Experimental study and analysis on fatigue stiffness of RC beams strengthened with CFRP and steel plate

The objective of this work is to investigate the fatigue behavior of reinforced concrete(RC) beams strengthened with externally bonded carbon fiber reinforced polymer(CFRP) and steel plate. An experimental investigation and theoretical analysis were made on the law of deflection development and stiffness degradation, as well as the influence of fatigue load ranges. Test results indicate that the law of three-stage change under fatigue loading is followed by both midspan deflection and permanent deflection, which also have positive correlation with fatigue load amplitude. Fatigue stiffness of composite strengthened beams degrades gradually with the increasing of number of cycles. Based on the experimental results, a theoretical model by effective moment of inertia method is developed for calculating the sectional stiffness of such composite strengthened beams under fatigue loading, and the calculated results are in good agreement with the experimental results.

Quasi-plane-hypothesis of strain coordination for RC beams seismically strengthened with externally-bonded or near-surface mounted fiber reinforced plastic

The application of fiber reinforced plastic（FRP）,including carbon FRP and glass FRP,for structural repair and strengthening has grown due to their numerous advantages over conventional materials such as externally bonded reinforcement（EBR） and near-surface mounted（NSM） strengthening techniques.This paper summarizes the results from 21 reinforced concrete beams strengthened with different methods,including externally-bonded and near-surface mounted FRP,to study the strain coordination of the FRP and steel rebar of the RC beam.Since there is relative slipping between the RC beam and the FRP,the strain of the FRP and steel rebar of the RC beam satisfy the quasi-plane-hypothesis;that is,the strain of the longitudinal fiber that parallels the neutral axis of the plated beam within the scope of the effective height（h 0） of the cross section is in direct proportion to the distance from the fiber to the neutral axis.The strain of the FRP and steel rebar satisfies the equation：ε FRP =βε steel,and the value of β is equal to 1.1-1.3 according to the test results.

Lagged strain of laminates in RC beams strengthened with fiber-reinforced polymer

Based on the theory of concrete structure, a new expression was derived for lagged strain of fiber-reinforced polymer （FLIP） laminates in reinforced concrete （RC） beams strengthened with FRP. The influence of different preloaded states and nonlinear stress-strain relationship of compressed concrete were both taken into account in this approach. Then a simplified expression was given by ignoring tensile resistance of concrete. Comparison of analytical predictions with experimental results indicates satisfactory accuracy of the procedures. The errors are less than 8% and 10% respectively when the tensile resistance of concrete is or not considered. While the maximum error of existing procedures is up to 60%.

Nonlinear Finite Element Analysis of Steel Fiber Reinforced Concrete Deep Beams

By the nonlinear finite element analysis （FEA） method, the mechanical properties of the steel fiber reinforced concrete （SFRC） deep beams were discussed in terms of the crack load and ultimate bearing capacity. In the simulation process, the ANSYS parametric design language （APDL） was used to set up the finite element model; the model of bond stress-slip relationship between steel bar and concrete was established. The nonlinear FEA results and test results demonstrated that the steel fiber can not only significantly improve the cracking load and ultimate bearing capacity of the concrete but also repress the development of the cracks. Meanwhile, good agreement was found between the experimental data and FEA results, if the unit type, the parameter model and the failure criterion are selected reasonably.

Fatigue properties of special kind of reinforced concrete composite beams

The special reinforced concrete composite beam consists of a steel fiber reinforced self-stressing concrete composite layer and a reinforced concrete T-beam, and constructional bars are set up at their bonding interface. Fatigue properties of the composite beam under the action of negative moment were experimentally studied. Through inverted loading mode the load-beating state of a composite beam was simulated under the action of negative moment. With the ratios of constructional bars being 0, 0.082% and 0.164% respectively as parameters, the effects of constructional bars on the properties of composite beam, such as fatigue life, crack propagation, rigidity loss as well as damage behavior of bonding interface, were studied. The mechanism of the constructional bars on the fatigue properties of the composite beams and the restriction mechanism of crack widths and rigidity loss were analyzed. The test results show that the constructional bars can enhance the shear resistance of the bonding interface between composite layer and old concrete beam and restrict expanding of steel fiber reinforced self-stressing concrete, which are beneficial to synergistic action of composite layer and old concrete beam, to reducing the stress amplitude of bars and the crack width of composite layer, and to increasing the durability and fatigue life of the composite beam.

