HPFL加固受火RC梁二次受力正截面承载力研究

 高性能复合砂浆钢筋网(high performance ferrocement laminate, HPFL)作为一种新型的加固方式,具有防火、耐高温、施工简易等优点．为研究其加固受火钢筋混凝土（reinforced concrete, RC）梁的性能,结合已有的对高性能复合砂浆钢筋网的试验研究和对受火后混凝土梁强度、弹性模量等性能的研究成果,采用ANSYS中的PLANE55单元对高温后RC梁截面的温度场进行模拟,并利用计算二台阶模型简化成等效T形截面,考虑未卸载完全下高性能复合砂浆钢筋网同原材料间的应力—应变滞后现象,计算初始荷载下待加固构件的滞后应变,在此基础上结合构件受力情况推导出高性能复合砂浆钢筋网加固受火RC梁二次受力下的正截面承载力计算公式,将计算结果同试验数据进行比较,并给出了工程实际算例．结果表明,理论值与试验值吻合较好,采用高性能复合砂浆钢筋网加固后能提高受火RC梁的承载力,可供有关混凝土结构加固设计参考．     

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。     

高延性混凝土加固RC梁抗剪性能试验研究

剪跨比对FRP抗剪加固梁的裂缝开展和破坏模式有重要影响,但对FRP加固梁抗剪强度及尺寸效应的影响研究较少。采用三维细观数值模拟方法,考虑混凝土细观组成的非均质性及碳纤维布(CFRP)与混凝土之间的相互作用,建立了CFRP加固无腹筋钢筋混凝土梁剪切破坏力学分析模型。在验证细观模拟方法合理性的基础上,拓展模拟与分析了剪跨比对CFRP加固钢筋混凝土梁剪切破坏及尺寸效应的影响机制与规律。研究结果表明：剪跨比对CFRP抗剪加固梁剪切破坏模式影响较大,剪跨比越大,加固梁愈趋近于延性较好的斜拉破坏;剪跨比对CFRP加固梁抗剪承载力有较大影响,对抗剪强度尺寸效应影响较小;剪跨比对加固梁中的CFRP剪切贡献影响较大,剪跨比越大,CFRP对加固梁的抗剪效果越好,其中对中型剪跨比(λ=2.5)的梁加固效果最有效。     

高延性混凝土加固RC梁抗剪性能试验研究

为利用高延性混凝土（HDC）良好的拉伸和剪切变形能力,提高无腹筋钢筋混凝土梁的受剪性能,该文通过对9根HDC加固梁、1根高性能复合砂浆加固梁及3根未加固梁进行静力试验,研究剪跨比、加固层厚度和加固层是否配置箍筋对梁破坏形态、受剪承载力及变形能力的影响。结果表明：采用HDC面层对无腹筋梁进行抗剪加固,可以显著提高梁的抗剪承载力和变形能力;HDC面层可代替部分箍筋的抗剪作用,改善无腹筋梁的剪切破坏形态,并提高梁的剪压比限值;HDC加固层越厚,其受剪承载力和变形能力提高越明显,但加固层厚度较大时,需采用措施防止HDC面层间发生剥离破坏;HDC面层配置附加箍筋,可进一步提高试件的受剪承载力和耐损伤能力。基于试验结果,该文提出了HDC加固试件的受剪承载力计算公式,其计算值与试验结果吻合较好。     

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。     

外壳预制核心现浇装配整体式RC梁抗剪性能的试验研究

该文以研究外壳预制核心现浇装配整体式钢筋混凝土(RC)梁的抗剪性能为目的,制作了2根新型装配整体式RC梁和1根现浇RC梁,开展了RC梁的抗剪承载力试验,考察新型装配整体式RC梁的荷载-挠度关系、开裂荷载、极限承载力、箍筋应变发展特点及破坏模式,并与现浇RC梁的抗剪性能进行比较,试验研究表明:新型装配整体式RC梁与整浇RC梁具有完全相同的抗剪承载力特性;进一步探讨新型装配式RC梁的极限抗剪承载力计算理论,为装配整体式RC梁的设计提供参考。     

