建筑模网混凝土墙体抗震试验研究与有限元分析

为研究建筑模网混凝土这种新型免模板组合结构体系的抗震性能,该文首先进行了6个模网混凝土矮墙体和3个模网混凝土高墙体试件的抗震拟静力试验,研究了这种新型墙体的破坏过程和破坏形态、滞回特性、承载力和变形能力等。在此基础上建立了模网混凝土墙体的非线性有限元模型,并进行了墙体受力全过程的模拟分析。研究表明:模网混凝土墙体的破坏过程与普通混凝土墙体基本相似,6个矮墙体试件均发生剪切破坏,而3个高墙体试件则分别发生弯曲破坏和纵筋粘结破坏。模网混凝土矮墙表现出较好的抗剪能力,但变形能力略低于普通钢筋混凝土墙体,发生弯曲破坏的高墙体试件表现出较好的变形能力,而含有纵筋搭接的试件变形能力偏低。所建立的有限元模型可较好的模拟试件至中度破坏阶段的滞回曲线、破坏过程和破坏形态。     

Deformation capacity of RC piers wrapped by new fiber-reinforced polymer with large fracture strain

One of the major drawbacks of structure strengthening by fiber reinforced polymer wrapping using materials such as CFRP and AFRP, whose strength and stiffness are high, is the brittle nature of failure mode, which is caused by fracture of the fiber due to low fracturing strain. A series of experiments were conducted to investigate the efficiency of using two new types of fibers, polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) fiber, for seismic strengthening of RC piers. These fibers have the properties of low stiffness and high fracturing strain. Specimens strengthened by PET and PEN fiber sheets wrapping showed considerable improvement in shear capacity and ductility compared to the control specimen. Both PET and PEN showed no tendency to fiber breakage before the pre-defined ultimate deformation. Pier behaviors such as shear deformation and strain development in both fiber and steel shear reinforcement, and the piers, ultimate failure modes, were carefully examined. Shear deformation increases rather rapidly after peak load and concrete shear capacity decreases with the increase in shear deformation. Stiffness of fiber affects the development of shear deformation and the descending branch of the load–deformation curve after the peak load. A simple model to predict the piers deformation capacity, based on the experimental results, was proposed.     

考虑非线性剪切效应的RC桥墩抗震分析模型

剪跨比较小或配箍不足的钢筋混凝土桥墩易发生剪切破坏,而现有的纤维单元模型忽略了剪切变形,不能合理评估弯剪或剪切破坏桥墩的抗震能力。为有效模拟剪切作用影响下钢筋混凝土桥墩的抗震性能,以36个剪切及弯剪破坏圆形截面钢筋混凝土桥墩抗震拟静力试验结果为依据,建立了墩柱剪切破坏时墩底转角的计算公式。利用OpenSees分析平台,建立了基于非线性纤维梁柱单元和零长度剪切弹簧单元的数值分析模型,以此来考虑弯曲和剪切效应的耦合作用。以数值模型中墩底转角来监测试件剪切破坏的发生,剪切破坏发生前模型以纤维梁柱单元模拟的弯曲变形为主;此后,桥墩地震反应以剪切弹簧单元控制,以模拟试件由于剪切破坏导致的强度和刚度退化等行为。通过对12个剪切及弯剪破坏圆形截面桥墩抗震拟静力试验的模拟结果表明,模拟的滞回曲线与试验结果吻合较好,并且能很好地模拟钢筋混凝土结构由于剪切作用引起的刚度与强度的退化现象,验证了模型的合理性。     

低周反复荷载下型钢再生混凝土短柱抗震性能试验研究

通过8个不同再生粗骨料取代率、轴压比、体积配箍率下的型钢再生混凝土短柱的低周反复加载试验,观察其受力过程及破坏形态,分析了不同设计参数对短柱的荷载-位移滞回曲线、骨架曲线、承载能力、刚度退化、延性及耗能等力学性能的影响。试验结果表明:型钢再生混凝土短柱的主要破坏形态为剪切斜压破坏;试件荷载-位移滞回曲线基本呈梭形;试件达到峰值荷载后,承载力下降较快、变形小、延性较差;再生粗骨料取代率对试件承载力影响不大,延性耗能随着取代率增大而有所减低;随着轴压比的增大,试件承载力提高但延性耗能降低幅度大;随体积配箍率的增大,试件承载力及延性耗能均相应增大。除轴压比较小的短柱外,其余型钢再生混凝土短柱的延性系数均小于3,表明短柱抗震性能较差。因此,在实际工程中应采取相应的措施以改善短柱抗震性能。     