Experimental and analytical study on seismic behavior of steel-concrete multienergy dissipation composite shear walls

In this paper, a steel-concrete multi-energy dissipation composite shear wall, comprised of steel-reinforced concrete （SRC） columns, steel plate （SP） deep beams, a concrete wall and energy dissipation strips, is proposed. In order to study the multi-energy dissipation behavior and restorability after an earthquake, two stages of low cyclic loading tests were carded out on ten test specimens. In the first stage, test on five specimens with different number of SP deep beams was carried out, and the test lasted until the displacement drift reached 2%. In the second stage, thin SPs were welded to both sides of the five specimens tested in the first stage, and the same test was carried out on the repaired specimens （designated as new specimens）. The load-bearing capacity, stiffness, ductility, hysteretic behavior and failure characteristics were analyzed for both stages and the results are discussed herein. Extrapolating from these results, strength calculation models and formulas are proposed herein and simulations using ABAQUS carried out, they show good agreement with the test results. The study demonstrates that SRC columns, SP deep beams, concrete wall and energy dissipation strips cooperate well and play an important role in energy dissipation. In addition, this study shows that the shear wall has good recoverability after an earthquake, and that the welding of thin SP＇s to repair a deformed wall is a practicable technique.

Experimental research and numerical simulation of RC beams strengthened with bonded steel plates

It is a common method to strengthen the damaged RC structures with bonded steel plates. At present the ultimate bearing ca- pacity of RC structures strengthened with bonded steel plates is calculated mostly using the theory based on the test. Four beams, including one reference beam, two strengthened concrete beams in primary force and secondary force respectively, and one strengthened concrete beam which was not anchored enough, were tested under four-point bending (4PB) in order to get the data of strain of longitudinal bars, bonded bottom steel plate in tension and deflection of beams in the middle span. The experimental program was supported by a three-dimensioned finite analysis using ABAQUS. At the end of experiments and finite analysis, it is concluded that the investing strengthening technique can significantly improve the load-carrying capacity and the phenomenon of stress concentration at the end of interface, as well as the damage at interface, can be well simulated with cohesive element provided by ABAQUS.

带扇叶形锚固板钢筋机械锚固性能试验研究

为避免型钢混凝土节点钢筋锚固时导致的大量型钢穿孔或钢筋焊接,设计一种新型扇叶形锚固板,并通过带扇叶形锚固板钢筋中心拔出试验,分析锚固板形式、钢筋直径、锚固长度对带锚固板钢筋机械锚固性能的影响。试验结果表明:带扇叶型锚固板钢筋可避开抗剪栓钉,具有施工方便的优点,同时拥有良好的锚固性能;当钢筋锚固长度为5d~7d时,发生混凝土劈裂破坏,当锚固长度为8d~12d时,发生钢筋拉断破坏,且钢筋的锚固系数大于1.25,具有良好的锚固性能;带扇叶形锚固板钢筋极限粘结强度随钢筋直径、钢筋锚固长度增大而减小,建议钢筋的锚固长度取为8d;提出了适用于带扇叶形锚固板钢筋极限粘结强度的计算公式,能较准确地反映扇叶形锚固板对混凝土产生的挤压和劈裂作用。

考虑粘结滑移本构模型的托换梁承载特性分析

粘结滑移有限元分析是掌握型钢混凝土托换梁变形特性的关键手段。采用有限元分析软件建立了考虑和不考虑型钢与混凝土粘结滑移两种有限元模型,分析了托换梁荷载-挠度曲线、型钢应变及箍筋应变的变化规律。结果表明:不考虑粘结滑移时,托换梁的极限荷载、跨中挠度与试验值差值百分比范围分别为1.0%~6.8%和11.3%~24.5%,受剪段中部、梁跨中位置的腹板应变和内、外侧箍筋应变与试验值的差值百分比分别为23.1%、46.4%、15.8%和45.8%;考虑粘结滑移后,托换梁的极限荷载、跨中挠度与试验值差值百分比范围分别为0.7%~4.5%和5.7%~18.2%,受剪段中部、梁跨中位置的腹板应变和内、外侧箍筋应变与试验值的差值百分比分别为2.7%、1.3%、11.6%和27.7%;考虑型钢与混凝土粘结滑移的有限元模型可更准确地模拟梁的承载力和变形。

功能可恢复RCS混合框架结构研究进展

钢筋混凝土柱-钢梁(RCS)混合框架结构以其结合了混凝土优异的抗压性能及钢材优异的抗弯性能而受到广泛关注,而可恢复功能结构以其震后快速恢复使用功能的能力,也成为地震工程界研究的新热点。功能可恢复RCS混合框架结构可以在弯矩较大的梁端和柱脚部位设置可更换构件,实现结构的功能可恢复能力。文中简述了近年来功能可恢复RCS混合框架结构研究进展,重点关注各类型功能可恢复钢梁、功能可恢复摇摆柱脚的构造研究,介绍了功能可恢复RCS混合框架结构性能分析研究进展。最后,对功能可恢复RCS混合框架结构仍需深入研究的问题进行了展望。

