FRP筋混凝土梁正截面抗弯承载力设计研究

基于本课题组9根、国内外其他学者102根FRP筋混凝土梁的试验结果以及本课题组完成的38根FRP筋混凝土梁的有限元参数分析结果,对FRP筋混凝土梁的正截面抗弯承载力进行了较系统的研究.研究表明FRP筋混凝土梁的破坏模式有受拉破坏、平衡破坏和受压破坏三种.确定了FRP筋混凝土梁的最小配筋率以及配筋率与破坏模式的关系;给出了FRP筋"名义屈服强度"的计算公式,并较系统地提出了FRP筋混凝土梁正截面抗弯承载力的设计建议.与ACI 440.1R-01中的设计方法相比,基于该文设计建议的计算值与试验结果更为接近.     

FRP筋-钢筋增强ECC-混凝土组合柱抗震性能研究

提出一种在塑性铰区域采用高延性纤维增强水泥基复合材料(ECC)替代混凝土来改善FRP筋-钢筋增强混凝土柱抗震性能的新方法。对FRP筋-钢筋增强ECC-混凝土构件进行了低周往复荷载试验,系统地考察了基体材料、筋材种类、轴压比对构件破坏模态、裂缝模式、承载力、残余变形、延性和耗能能力的影响。结果表明,将ECC替代塑性铰区域混凝土能够有效避免FRP筋的受压屈曲,进而显著提升组合柱的抗震性能。与钢筋增强ECC-混凝土组合柱相比,复合筋增强ECC-混凝土组合柱的残余变形明显更小,且屈服后的刚度更高。随着轴压比的增大,构件极限强度升高但变形能力降低。通过有限元参数分析可知,组合柱的承载力和变形能力均随着ECC抗压强度及总配筋率的增大而增大;在总配筋率不变的情况下,FRP筋占比越高,构件的延性越好。     

有粘结和无粘结相结合的预应力FRP筋混凝土梁抗弯承载力研究

纤维增强塑料筋(简称FRP 筋)是一种高强线弹性材料,非常适合用做侵蚀环境下的预应力筋,采用有粘结和无粘结相结合是提高预应力FRP 筋混凝土梁延性的一种新方法。对有粘结和无粘结相结合的预应力FRP 筋混凝土梁的抗弯承载力进行了理论分析和试验研究,基于平衡配筋率定义了有粘结和无粘结相结合的预应力FRP筋混凝土梁的破坏形态,推导了平衡配筋率和相应抗弯承载力的计算公式。为了验证公式的正确性,进行了9 根预应力FRP 筋混凝土梁的试验研究,计算结果与试验结果吻合良好。研究结果表明,在相同配筋的条件下,体内有粘结预应力FRP 筋混凝土梁的承载力最高,体内无粘结预应力FRP 筋混凝土梁的承载力其次,而无转向块的体外无粘结预应力FRP 筋混凝土梁的承载力最低。采用体内有粘结和无粘结预应力相结合,可以改善预应力FRP筋混凝土梁的延性。     

冲击荷载下CFRP加固无腹筋梁的抗剪失效机理试验研究

对剪跨比为3.36的1根无腹筋钢筋混凝土梁和2根FRP加固无腹筋钢筋混凝土梁进行了落锤冲击试验,研究无腹筋混凝土梁在冲击荷载作用下的动力响应和FRP加固形式对其抗冲击性能的影响;为了对比动态冲击承载力,还进行了1根FRP加固无腹筋钢筋混凝土梁的静载试验。试验结果表明,黏贴FRP条带尤其是端部锚固FRP条带加固可显著提高无腹筋混凝土梁的抗冲击承载力。通过对实测的冲击力、跨中位移及纵向钢筋应变时程曲线等试验数据进行分析,并结合试件的破坏模式,获得了FRP加固无腹筋混凝土梁的动态抗剪失效机理,即冲击荷载下无腹筋混凝土梁的失效过程分为两个阶段:跨中局部受冲击瞬间的剪切破坏和随后的冲击作用点指向支座处的剪切破坏阶段。分两个阶段讨论了冲击荷载下FRP对抗剪承载力的贡献值,并与各规范理论承载力进行比较,数据比较表明两个阶段FRP动态抗剪承载力均高于静态抗剪承载力和理论值,并与以往CFRP-混凝土界面动态抗剪承载力评估方法比较,为获得合理的FRP抗剪承载力评估方法提供有价值的参考。     