FRP约束RC矩形空心截面桥墩分析模型及试验验证

针对纤维复合材料(FiberReinforcedPolymer,FRP)约束钢筋混凝土(RC)矩形空心截面墩的抗震性能分析问题,该文提出了一种考虑有效强度系数和面积配箍率的FRP有效侧向约束力的简化计算方法。并通过与试验体桥墩的墩顶水平位移-承载力、墩底截面转动变形-弯矩曲线的对比分析,验证了该文提出简化计算模型的正确性。最后,基于该文提出的简化计算方法,对不同种类FRP约束RC矩形空心截面墩截面的抗弯承载力、曲率、塑性转动能力等抗震性能参数进行了研究,结果表明环包FRP布对空心墩的延性贡献较大,对提高其承载力影响较小。     

Experimental and analytical studies of innovative prestressed concrete box-girder bridges

This paper presents experimental and analytical results of four scaled prestressed concrete box-girder bridges with corrugated steel webs. The location of prestressing strands at both ends of the specimens and the thickness of end diaphragms are the two major parameters. Based on the experimental results of all four specimens, their seismic behavior is critically examined, including hysteretic loops, ductility factor, dissipated energy, and failure mode, etc. It was found that both the thickness of end diaphragms and the location of prestressing strands at both ends of the specimens are insignificant when the specimens failed at the mid-span due to concrete crushing, and the proposed analytical model can be used to predict the load-displacement relationship of such bridges.     

A study of reinforced concrete bridge columns retrofitted by steel jackets

Abstract

In this paper, theoretical and experimental results of two as‐built circular reinforced concrete (RC) bridge columns and two columns retrofitted with steel jackets are presented. A constitutive model for concrete confined by a steel jacket is proposed. The proposed model is implemented into a sectional analysis to predict the lateral load‐deformation relationship of retrofitted columns. 2/5 scaled RC bridge columns are designed based on the standard details of the existing bridge columns mostly built in late 1980s and early 1990s, in Taiwan (Ministry of Transportation and Communication, 1987; 1995). The columns are expected to have a flexural failure mode during severe ground shaking. Displacement‐controlled cyclic loading tests were conducted to obtain the seismic performance of the columns. The experimental results showed that the bridge column retrofitted with steel jacketing could greatly improve seismic performance measured based by the strength and ductility. The analytical results showed that the proposed constitutive model, implementing sectional analysis, could well capture the lateral force‐displacement relationship of the bridge columns retrofitted with steel jackets.     

Retrofit of RC hollow piers with CFRP sheets

Hollow bridge piers, particularly those built before the seventies, often have insufficient shear capacity due to inadequate transverse reinforcement details. Therefore, special attention must be given to this very important aspect when reinforced concrete (RC) piers with hollow sections are analysed and retrofitted. This paper covers the experimental analysis of retrofit solutions using CFRP sheets along the piers’ entire height to prevent shear failure. Experimental cyclic tests were carried out to evaluate the shear retrofit strategy efficiency on a set of RC piers with square hollow sections. This work also covers the study of design procedures for CFRP shear retrofitting and the evaluation of the associated ductility capacity improvement. The various transverse reinforcement detailing scenarios were assessed to determine their shear-failure prevention efficiency. The corresponding cyclic response behavior was also evaluated. The most relevant experimental information is presented in the paper, such as the evolution of the outer damage pattern. Finally, shear retrofit solutions, with a 40% increase over the maximum flexural force, show that this strategy is adequate to allow satisfactory ductility behavior.     