HPC端部加强双钢板组合剪力墙的抗震性能

为研究高性能混凝土端部加强双钢板组合剪力墙受力机理及破坏形态,以轴压比、腹部普通混凝土强度等级为关键参数,设计了4片普通试件,7片HPC端部加强试件,运用ABAQUS构建其有限元模型,研究其抗震性能。结果表明:同轴压比下,HPC端部加强试件相比普通试件屈服荷载提高16.30%,峰值荷载提升13.40%;随着轴压比提高,HPC端部加强试件峰值荷载和屈服荷载分别提高7.22%和2.72%,随着轴压比减小,HPC端部加强试件延性提升22.26%;提高腹部腔体混凝土强度等级,HPC端部加强试件的屈服荷载和峰值荷载分别提高13.01%和11.14%,延性提升16.91%。

碳纤维板加固H型钢梁抗剥离夹具研制及应用试验

外贴碳纤维板是钢梁抗弯加固的常用方法,但其端部易因界面应力集中导致剥离破坏,严重影响高性能材料的有效利用,特别是结构加固后的安全服役.为此开发出一种适用于H型钢梁的简易夹具——C形槽板夹,以加强碳纤维板的端部锚固.通过多根带夹碳纤维板加固梁的静力加载试验,验证了此夹具的可靠性,并考察了碳纤维板伸入剪跨段长度与剪跨段长度之比及锚固方式(纯粘、端锚和混锚)对加固效果的影响.研究发现端锚加固不同于纯粘,只要梁的控制截面仍在夹具之间,碳纤维板的极限应力、加固效果及利用效率均随其长度缩短而提高,当碳纤维板长度分别为600、750 mm时,前者极限应变和承载力比后者分别高27.3%和8.1%.由于钢梁表面处理质量较差,混锚加固梁均发生突然剥离,后期退化为端锚加固梁,因而相比端锚加固梁加固效果改善不大,需要提高表面处理质量再做类似研究.尽管如此,相比纯粘加固梁,混锚加固梁采用C形槽板夹后剥离破坏被延迟,抗弯性能大为改善.试验过程中还用压电阻抗法对界面剥离情况进行了检测,结果符合实际.

疲劳加载历史对型钢再生混凝土黏结性能的影响

型钢再生混凝土结构既可以实现废弃骨料的再生利用,又具有较高的刚度、承载力及良好的抗震性能,是一种兼顾节能环保与结构性能的新型组合结构。为了研究疲劳加载历史对型钢再生混凝土黏结性能的影响,文章设计了梁式试件,并研制了一种带有球铰的梁式加载装置,先对试件进行了以加载频率和应力水平为关键参数的200万次疲劳加载,而后进行静力加载。试验结果表明:试件最终破坏模式为静力荷载作用下的黏结滑移破坏,证明文章的试件设计和加载方案的有效性。经历疲劳加载后,试件的破坏过程与原静力试验相似;型钢应变和滑移沿锚固长度方向上的分布规律与原静力试验相同,均在荷载上升段呈负指数分布,在荷载下降段呈线性分布;一定范围内,增大应力水平和加载速率,试件剩余承载力降低。

水工混凝土结构修补加固关键技术探析

我国多数水库大坝建设年代早,水工混凝土结构存在各种老化安全问题,亟待采取修补加固处理。针对水工混凝土结构缺陷类型较多,缺陷修补加固技术复杂,本文根据水工混凝土结构的运行环境和常见缺陷类型,对其修补加固方案、加固材料及施工工艺等进行了技术总结,结合漳河水库水工混凝土结构缺陷问题,详细阐述混凝土裂缝、混凝土表面剥蚀、局部结构强度不足等缺陷产生原因和最新加固技术,相关研究成果和实践经验可供类似工程借鉴。

轴压比和面承板厚度对混合节点抗震性能的影响

为了研究新型柱全截面隔板式钢筋混凝土柱-钢梁(RCS)混合框架节点形式的抗震性能,考虑不同轴压比和面承板厚度的影响,对2组共6个3/4比例的梁柱节点进行低周往复加载试验研究.试验中所有试件均发生设计预期的节点剪切破坏,滞回曲线呈弓型,表明节点具有良好的抗震性能.试件最终因节点区的混凝土开裂剥落而丧失承载力.试验结果表明,当轴压比为0~0.25时,随着轴压比的增大,RCS节点开裂荷载有所增大,峰值荷载前斜裂缝数量减少、宽度减小,试件的承载力、刚度和耗能能力均有所提高.节点域柱纵筋黏结应力随轴压比增大而减小,表明节点域内黏结状况有明显改善.相较于单向面承板试件,双向面承板试件在承载能力、延性和耗能能力方面均表现出显著提高;当双向面承板厚度由6 mm增加至10 mm时,试件峰值承载力和刚度的提升幅度相对有限.