FRP筋混凝土T形和矩形截面梁抗弯承载力计算方法

为建立纤维增强复合材料(fiber-reinforced polymer,FRP)筋混凝土T形和矩形截面梁抗弯承载力简化计算方法,根据平衡破坏状态下的截面分析,定义了等效FRP配筋率ρ_ef和相应的平衡配筋率ρ_{ef, b}。在此基础上,基于257根FRP筋混凝土梁试验结果的统计分析,改进了受拉破坏和受压破坏皆可能发生的过渡区范围(ρ_{ef, b} <ρ_ef≤1.5ρ_{ef, b})。编制了受拉破坏控制截面的非线性分析程序,考虑多个设计参数的影响,开展了25 344个截面的参数分析。通过对参数分析结果的多元回归分析,推导了受拉破坏控制截面的抗弯承载力简化计算公式。此外,基于截面内力平衡和协调条件,推导了受压破坏控制截面的抗弯承载力计算公式。以国内外257根梁抗弯承载力试验结果,验证了所提方法的适用性。     

基于简化四阶矩法的各种截面钢管混凝土轴压承载力可靠度分析

该文采用新点估计法和简化四阶矩法对丁发兴提出的钢管混凝土轴压承载力公式进行可靠度分析,该公式考虑了不同截面钢管形状约束系数,且探讨了不同截面形状、混凝土等级、钢材强度等级、两种荷载组合以及不同荷载比对可靠指标的影响。分析结果表明,不同截面形状的钢管混凝土轴压承载力公式的可靠指标均高于3.7,满足目标可靠指标3.2的要求;当办公室活恒载比为1.0时,混凝土强度越高时,可靠指标越大。     

BFRP筋钢纤维高强混凝土梁受弯承载力试验与理论

通过11根玄武岩纤维增强聚合物复合材料（BFRP）筋钢纤维高强混凝土梁的受弯性能试验,研究了钢纤维混凝土层厚度、钢纤维体积分数和BFRP筋配筋率对BFRP筋钢纤维高强混凝土梁受弯破坏形态及其承载力的影响。结果表明,BFRP筋钢纤维高强混凝土梁的破坏模式可分为受压破坏、受拉破坏和平衡破坏3种;钢纤维混凝土层厚度和钢纤维体积分数的变化对于BFRP筋钢纤维高强混凝土梁受弯承载力具有一定程度的影响,当BFRP筋配筋率为0.77%时,掺加体积分数为1.0%钢纤维的梁受弯承载力较无钢纤维梁提高了22.7%,在受拉区0.57倍截面高度内掺加1.0vol%钢纤维的梁受弯承载力达到全截面钢纤维混凝土梁受弯承载力的86.7%;增大BFRP筋配筋量可显著提高BFRP筋钢纤维高强混凝土梁的受弯承载力,BFRP筋配筋率为1.65%的试验梁受弯承载力较配筋率为0.56%的试验梁提高了39.4%。针对不同的破坏模式,提出了BFRP筋钢纤维高强混凝土梁受弯承载力和平衡配筋率的计算方法,并结合安全配筋率的概念对试验梁的破坏模式进行了预测,试验结果与分析结果吻合良好。     

