粘结层和预应力对CFRP板加固损伤钢梁抗弯性能的影响

为了对比粘结层和预应力对碳纤维增强聚合物复合材料(CFRP)板加固损伤钢梁抗弯性能的影响,进行了5根H型损伤钢梁的抗弯试验,分析了特征荷载、荷载-挠度曲线、CFRP板应变及其强度利用率的变化。试验结果表明:有粘结和无粘结CFRP板具有相近的加固效果,特征荷载差值小于2%;非预应力CFRP板在正常使用阶段的加固效果很小,而预应力CFRP板加固钢梁的特征荷载比非预应力CFRP板提高了近30%。平截面假定适用于有粘结CFRP板-钢梁复合截面,而不适用于无粘结CFRP板-钢梁复合截面。相比于非预应力CFRP板,对CFRP板施加预应力可以显著提高CFRP板的强度利用率。建立的有限元模型可以较好地预测试件的抗弯性能,增加CFRP板的预应力、厚度和弹性模量可以提高损伤钢梁的抗弯加固效果。      

FRP-钢管-混凝土构件抗震性能试验研究

为了研究低周循环往复荷载作用下GFRP(glass fiber reinforced polymer)-钢管-混凝构件的力学性能以及对比CFRP(carbon fiber reinforced polymer)-钢管-混凝土构件的性能差异, 对尺寸相同而加固方式不同的圆形截面FRP(GFRP、CFRP)-钢管-混凝土试件进行了拟静力试验, 荷载采用轴压、双向弯曲的组合来模拟地震动力。结果表明: FRP(GFRP、CFRP)的加固可以有效地提高构件抗动态弯曲的能力; GFRP-钢管-混凝土构件延性高于相同情况下CFRP-钢管-混凝土构件; 与普通钢管-混凝土相比, 环向、纵向和双向包裹的GFRP-钢管-混凝土构件的耗能系数分别提高2.0%、7.0%和12.7%, 而CFRP-钢管-混凝土分别提高2.0%、5.8%和6.7%。     

CFRP板加固RC&PPC梁抗剪性能试验研究

通过10片普通钢筋混凝土(RC)梁及4片部分预应力混凝土(PPC)梁采用CFRP板抗剪加固的试验研究和非线性有限元分析,研究不同损伤程度、剪跨比、配箍率及预应力水平等因素对CFRP板加固RC&PPC梁抗剪性能的影响。结果表明:采用CFRP板对RC&PPC梁进行抗剪加固能够有效抑制斜裂缝的开展,提高加固梁斜截面抗剪承载能力,并改善梁的延性;RC梁损伤后加固,随着配箍率的增大以及剪跨比的减小,将提高加固RC梁的斜向开裂荷载、箍筋屈服荷载以及抗剪极限承载能力;随着预应力水平的提高,PPC加固梁的极限承载力增大,CFRP板抗剪加固效果比较显著;非线性有限元模型能够预测CFRP加固RC/PPC梁的抗剪性能,有限元计算结果与试验结果吻合良好;在进行CFRP板抗剪加固设计时,应对CFRP板的强度进行有效折减。     

表层嵌贴预应力CFRP-strip加固钢筋混凝土梁的受力性能研究

体外粘贴预应力FRP技术和表层嵌贴FRP加固技术均是FRP应用于混凝土结构加固的重要技术,但存在各自的局限和不足。表层嵌贴预应力FRP技术有望结合上述两种技术的优点,进一步提高FRP加固混凝土结构的优势和效能。该文在研制成功FRP板条夹具的基础上,加固并进行了5根钢筋混凝土受弯构件的试验研究,深入考察了各试件尤其是表层嵌贴加固试件的力学行为与破坏形态,对比了体外与表层嵌贴加固试件的承载与变形性能差异,分析了预应力的存在对表层嵌贴加固构件力学性能与破坏模式的影响。试验结果表明:表层嵌贴预应力FRP板条加固显著提高了受弯构件的承载性能,其改善效果与体外粘贴预应力FRP板加固非常接近;嵌贴方式可使粘结树脂代替机械锚具锚固预应力FRP板条,但该文试验中表层嵌贴加固试件的破坏形态为粘贴端部的树脂-混凝土界面剥离和保护层混凝土撕裂,因此有需要就提高界面粘结能力和抑制保护层混凝土撕裂的构造措施开展进一步研究。     

