碳纤维布加固混凝土梁弯曲性能的试验研究

通过对4根矩形截面钢筋混凝土梁的静力加载试验,研究了碳纤维布对抗弯加固梁的破坏形态、刚度变化、极限承载力、变形能力和裂缝开展情况的影响,分析了碳纤维布粘贴层数和加固梁是否欲裂对碳纤维加固效果的影响.结果表明:碳纤维布可明显增强加固梁的极限承载力,改变加固梁的破坏形态,改善延性,延缓裂缝的发展,提高加固梁的整体刚度;同时碳纤维布粘贴层数越多,加固梁的极限承载力越大,但其提高程度并不与粘贴层数成正比;加固预裂梁后其极限承载力明显提高,但其延性降低.最后,针对现有的规范及理论研究结果,提出了抗弯加固梁的极限承载力计算公式,理论计算结果与试验值符合较好,满足工程实际要求.     

碳纤维布抗弯加固混凝土梁的火灾行为

对4根碳纤维布抗弯加固混凝土梁和1根未加固对比梁进行了明火试验,前者碳纤维布表面涂抹有非膨胀型防火涂料。试验考察了梁跨中裂缝对受拉钢筋温度的影响,以及防火涂料厚度相对较薄时加固梁的破坏形态、高温变形和耐火极限。试验结果表明：1）加固梁在达到耐火极限之前相当长一段时间内的挠度及裂缝宽度和深度较小,跨中裂缝对受拉钢筋温度影...     

模拟不中断交通状况下粘贴碳纤维布加固钢筋混凝土梁试验研究

为了调查动荷载作用下碳纤维布与钢筋混凝土梁的粘贴性能及加固效果,进行了5根模拟交通荷载(等幅正弦波形动荷载)作用下粘贴碳纤维布加固钢筋混凝土梁和1根保持荷载下粘贴碳纤维布加固钢筋混凝土梁以及2根对比梁的试验研究。试验中考虑了混凝土等级、配筋率、有无锚固条、粘贴长度、荷载幅值5个变化参数。试验结果表明,在模拟交通荷载的作用下,碳纤维布加固的钢筋混凝土梁粘贴性能满足要求,粘贴效果良好。在模拟交通荷载后的静载作用下,试验梁的抗弯承载力提高较多,加固效果明显,进一步验证了粘贴效果。     

混杂纤维布加固钢筋混凝土梁抗弯性能试验及理论研究

该文提出了碳/芳纶/玻璃三种纤维混杂思路,高强、高弹模碳纤维提高承载能力,高延伸率玻璃纤维改善延性,而芳纶纤维使应力从碳纤维向玻璃纤维平稳转移。通过对11根钢筋混凝土梁的抗弯试验,研究了不同混杂方式、混杂结构、纤维布层数对梁抗弯性能的影响。结果表明:如果应力转移不平稳,混杂纤维布将与混凝土发生局部剥离,导致混杂纤维布加固效果降低;在相同纤维布层数条件下,与单一碳纤维布加固梁相比,碳/芳纶/玻璃层间混杂纤维布加固梁的初裂、屈服、峰值和极限荷载分别降低了22%、12%、12%和16%,而位移延性系数提高了20%,表明碳/芳纶/玻璃层间混杂纤维布能够显著降低单一碳纤维布的脆性。在试验研究的基础上,采用弹塑性截面分析法计算了混杂纤维布加固梁的承载力,理论计算值与试验值吻合良好。     

CFRP布端绕双杆自锁加固混凝土窄梁抗弯试验

为了抵抗粘贴碳纤维增强聚合物基复合材料（CFRP）加固钢筋混凝土结构中常见的剥离破坏,发明了将CFRP布端部以特定方式绕平行双杆实现自锁的方法。鉴于窄梁截面宽度有限,提出将CFRP布贴梁受拉底面布置后,用安装在梁侧面的双L形端锚装置固定双杆,形成侧锚底贴加固方案。完成了5根混凝土强度较低的矩形截面梁四点弯曲试验,其中4根采用上述锚固方式抗弯加固,检验了锚固效果,考察了CFRP布宽度及其沿全长与梁底面是否粘结对加固效果的影响。试验结果表明,采用本文方法进行加固后,端部剥离得以避免,中部剥离即使发生,或在无粘结加固梁受力后期,CFRP布仍能承担较大拉力,因此,极限荷载较对比梁有明显提高。比较而言,CFRP布与梁底有粘结时加固效果更好,CFRP布宽度加大也对提高承载力有益。     

