Damaged RC beams repaired by bonding of CFRP laminates

This paper summarizes the results of experimental studies on damaged reinforced concrete beams repaired by external bonding of carbon fiber reinforced polymer (CFRP) composite laminates to the tensile face of the beam. Two sets of beams were tested in this study: control beams (without CFRP laminates) and damaged and then repaired beams with different amounts of CFRP laminates by varying different parameters (damage degree, CFRP laminate width, concrete strength class). All beams were tested in four-point bending over a span of 1800 mm. The tests were carried out under displacement control. The most investigated parameter in this experimental study is damage degree (ratio between pre-cracked load and load capacity of control beam). Repairing damaged RC beams with externally bonded CFRP laminates were successful for different degrees of damage. The observed failure modes were peeling off and interfacial debonding. These failure modes depend only on the laminate width.The results indicate that the load capacity and the rigidity of repaired beams were significantly higher then those of control beam for all tested damage degrees. The authors remarked that for a load capacity improvement, reinforcement with a CFRP having about a half width of the beam is satisfactory. Finally, the contribution of CFRP laminates on the load capacity and rigidity of repaired RC beams is significant for any concrete strength class.     

The problem of shear in RC beams strengthened with CFRP laminates

The effectiveness of externally bonded reinforcement of a strengthened Reinforced Concrete (RC) beam subjected to a shear-dominant loading regime is not well-established. The aim of this paper is to clarify the structural performance of RC beams without any internal shear reinforcement but strengthened with Carbon Fibre Reinforced Polymer (CFRP) laminates when the primary mode of failure of the un-strengthened beam is in shear. Four RC beams were specifically designed without and with an externally anchorage system, which was carefully detailed to enhance the benefits of the strengthening lamina and counteract the destructive effects of shear forces. All the four beams were identical in terms of their geometry, internal reinforcement and concrete strength but varied in their test loading regime to highlight the role of shear. All the beams were tested under four point bending and extensively instrumented to monitor strains, cracking, load capacity and failure modes. The structural response of the four beams is then critically analysed in terms of deformability, strength and failure processes under a shear loading regime. It is shown that with a carefully designed anchorage system, a predominantly brittle shear failure of a strengthened beam can be transformed to an almost ductile failure with well-defined enhancement of structural performance in terms of both deformation and strength. The results presented in this paper should enable engineers to totally avoid shear failure in strengthening beams with little or even no internal shear reinforcement.     

基于纤维梁柱单元的RC带翼缘剪力墙抗震性能分析

为高效准确地模拟钢筋混凝土构件在复杂荷载作用下非线性行为,采用OpenSees中基于刚度法的纤维梁柱单元,建立一种考虑弯曲和剪切共同作用的RC带翼缘剪力墙非线性分析模型,并对已完成的4个不同边缘构件和截面形式的RC带翼缘剪力墙的拟静力试验进行数值模拟;通过比较数值模拟结果与试验结果,验证有限元模型的准确性;通过有限元分析,研究轴压比(0.1~0.3)、剪跨比(1.8~3.0)、翼缘宽度与腹板高度比(0.5~1.1)、混凝土强度(C30~C45)、纵筋配筋率(0.73%~2.22%)以及箍筋配箍率(0.74%~5.19%)对RC带翼缘剪力墙抗震性能的影响。研究表明：随着轴压比、翼缘宽度与腹板高度比、混凝土强度以及纵筋配筋率的增大,带翼缘剪力墙的承载力逐渐增大,其极限变形能力在翼缘受拉方向也相应增大,而在翼缘受压方向不断减小。剪跨比的增大使得带翼缘剪力墙的承载力明显减小,但是变形能力大幅提高。箍筋配箍率的提高可以有效延缓带翼缘剪力墙翼缘受拉方向的破坏。     