钢板-纤维增强混凝土连梁抗震性能研究

为提升小跨高比钢筋混凝土连梁的抗震性能,提出一种新方案,即钢板-纤维增强混凝土连梁,通过对内置钢板-混凝土连梁和钢板-纤维增强混凝土连梁试件进行低周反复加载试验,研究连梁的破坏过程及滞回性能.结果表明:钢板-混凝土连梁在加载过程中,主剪切裂缝发展明显,最终发生弯曲剪切型破坏,而钢板-纤维增强混凝土在加载过程中,相比较于弯曲裂缝,剪切裂缝发展缓慢,加载到中后期,剪切裂缝基本停止发展,表现出较好的变形能力,直至试件破坏钢板-纤维增强混凝土连梁试件整体保持形态完整,最终发生以弯曲控制为主的破坏.纤维的加入能够有效地限制混凝土裂缝宽度,保持试件的完整性,并能在一定程度上改善连梁的破坏模式.在此基础上,通过有限元软件ABAQUS对钢板-纤维增强混凝土连梁进行参数分析,对钢板-纤维增强混凝土连梁的抗震性能进行研究,探究跨高比、钢板配板率、纤维增强混凝土抗压强度、纵筋配筋率和箍筋配筋率等因素对其性能的影响,为其实际应用提供理论支持.

粘贴钢板加固竖向开裂T梁加固效果评价

为研究粘贴钢板对竖向开裂预应力混凝土T梁的加固效果,通过破坏性试验研究2片20 m预应力混凝土竖向开裂T梁的受力性能。分别从裂缝、位移、应变等方面对加固效果进行评价。结果表明:竖向开裂T梁的结构安全储备不足,但相比于未加固梁,通过粘贴钢板加固,开裂后的刚度提升了33.2%,屈服荷载和极限承载力分别提升了34.7%、52.9%;减少了33.7%的裂缝产生与扩展;并且在混凝土进入软化阶段前,钢板与结构的协同受力能力优异。可见,粘贴钢板加固预应力混凝土竖向开裂T梁的加固效果优异。

型钢混凝土组合结构梁板柱施工质量控制要点分析

型钢混凝土组合结构梁板柱是一种目前应用广泛的新型建筑结构,具有高刚度、高强度和抗震性能好等优点。但施工中也会存在一些质量问题,如型钢混凝土梁板柱的连接、型钢混凝土界面黏结等,型钢混凝土梁板柱施工质量控制对结构性能和整体稳定性具有较大影响。通过对型钢混凝土组合结构梁板柱的施工质量控制要点的分析,从型钢与混凝土界面的黏结性能、型钢混凝土梁板柱连接的方式等方面进行了论述,为型钢混凝土组合结构梁板柱的施工质量控制提供了一定的理论参考。

侧贴预应力CFRP板加固混凝土梁抗弯性能的试验研究

采用自主研发的碳纤维增强(CFRP)片材锚具及张拉装置,对8根用CFRP板不同形式加固的钢筋混凝土梁模型试件进行抗弯性能试验,研究预应力碳纤维板侧面加固对被加固钢筋混凝土梁的承载能力、使用阶段变形和裂缝的影响,以及被加固钢筋混凝土梁使用阶段碳纤维板的应力分布和延性。试验结果表明:侧贴预应力碳纤维板加固可明显提高受弯构件开裂荷载及屈服荷载,减小构件使用阶段的变形及裂缝;两端可靠锚固能防止剥离破坏,充分利用材料强度,还能同时改善构件的延性性能。

混凝土梁侧面粘贴CFRP布的结构加固性能的试验研究

研究采用在混凝土构件侧面粘贴碳纤维布这种新形式加固受弯构件的受力性能 .试验研究共设计了 4根少筋梁 ,试验时 ,先通过 2个对称的集中荷载将梁预加载至纯弯段出现一道主裂缝并失效 ,然后 ,卸载并用碳纤维布粘贴于梁侧面受拉区予以加强 ,待粘贴树脂固化后 ,再重新加载至梁的极限荷载 .试验重点研究了该种加固梁的极限荷载、变形、开裂和碳纤维布粘贴形式对加固效果的影响 .试验结果表明 ,该种加固梁不但承载力提高显著 ,而且具有很好的延性 ,消除了原来在梁底粘贴碳纤维加固梁在极限状态时因碳纤维布突然断裂而出现的脆性破坏现象 .基于试验研究结果 ,导出了这种加固梁承载力的实用计算方法 ,该方法计算精度较好且偏于安全 ,可直接应用于实际加固工程 ,特别是当构件底面有管道等障碍物时 .