复合砂浆钢筋网加固抗弯RC梁的非线性分析

复合砂浆钢筋网薄层加固是一种有效的加固方法,能够显著地提高钢筋混凝土梁的抗弯承载力、变形能力以及抗裂性能。以8根复合砂浆钢筋网加固RC梁的试验研究结果为参考,通过非线性有限元分析广泛地研究了加固梁纵向配筋率、配箍特征值、梁高宽比对极限荷载提高幅度的影响,并初步分析了少筋梁和超筋梁加固后的荷载-跨中挠度曲线的变化规律。根据分析和试验结果,通过等效假定给出了复合砂浆钢筋网加固RC梁的极限承载力计算公式和抗弯刚度计算公式。     

碳纤维布加固RC梁中粘结性能的非线性有限元分析

碳纤维布加固钢筋混凝土(RC)梁中,碳纤维布与梁底混凝土的剥离破坏使碳纤维布的强度不能得到充分发挥。分析碳纤维布与梁底混凝土的粘结应力,是研究碳纤维布加固剥离破坏承载力的基础问题。根据4根碳纤维布加固RC梁的试验研究结果,采用商业有限元程序MSC.Marc建立有限元模型,进行了非线性计算分析。通过分离总粘结应力中的局部粘结应力,得到粘结延伸长度范围内的锚固粘结应力分布,并结合试验数据对其分布规律进行了研究。根据分析和试验结果,引入了“有效锚固粘结长度”和“锚固粘结应力”的概念,给出了极限荷载下锚固粘结应力的计算建议。     

钢绞线(丝)网-聚合砂浆加固钢筋混凝土梁受弯性能研究

钢绞线(丝)网-聚合砂浆加固技术是一项新型加固工艺,具有耐火、耐腐蚀、耐老化、施工速度快等优点,已被逐渐应用于钢筋混凝土结构的加固补强中。采用该技术抗弯加固钢筋混凝土梁的受力性能可分为三个阶段:未裂阶段、裂缝阶段和破坏阶段。已有研究多数集中于加固混凝土梁正常使用阶段的抗弯性能分析,对受力纵筋屈服后破坏阶段的抗弯性能分析则鲜有涉及。该文在以往试验研究的基础上,采用换算截面法计算加固钢筋混凝土梁屈服阶段和极限阶段的等效刚度,对加固梁在集中荷载作用下抗弯性能全过程进行受力分析,并通过10根加固梁的试验数据对其验证,吻合良好。     

内嵌碳纤维增强塑料板条抗弯加固混凝土梁试验研究

按照正常配筋浇筑了15根钢筋混凝土梁,在部分混凝土梁受拉区保护层内按照不同尺寸沿梁轴向开槽,在槽内嵌入碳纤维增强塑料(Carbon Fiber Reinforced Plastic,简称CFRP)板条,用专用树脂对槽道进行充填,并对这些梁进行弯曲试验。研究了内嵌碳纤维增强塑料板条加固后混凝土梁的破坏形态、开裂弯矩、极限承载力情况,并与外贴等量碳纤维板条的混凝土梁进行了比较;分析了碳纤维板条加固量及开槽尺寸对承载力的影响及混凝土梁的变形和裂缝发展随加固量及开槽尺寸变化的情况。研究表明,与未加固梁相比,内嵌CFRP板条加固梁的极限承载力提高了11.2%―41.7%;与外贴CFRP板条加固梁相比,其极限承载力提高了15.5%―22.7%。     

钢丝网复合砂浆加固混凝土受弯构件非线性分析

对用钢丝网复合砂浆加固的钢筋混凝土梁进行了正截面抗弯试验研究。试验包括16根用钢丝网加固的梁和两根未加固的对比梁,采用U形三面的加固方式(钢丝网复合砂浆包裹了梁的受拉面及两个侧面)。试验中对比了加固与未加固构件的裂缝开展情况、跨中挠度以及极限荷载。试验结果表明,钢丝网复合砂浆薄层可以明显地提高钢筋混凝土梁的抗弯承载力,提高抗裂性能,增强构件的抗弯刚度。理论部分采用非线性的方法得到加固构件的荷载-挠度曲线,与试验结果比较,有较好的吻合。     