A comparison of engineered cementitious composites versus normal concrete in beam-column joints under reversed cyclic loading

Engineered cementitious composites (ECC) are a class of high-performance fiber reinforced cementitious composite with strain hardening and multiple cracking properties. For a reinforced concrete member, substitution of conventional concrete with ECC can significantly improve the deformation characteristics in terms of reinforced composite tensile or shear strength and energy dissipation ability. In this paper, a number of RC/ECC composite beam-column joints have been tested under reversed cyclic loading to study the effect of substitution of concrete with ECC in the joint zone on the seismic behaviors of composite members. The experimental parameters include shear reinforcement ratio in the joint zone, axial load level on the column and substitution of concrete with ECC or not. According to the test results, for the specimens without shear reinforcement in the joint zone, substitution of concrete with ECC in the joint zone cannot change the brittle shear failure in the joint zone, but can significantly increase the load capacity and ductility of the beam-column joint specimens, as well as the energy dissipation ability due to high ductility and shear strength of ECC material. For the specimens with insufficient or proper shear reinforcement ratio, substitution of concrete with ECC in the joint zone can lead to failure mode change from brittle shear failure in the joint zone to a more ductile failure mode, i.e. flexural failure at the base of the beam, with increased load capacity, ductility and energy dissipation ability. Increase of axial load on column and shear reinforcement in the joint zone have little effect on seismic behaviors of the members when they failed by flexural failure at the base of beam. In a word, the substitution of concrete with ECC in the joint zone was experimentally proved to be an effective method to increase the seismic resistance of beam-column joint specimens.     

高强钢筋混凝土桥墩抗震性能试验研究与分析

通过拟静力试验研究配置高强钢筋混凝土桥墩的抗震性能。分析桥墩试件的破坏形态,对往复荷载作用下桥墩试件的滞回特性、承载能力、延性性能、耗能能力等抗震性能指标进行比较研究。分析轴压比、剪跨比、箍筋间距及钢筋强度等对抗震性能的影响规律。研究表明:配置高强钢筋混凝土桥墩试件的破坏形态与配置普通钢筋的混凝土桥墩的一致,剪跨比较小的桥墩变形能力有限,呈弯剪破坏形态;剪跨比较大的桥墩变形能力较大,呈弯曲破坏形态。提高轴压比虽能提高试件的承载能力,但使其抗震性能指标降低,不利于桥墩抗震。提高钢筋强度和加密箍筋能提高其各方面的抗震性能指标,有利于结构抗震。     

无端板矩形钢管混凝土构件基本剪切性能研究

该文进行了8个无端板矩形钢管混凝土构件基本剪切性能试验,考察了截面尺寸和剪跨比（0.3~0.8）对构件抗剪承载力及钢管和混凝土滑移的影响规律。结果表明:剪跨比为0.3时构件发生剪切破坏,随着剪跨比增大,构件破坏模式从剪切破坏逐步向弯曲破坏转化,并且随着剪跨比增大,构件抗剪承载力显著降低,核心混凝土滑移量也呈现减小趋势。同时,用有限元软件ABAQUS对试验结果进行了数值模拟,计算结果与试验结果总体上吻合良好,验证了建模方法的可靠性。在此基础上,研究了钢管与核心混凝土之间的摩擦粘结、构件有无端板及加载主轴方向对矩形钢管混凝土构件基本剪切性能的影响规律。表明钢管与混凝土接触面摩擦系数取0.25时与试验结果符合程度较好;端板对构件荷载-位移关系曲线屈服荷载无太大影响,但对曲线后期强化有一定影响;不同加载主轴方向对构件抗剪承载力有显著影响。     

高延性混凝土低矮剪力墙抗震性能试验研究及抗剪承载力计算

该文提出采用高延性混凝土(HDC)提高低矮剪力墙的抗震性能,设计并制作了5片剪跨比均为1.0的剪力墙,并通过拟静力试验,分析轴压比、水平分布钢筋及内置钢板对低矮剪力墙的破坏形态、延性和耗能能力的影响。试验结果表明:与高强混凝土剪力墙相比,HDC剪力墙的变形能力明显提高;HDC低矮剪力墙的耗能能力、变形能力随着轴压比的增大而减小,随水平分布钢筋数量的减小而减小;HDC与钢板协同工作提高了低矮剪力墙的承载能力和耗能能力。基于软化拉-压杆模型,并考虑HDC材料的受压软化特性,该文提出了高延性混凝土低矮剪力墙抗剪承载力的计算公式,计算结果与试验结果吻合较好。     