锈蚀预应力混凝土梁承载力及破坏模式研究

随着服役时间增长,侵蚀环境下预应力混凝土梁因受力筋发生锈蚀而造成其延性与承载力降低,严重影响结构的安全使用。为分析侵蚀环境下预应力混凝土梁的承载性能,以集中荷载作用下锈蚀预应力混凝土梁为研究对象,分析混凝土梁锈蚀后各材料性能的劣化与预应力对其承载能力的影响,基于桁架-拱模型给出了桁架作用与拱作用的荷载分配系数,建立了预应力混凝土梁承载力计算模型及破坏模式判别方法,并通过76根预应力混凝土梁的试验数据对建议模型进行验证。研究结果表明:预应力混凝土梁承载力试验值与计算值之比的平均值为1.116,方差为0.033,吻合较好;基于建议分析模型对预应力混凝土梁破坏模式的预测判别与试验梁破坏模式符合程度较高,且该模型能反映预应力混凝土梁随着锈蚀程度增大其破坏模式发生演变这一特征。该文建议的理论模型可用于锈蚀预应力混凝土梁的承载力计算与破坏模式预测分析。     

钢筋混凝土偏心受压构件增大截面加固后可靠度分析

偏心受压构件增大截面加固后的可靠度与初始偏心距、荷载比和纵筋配筋率有密切的关系。该文首先推导了大、小偏心受压构件在对称配筋下增大截面加固后的计算公式和Nu-Mu相关曲线方程,并在此基础上建立其极限状态方程。采用蒙特卡罗法,分析了四组不同截面的构件在不同初始偏心距、不同荷载比和不同纵筋配筋率下,偏心受压构件增大截面加固后的可靠度。结果表明:截面尺寸大小对可靠指标的影响不是很显著,可靠指标随着初始偏心距和荷载比的增大而减小,随着纵筋配筋率的增大而增大。     

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。     

Strengthening R/C beams with opening by externally installed FRP rods: Behavior and analysis

This paper discusses the strengthening of opening in R/C beams by FRP rods. A total number of thirteen beams with circular and square opening have been tested. The opening is shown to significantly reduce the shear capacity of beam. Two patterns of strengthening by FRP rod are investigated: one is to place FRP rods enclosing the opening and the other is to place FRP rods diagonally throughout the entire depth of the beam. It is found that simply placing FRP rods around the opening is not fully effective because a diagonal crack can propagate through the beam with the crack path diverted to avoid intersecting with the FRP rod. When FRP rods are placed throughout the entire beam’s depth, a significant improvement in loading capacity and ductility is achieved, similar to strengthening by pre-fabricated internal steel bars. The flexural failure mode is restored. A nonlinear finite element analysis, based on smeared crack approach, is conducted for numerical verification and examining the effect of length, position and inclination of FRP rods. The plot of analytical principal compressive stress illustrates two strut mechanisms associated with FRP rod. The inclined rods are found to be more effective than vertical ones.     

应用Monte Carlo-JC法评估FRP加固RC梁受弯承载力可靠度

将Monte Carlo随机抽样方法与JC法相结合(称为Monte Carlo-JC法), 利用Matlab软件自带的随机数发生器编制了程序, 针对ACI 440.2R-02设计指南(称为ACI指南)中的FRP抗弯加固条款进行了较为系统的可靠度评估。可靠度分析结果表明: 混凝土强度f' _c、 CFRP片材配筋率ρ_f及CFRP片材性能是影响抗力比值均值和标准差的3个主要因素; 可靠度指标的平均值随着折减系数的增大而逐步减小, 且随着荷载效应比值L_n/D_n的增大而减小。对所有可靠度指标进行统一考虑, 得到整体抗弯设计指标β₀为4.40, 可见该指南的可靠度水平偏高。基于对抗力折减系数的参数研究结果, 无论钢筋的应变水平如何, 建议取固定值0.90。在所有相关设计指南中, ACI指南最具有代表性, 对该指南的可靠度评估具有普遍意义。      

Micro-mechanical analysis of splitting failure in concrete reinforced with fiber reinforced plastic rods

The present investigation provides a micro-mechanical model for the splitting failure analysis of fiber reinforced plastic (FRP) reinforced concrete members subjected to longitudinal tensile stresses. The model consists of three co-axial cylinders: (a) the inner elastic FRP rod; (b) the mid cracked part of concrete; and (c) the outer elastic part of concrete. The anisotropic properties of reinforcement, the compatibility of longitudinal strain at interface and the effect of Poisson's ratio of concrete are taken into account in the analysis. The method can be used to predict the stress distributions in the hybrid structure and the relations between the growth of cracks and the applied end forces. It is found that the number of splitting cracks and the material properties of the anisotropic FRP rods are not the dominant factors in splitting failure. It is also observed that neglecting Poisson's ratio of cracked concrete may under-estimate stresses in the hybrid structure.     

