Study of three- and four-point shear testing of unidirectional composite materials

Both the three- and four-point shear test methods for unidirectional composite materials were studied using a three-dimensional elastic-plastic finite element analysis. The span-to-thickness ratios of the test specimens were varied to study the shear stress distributions. Specimens with lower span-to-thickness ratios were found to yield higher apparent interlaminar shear strengths. This prediction coincides with many available experimental results. The dependence of apparent interlaminar shear strength on span-to-thickness ratio, confirmed by both analytical and experimental studies, shows that both the three- and four-point shear test methods should be used with caution in this regard when measuring the interlaminar shear strength of unidirectional composite materials.     

钢-混凝土组合梁抗剪研究中的塑性分析方法

为了研究钢－混凝土组合梁正弯矩区的组合抗剪性能，本文对16根密实截面钢－混凝土组合梁的组合抗剪性能进行了试验研究。在试验研究中，为了分离组合梁各抗剪部分承担的剪力，需要计算钢梁腹板所承担的剪力。本文介绍一个钢梁腹板在塑性流动阶段的剪应力计算方法，并且该方法还能判断钢材是否进入强化阶段。为了验证这一方法的正确性，作者还进行了2个纯钢梁试件的抗剪试验，试验结果与计算值吻合良好。     

灰粉比对苯丙乳液基水泥复合材料静态力学性能及破坏形态的影响

对不同灰粉比的苯丙乳液基水泥复合材料进行定伸、拉伸和剪切试验,通过测量弹性恢复率、拉伸剪切力学性能指标、变形性能指标、能耗性能指标和负荷位移,研究了灰粉比对苯丙乳液基水泥复合材料定伸黏结性能、拉伸力学性能、剪切力学性能及破坏形态的影响,结合FESEM试验和压汞测孔(MIP)试验结果,分析了灰粉比对苯丙乳液基水泥复合材料力学性能及破坏形态影响规律的微观机制。结果表明:适当增大灰粉比能够改善苯丙乳液基水泥复合材料的微观形貌,优化孔隙结构,提高密实度,显著增强了复合材料的力学性能;随着灰粉比的增大,苯丙乳液基水泥复合材料的定伸黏结性能逐渐降低,拉伸剪切力学性能不断增强,拉伸剪切变形性能和能耗性能均先提升后降低。灰粉比为30%~35%时,苯丙乳液基水泥复合材料的拉伸剪切力学性能最佳;灰粉比为45%时,苯丙乳液基水泥复合材料的拉伸剪切变形性能和能耗性能均低于灰粉比为20%的苯丙乳液基水泥复合材料。随着灰粉比的增大,苯丙乳液基水泥复合材料能够承受的拉伸和剪切负荷位移均先增大后减小,其破坏形态逐步由“内聚破坏”转为“黏结破坏”。      

高强箍筋高强混凝土梁柱节点抗震性能试验研究

为研究高混凝土梁柱节点的抗震性能,进行了4个高强箍筋混凝土节点和1个普通箍筋混凝土节点的低周往复荷载加载试验,研究了高强混凝土节点的破坏形态、滞回特性、耗能能力、受剪性能及箍筋的应力水平,分析了箍筋强度、体积配箍率和箍筋形式对节点承载力、延性、耗能和剪切变形的影响。结果表明:高强箍筋节点的破坏过程与普通箍筋节点类似;提高箍筋屈服强度对节点的承载力提高效果有限,但可有效提高位移延性和耗能能力,同时限制了节点核心区的剪切变形;试件达到极限位移时,普通箍筋试件箍筋已屈服,复合高强箍筋试件箍筋强度发挥比较充分,表现出较好的抗震性能。     

