Static and dynamic behaviour of RC beam model strengthened by CFRP-sheets

The aim of this paper is to analyse the static and dynamic behaviour of RC beams strengthened by CFRP-sheets after damage by cracking. An experimental program has been developed considering RC beam models with or without strengthening by CFRP-sheets on the tensile zone subjected both to static and dynamic tests. The tests on the RC beam models were repeated under different conditions to evaluate the structural responses during the life of RC beams. The experimental results by static tests are compared with the data obtained by theoretical model. The static behaviour of RC beams strengthened by CFRP-sheets is described up to failure. Finally, theoretical estimates variations in frequency values are compared with the data obtained by experimental dynamic tests.     

Effect of bond and corrosion within partial length on shear behaviour and load capacity of RC beam

This paper describes an experimental investigation into the effect of corrosion damaged partial length in one shear span on the shear behaviour and load capacity of reinforced concrete (RC) beams, where 14 RC beams were tested in four-point bending. Two shear span-to-effective depth ratios 2.0 and 3.0, two different partial lengths and three bond characteristics within the designed partial length were considered. Test results of the RC specimens were compared with theoretical results of the corresponding noncorroded bond-perfect RC beams, and the differences were analyzed to deduce the influence of the bond and corrosion within partial length on behaviour and load capacity of RC beams. The results indicate that the mechanical behaviour and load capacity of the test specimens are greatly influenced by the bond characteristics and high corrosion-induced damage within the partial length. Artificial elimination of the bond and neglecting of the corrosion-induced damage in the longitudinal bars and the connected stirrups within the partial length may lead to overestimate the residual capacity of the corrosion damaged RC beam. In assessing the residual life span and reliability of the in-service RC structures, it is very important to consider the severe corrosion damage within certain length of the RC elements.     

CFRP加固损伤钢筋混凝土梁的性能试验

为研究碳维纤复合材料(CFRP)加固初始损伤钢筋混凝土梁的性能,进行了17片试验梁的加载试验。结果表明:腐蚀损伤、预加载损伤对CFRP加固试验梁的性能影响不大;同时黏贴纵、横向CFRP加固对试验梁的极限承载力提高效果显著;CFRP的加固作用主要体现在梁开裂以后的工作阶段;有腐蚀和预加载损伤的CFRP加固试验梁的荷载-挠度曲线接近双直线的折线形状;梁的承载试验结果略高于按照中国《碳纤维片材加固修复混凝土结构技术规程》(CECS 146:2003)中抗剪承载力公式计算的结果;出于安全考虑,CFRP加固损伤钢筋混凝土梁抗剪承载力公式可参照该规程,并引入合适的折减系数。     

考虑海洋环境损伤的钢筋混凝土框架节点受火性能试验研究

为了研究海洋环境下锈胀裂缝对钢筋混凝土框架节点受火性能的影响,设计了5个配筋相同的足尺钢筋混凝土框架节点试件,以沿梁、柱箍筋方向裂缝宽度最大值为损伤指标,通过快速氯离子侵蚀试验模拟海洋环境下氯离子侵蚀,使4个试件产生不同宽度的锈胀裂缝,然后对4个已损伤框架节点试件以及未损伤的对比节点试件进行火灾试验。结果表明：通过快速氯离子侵蚀试验产生了横向裂缝,其位置与箍筋位置大致相同,其间距与箍筋间距大致相等;初始裂缝宽度对构件高温下的梁、柱端位移变化速率影响显著,锈胀裂缝越宽,构件高温下梁、柱端位移变化速率越快;裂缝的存在加快了热量的传输,导致截面温度场发生畸变;裂缝的存在也会提高钢筋和混凝土的升温速度,加快其力学性能退化,对构件高温下的承载力退化影响显著。     

Damaged RC beams repaired by bonding of CFRP laminates

This paper summarizes the results of experimental studies on damaged reinforced concrete beams repaired by external bonding of carbon fiber reinforced polymer (CFRP) composite laminates to the tensile face of the beam. Two sets of beams were tested in this study: control beams (without CFRP laminates) and damaged and then repaired beams with different amounts of CFRP laminates by varying different parameters (damage degree, CFRP laminate width, concrete strength class). All beams were tested in four-point bending over a span of 1800 mm. The tests were carried out under displacement control. The most investigated parameter in this experimental study is damage degree (ratio between pre-cracked load and load capacity of control beam). Repairing damaged RC beams with externally bonded CFRP laminates were successful for different degrees of damage. The observed failure modes were peeling off and interfacial debonding. These failure modes depend only on the laminate width.The results indicate that the load capacity and the rigidity of repaired beams were significantly higher then those of control beam for all tested damage degrees. The authors remarked that for a load capacity improvement, reinforcement with a CFRP having about a half width of the beam is satisfactory. Finally, the contribution of CFRP laminates on the load capacity and rigidity of repaired RC beams is significant for any concrete strength class.     

Deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion

A three-dimensional reinforced concrete (RC) deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion is presented in this study. The finite element formulation accounts for both material and geometrical nonlinearity. Damage modelling considers uniform and pitting corrosion and includes the reduction of cross-sectional area of corroded bars, the reduction of ductility of reinforcing steel and the deterioration of concrete strength due to splitting cracks, delamination and spalling of the concrete cover. The beam finite element is validated with reference to the results of experimental tests carried out on RC beams with corroded reinforcement. The application potentialities of the proposed formulation are shown through the finite element analysis of a statically indeterminate RC beam and a three-dimensional RC arch bridge under different damage scenarios and corrosion penetration levels. The results indicate that the design for durability of concrete structures exposed to corrosion needs to rely on structural analysis methods capable to account for the global effects of local damage phenomena on the overall system performance.     

Steel corrosion on RC structures under sustained service loads — A critical review

This paper reviews previous studies carried out to investigate the effects of simultaneous load and steel corrosion on the rates of corrosion and the behaviour of RC structures. It highlights the need to perform corrosion tests on laboratory specimens whilst they are under a sustained load so as to better understand the behaviour of corroding in-service structures. Furthermore, it provides a critical discussion on loading systems previously used to corrode RC beams under load and key areas that need further research. The review showed that there were contrasting results on the effects of loading on the rate of corrosion and on corrosion crack widths. Corrosion under load was however found to significantly increase deflections of specimens. In addition, and perhaps more importantly, deflections showed that there was never a gain in stiffness during the corrosion process which is often observed at early corrosion stages on structures corroded in the absence of a sustained load.     

碳纤维增强复合材料布加固损伤预应力混凝土梁剥离性能试验分析

碳纤维增强复合材料(CFRP)布用于普通混凝土结构加固性能研究较为深入,而对于预应力混凝土结构加固性能的研究相对较少。为了研究CFRP布加固损伤预应力混凝土结构黏结性能对其受力性能的影响,通过对3根CFRP布加固不同损伤程度的高强预应力钢筋混凝土梁进行静载试验,研究损伤程度及预应力度对其黏结性能的影响。试验发现,试件破坏前CFRP布均发生剥离,达到破坏时,CFRP布完全剥离、拉断或受压区混凝土被压碎。通过CFRP布应变-荷载曲线及试件挠度-荷载曲线分析表明,试件的剥离荷载与其损伤程度呈反比,而与预应力度呈正比。     

冲击受损RC梁残余力学性能试验

为给冲击受损后钢筋混凝土（RC）梁的修复加固和结构安全评估提供参考,开展了3根RC梁落锤冲击受损后的静载试验及1根静载梁的对比试验,通过变化冲击能量使RC梁遭受不同程度的冲击损伤,对冲击受损后RC梁的残余力学性能进行研究。比较分析了不同冲击能量下受损梁的裂缝发展形态以及冲击力、支座反力、跨中挠度和纵筋应变变化规律;重点研究了不同受损程度梁的残余承载力、残余抗弯刚度和残余变形能力。在综合分析相关文献试验数据并对冲击能量进行标准化的基础上,拟合出冲击受损后RC梁残余承载力与残余抗弯刚度的计算公式。结果表明:随着冲击能量增大,冲击损伤梁挠跨比也增大,残余承载力和刚度总体呈下降趋势;相比未损伤梁,冲击损伤梁弹性抗弯刚度和极限抗弯承载力先增大后减小,但加载后期延性明显降低。     

碳纤维加固锈蚀混凝土梁短期疲劳性能研究

在不同荷载条件下,对8根钢筋混凝土梁进行试验,研究短期疲劳荷载作用下的变形、应力分布以及短期疲劳荷载作用后的力学指标。试验结果和分析表明:疲劳荷载对锈蚀钢筋混凝土梁的影响较大,明显降低试验梁的极限强度和延性;碳纤维加固后的锈蚀混凝土梁的极限承载力明显提高,且在破坏时具有良好的延性,承载力极限值可以提高22%～47%。碳纤维"U"形箍对试验梁的性能影响较大,没有粘贴"U"形箍的碳纤维加固试验梁在后期加载过程中,由于混凝土保护层的突然脱落而发生破坏。采用碳纤维材料加固后的较低锈蚀率的钢筋混凝土梁在经过短期疲劳荷载后依然能够具有良好的力学性能。     

