameters measured from the on-site test were employed to calibrate the parameters of the diagonal strut in the FE models. The SAP2000 models with calibrated elastic modulus were used to evaluate the seismic response in the elastic state. Based on the load-displacement relationship of the infill wall, nonlinear dynamic analysis models were built in PERFORM-3 D and calibrated using the measured modal periods. The analysis results revealed that the structural performance under small/large earthquake records were both strengthened by infill walls, and the contribution of infill walls should be considered for better accuracy in the design process.

西咸自由贸易企业服务中心超高层建筑结构设计

西咸自由贸易企业服务中心地处高烈度区,与渭河断裂之间的距离约2km,应考虑近场效应。项目采用钢管混凝土框架(钢梁)+钢筋混凝土核心筒混合结构,存在扭转不规则、刚度突变、有加强层和通高层等不规则项。为提高结构刚度,在避难层设置了2道伸臂桁架加强层。采用YJK、MIDAS Building软件进行了小震弹性对比分析,采用YJK进行了小震弹性时程分析。根据设定的抗震性能目标,对主体结构主要部位和关键构件进行了性能化设计;采用SAUSAGE软件进行了罕遇地震作用下的动力弹塑性时程分析;采用ANSYS软件对伸臂桁架关键节点进行有限元分析。结果表明:各项指标均符合设计要求,结构及构件均达到预设性能目标,结构体系合理,安全可靠。本工程部分墙体为钢板混凝土剪力墙,设计中应注重钢板混凝土剪力墙的构造措施,施工中应采取措施控制钢板变形。

某超限高层剪力墙结构分析与设计

8度区某办公楼项目采用剪力墙结构体系,房屋总高度143.7m,存在两项超限,分别为高度超限和第四层刚度突变。设计时在保证超限结构满足现行规范要求的同时,还要使结构两个方向的动力特性相近。选用YJK和Midas-building软件对结构进行计算,计算内容包括多遇地震反应谱分析、多遇地震弹性时程分析、设防地震下墙肢名义拉应力验算、罕遇地震弹塑性时程分析。并对结构关键部位进行了剪力墙模型以及实体单元模型的补充验算,保证了结构设计的可靠性。结果表明:通过合理的结构平面布置,提高了结构效率,使结构在多遇地震和罕遇地震作用下都能保证良好的抗震性能,安全可行。

广州某部分框支剪力墙结构设计

广州市某超限高层项目采用部分框支剪力墙结构,属于A级高度的超限高层建筑,结构同时存在扭转不规则、组合平面及构件间断共3项不规则情况。设计基于性能化进行抗震设计,采用YJK、SATWE两个有限元程序进行小震弹性分析、中震等效弹性分析、大震等效弹性分析,Perform-3D对超限结构进行了罕遇地震作用下的弹塑性动力时程分析,并采取了针对超限的加强措施。计算及研究分析结果表明,通过对部分关键构件的加强,结构整体的抗震性能满足“小震不坏、中震可修、大震不倒”,结构体系安全可行。

广州某超限连体高层结构设计

广州某超限高层为带连体的部分框支剪力墙结构,两栋结构高度分别为9725、9275m,在4层、11~13层通过连廊连接。为了验证结构布置的可靠性和安全性,采用YJK和ETABS软件对建筑结构进行整体计算分析及弹性时程分析,同时借助Perform-3D软件,对结构的动力弹塑性进行深入分析,并对连接体结构受力情况做专项分析。结果表明,两栋塔楼的转换构件及连接体结构受力体系合理可靠。根据结构的受力特征,通过对关键构件及其他受力构件的加强处理,确保结构整体上满足各项预先设定的抗震性能目标的要求。

某超限高层剪力墙结构抗震性能研究

文中以广西南宁市某超限工程为例,重点讨论了在结构设计中,需要解决的超限判定、计算要点、步骤、优化方法等问题。首先利用YJK和PKPM两个软件建立对比模型,从而相互验证所研究结构的刚度及承载力影响,完成了小震、中震的性能化分析;再用Midas/Building实现了模拟大震作用下的动力弹塑性损伤分析。结果表明,采取的结构加强措施能够基本满足设定的性能目标。

磁流变阻尼器受控RC框剪结构的计算模型及减震研究

为了分析加入磁流变阻尼器(MRD)框剪结构的多维减震性能,基于空间梁单元和壳单元建立了MRD受控框剪结构的三维计算模型。以6层钢筋混凝土(RC)框剪结构为例,采用MATLAB软件开发了未控和MRD受控RC框剪结构的三维计算模型程序,通过将模型程序计算结果与ANSYS软件建立的有限元模型计算结果进行对比,验证了模型及程序的有效性。在兰州波和唐山波作用下,对未控和MRD受控下结构的位移、加速度以及各层层间位移角进行计算。结果表明,未控和MRD受控RC框剪结构的三维计算模型程序能有效模拟结构的三维动力响应及减震效果,在整个地震波持时内,MRD受控RC框剪结构的位移响应均小于对应时间下未控结构的位移响应。