小剪跨比钢板-混凝土组合板抗剪性能的试验研究

通过2块小剪跨比钢板-混凝土组合板试件在集中力作用下抗剪性能试验,对组合板抗剪性能进行了初步分析。试验中主要变化了钢板厚度,得到组合板的极限承载力、变形、受剪破坏形态以及裂缝的发展情况。试验结果表明:小剪跨比钢板-混凝土组合板试件中混凝土最终破坏以斜压破坏为主;通过栓钉的连接,钢板和混凝土协同工作性能良好;截面应变分布基本符合平截面假定。钢板通过栓钉与混凝土的组合效应,显著提高了混凝土的抗剪能力,同时也改善了构件整体延性,该试验的组合板中钢板承担的剪力占总剪力的50%左右。     

压型钢板-高延性水泥基材料组合楼板纵向剪切性能及承载力研究

通过2组8个压型钢板-高延性水泥基材料(ECC)组合楼板静力加载试验,研究上述试件破坏模式、承载力、刚度、应变分布及滑移等受力性能。试验结果表明：峰值荷载时,端部设置栓钉的压型钢板-ECC组合楼板试件滑移值较大,达到峰值荷载后,试件承载力下降平缓,表现为延性剪切破坏;而端部未设置栓钉的试件表现为脆性剪切破坏。分析了剪跨、压型钢板厚度、组合楼板截面高度及端部栓钉等因素对压型钢板-ECC组合楼板纵向剪切性能及剪切承载力影响规律。在试验研究基础上,分别基于欧洲规范(Eurocode-4)和组合楼板设计与施工规范(CECS273:2010)的m-k法,提出适用于压型钢板-ECC组合楼板的纵向剪切承载力计算公式,经比较分析计算结果与试验结果吻合较好。     

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.     

新型双层钢板-混凝土组合剪力墙力学性能研究

提出一种在剪力墙和边缘构件之间设置竖向缝、墙体钢板通过盖板连接件螺旋连接的新型双层钢板-混凝土组合剪力墙,并进行了4个试件的拟静力试验,讨论该新型组合剪力墙的抗震性能,并与未设竖向缝及墙体钢板焊接的同类型试件进行对比。试验结果表明:新型的双层钢板-混凝土组合剪力墙抗震性能良好,4个试件的屈服位移角平均值为 1/169,极限位移角平均值为1/37;竖向缝对于试件的承载力有所削弱,但对延性和耗能性能有所提高;试件的破坏均表现为墙体底部的弯压破坏,表明通过盖板连接件螺旋连接的措施可保证连接缝应力的有效传递。采用有限元软件ABAQUS建立该新型双层钢板-混凝土组合剪力墙模型并进行分析。基于有限元模型,分析了盖板连接件处螺栓群受力机理,竖向缝对边柱破坏形态影响,以及材料强度、轴压比和剪跨比对该新型剪力墙力学性能的影响。     

Shear strength of polymers and fibre composites: 2. carbon/epoxy pultrusions

Pultrusions were made with carbon fibres and an epoxy resin. Three different curing agents were used, so that the matrices were resins with different glass transition temperatures. The composites were tested for shear strength at different temperatures, so that the effect of the resin shear strength on composite shear strength could be observed, with a fixed fibre architecture. It was found that the composite was always much stronger than the resin both for the 0 and 90° fracture modes. The 90° fracture surfaces contained many broken fibres, and shear hackles were observed in the resin-rich regions. These suggested that shear failure (rather than tensile failure) took place in the Iosipescu test for the 90° specimens. It was concluded that the fibre architecture played a dominant role in the composite shear strength, with interphase effects being involved also.     