侵蚀环境下FRP条带加固锈蚀钢筋混凝土圆柱轴心受压试验

通过侵蚀环境下碳纤维增强聚合物(CFRP)复合材料条带和玻璃纤维增强聚合物(GFRP)复合材料条带加固锈蚀钢筋混凝土圆柱试验,分析了侵蚀环境对混凝土强度、纤维增强聚合物基复合材料加固锈蚀柱的极限荷载和荷载-轴向位移曲线的影响。结果表明,混凝土强度受冻融环境影响较大,受干湿环境影响较小;纤维增强聚合物(FRP)复合材料加固锈蚀柱的轴向极限荷载与冻融循环次数、钢筋锈蚀率及FRP复合材料种类有关,随冻融循环次数分别增加到25次、50次、75次,GFRP复合材料条带和CFRP复合材料条带加固锈蚀钢筋混凝土圆柱的轴向极限荷载分别降低了10.97%、13.37%、16.04%和5.95%、4.66%、4.33%;FRP复合材料加固锈蚀柱的刚度和耗能受侵蚀环境种类、侵蚀环境作用次数、锈蚀率及FRP复合材料种类的影响。在试验研究的基础上,通过理论分析侵蚀环境下混凝土强度损伤系数和锈蚀钢筋强度退化方程,提出了侵蚀环境下FRP复合材料条带加固锈蚀钢筋混凝土圆柱轴心受压承载力计算方法。      

悬臂梁支座附近表层嵌入FRP筋后性能研究

对悬臂梁支座附近受弯面和侧面表层嵌入FRP筋材后的性能开展了试验研究,探讨了FRP筋类型、试验梁侧面开槽嵌粘方式和初始荷载对悬臂梁性能影响,分析了试验梁的特征荷载、悬臂端挠度、钢筋和FRP筋材的应变。试验结果显示,内嵌FRP筋能够提高悬臂梁的开裂荷载、屈服荷载和极限荷载,试验梁的极限荷载提高范围为48.9%~64.2%;内嵌FRP筋有效地抑制悬臂端挠度,控制了悬臂梁的变形,持续荷载作用下试验梁加固后特征荷载要比其它无初载作用的加固试验梁略低,变形略大,不过,加固效果仍很明显。由此可见,悬臂梁采用FRP筋嵌粘是一种有效的加固方法。     

预应力CFRP加固钢筋混凝土受弯构件的抗力概率模型研究

预应力CFRP 加固混凝土结构技术因其在材料性能利用方面的优越性能已成为CFRP 加固的热点方向,其中预应力CFRP 加固结构的可靠性是这一方向研究的重要内容。该文分析了影响预应力CFRP 板加固钢筋混凝土受弯构件承载力的主要变量的概率特征,考虑CFRP 板尺寸效应和应力分布的影响,采用Weibull 分布推导了CFRP 板的极限强度概率分布函数,根据预应力CFRP 张拉工艺,分析了预应力损失随机变量,建立了在不同失效模式(破坏形态)下的受弯构件抗力概率模型,并开展了参数敏感性分析,获得各个失效模式下抗力概率模型的主要影响因素。研究结果表明:抗力概率模型是预应力CFRP 加固结构的失效概率计算与可靠度校准的重要内容之一,各参数的影响规律与各失效模式的破坏形式密切相关。     

FRP钢管混凝土构件抗冲击性能仿真分析

FRP-钢管混凝土结构是一种新型复合结构形式,该结构由在外壁为FRP（CFRP/GFRP,碳/玻璃纤维增强树脂）材料、内壁为钢材的复合圆管内浇筑混凝土而形成。本文应用有限元方法分析FRP钢管混凝土构件的抗冲击性能,通过变化FRP种类、包裹层数、包裹形式以及钢管的厚度考查不同冲击力下的结构响应,得出冲击力和变形的时程曲线。研究发现利用FRP加固的方法有效地提高了钢管混凝土构件的抗冲击刚度,其增强效果与FRP种类以及FRP的包裹方式和厚度相关,其中以纵向包裹CFRP的试件挠度为最小。为验证数值模拟方法和策略的正确性,对已有钢管混凝土的冲击实验案例进行仿真模拟,模拟结果与实验结果对比良好。     