预应力混凝土深受弯构件的裂缝实验研究

结合4根预应力深受弯构件的实验,分析不同剪跨比和不同预应力筋对构件抗剪承载力的影响。分析表明,剪跨比影响不大。通过开裂荷载和极限荷载的计算值与实验测试值的对比可以看出,有效预应力的作用规范偏于保守,因此该文提出考虑预应力影响的深受弯构件的承载力公式,此承载力公式与实验值符合较好。试验表明:施加预应力后,开裂荷载明显提高。从裂缝分布图看出:预应力混凝土深受弯构件在受剪过程中的受力可比拟为桁架拱模型。     

冷弯薄壁型钢框架-开缝钢板剪力墙力学性能研究

为研究适用于低层和多层冷弯薄壁型钢建筑的冷弯薄壁型钢框架-开缝钢板剪力墙(Cold-formed steel Framed Shear Wall with Slits,简称CFS-WS),该文开展了1面普通CFS-WS和3面加劲CFS-WS的拟静力试验,得到了CFS-WS的破坏形态、滞回曲线、骨架曲线和耗能能力等力学性能,提出了其抗剪承载力设计值。试验结果表明:CFS-WS加载时依靠竖缝间钢板"扭转-恢复-逆向扭转"和型钢框架变形来共同抵抗水平荷载和耗散能量,试件破坏时钢板撕裂,帽形柱端部屈曲;CFS-WS具有良好的承载力、塑性、延性和耗能能力,但其滞回曲线捏缩现象较为严重;加劲CFS-WS较普通CFS-WS而言,其抗剪刚度、承载能力和耗能能力更高,滞回曲线捏缩现象有所减轻。此外,通过加劲肋连接件将加劲肋和冷弯薄壁型钢梁柱连接成钢框架,可有效提高CFS-WS的前期抗剪刚度、承载力和耗能能力,大大改善结构的抗震性能。     

HPFL加固负载下有震损RC圆柱抗震性能的有限元分析

基于采用高性能水泥复合砂浆钢筋网薄层(HPFL)加固4根钢筋混凝土足尺圆柱在不变轴力和周期水平荷载作用下抗震性能的试验研究结果,该文对试件进行了数值模拟分析,研究被加固柱的抗震承载力、延性、刚度、耗能能力等的性能特征。同时,还提出了可用于负载下有震损RC柱的加固方法和该类结构的抗弯承载力简化计算方法。在此基础上,利用新加固方法和有限元分析手段,研究影响负载下有震损RC柱抗震性能的主要因素,包括轴压比、剪跨比、横向网筋配箍率和配筋形式,研究表明:有限元模拟值、理论值和试验值吻合良好;采用HPFL加固后,构件的承载力、延性、耗能能力均有明显改善,刚度的退化速率明显减小,加固层纵筋锚入基座后,抗震性能的提升改善更加优越;随着轴压比的增加,承载力有较大的增长,延性发挥不足;剪跨比增大时,试件的承载力和延性降低;负载级差越大,后期变形能力明显越弱;采取螺旋配筋形式与采取环形配筋形式相比,两者初始刚度相当,前者延性更好,后者承载能力更高。     

考虑不均匀腐蚀影响的钢筋混凝土桥墩抗震性能研究EI北大核心CSCD

对于剪跨比较小的钢筋混凝土桥墩,近海环境下的腐蚀可能会改变结构破坏形态,研究箍筋纵筋同时腐蚀对抗震性能的影响十分必要。采用电化学加速腐蚀方法制备了4个剪跨比为2、不同腐蚀程度的桥墩,通过振动台试验研究腐蚀对桥墩抗震性能的影响。在地震激励作用下,对桥墩的破坏形态、自振周期、阻尼比、加速度和位移响应、累积残余位移及地震耗能能力等方面进行了分析。试验结果表明:随着地震强度的增大,腐蚀构件的耗能能力降低,抗震性能退化明显;无腐蚀桥墩的最终破坏形态是弯曲破坏,而腐蚀程度较为严重的桥墩在加载后期表现为纵筋过早屈服,部分箍筋无法为试件提供足够的抗剪承载能力,试件最终呈现出弯剪破坏形态。     