带现浇暗柱齿槽式预制钢筋混凝土剪力墙抗震性能试验

介绍了3片剪跨比为2.13的钢筋混凝土剪力墙试件在特定轴压比下的拟静力试验,其中1片为现浇试件CW-1,另外2片为采用预制墙板,两端暗柱与水平齿槽现浇混凝土在墙体底部实现与之连接的预制试件。预制试件的主要区别是一片在齿槽内不设竖向分布钢筋的试件PW-1,另一片齿槽内竖向分布钢筋自由搭接的试件PW-2。试验结果表明：通过齿槽连接的预制墙体,其破坏形态与现浇试件基本相同,墙体两端暗柱底部混凝土受压破坏、竖向钢筋受拉屈服;预制试件的极限位移角为1/48~1/53;齿槽式连接能够保证剪力墙在正常工作状态下的受剪承载力;预制试件PW-2的滞回曲线饱满,受剪承载力与现浇试件相当,其延性性能满足抗震要求,齿槽区域墙体竖向分布钢筋自由搭接的连接方式在一定轴压比下可行,经进一步的试验和分析研究后可推广应用。     

RC联肢剪力墙宏观数值计算模型研究

已有的钢筋混凝土联肢剪力墙宏观数值计算模型在墙体单元和连梁单元连接处采用水平变形协调,即连梁单元的梁端转动与墙体单元水平刚性梁的转动变形相协调。然而,水平变形协调并不能反映墙体和连梁的实际变形协调条件。为此,提出了一种钢筋混凝土联肢剪力墙宏观数值计算模型,该模型中墙体单元为具有分布式剪切弹簧且考虑平面外自由度的三维宏观墙体单元模型,连梁单元为具有3个子单元串联的一维杆单元模型,墙体单元与连梁单元的连接采用竖向变形协调,即连梁单元的梁端转动与墙体单元边垂直杆元的变形相协调。并通过算例对其模拟的准确性进行校验。结果表明：采用竖向变形协调方式建立的计算模型能更加准确地模拟联肢剪力墙的力学行为,提出的钢筋混凝土联肢剪力墙宏观数值计算模型可用于三维的非线性分析,其中墙体单元能更好地模拟剪切变形和面外变形,连梁单元能够更好地模拟与墙肢的变形协调。     

带可更换部件的联肢剪力墙抗震性能研究

钢筋混凝土联肢剪力墙结构在地震作用下,钢筋混凝土连梁和剪力墙的墙脚常遭到严重破坏,修复困难。为此,提出了一种带有可更换连梁和可更换墙脚部件的可恢复功能联肢剪力墙,介绍了带可更换部件的联肢剪力墙的设计方法。为了研究带可更换部件的联肢剪力墙的抗震性能和破坏模式,以一片10层联肢剪力墙为例,对带有可更换部件的联肢剪力墙和传统联肢剪力墙进行了地震反应时程对比分析。计算结果表明,在地震作用下,可更换连梁和可更换墙脚部件先后屈服,破坏集中在可更换部件上,带可更换部件的联肢剪力墙的抗震性能显著提高。     

整体式与带缝分体式空心RC剪力墙抗震性能试验研究

进行了四个整体式及四个带缝分体式空心钢筋混凝土剪力墙试件在低周反复水平荷载下的试验,研究了试件的承载力、刚度及衰减过程、延性、耗能性能、滞回特性、破坏特征、钢筋的应变情况。结果表明:整体式空心剪力墙的裂缝分布形态主要以剪切斜裂缝为主,呈现出剪切破坏形态;带缝分体式空心钢筋混凝土剪力墙以弯剪裂缝为主,呈现出延性的弯剪破坏形态;改变带缝空心钢筋混凝土剪力墙竖缝两侧暗柱配筋,可使墙体抗剪承载力不降低而其延性与变形能力得到提高。     