预应力型钢超高强混凝土梁抗弯性能试验研究

预应力型钢超高强混凝土梁是融合了超高强混凝土材料、钢结构和预应力技术所形成的一种新型组合构件。为了研究预应力型钢超高强混凝土梁的抗弯性能,进行了14根预应力型钢超高强混凝土简支梁在竖向静力荷载作用下的受弯性能试验,分析了试件受力过程、破坏形态、裂缝开展与分布规律等相关试验数据。结果表明:超高强混凝土脆性破坏显著,导致预应力型钢超高强混凝土梁极限状态后承载力骤降,但内置型钢有效提高了试验梁极限状态后的持载能力;预应力型钢超高强混凝土梁以普通受拉纵筋屈服作为试验梁进入屈服阶段的标志,以受压区混凝土崩裂作为试验梁达到极限状态的标志;荷载达到0.9t up之前,试验梁跨中控制截面基本符合平截面假定。在不考虑型钢与混凝土粘结滑移的基础上,采用ANSYS有限元程序对预应力型钢超高强混凝土梁进行数值模拟计算,试验梁开裂荷载、屈服荷载以及极限荷载的计算值与试验值吻合较好,验证了有限元模型的正确性。     

FRP-PVC管混凝土受弯构件力学性能研究

为了揭示FRP-PVC管混凝土受弯构件的力学性能,该文进行了6根试件的弯曲试验,并编写了有限元分析程序,在验证有限元分析结果正确的基础上,研究了FRP包裹层数、FRP包裹类型和FRP包裹方式对FRP-PVC管混凝土受弯性能如破坏模式、极限弯矩承载力及应力-应变关系的影响。通过分析其工作机理,得出简化的极限承载力公式。研究表明受弯构件的受力过程分为弹性阶段、弹塑性阶段和破坏阶段3个阶段;与同条件下无FRP包裹的PVC管混凝土相比,承载力随FRP体积率增大而增大、随混凝土强度提高而增大;相同FRP体积含量下CFRP与BFRP包裹方式相比,在承载力和延性上有很大的提高。     

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。     

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.     

Prestress Losses in NSM‐CFRP Flexurally Strengthened RC Beams

The use of prestressed near‐surface mounted fibre‐reinforced polymers (NSM‐FRP) has been long acknowledged to be a suitable approach to strengthen and retrofit existing reinforced concrete structures. The application of a certain amount of prestress to the FRP prior to its installation provides a number of benefits, mainly related to crack width and deflection requisites at serviceability limit state conditions. After transferring the prestress to a structural element, some of the existing cracks can be closed, decreasing the vulnerability of the element to corrosion, and a certain amount of deflection can be recovered due to the introduced negative curvature. However, these benefits can only be assured if the prestress is properly preserved over time. In this context, three series of reinforced concrete beams, in a total of 10 beams, were strengthened with a prestressed carbon FRP laminate (CFRP) and monitored for about 40 days. The data obtained from these tests is in this paper presented and analysed. The observed losses of strain in the CFRP laminate were found to be mainly located in the extremities of the bonded length, while in the central zone, most of the initial strain was well‐preserved over time. Additionally, the highest CFRP strain losses were observed in the first 6 to 12 days after prestress transfer, suggesting that the benefits of prestressed NSM‐FRP will not be considerably lost over time.     

偏心受拉作用下预应力CFRP筋-型钢混凝土构件抗裂试验

为解决我国型钢混凝土桁架转换层拉杆及低层角柱在正常使用阶段易出现大面积拉裂缝的问题,以轻质高强、防腐的碳纤维增强树脂复合材料(CFRP)筋为预应力筋,提出可有效控制裂缝的预应力CFRP筋-型钢混凝土结构体系,并对其偏心受拉作用下的抗裂性能进行系统研究。以预应力水平、偏心距、纵筋直径及型钢翼缘厚度为主要参数制作11个构件,通过自行研发的拉-压转换桁架实现偏拉加载。结果表明:引入CFRP筋后CFRP筋-型钢混凝土构件抗裂度大幅提升,相较于普通偏拉构件,预应力大偏拉构件开裂荷载提高了64.8%~102.3%,预应力小偏拉构件提高了61.7%~117%,其抗裂性能与预应力水平、纵筋直径和型钢翼缘厚度正相关,与偏心距负相关。参照组合结构设计规范,提出构件开裂阶段中和轴的三种位置分布,并推导出开裂荷载公式,与试验值比较吻合度较高,可为其他复合材料筋在预应力偏拉体系的应用提供参考。      

External CFRP tendon members: Secondary reactions and moment redistribution

The response of prestress secondary reactions in the post-elastic range has been a topic of much controversy. Due to the brittleness of FRP (fiber reinforced polymer) composites, external FRP tendon members may have different moment redistribution characteristics compared to conventional concrete members. This paper presents a numerical investigation into the secondary reactions and moment redistribution in prestressed concrete continuous members with external CFRP tendons. The investigation parameters include the initial prestress level and the pattern of loading. The secondary reactions are computed using a newly developed method based on the linear transformation concept combined with a nonlinear finite element analysis. The results indicate that the secondary reactions increase quicker after concrete cracking and nonprestressed steel yielding. As a consequence, the secondary moment should be included in the design moment. The moment redistribution behavior for symmetrical loading is shown to be quite different from that for unsymmetrical loading. The study also shows that the effect of initial prestress on the moment redistribution is rather important.     