一方向为短肢墙的高层住宅楼抗震性能分析

在高层板式住宅楼中,一个方向设置门窗洞口后剪力墙数量较少或截面长度较短,另一个方向分室、分户剪力墙数量较多。由于结构两个主轴方向剪切刚度差别较大,合理调整结构布置可以使结构两个方向的基本周期和地震作用下最大层间位移角基本相当,但地震作用下结构两个主轴方向的变形特征仍存在明显差异,分别为弯剪型和弯曲型。另外,地震作用下各墙肢轴力分布不均匀,而规范中对剪力墙的轴压比计算不考虑地震作用参与组合且采用同样的限值,不能真实地反映剪力墙延性;补充双向地震作用分析并控制墙肢名义拉应力则可以有效地提高剪力墙延性。罕遇地震动力弹塑性分析结果亦表明,剪力墙损伤程度与考虑多遇地震作用组合下轴压比和设防地震作用名义拉应力大小一致。

常规混凝土框剪结构连续倒塌动力响应分析

多高层办公建筑主要采用混凝土框剪结构,其在局部结构构件失效下的整体结构连续倒塌可能引发严重的经济损失和社会影响。该文针对常规结构布置的典型框剪结构开展了动力连续倒塌分析,总结其规律为结构毁伤下的连续倒塌快速评估提供依据。主要工作包括:按照不同抗震设防烈度、跨度、层数设计了18个典型结构布置的框剪结构,并采用纤维梁单元和分层壳单元建立了整体结构的数值模型库;采用非线性动力拆除构件法对整体结构开展了计算分析,获得结构系统在局部构件失效下的动力响应;对比分析不同结构的连续倒塌动力响应,研究不同参数对连续倒塌后果的影响。

基于IDA方法的地铁车辆基地TOD开发全框支剪力墙结构抗震性能评估

全框支剪力墙结构因上部塔楼剪力墙完全不落地而存在竖向构件不连续、刚度突变、大底盘多塔等不规则项,为综合有效评估此种超限结构的抗震性能,基于增量动力分析(IDA)方法得到不同地震烈度下结构最大层间位移角分布情况,并将结构性能水准划分5个等级,最终分析其地震易损性和损伤风险性。研究结果表明,结构随地震动峰值加速度(PGA)增大逐渐屈服并最终倒塌,不同地震记录时结构IDA曲线具有明显离散性;结构在7度多遇地震作用下处于正常使用性能水准的概率为97.914%,罕遇地震作用下结构倒塌的概率仅为0.053%;生命安全和接近倒塌性能水准对应的PGA中位数分别为1.287g和1.411g,远高于预估罕遇地震PGA;结构正常使用、基本可用、修复可用和接近倒塌性能水准50年超越概率分别为4.89%、1.74%、0.112%和0.046%。综上所述,结构满足预设抗震性能目标,具有良好的抗震性能及抗倒塌能力。

新型混合装配式剪力墙结构罕遇地震动力弹塑性分析

基于非线性有限元分析软件MSC.Marc,对一个10层新型混合装配式剪力墙结构进行了罕遇地震作用下动力弹塑性分析。分析结果表明,罕遇地震作用下,连梁应力较大,起到耗能作用;墙肢受压损伤主要出现在1层-3层墙体暗柱处,暗柱内的纵筋屈服;内外墙协同工作性能良好。新型混合装配式剪力墙结构弹塑性层间位移角满足规范要求的1/120限值要求,结构具有较好的抗震性能,满足大震不倒的性能要求。

某大高宽比超高层住宅结构抗震设计要点分析

结合某工程实例,对存在扭转不规则、大高宽比且超B级高度的超高层结构进行分析,并根据超限水平、结构特点及经济性评价等综合因素,选定结构的抗震性能目标。详细阐述主体结构在多遇地震、设防地震及罕遇地震作用下的设计控制指标及设计要点。通过计算分析,验证了结构在不同工况下的整体指标满足规范要求,发现结构薄弱部位并采取相应的加强措施,以达到设计提出的性能目标,结构具备一定的安全储备和良好的抗震性能。

某规则性超限高层酒店结构抗震性能研究

某酒店为规则性超限高层建筑,房屋高度98.90m,采用框架-剪力墙结构体系。本工程存在扭转不规则、楼板不连续、刚度突变、局部穿层柱、竖向抗侧力构件间断等5项不规则项,对本工程进行了抗震性能化设计,利用两种软件进行了多遇地震下的反应谱分析和弹性动力时程分析,中震弹性和不屈服的承载力复核,采用弹塑性动力时程分析对结构在罕遇地震下的动力特性及损伤退化开展进行了研究。结果表明:结构抗震性能良好,结构体系合理可行,能够达到小震弹性、中震可修、大震不倒的抗震性能目标。针对二层顶局部托柱转换,对转换柱及转换大梁均采用型钢混凝土构件并按中震弹性设计,且增加转换层板厚并对楼板进行应力分析及抗剪验算。利用有限元软件MIDAS-FEA对单榀转换框架进行精细分析,细化了构件损伤、材料应力状态及性能目标等各项指标。