Seismic behavior of semi-supported steel shear walls

During the recent past decade semi-supported steel shear walls (SSSW) have been introduced as an alternative to the traditional type of steel plate shear walls. In this system the shear wall does not connect directly to the main columns of the building frame; instead it is connected to a pair of secondary columns that do not carry vertical gravity loads. In this paper, the interaction between the wall plate and the surrounding frame is investigated experimentally for typical SSSW systems in which the wall-frame has a bending-dominant behavior. Based on the possible storey failure mechanisms a simple method is proposed for design of the floor beams. A quasi static cyclic experimental study has been performed in order to investigate the collapse behavior of the wall-plate and surrounding frame. Furthermore the test setup has been developed in order to facilitate standardized cyclic tests corresponding to those described by ECCS. From this investigation hysteresis loops are obtained and it is seen that pinching occurs in the loops, since the plate system is un-stiffened. The results of the experimental study are compared to the results obtained using the proposed analytical method. As predicted the study shows that the frame has the capability of developing a tension field in the wall plate, so that the wall plate yields before the frame.     

两边连接薄钢板剪力墙加固损伤RC框架结构抗震性能

为了提高损伤RC框架的抗震性能,采用两边连接薄钢板剪力墙对其进行加固.通过2个1/3缩尺比单跨2层两边连接薄钢板加固损伤RC框架的低周往复加载试验,对其抗震性能进行了研究,并与未损伤RC框架试验结果进行对比分析.结果 表明:设置两边连接钢板剪力墙,可显著提高损伤RC框架的承载力、抗侧刚度和延性;加固后的结构钢板剪力墙屈...     

槽形CFRP板条嵌入式增强混凝土梁受剪性能试验研究

为了进一步研究嵌入式CFRP板条对混凝土梁受剪承载力的增强效果,对以往研究成果进行分析总结,提出两种新型的嵌入式受剪增强方式:槽形CFRP板条正向垂直和侧向平行嵌入.试验共设计制作2组4根CFRP嵌入式增强梁,两个对比梁.试验梁采用四点加载,研究CFRP板条的嵌入方式、间距和配箍率对受剪承载力提高的影响,同时分析CFRP板条强度的发挥程度,增强梁的破坏形态以及斜裂缝开展规律.基于破坏形态,对比已有的计算方法,提出CFRP板条抗剪贡献计算方法.研究结果表明所提出的两种嵌入式槽形CFRP板条能够更加充分地利用CFRP的强度,尤其是侧向平行嵌入方式,能够使嵌入式增强梁的受剪承载力提高更为显著;CFRP抗剪贡献计算方法能够适用非剥离破坏形态,具有较高的精度,不过该公式仍需进一步完善才可适用于普遍情况.     

钢筋混凝土剪力墙构件地震损伤性能试验

为了研究剪力墙的地震损伤和基于位移的抗震性能设计,对7片不同设计参数的钢筋混凝土剪力墙构件进行了低周反复加载试验,记录了构件各损伤阶段的变形和裂缝宽度。根据试验结果,对比研究了轴压比、边缘构件配箍率、截面形式对剪力墙构件延性、承载力、变形特点和地震损伤的影响规律。研究结果表明:随着轴压比增大,构件承载力增大,剪切效应增大,延性降低,残余裂缝率减小;随着变形的增大和损伤加剧,构件剪切效应增强;工字形截面构件剪切效应更明显,裂缝开展较慢。     

钢筋混凝土自复位剪力墙抗震性能试验研究

自复位剪力墙是通过无黏结预应力钢绞线将预制墙板与预制墙板/基础连接成整体,其震后恢复能力良好。通过1个现浇钢筋混凝土剪力墙试件和3个自复位剪力墙试件的拟静力试验,研究了地震作用下自复位剪力墙的破坏特征、滞回性能、自复位特性及耗能能力等。研究结果表明：与现浇剪力墙相比,自复位剪力墙震后残余变形较小,破坏轻微,易于修复;自复位剪力墙滞回曲线捏拢明显,滞回环呈旗帜形;随着弯矩贡献比的增大,试件的自复位能力逐渐提高,但耗能能力有所下降。     