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。     

Ductile strengthening using externally bonded and near surface mounted composite systems

Externally bonded fiber reinforced polymers (FRP) has been established as an effective technique for strengthening concrete members. Other techniques, like near surface mounted (NSM) FRP bars, and steel reinforced polymers (SRP) have emerged as viable alternatives. In this study, four composite-based strengthening systems were used to provide equivalent flexural performance, namely: externally bonded CFRP sheets, NSM prefabricated CFRP strips, externally bonded SRP sheets and NSM stainless steel bars. The strengthening design was based on achieving approximately 38% increase in flexural capacity over the unstrengthened control beams. The mode of failure by design was brittle failure controlled by concrete crushing at 0.003 strain. However, the experimental program was designed to demonstrate the effectiveness of transverse anchoring reinforcement to control premature debonding failure modes and fully utilize the high strength of the composite systems. A more ductile behavior was also observed as a result of transverse strengthening and concrete confinement effects. Accordingly, an increase of approximately 50% in flexural strength is accomplished.     

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。     

Reliability-based bond design for GFRP-reinforced concrete

Most of proposed models available so far associated with the evaluation of design embedded length of fiber reinforced polymer (FRP) rods in concrete are not reliability-based. This paper made an attempt, from the probabilistic standpoint, to determine the design embedded length of a glass fiber reinforced polymer (GFRP) rod in the case of splitting bond failure from concrete. The mathematical model put forward by Orangun et al. for evaluating the average bond strength of reinforcing bars in concrete for splitting failure has been adopted to develop the nonlinear limit state function corresponding to GFRP’s splitting bond failure in which five independent random variables, i.e. concrete strength, GFRP tensile strength, embedded length, GFRP diameter and computational uncertainty factor, are included. As the result of the probabilistic calibration procedures using the Rackwitz–Fiessler method, a non-dimensional factor K associated closely with the design embedded length of a GFRP rod in concrete is proposed to be 0.0306 with the suggested additional target reliability index of 1.10. The effects of some factors on GFRP’s design embedded length have been identified through the following parametric study. Although the calibration process is case-dependent to some extent, the proposed formula is thought to be acceptable for general bond design purposes of GFRP-reinforced concrete components.     

Bond failure performances between near-surface mounted FRP bars and concrete for flexural strengthening concrete structures

Near-surface mounted (NSM) fiber reinforced polymer (FRP) has been established as an effective technique for strengthening concrete member. In preview literatures, bond failure was observed usually in the strengthened beam test for increasing flexural capacity. Bond behavior is of primary importance for the transfer of stress between the concrete and the FRP reinforcement to develop composite action. In this paper, a total of 22 tests were conducted to study the bond failure performance between NSM FRP bars and concrete besides only one test as a comparison. Failure modes, load–deflection curves, strain distribution of FRP bars, and local bond stresses at the FRP-epoxy adhesive interface from the tests were analyzed in detail. Some of the factors expected to affect bond performance were presented, namely: diameter of FRP bars, type to FRP material, concrete compressive strength and bonded length. The test results reported in this paper should be useful for further establishing local bond–slip constitute relationship and further verification of numerical simulation models, in addition to gaining a better understanding of bond failures for flexural strengthening concrete structures with NSM FRP bars.     

Strength and fracture resistance of FRP reinforced concrete flexural members

A theoretical method to predict the loading capacity and fracture resistance of FRP reinforced concrete flexural beams is developed. No slip between FRP rods and plain concrete matrix is assumed and only Mode I fracture propagation is considered. The model is valid for any crack length and for any span-to-depth ratio larger than 2.5. The influence of the bridging stresses provided by the fracture process zone at the tip of fictitious fracture is examined. The numerical results are compared with existing experimental results which were obtained for steel reinforcement.