改进的新型全装配式组合梁抗剪连接件试验研究

该文主要研究一种改进的新型全装配式组合梁结构,主要包括:全预制混凝土楼板、TJ型紧固件(抗剪连接件)、C型钢导槽、钢梁,其具有无现场湿作业,安装制作精度要求低,可局部更换、循环使用等优点。为研究此新型组合梁连接件的抗剪性能,在考虑钢导槽间距、紧固件预紧力、紧固件类型等因素的基础上,设计制作了6组试件,共12次推出试验。根据螺杆顶帽的不同,紧固件类别分为A、B两类,A类紧固件的螺杆端部万向铰为工厂加工成型,B类紧固件的螺杆端部万向铰为德国产的标准件(直接拧入螺杆端部即可,无需加工螺杆端部)。在试验参数的基础上,建立了紧固件和新型组合梁的有限元模型进行对比分析。结果表明:A类各试件表现出良好的残余强度稳定性,B类试件的荷载滑移曲线较A类曲线更为光滑,具有明显的强度下降段;组合梁连接件拆卸后重新安装不会导致抗剪性能的降低;组合梁连接件受力后不拆卸并复拧(再次施加扭矩)后抗剪性能有所提升;300 mm钢导槽间距试件的抗剪性能明显优于450 mm与600 mm;该文提出的紧固件预紧力计算公式与试验和有限元模拟结果吻合较好,建立的有限元模型能够较好地模拟紧固件的抗剪性能。     

新型组合剪力键抗剪机理及承载力计算方法研究

提出了一种带横向栓钉的新型组合PBL剪力键（简称组合剪力键）,并开展了6个组合剪力键试件的静力推出试验。建立了组合剪力键的精细化有限元模型,在试验验证的基础上,开展了216个试件的数值模拟和参数分析。基于试验研究和有限元分析结果,对组合剪力键的受力机理进行了分析。研究表明:该组合剪力键具有良好的抗剪性能,其抗剪承载力由PBL部分的混凝土榫柱和横向栓钉共同提供,可按叠加原理进行计算。参数分析表明:增加栓钉直径和混凝土强度均可有效提高组合剪力键抗剪承载力。其中,当栓钉直径由16 mm增至22 mm时,其承载力约提高27.7%;当混凝土强度等级由C30提高至C50时承载力约提高20.6%。但增加开孔直径和肋板厚度对抗剪承载力的提高影响并不明显基于可靠度分析和叠加原理提出了该组合剪力键抗剪承载力计算公式。研究结果可为该新型剪力键的工程应用和后续研究提供参考。     

内置钢板-高延性混凝土组合连梁抗震性能试验研究

为提高钢板与混凝土的协同变形能力,提出采用高延性混凝土(HDC)代替普通混凝土,设计了2个内置钢板-高延性混凝土(HDC)组合连梁与2个内置钢板-混凝土组合连梁对比试件。通过拟静力试验,研究试件的破坏过程、破坏形态、滞回特性、耗能能力及刚度退化等。结果表明:跨高比为1.5的试件均发生剪切破坏,跨高比为2.5的试件均发生剪切黏结破坏;与混凝土组合连梁相比,HDC组合连梁的延性和耐损伤能力均得到明显提高;试件发生剪切破坏时,HDC组合连梁较混凝土组合连梁的极限位移角和累积耗能分别提高了44.4%和83.5%;试件发生剪切黏结破坏时,HDC组合连梁的耗能能力仍有较大幅度提高。根据4个小跨高比组合连梁试验结果,计算得到其设计剪压比为0.48~0.57,明显高于小跨高比连梁的剪压比限值。基于试验结果和受剪机制分析,提出了小跨高比组合连梁的受剪承载力计算公式,其计算值与试验值吻合较好。     

Determination of shear strength of unidirectional composite materials with the Iosipescu and 10° off-axis shear tests

The purpose of this research was to determine the shear strength of a unidirectional carbon-fibre/epoxy composite by means of the 10° off-axis and 0° Iosipescu specimens subjected to shear. Detailed non-linear finite-element computations of these two tests were conducted, taking into account the actual non-linear material behavior of the composite. The tests were compared in terms of stresses and strains at failure. It was found that the shear strength of the composite can be very accurately determined by using the two independent testing techniques only if fully non-linear finite element computations of the tests are performed. The stresses and strains at failure in the 10° off-axis specimen closely match the stresses and strains at the onset of intralaminar damage near the roots of the notches in Iosipescu specimens. Owing to the difficulties associated with the measurement of the shear strength of the composite using the Iosipescu test, and in particular, with the interpretation of the experimental data, this test was found to be almost impractical for the determination of shear strength. The test can only be used if fully non-linear finite element computations of uncracked and axially cracked Iosipescu specimens are conducted in conjunction with the continuous monitoring of intralaminar damage near the roots of the notches during testing. In addition, the shear strength results obtained from the Iosipescu specimen should be independently verified by using another method, such as the 10° off-axis test.     