CFRP布加固方案对RC梁剪切性能及尺寸效应影响分析EI北大核心CSCD

采用同时考虑混凝土材料非均质性、钢筋与混凝土之间的相互作用以及CFRP布与混凝土之间的相互作用影响的三维细观数值模拟方法,建立了CFRP布加固RC梁剪切破坏力学分析模型。在验证了细观数值方法合理性的基础上,设计并建立了12根CFRP布加固RC梁细观模型,探究相同CFRP配纤率(用布量)前提下,不同CFRP布加固方案对单调荷载作用下RC梁的剪切性能及尺寸效应的影响。结果表明:CFRP布应变分布与裂缝位置紧密相关,越靠近裂缝位置的CFRP布应变越大,提供的抗剪贡献越多;在CFRP配纤率一致的前提下,CFRP布宽度大厚度小的加固方案优于CFRP布厚度大宽度小的加固方案;CFRP布U型加固RC梁剪切强度存在尺寸效应现象,但相同CFRP配纤率下,不同CFRP布加固方案对名义抗剪强度尺寸效应的影响较小,可以忽略。     

Experimental and analytical investigation of reinforced high strength concrete continuous beams strengthened with fiber reinforced polymer

Carbon and glass fiber reinforced polymer (CFRP and GFRP) are two materials suitable for strengthening the reinforced concrete (RC) beams. Although many in situ RC beams are of continuous constructions, there has been very limited research on the behavior of such beams with externally applied FRP laminate. In addition, most design guidelines were developed for simply supported beams with external FRP laminates. This paper presents an experimental program conducted to study the flexural behavior and redistribution in moment of reinforced high strength concrete (RHSC) continuous beams strengthened with CFRP and GFRP sheets. Test results showed that with increasing the number of CFRP sheet layers, the ultimate strength increases, while the ductility, moment redistribution, and ultimate strain of CFRP sheet decrease. Also, by using the GFRP sheet in strengthening the continuous beam reduced loss in ductility and moment redistribution but it did not significantly increase ultimate strength of beam. The moment enhancement ratio of the strengthened continuous beams was significantly higher than the ultimate load enhancement ratio in the same beam. An analytical model for moment–curvature and load capacity are developed and used for the tested continuous beams in current and other similar studies. The stress–strain curves of concrete, steel and FRP were considered as integrity model. Stress–strain model of concrete is extended from Oztekin et al.’s model by modifying the ultimate strain. Also, new parameters of equivalent stress block are obtained for flexural calculation of RHSC beams. Good agreement between experiment and prediction values is achieved.     

Structural behaviour of RC beams with external flexural and flexural–shear strengthening by FRP sheets

This paper presents experimental research on reinforced concrete (RC) beams with external flexural and flexural–shear strengthening by fibre reinforced polymer (FRP) sheets consisting of carbon FRP (CFRP) and glass FRP (GFRP). The work carried out has examined both the flexural and flexural–shear strengthening capacities of retrofitted RC beams and has indicated how different strengthening arrangements of CFRP and GFRP sheets affect behaviour of the RC beams strengthened. Research output shows that the flexural–shear strengthening arrangement is much more effective than the flexural one in enhancing the stiffness, the ultimate strength and hardening behaviour of the RC beam. In addition theoretical calculations are developed to estimate the bending and shear capacities of the beams tested, which are compared with the corresponding experimental results.     

预应力FRP加固混凝土结构技术研究与应用

介绍了笔者进行的预应力芳纶纤维布和碳纤维筋加固混凝土结构的一些主要研究成果,内容包括:预应力芳纶纤维布永久锚具的开发;预应力芳纶纤维布的应力松弛损失研究;预应力芳纶纤维布加固混凝土梁的受弯、受剪性能研究;温度对芳纶纤维布配套粘结材料的力学性能影响研究;体外预应力碳纤维筋局部加固混凝土梁的力学性能研究;碳纤维筋预应力粗纤维混凝土梁的抗震性能研究;预应力纤维布加固混凝土结构的工程应用等。     

Long-term behavior of existing low-strength reinforced concrete beams strengthened with carbon fiber composite sheets

This paper presents the results of an experimental study of the short- and long-term behavior of low-strength reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP). A numerical analysis model was developed and verified for the calculation of the long-term deflection and maximum allowable long-term load of such RC beams. A parametric study was also conducted and it was found that the maximum allowable long-term load of a CFRP-strengthened beam was dominated by the deflection of RC beam when the cubic compressive strength of concrete was less than a certain value. For concrete of higher strength, the maximum allowable long-term load was dominated by the stress levels of the steel bars. It was also found that the yielding load of the strengthened beams increased significantly with areas strengthened by CFRP sheets and steel bars, while the maximum allowable long-term load only increased slightly.     