Seismic behavior of code designed steel plate shear walls

The AISC Seismic Design Provisions now include capacity design requirements for steel plate shear walls, which consist of thin web plates that infill frames of steel beams, denoted horizontal boundary elements (HBEs), and columns, denoted vertical boundary elements (VBEs). The thin unstiffened web plates are expected to buckle in shear at low load levels and develop tension field action, providing ductility and energy dissipation through tension yielding of the web plate. HBEs are designed for stiffness and strength requirements and are expected to anchor the tension field formation in the web plates. VBEs are designed for yielding of web plates and plastic hinge formation at the ends of the HBEs.This paper assesses the behavior of code designed SPSWs. A series of walls are designed and their behavior is evaluated using nonlinear response history analysis for ground motions representing different hazard levels. It is found that designs meeting current code requirements satisfy maximum interstory drift requirements considering design level earthquakes and have maximum interstory drifts of less than 5% for maximum considered earthquakes. Web plate ductility demands are found to be significantly larger for low rise walls than for high rise walls where higher modes of vibrations impact the response. The percentage of story shear resisted by the web plate relative to the boundary frame is found to be between 60% and 80% and is relatively independent of panel aspect ratio, wall height, or hazard level, but is affected by transitions in plate thickness. Maximum demands in VBEs in design level shaking are found to be considerably less than those found from capacity design for SPSWs with 9 or more stories.     

碳纤维布加固钢筋混凝土梁抗剪性能试验研究

通过对5根碳纤维布加固钢筋混凝土梁抗剪性能的试验研究,观测并分析了实验梁发生破坏的全过程和破坏形态特点、抗剪承载力的提高程度和斜截面纤维应变的分布特征,并得出了一些有益于实践的结论,以供参考。     

预制RC框架内嵌带竖缝剪力墙结构抗震性能研究

为研究预制钢筋混凝土框架内嵌带竖缝剪力墙(PRCFW)结构的抗震性能,对2个单跨两层、缩尺比为1∶2的PRCFW试件进行了拟静力试验研究。考察了PRCFW结构的变形和延性、滞回耗能能力、承载力及刚度退化等性能,分析了框架与内填墙之间的抗剪连接件对结构整体性能的影响。试验结果表明：在加载过程中,设计的抗剪连接件性能可靠,未发生疲劳剪断或锚固破坏;内填墙设置竖缝对PRCFW结构的初期刚度影响较小;进入屈服段后,预制竖缝阻碍了斜裂缝的发展和贯通,缝间墙段以弯曲变形为主,承载力和刚度退化缓慢,使结构整体具有良好的延性和耗能能力。不同轴压比下的框架柱和现浇节点基本完好,破坏主要发生在内填墙和梁端。结合试验和分析结果,提出了PRCFW结构在工程设计时的若干补充计算及构造措施建议。     

新型钢筋混凝土叠合剪力墙抗震性能试验研究

进行了2榀新型叠合剪力墙的低周反复试验,研究了叠合剪力墙的破坏形态、滞回特性、变形能力、刚度退化、耗能能力.试验结果表明,剪式支架能够较好的连接两侧预制板,并使其与现浇层协同工作,保证叠合剪力墙的整体工作性能.     