An experimental investigation of the static and fatigue fracture behaviour of hybrid composite/metal joints for a tilting car body

The hybrid composite joint structures considered in this work, for application in a tilting railroad car body, are subjected to shear and bending loads. Two types of the joint specimens were fabricated and tested under both static and fatigue conditions: a hybrid bolted-joint specimen subjected to a shear loads, and a hybrid beam-joint specimen for the bending tests. The fracture behaviours of these specimens under static loads were different from those under cyclic loads. For the hybrid bolted-joint specimens, static shear loads caused a pure shear fracture in the bolt pin body itself. However, cyclic fatigue shear loads brought about an opening-mode fracture at the local site of the bolt which was the valley of the screwed region of the bolt pin and/or the perpendicularly angled region between the bolt head and the pin body. On the other hand, for the hybrid beam-joint specimens, static bending loads caused shear deformation and fracture in the honeycomb core region, while fatigue cyclic bend loading caused delamination along the interface between the composite skin and the honeycomb core, and/or caused a fracture in the welded part jointed with the steel under-frame. These fracture behaviours could arise in other industrial hybrid joints with similar sub-structures, and were used in developing a design parameter to improve a hybrid joint structure.     

型钢再生混凝土柱-钢梁组合框架节点抗剪承载力研究

为研究型钢再生混凝土柱-钢梁（SRRC柱-S梁）组合框架节点的抗剪承载力,该文对8个组合框架节点试件进行低周反复荷载试验,观察试件破坏过程及破坏形态,获得各加载阶段试件中型钢和钢筋的应变,分析再生粗骨料取代率和轴压比对节点抗剪承载力的影响规律。结果表明:节点抗剪承载力随取代率的增大而降低,但降低幅度不大;适当增大轴压比可以提高节点的抗剪承载力;试件屈服前,节点剪力主要由核心区再生混凝土承担;屈服后型钢腹板和箍筋起主要抗剪作用。在此基础上,分析节点区受力机理,推导型钢腹板、箍筋和再生混凝土各部分抗剪计算方法,最后通过叠加法建立该节点的抗剪承载力公式,计算结果与试验结果吻合较好,研究结果可为型钢再生混凝土柱-钢梁组合框架节点的工程应用提供参考。     

Monotonic and cyclic short beam shear response of 3D woven composites

Monotonic, multi-step and cyclic short beam shear tests were conducted on 2D and 3D woven composites. The test results were used to determine the effect of z-yarns on the inter-laminar shear strength as well as the multi-loading behavior. The presence of z-yarns was found to affect not only the inter-laminar shear strength of the composite but also the behavior of the composite beyond the elastic limit. Microscopic examination of the damaged specimens revealed large delamination cracks in 2D woven composites while delamination cracks were hindered by z-yarns in 3D composites. This crack arrest phenomena resulted in a reduction in inter-laminar crack lengths and a higher distribution of the micro-cracks throughout the 3D composite. The multi-step and cyclic loading tests are found to be useful in the monitoring of specimen behavior during short beam shear testing. The induced damage was quantified in terms of the loss of strength and stiffness during each loading cycle. It was found that while the 2D composites have higher damage resistance, the 3D composites have a higher damage tolerance.     