纤维编织网增强地聚物砂浆加固钢筋混凝土梁受剪性能研究

为研究纤维编织网增强地聚物砂浆（TRGM）加固钢筋混凝土构件的可行性,首先通过双剪试验探讨了地聚物砂浆与碳纤维编织网在常温下和高温后的粘结性能,随后开展了地聚物砂浆粘贴不同层数（1层、2层、3层）碳纤维编织网抗剪加固钢筋混凝土梁的静载试验,并与未加固梁、环氧树脂粘贴碳纤维编织网抗剪加固混凝土梁进行了试验比较。试验结果表明,地聚物砂浆与碳纤维编织网的常温粘结强度达2.02 MPa,在温度不高于300℃时强度退化不显著;在未采取任何锚固措施的情况下,采用地聚物砂浆粘贴单层碳纤维编织网加固梁的抗剪承载力相比于未加固梁提高47.1%,提高幅度约为采用环氧树脂粘贴加固的一半;两层TRGM加固梁中的纤维作用发挥得最充分。最后,提出了TRGM抗剪加固梁斜截面承载力的简化计算模型,模型计算结果与试验结果吻合较好。     

CFRP网格-聚合物水泥砂浆加固RC梁抗剪承载力计算方法

为揭示碳纤维增强树脂复合材料(Carbon fiber reinforced polymer,CFRP)网格-聚合物水泥砂浆(Polymer cement mortar,PCM)抗剪加固钢筋混凝土(RC)梁的受剪机制并建立其承载力计算方法,对RC梁进行了四点弯曲试验和有限元模拟,重点分析了CFRP网格对RC加固梁的抗剪贡献,建立了基于改进的桁架拱模型的抗剪承载力计算方法。结果表明：RC梁侧粘贴CFRP网格-PCM加固层不仅可以抑制斜裂缝的发展,而且还提高了抗剪承载力;CFRP网格与钢筋之间具有良好的协同工作性能,其中,横向CFRP网格筋分担了约16%的箍筋应变;回归分析指出纵向CFRP网格筋的应变约为横向CFRP网格筋应变的0.29倍;综合考虑纵向CFRP网格的销栓作用和横向CFRP网格分担的箍筋应变,提出了基于改进桁架-拱模型的承载力计算方法,具有更好的适用性和准确性,能够满足设计要求。     

纤维网格高延性混凝土加固RC柱抗剪性能试验研究

箍筋配置不当、剪跨比较小和轴压比较大的钢筋混凝土(RC)框架柱在地震作用下通常发生脆性剪切破坏。为提高框架柱的抗剪性能,提出采用碳纤维(CFRP)网格和高延性混凝土(HDC)复合加固RC柱。设计了6个RC柱试件,通过低周反复荷载试验,研究加固方式、纤维网格层数和轴压比对加固柱破坏形态、受剪承载力、延性及耗能能力的影响。结果表明：采用HDC和CFRP网格复合加固,可显著提高柱的抗剪承载力,明显改善其延性、变形性能和耗能能力;提高加固层的网格层数,对抗剪承载力影响较小,但加固柱的延性和变形能力得到较大改善;轴压比增大,复合柱的抗剪承载力稍有提高,但试件的延性、变形能力和耗能能力均降低;增加网格层数对高轴压比加固柱的增强效果和对低轴压比柱基本一致。最后基于桁架-拱模型,提出加固柱的抗剪承载力计算公式,计算结果与试验值吻合较好。     

U形CFRP条带混锚加固混凝土梁抗剪试验

为解决纯粘贴U形纤维增强聚合物基复合材料（FRP）加固钢筋混凝土梁中FRP端部容易发生剥离破坏等问题,自主研发了对纤维布条带端部进行自锁锚固的方法和锚板,提出了端锚与粘贴并用的混锚U形条带抗剪加固方法。通过2根未加固梁、1根纯粘贴和2根混锚U形碳纤维增强聚合物基复合材料（CFRP）带抗剪加固梁的对比试验,证实了混锚抗剪加固的有效性：混锚能够对纤维带端部进行可靠锚固,阻止端部剥离破坏的发生,实现纤维拉断破坏,大幅度提高材料强度利用率。混锚加固在抑制混凝土梁斜裂缝开展、延缓箍筋屈服、提高箍筋和CFRP的极限应变以及提高抗剪承载力等多个方面的表现均明显优于纯粘贴加固。     