Prediction of steel fibre reinforced concrete under flexure from an inferred fibre pull-out response

Steel fibre-reinforced concrete (SFRC) is being used in a variety of structural applications, yet there is still considerable debate how to express and evaluate flexural toughness for design purposes. This is holding back the material's development as a permanent structural material. Existing beam and slab test methods have problems with variability or their application in structural design. Furthermore, existing models of SFRC flexural behaviour do not fully capture what happens at the cracked section in terms of the fibre-matrix interactions. Typical of these approaches is the modelling of the tension zone from single fibre pull-out tests, which is problematic in measurement of the load-displacement relationship, the interaction of groups of fibres and the extensive testing required to cover all permutations of fibre geometry. An alternative approach is proposed where the average pull-out response of the fibres bridging the cracked zone is inferred from flexural beam tests. The characteristic load versus crack-mouth opening displacement behaviour for a particular fibre concrete then forms part of the stress and strain/displacement profile in a flexural analysis to predict moment capacity in a design calculation. The model is explained together with its validation by comparing the predicted load-displacement response for a range of fibre volumes in sprayed and cast SFRC. It is concluded that the analysis of beam load/deflection curves to infer the fibre pull-out response is a viable approach. It offers a promising solution to the need for a flexural design model combined with a practical method of characterizing the tensile contribution of steel fibres.     

采用螺栓连接的工字形全装配式RC剪力墙试验研究

采用连接钢框、高强度螺栓将带有内嵌边框的纵横向预制钢筋混凝土（RC）剪力墙连接起来,形成工字形剪力墙。为研究该全装配式剪力墙的受力性能和抗震性能,进行了3榀墙体的单调加载试验和1榀墙体的低周反复荷载试验,分析了该全装配式工字形剪力墙的承载能力、刚度、延性性能、耗能能力、连接件的应变分布以及连接件间的相对滑移等,最后探讨了试件的极限抗剪抵抗机制。研究结果表明:该全装配式剪力墙具有较高的承载能力、较好的延性性能以及耗能能力,位移延性系数约为3~6;高强度螺栓的直径、连接钢框钢板的厚度对装配式剪力墙的抗侧刚度及峰值荷载有一定的影响;内嵌边框既传递了分布钢筋的应力,也起到了约束混凝土、增加RC剪力墙延性性能的作用。     

考虑压-弯-剪相互作用的纤维混凝土剪力墙变形能力分析

为了准确预测地震作用下高性能纤维增强混凝土剪力墙的受力性能,综合考虑压、弯、剪相互作用的破坏机理以及纤维增强混凝土超高受拉应变硬化性能,基于修正压力场理论和单向弯剪模型,提出了高性能纤维增强混凝土剪力墙变形能力分析模型。通过与4片高性能纤维增强混凝土剪力墙低周往复试验骨架曲线的对比研究,验证了剪力墙分析模型的准确性,讨论了影响其变形能力的的主要因素。研究结果表明:该文提出的考虑轴力-弯矩-剪力相互作用的高性能纤维增强混凝土剪力墙荷载-变形模型,可用于单调荷载作用下剪力墙的变形能力分析。     

不同改进形式钢板剪力墙滞回性能研究

钢板剪力墙的构造形式能够改善结构破坏模式、提高耗能能力及延性。为了系统全面地对比不同改进构造形式对钢板剪力墙滞回性能的影响,利用通用有限元软件ABAQUS建立非线性有限元数值模型,采用国内外已有拟静力试验,验证数值分析手段能够真实地预测结构的受力行为。通过建立8种不同改进形式的钢板剪力墙模型,对承载性能、滞回性能、退化特性、断裂性能、破坏形态以及耗能能力等问题进行对比分析,探讨不同改进形式钢板剪力墙的延性、平面外变形、拉力场对柱子影响等关键问题,为工程应用提供参考依据。分析结果表明:通过改变结构的构造形式,能够有效改善结构的滞回性能;在高烈度区需要综合考虑抗震性能、延性、破坏形态、建筑要求以及经济指标选取合适的钢板剪力墙改进构造形式;低屈服点钢板剪力墙由于其材料的特殊性,承载效率较高,耗能能力强,延性优势突出,但需要通过一定的措施抑制提早屈曲,提高侧向刚度。