钢-超高性能混凝土组合箱梁弹性弯曲性能试验研究及解析解

钢-超高性能混凝土(Ultrahigh performance concrete,以下简称UHPC)组合箱型桥面系在大跨径桥梁建设中具有良好的应用前景。以实际桥梁工程为背景,设计两个大比例钢-UHPC组合箱梁模型试验,主要研究弹性状态下的组合箱梁的弯曲受力行为,重点测试试件加载过程中挠度、应变分布等;建立同时考虑剪力滞后、滑移效应以及钢腹板剪切变形的组合箱梁分析模型,并推导得出解析解。研究结果表明:集中荷载作用下钢-UHPC组合箱梁的剪力滞效应显著,UHPC板跨中截面纵向压应变的最大值与最小值之比约为5~7;UHPC板厚越大,钢-UHPC组合箱梁的刚度越大,相同荷载下,UHPC板和钢梁应变越小;该文同时考虑剪力滞后、滑移效应以及钢腹板剪切变形的解析解与试验结果基本吻合,相比于不考虑钢腹板剪切变形的模型结果具有明显改善。     

型钢混凝土空腹叠合梁受剪承载力试验研究

为更加深入研究型钢混凝土叠合梁的受剪机理,提出更为优化的截面形式,该文完成了10个足尺型钢混凝土叠合梁在单调集中荷载作用下的静力试验研究。通过考察剪跨比、截面形式（空腹和实腹）等参数对受剪性能的影响,着重研究了足尺型钢混凝土空腹叠合梁的受剪性能。结合试验结果对各试件的裂缝形态、破坏特征、承载能力、变形等性能进行了分析研究。采用桁架-拱模型并基于变形协调条件将桁架、拱和型钢三者对受剪承载力的作用相结合,建立了适用于型钢混凝土叠合梁的受剪承载力计算方法。结果表明:型钢混凝土空腹叠合梁与实腹叠合梁具有相似的受剪性能和破坏形态,承载力随剪跨比的增大而减小,试件整体性良好;采用JGJ 2016和YB 9082-2006计算的受剪承载力离散型偏大,该文建立的修正桁架-拱模型计算值与试验结果吻合较好。     

GFRP-混凝土组合板界面抗剪连接性能的试验研究

FRP-混凝土组合板界面的可靠连接是保证其正常工作的基础。为考察组合板中的界面粘结性能,该文对采取4种连接方式的27个玻璃FRP（GFRP）-混凝土组合构件进行双剪推出试验,根据试验结果分析构件的破坏模式、承载力变化及界面滑移情况。研究结果表明:4种连接方式均获得了较高的粘结强度,可考虑作为GFRP-混凝土组合板的界面抗剪构造措施;GFRP-混凝土界面粘结强度与混凝土强度等级、界面粗糙程度、胶结剂的粘结能力、剪力键布置方式有关,且随混凝土强度等级的提高而有所增大。基于该文的试验设计和试验结果,对试验中的3个试件进行了三维非线性有限元分析。     

高轴压比、低剪跨比双钢板-混凝土组合剪力墙拟静力试验研究

双钢板-混凝土组合剪力墙可减小墙体厚度、提高承载力和延性,为研究双钢板-混凝土组合剪力墙高轴压比下的抗震性能,完成了5个剪跨比为1.0的双钢板-混凝土组合剪力墙试件的拟静力试验,研究了剪力墙在低周往复荷载作用下的受力性能和破坏模式等,分析了轴压比、距厚比等因素对抗震性能的影响。试验结果表明:低剪跨比试件发生弯剪破坏;墙体钢板在平均位移角1/83时发生局部屈曲,初始屈曲形态受距厚比影响显著;试件峰值荷载、位移延性系数、刚度等受轴压比、距厚比的影响较小;试件平均极限位移角达1/72、平均有效破坏位移角达1/52,具有良好的变形能力;距厚比增大,试件滞回性能稳定性降低;试件耗能随变形增大而迅速增长,抗震性能良好。建议低剪跨比双钢板-混凝土组合剪力墙轴压比限值取0.7。