Experimental investigations and verification of debonding strain of RHSC continuous beams strengthened in flexure with externally bonded FRPs

Although many in-situ RC beams are of continuous constructions, there has been very little research on the behavior of such beams with external reinforcement. This article presents an experimental program conducted to study the flexural behavior and redistribution of moment of reinforced high strength concrete (RHSC) continuous beams strengthened with carbon and glass-fiber-reinforced polymer (CFRP and GFRP) sheets. The program consists of six RHSC continuous (two-span) beams with overall dimensions equal to 250 × 150 × 6000 mm. One beam was not strengthened and was tested as a control beam. Five beams were strengthened with CFRP and GFRP in flexure along their sagging and hogging regions. The main parameters including type of FRP (GFRP or CFRP), the different ratios of CFRP sheet and effectiveness of end anchorage. The test results showed that the use of GFRP sheet in strengthening of continuous beam reduced loss in ductility and moment redistribution but it did not significantly increase the ultimate strength of them. The use of end anchorage in strengthened continuous beams increased the ultimate strength and moment redistribution. The moment enhancement ratio of the strengthened continuous beams was significantly higher than the ultimate load enhancement ratio in the same beam. Also existing international codes and model such as ACI, fib, JSCE, Teng and Toutanji for prediction of IC debonding strain or stress of strengthened continuous beams are verified. Verifications were carried out based on the test results in this research and the published literature on RC continuous beams strengthened with FRP.     

Flexural behavior of reinforced concrete (RC) beams retrofitted with hybrid fiber reinforced polymers (FRPs) under sustaining loads

This paper reports experimental studies of reinforced concrete (RC) beams retrofitted with new hybrid fiber reinforced polymer (FRP) system consisting carbon FRP (CFRP) and glass FRP (GFRP). The objective of this study is to examine effect of hybrid FRPs on structural behavior of retrofitted RC beams and to investigate if different sequences of CFRP and GFRP sheets of the hybrid FRPs have influences on improvement of strengthening RC beams. Toward that goal, 14 RC beams are fabricated and retrofitted with hybrid FRPs having different combinations of CFRP and GFRP sheets. The beams are loaded with different magnitudes prior to retrofitting in order to investigate the effect of initial loading on the flexural behavior of the retrofitted beam. The main test variables are sequences of attaching hybrid FRP layers and magnitudes of preloads. Under loaded condition, beams are retrofitted with two or three layers of hybrid FRPs, then the load increases until the beams reach failure. Test results conclude that strengthening effects of hybrid FRPs on ductility and stiffness of RC beams depend on orders of FRP layers.     

Flexural response predictions of reinforced concrete beams strengthened with prestressed CFRP plates

Existing experimental studies showed that the reinforced concrete (RC) beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates had three possible flexural failure modes (including the compression failure, tension failure and debonding failure) according to the CFRP reinforcement ratio. Theoretical formulas based on the compatibility of strains and equilibrium of forces were presented to predict the nominal flexural strength of strengthened beams under the three failure modes, respectively, and a limitation on the tensile strain level developed in the prestressed CFRP plate was proposed as the debonding failure occurred. In addition, the calculation methods for cracking moment, crack width and deflection of strengthened beams were provided with taking into account the contribution of prestressed CFRP plates. Experimental studies on five RC beams strengthened with prestressed CFRP plates and a nonlinear finite element parametric analysis were carried out to verify the proposed theoretical formulas. The available test results conducted by other researchers were also compared with the predicted values.     

智能CFRP 加固RC 梁荷载效应的实时模拟与测评

制备了4 根炭纤维复合材料(CFRP) 加固钢筋混凝土(RC) 实验梁, 并在梁内钢筋、混凝土及加固CFRP中预置了布拉格光栅光纤传感器(FBG) 和电阻应变片两种传感器。根据钢筋混凝土理论和ANSYS 有限元软件编制了实验梁受弯荷载效应模拟计算程序。实验表明, 实验梁在受弯承载过程中, 布拉格光栅光纤传感器与传统应变片有完全一致的线性关系; 模拟计算出的实验梁受拉钢筋、压区混凝土应变值及挠度与荷载的关系与CFRP 中FBG的实测值吻合较好。由于对既成RC 结构不能在内部装置传感器(会破坏结构降低抗力) , 采用智能CFRP 加固RC 结构可实现加固和实时健康测评双重功能。