坑蚀对钢筋混凝土梁抗弯承载力的影响

比较了均匀锈蚀和坑蚀对锈蚀钢筋混凝土梁抗弯承载力的影响,定义了描述钢筋均匀锈蚀和坑蚀的两种参数。用试验数据比较了两种参数和锈蚀钢筋混凝土梁剩余抗弯承载力的关系,指出仅仅用均匀锈蚀描述锈蚀钢筋混凝土梁的抗弯承载力是不够的,还应考虑坑蚀的影响。研究了不同坑蚀系数下均匀锈蚀率和坑蚀锈蚀率的关系,指出确定钢筋坑蚀量的关键在于确定坑蚀系数的值,对坑蚀系数的选取应当慎重。给出了同时考虑协同工作系数和坑蚀系数的锈蚀钢筋混凝土梁抗弯承载力的计算公式,公式的计算结果与14根梁的试验结果可以很好吻合,表明所提出的公式可用于既有混凝土梁剩余抗弯承载力的评估。     

碳纤维薄板增强RC梁刚度分析

碳纤维薄板(CFL)加固RC梁技术已成功地应用于桥梁工程.该技术的关键问题之一是增强构件刚度的确定.本文参考规范ACI 440.1,ISIS M03-01和GB 50010,结合静载和疲劳试验,探讨了CFL增强RC梁弯曲刚度的变化规律和计算方法.分析结果表明:(1)CFL增强RC梁允许挠度增加,塑性显著增强,刚度减小;(2)疲劳荷载下构件的刚度发展分为3个阶段,其中稳定扩展阶段是疲劳寿命的主要组成部分,在此阶段随着疲劳加载次数的增加构件刚度平稳减小;(3)采用本文提出的计算公式,可以有效地确定静载和疲劳荷载作用下CFL增强RC梁的刚度.     

初始损伤对CFRP加固混凝土梁受弯性能的影响

通过9根碳纤维布加固的具有初始损伤钢筋混凝土梁、6根碳纤维布直接加固钢筋混凝土梁及3根对比钢筋混凝土梁的抗弯性能试验,分析了初始荷载、初始裂缝及加载历史等对加固梁裂缝发展、屈服荷载、刚度、极限荷载的影响。试验结果表明,采用碳纤维布加固钢筋混凝土梁可以有效的提高其抗弯性能。初始荷载、初始裂缝及加载历史等对加固梁的裂缝发展、刚度、屈服荷载和极限荷载均有不同程度的影响。     

纤维束编织网增强混凝土加固钢筋混凝土梁疲劳破坏试验研究

为研究纤维束编织网增强混凝土加固钢筋混凝土梁的疲劳性能,首先制作10根钢筋混凝土梁试件,并对其中的9根用纤维束编织网增强混凝土进行加固,1根作为对比梁未进行加固,然后采用三分点弯曲加载对试件施加疲劳荷载。试验研究了加固方式、配网率、配筋率、损伤程度等4个因素对加固梁的疲劳裂缝扩展及变形发展的影响。试验结果发现：纤维束编织网增强混凝土加固可以显著提高RC梁的受弯疲劳寿命。加固梁的裂缝数量多于非加固梁,裂缝宽度小于非加固梁。在疲劳荷载作用下,加固梁的裂缝及挠度发展都呈现初始发展、稳定发展、迅速发展三个阶段。针对加固形式,三面加固对斜裂缝的控制优于单面加固。加固前的静力损伤会影响加固梁的裂缝宽度,静力损伤越大,疲劳加载时的裂缝宽度越宽。配网率会影响加固梁最终破坏时的挠度,当配网率大于某一值时,加固梁最后破坏时的挠度明显增加;配筋率的增加可以延长挠度的稳定发展阶段。最后通过回归分析,得到了加固梁的疲劳刚度的算式,由该式计算的结果与试验结果符合良好,可为工程使用提供理论依据。     

钢筋坑蚀对混凝土梁抗弯性能的影响

与钢筋均匀锈蚀相比,钢筋坑蚀具有显著的不确定性和截面损失等特点,对混凝土构件的抗弯性能具有一定的影响。结合国内外相关资料,通过实际工程中钢筋坑蚀的试验统计,验证了坑蚀系数服从极值I型的分布。基于钢筋的坑蚀概率模型,借助MonteCarlo模拟,分析了锈蚀钢筋混凝土梁的抗弯承载力,研究了钢筋坑蚀对混凝土受弯构件承载能力的影响。结果表明,钢筋坑蚀的随机性对梁的可靠性有很大影响,钢筋坑蚀构件抗弯承载力的下降速度比均匀锈蚀更快,对梁的耐久性具有潜在危害。     