Fatigue lives of RC beams strengthened with CFRP at different temperatures under cyclic bending loads

Fatigue performance of reinforced concrete (RC) components strengthened with fibre reinforced polymer (FRP) is largely improved. However, temperature changes of service environment have a great effect on the fatigue behaviour of RC components strengthened with FRP. Concerning about temperature variations in subtropical areas such as South China, this paper analyses the fatigue behaviour of RC beams strengthened with carbon fibre laminate (CFL) from experimental studies and theoretical analysis under four different temperatures (5 °C, 20 °C, 50 °C, 80 °C) and five different stress levels (0.60, 0.66, 0.72, 0.78, 0.84). The paper discusses temperature fatigue behaviour of RC beams strengthened with CFL under cyclic bending loads in different service environments, and proposes a calculation formula of fatigue lives of RC beams strengthened with CFL under environmental temperatures and external forces coupling. Experimental results show that the formula not only effectively predicts the fatigue lives of the RC beams strengthened with CFL under environmental temperatures and bending loads coupling but also estimates the fatigue limits.     

Effective strain of RC beams strengthened in shear with FRP

The failure modes of Reinforced Concrete (RC) beams strengthened in shear with Fiber Reinforced Polymer (FRP) sheets or strips are not well understood as much as those of RC beams reinforced with steel stirrups. When the beams are strengthened in shear with FRP composites, beams may fail due to crushing of the concrete before the FRP reaches its rupture strain. Therefore, the effective strain of the FRP plays an important role in predicting the shear strength of such beams. This paper presents the results of an analytical and experimental study on the performance of reinforced concrete beams strengthened in shear with FRP composites and internally reinforced with conventional steel stirrups. Ten RC beams strengthened with varying FRP reinforcement ratio, the type of fiber material (carbon or glass) and configuration (continuous sheets or strips) were tested. Comparisons between the observed and calculated effective strains of the FRP in the tested beams failing in shear showed reasonable agreement.     

Artificial intelligence techniques for prediction of the capacity of RC beams strengthened in shear with external FRP reinforcement

The prediction of the shear capacity of reinforced concrete beams retrofitted in shear by means of externally bonded FRP is very complex as demonstrate the studies carried out up to date. As alternative to the conventional methods two approaches based on artificial intelligence are proposed for the first time. Firstly, the use of neural networks as a means of predicting shear capacity without the need of using complex models and, secondly, the use of genetic algorithms as a means of determining suitably how the shear mechanism works. Predictions obtained with both approaches are compared to experimental values.     

纤维织物增强高延性混凝土加固受损RC梁受剪性能试验

为研究二次受力对纤维织物增强高延性混凝土(TRHDC)加固钢筋混凝土(RC)梁受剪性能的影响,对8根TRHDC加固梁和1根对比梁进行了静载试验,分析了纤维织物层数、损伤程度及持载水平对梁破坏形态、荷载-挠度曲线、荷载-箍筋应变曲线及荷载-织物应变曲线的影响。试验结果表明：所有梁均发生了剪压破坏,仅一根梁出现剥离现象;TRHDC可有效限制斜裂缝的发展,延缓箍筋屈服和刚度退化;TRHDC加固显著地提高了梁的受剪承载力和变形能力,最高分别达67%和54%;加固效果未完全随纤维织物层数的增大而提高,与TRHDC面层利用率有关;原梁箍筋屈服之前,损伤程度对加固梁受剪性能的影响不明显,原梁箍筋屈服之后,加固梁受剪承载力随损伤程度的增大而降低;加固效果随持载水平的提高而降低;两层纤维织物的TRHDC可有效修复完全受损RC梁的受剪性能;建立了考虑二次受力的TRHDC加固RC梁受剪承载力的计算公式,且计算值与试验结果吻合较好。     