组合式冗余剪力墙抗震性能试验研究

地震作用下普通剪力墙破坏形态单一,破坏过程不具有明显的层次性。提出了一种由壁式框架与哑铃型剪力墙或带暗支撑剪力墙组合而成的冗余型剪力墙,对两种剪力墙分别设计了2片2层1/2缩尺的剪力墙模型,并进行低周反复荷载试验。重点分析了试件的承载力、刚度、延性、滞回特性、衰减过程及各阶段的破坏形态,提出可以采用不同受力破坏阶段墙体的层间位移角作为墙体性能的初步量化指标。试验结果表明,组合式冗余剪力墙有良好的抗震性能,受力破坏时具有明显的层次性,在墙体的一种结构形式破坏后另一种结构形式能继续承受荷载。这种墙体的试验研究在国内外尚未见,该试验是组合式冗余剪力墙的探索性试验。     

中等剪跨比RC剪力墙拉-弯-剪受力性能试验研究

为研究中等剪跨比钢筋混凝土(RC)剪力墙的拉-弯-剪受力性能，对4个RC剪力墙开展了在恒定轴拉力和往复水平力作用下的拟静力试验。RC墙剪跨比为1.5，尺寸和配筋均相同，仅轴拉力变化。结果表明：RC墙分别发生了剪切破坏、弯曲-剪切破坏和弯曲破坏；轴拉力致使RC墙的水平承载力降低，竖向钢筋平均拉应力比ns从0.20增大到0.80时，RC墙峰值荷载降低了约55%；中等剪跨比RC墙弯曲-剪切耦合效应明显，墙底部截面弯曲屈服后，塑性铰区的剪切变形也表现出显著的非线性；轴拉力和往复水平力作用下墙体发生显著的轴向伸长，引起墙体受剪承载力退化，竖向钢筋平均拉应力比ns=0.40的RC墙，其受力由弯曲机制向剪切机制转变，出现了弯曲-剪切破坏，基于转动角软化桁架模型和轴向伸长的实测数据，定量计算了该类墙体的受剪承载力退化，揭示了弯曲-剪切破坏机理。最后，验证了美国ACI 318—14和中国JGJ 3—2010中RC墙正截面拉弯承载力计算方法和公式的适用性。     

中等剪跨比RC剪力墙拉-弯-剪受力性能试验研究

为研究中等剪跨比钢筋混凝土(RC)剪力墙的拉-弯-剪受力性能,对4个RC剪力墙开展了在恒定轴拉力和往复水平力作用下的拟静力试验。RC墙剪跨比为1.5,尺寸和配筋均相同,仅轴拉力变化。结果表明：RC墙分别发生了剪切破坏、弯曲-剪切破坏和弯曲破坏;轴拉力致使RC墙的水平承载力降低,竖向钢筋平均拉应力比ns从0.20增大到0.80时,RC墙峰值荷载降低了约55%;中等剪跨比RC墙弯曲-剪切耦合效应明显,墙底部截面弯曲屈服后,塑性铰区的剪切变形也表现出显著的非线性;轴拉力和往复水平力作用下墙体发生显著的轴向伸长,引起墙体受剪承载力退化,竖向钢筋平均拉应力比ns=0.40的RC墙,其受力由弯曲机制向剪切机制转变,出现了弯曲-剪切破坏,基于转动角软化桁架模型和轴向伸长的实测数据,定量计算了该类墙体的受剪承载力退化,揭示了弯曲-剪切破坏机理。最后,验证了美国ACI 318—14和中国JGJ 3—2010中RC墙正截面拉弯承载力计算方法和公式的适用性。     

四角钢连接钢框架-钢板剪力墙结构抗震性能研究

基于半刚接框架-钢板剪力墙试件的低周反复加载试验,采用ANSYS有限元软件对其滞回性能进行了数值模拟。分析循环荷载作用下试件的滞回性能及承载能力,考察其应力、变形发展历程、耗能机理和破坏模式。试验和有限元分析结果均表明：内填板的设置缓解了节点区自身的延性要求,框架和钢板墙协同工作良好,结构体系耗能优异,安全储备高,是一种理想的抗侧力结构体系。有限元模拟结构应力和变形发展历程与试验结果基本吻合。由于初始偏心、焊接残余应力等原因,弹性工作阶段,有限元分析的峰值荷载与试验值比较接近;进入塑性阶段,有限元分析的峰值荷载比试验值大,滞回环更饱满。