Application of replaceable coupling beams to RC structures

An innovative structural component, replaceable coupling beam (RCB), was developed and used in reinforced concrete (RC) structures to enhance the structural performance. During strong earthquakes, damage may occur in replaceable devices to prevent severe damage in primary structural parts, and the damaged devices could be replaced after earthquake. This paper introduces the theory and design method as well as the application of RCBs to RC structures. First, a practical design procedure for RCBs was proposed. Then, cyclic static tests of the RC shear walls with and without RCBs were conducted. At last, a systematical RCB application to RC structure was introduced, and dynamic analysis for the entire structures was performed. The results indicate that RCB has good seismic performance by concentrating damage in the replaceable devices, while the global responses of the structures with and without RCBs changed slightly. Dynamic properties of the real structure were measured through the ambient vibration test, and the test results further validated the dynamic analysis to some extent. Copyright © 2016 John Wiley & Sons, Ltd.     

钢筋混凝土梁升降温全过程温度场分析

文章主要利用了SAFIR有限元分析软件对火灾下钢筋混凝土梁升降温全过程的温度场进行分析和计算,并采用该分析软件计算结果与火灾试验结果对比分析,探讨了高温下钢筋混凝土梁升降温全过程截面温度场的分布规律,为预测火灾后钢筋混凝土梁的损失提供参考依据。     

Remaining capacity assessment of corrosion damaged beams using minimum curves

The number of exposed steelwork structures used in various industries is steadily increasing as a result of building new structures and extending the life of older structures. Most of these structures are subjected to corrosion due to environmental exposure which can reduce their carrying capacity. Corrosion damage is a serious problem for these structures. Current assessment methods of corrosion damaged steelwork involve visual inspection which tends to be used very conservatively. There is a need for more accurate assessment method which can be used to make reliable decisions affecting the cost and safety. In this paper, various forms of corrosion are reviewed along with how uniform corrosion affects steel structures. Corrosion decay models are developed based on the information on the locations where corrosion occurs. The effects of corrosion on steel beams are analyzed by evaluating the remaining capacity with regard to bending stresses, shear failure, lateral torsional buckling, and bearing failure. Four samples of corrosion damaged beams, which were removed from a chemical works, were measured for their thickness loss and then subjected to load test for their ultimate capacities. The failure loads of the beams are compared with the calculated capacities of various corrosion damage models. In order to estimate the percentage remaining capacity of corrosion damaged I-beams, minimum curves for different types of universal beams which are developed can be used in conjunction with the information on the thickness loss.     

AE monitoring of corrosion process in cyclic wet–dry test

Recently, a number of deterioration of reinforced concrete (RC) structures due to salt attack have been reported. After corrosion of reinforcing steel-bar (rebar) is nucleated, expansion of corrosion products results in corrosion-induced cracks in RC. Thus, development of non-destructive evaluation (NDE) techniques is important for inspection of corrosion damage. It is reported that acoustic emission (AE) could identify the onset of corrosion in rebar and the nucleation of concrete cracking due to expansion of corrosion products in the corrosion process. In this study, AE techniques are applied to a cyclic wet–dry test of RC beams. It is confirmed that both the onset of corrosion and the nucleation of concrete cracking are clearly observed as two periods of high AE activity. Kinematics of micro-cracks are identified by SiGMA (Simplified Green’s functions for moment tensor analysis) analysis of AE. To compare with findings, cross-sections of rebars are observed by SEM (Scanning Electron Micrograph). From these results, a great promise for AE techniques to monitor the corrosion process in RC structures is clarified.     

Inelastic lateral-torsional buckling capacity of corroded web opening steel beams using artificial neural networks

Steel beams are extensively used as main structural in various building infrastructures such as bridge girders. Steel structures are prone to suffer various types of damage as they get older. Corrosion may be one of the most important types of damage in ageing steel structures. In a pessimistic state, an area of opening may be created along the bottom zone of the beam's web due to corrosion. The existence of opening in the web of a beam can reduce the resistance of the beam to shear, bending or buckling. This study deals with the stability of damaged steel I-beams with web opening. A three-dimensional finite element (FE) model using ABAQUS for inelastic analysis of beams has been developed to assess the effect of web opening on the lateral-torsional buckling (LTB) capacity. Artificial neural network approach has also been employed to derive empirical formula for predicting the residual ultimate LTB moment of damaged steel I-beams using obtained FE results. It is found out that the proposed formula can accurately predict ultimate capacities of doubly symmetric steel I-beams with different sizes of web opening. Hence, the results of this study can be used for better prediction of residual ultimate LTB moment of corrosion damaged girders of steel existing structures by practice engineers.