Improved model for plate-end shear of CFRP strengthened RC beams

In case of RC members strengthened by means of externally bonded reinforcement, a premature failure can be detected in addition to the conventional modes of failure observed in RC unstrengthened beams. The premature failure occurs mainly due to both shear and normal stresses induced in either the external reinforcement–concrete interface or at the level of steel reinforcement. This research is part of a complete programme aiming to set up design formulae to predict the strength of CFRP strengthened beams, particularly when premature failure through laminates-end shear or concrete cover delamination occurs. Series of RC beams were strengthened with carbon-fiber-reinforced plastic (CFRP) laminates and tested to estimate the extent of the applicability of the formulae proposed by the authors, as well as to study the influence of the layout of the external reinforcement in terms of unsheeted length (the distance between CFRP laminates-end and the nearer support) and cross-sectional area, on the behaviour of strengthened beams. The predictions using the proposed formulae are compared with the obtained experimental results, as well as with the calculated design limit states. The interfacial shear stress and the maximum deflection corresponding to the predicted values at maximum and service loads are also studied.     

Hysteretic behavior of RC shear walls strengthened with CFRP strips

The purpose of this study was to investigate the hysteretic behavior of shear deficient reinforced concrete (RC) walls that were strengthened with carbon fiber reinforced polymer (CFRP) strips. Totally, ½ scale five specimens with 1.5 aspect ratio walls were constructed. One of them was tested without any retrofitting as a reference specimen and four of them were retrofitted specimens with CFRP strips. All of the specimens were tested under cyclic lateral loading. CFRP strips with different configurations were tested like X-shaped, horizontal and parallel strips or combinations of them. All of the CFRP configurations were symmetrically bonded to both sides of the shear wall and were anchoraged to the wall. The research focuses on the effect of using CFRP strips for enhancing strength and increasing ductility of the non-seismic detailed shear walls. Test results shows that all of the CFRP strip configurations significantly improves the lateral strength, energy dissipation and deformation capacity of the shear deficient RC walls. The specimen that was strengthened with X-shaped CFRP strips was failed with premature shear failure. The specimen that was strengthened with horizontal strips was showed flexural hysteretic behavior and plastic hinge was developed at the wall base. CFRP strips were controlled shear crack propagation and resulted in improvement of displacement capacity.     

外加钢筋混凝土梁柱砖砌体房屋抗震性能试验研究

分别对外加钢筋混凝土梁柱加固的砖砌体结构、未采取抗震设防措施的普通砖砌体结构、按现行抗震规范要求设置构造柱和圈梁的砖砌体结构进行了拟动力抗震试验和低周反复加载试验,对比研究了这三类结构的破坏形态、滞回曲线、骨架曲线、极限承载力、极限变形及刚度退化曲线等特性。研究表明,经外加钢筋混凝土梁柱加固的砖砌体房屋能满足现行抗震规范的设防标准要求,外加的钢筋混凝土梁和柱能有效约束墙体和预制板,提高砖砌体结构的承载力和变形能力,并延缓结构的刚度下降。     

Fatigue behavior of RC beams strengthened with prestressed NSM CFRP rods

The fatigue performance of Reinforced Concrete (RC) beams strengthened using NSM CFRP rods was examined in this study. The testing matrix consisted of one un-strengthened beam and four beams strengthened using NSM CFRP rods prestressed to effective strain values of 0, 3260, 6899, and 9177 μ representing 0%, 20.4%, 43.1%, and 57.4% of the CFRP rod ultimate tensile strain, 1.6%. All beams were tested in four-point bending under fatigue conditions representing in-service loading for 3 million cycles at a frequency of 2 Hz. Upper and lower load limits were chosen to induce a stress range of 125 MPa in the tension steel during the first cycle. The fatigue results were compared with experimental test results of identical beams strengthened using prestressed NSM CFRP strips tested under identical fatigue conditions found elsewhere in literature. Test results showed that all strengthened beams experienced deflection increase lower than that of the un-strengthened beam which indicates the efficiency of the strengthening process in reducing the damage accumulation. Also, the percentage deflection increase as well as the stiffness degradation after 3 million cycles are almost the same for all the strengthened beams which indicates that damage accumulation is independent from the prestress level. The groove dimensionality, rather than the CFRP geometry, has a detrimental effect on the bond behavior.