An experimental investigation on flexural behavior of RC beams strengthened with prestressed CFRP strips using a durable anchorage system

This paper investigates the effectiveness and feasibility of a prestressed carbon fiber-reinforced polymer (CFRP) system for strengthening reinforced concrete (RC) beams. The proposed prestressing system with a novel anchorage allows the utilization of full capacity of the CFRP strips. Eight small-scale and two large-scale concrete beams strengthened different configuration of prestressed CFRP strips are tested under static loading conditions up to failure. The main parameters considered include the level of prestressing applied, ranging from 20% to 70% of the tensile strength of the CFRP strips, and the use of mechanical anchorages at both ends of the CFRP strips. Thanks to the durable anchorage, the full range of flexural behavior was investigated including post-debonding. The results indicate that the beams strengthened using prestressed CFRP strips exhibited a higher first-cracking, steel-yielding, and experimental nominal moments as the level of prestressing force increased up to a certain point. After analyzing prestress effects in small scale tests, an optimum prestress level for strengthening concrete beams using CFRP strips is proposed and verified in large scale tests.     

Analytical approach for the flexural analysis of RC beams strengthened with prestressed CFRP

The objective of this paper is to propose a simplified analytical approach to predict the flexural behavior of simply supported reinforced-concrete (RC) beams flexurally strengthened with prestressed carbon fiber reinforced polymer (CFRP) reinforcements using either externally bonded reinforcing (EBR) or near surface mounted (NSM) techniques. This design methodology also considers the ultimate flexural capacity of NSM CFRP strengthened beams when concrete cover delamination is the governing failure mode. A moment–curvature (M–χ) relationship formed by three linear branches corresponding to the precracking, postcracking, and postyielding stages is established by considering the four critical M–χ points that characterize the flexural behavior of CFRP strengthened beams. Two additional M–χ points, namely, concrete decompression and steel decompression, are also defined to assess the initial effects of the prestress force applied by the FRP reinforcement. The mid-span deflection of the beams is predicted based on the curvature approach, assuming a linear curvature variation between the critical points along the beam length. The good predictive performance of the analytical model is appraised by simulating the force–deflection response registered in experimental programs composed of RC beams strengthened with prestressed NSM CFRP reinforcements.     

无粘结CFRP筋部分预应力混凝土连续梁试验与分析

制备了9根两跨无粘结CFRP筋部分预应力混凝土连续梁,并完成了每跨三分点加载试验。考察了在加载过程中的开裂、中支座控制截面非预应力筋屈服、跨中控制截面非预应力筋屈服、极限破坏状态等阶段的受力特征,获得了无粘结CFRP筋在设计用承载能力极限状态和真实承载能力极限状态下的应力增长规律,基于试验结果提出了在这两个状态下的中支座两侧等效塑性铰长度计算公式,提出了分别以中支座控制截面综合配筋指标为自变量和以中支座控制截面相对塑性转角为自变量的弯矩调幅的计算公式。      

预应力高性能混杂纤维增强布加固HPC梁的DNLC单元研究

对于不同混杂配比的预应力高性能混杂纤维增强(HFRP)布,建立高性能HFRP布加固高性能混凝土(HPC)梁的双重非线性分层组合(DNLC)单元模型。根据实体退化单元理论,采用初应力等参层单元对高性能HFRP布的体外预应力效应进行模拟,同时正确地考虑HPC梁的材料非线性效应以及结构的几何非线性,验证DNLC单元分析模型的正确性,并对HPC梁的开裂荷载、普通钢筋应力、高性能HFRP布应力重分布等进行研究。结合试验资料分析表明,预应力碳/玻璃纤维混杂(CFRP/GFRP)布加固HPC梁的理论结果与试验数据吻合程度良好,采用等参层单元有效地模拟高性能HFRP布的预应力作用,及所推导的DNLC单元正确性。预应力GFRP纤维布加固的开裂荷载等均较低,预应力CFRP纤维布加固的开裂荷载等有所提高,但剩余强度过大。HPC梁开裂荷载前预应力高性能HFRP布应力发展缓慢,屈服荷载后,其发展迅速直至结构失效。