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。     

配筋超高性能混凝土梁受弯性能及承载力研究

对4根跨高比为16的配筋超高性能混凝土（Ultra High Performance Concrete,简称UHPC）简支梁进行了受弯性能试验及受弯承载力分析,试件变化参数为钢纤维体积掺量和纵向受拉钢筋配筋率。试验结果表明:钢纤维体积掺量从3%提高到5%时,试件的开裂荷载提高了6.0%~11%,极限荷载仅提高了1.4%~2.5%;纵筋配筋率为3.21%的梁发生适筋破坏,配筋率为6.74%的梁发生部分超筋破坏;增加纵筋配筋率可显著提高UHPC梁的受弯承载力（提高34.9%~36.5%）。基于截面平衡条件、平截面假定以及UHPC和钢筋材料本构关系,建立了UHPC梁受弯承载力计算模型,受弯承载力计算值与试验值吻合较好。     

GFRP筋橡胶集料混凝土梁受弯性能

为提高纤维增强聚合物复合材料(FRP)筋混凝土梁抗裂性能,改善其脆性破坏特征,将玻璃纤维增强聚合物复合材料(GFRP)筋与橡胶集料混凝土共同应用于梁构件中。采用ABAQUS对GFRP筋橡胶集料混凝土梁的受弯性能进行有限元模拟及参数分析,探究了橡胶掺量、GFRP筋配筋率、混凝土强度等级及截面高度对梁受弯性能的影响。结果表明:增加混凝土中橡胶颗粒的掺量可提高梁的开裂荷载,当橡胶掺量为15%时,开裂荷载提高了29%;增加配筋率可提高梁的开裂荷载和承载力,当受拉筋直径由10 mm增加至18 mm时,橡胶掺量为10%的GFRP筋橡胶混凝土梁开裂荷载提高了约15%,承载力提高了约85%,但配筋率增加至一定数值后,其影响不再明显;提高橡胶混凝土强度等级,可提高梁的开裂荷载及承载力,当橡胶混凝土强度等级由C25提高至C40时,开裂荷载提了高约53.7%,承载力提高了约23%;为更好地满足正常使用极限状态,GFRP筋橡胶混凝土梁的截面高度宜适当增加。      

GFRP/钢绞线复合筋混凝土梁的配筋率试验研究

破坏模式是GFRP/钢绞线复合筋(GFRP:Glass Fiber Reinforced Polymer,纤维增强塑料)混凝土梁力学性能的影响因素之一,而破坏模式主要由GFRP/钢绞线复合筋混凝土梁的配筋率决定。鉴于配筋率对GFRP/钢绞线复合筋混凝土梁力学性能的重要作用,该文设计了16根GFRP/钢绞线复合筋混凝土梁试件。试验变量为混凝土强度等级和GFRP/钢绞线复合筋的配筋率。通过对混凝土梁试件进行三分点静载试验,系统研究GFRP/钢绞线复合筋配筋率和混凝土强度等级对GFRP/钢绞线复合筋混凝土梁的破坏形式、抗裂承载力、正截面极限承载力、裂缝间距、裂缝宽度、裂缝深度、挠度等的影响。试验数据可为GFRP/钢绞线复合筋混凝土梁安全配筋率计算方法的确定提供参考和理论依据。     

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。     

CFRP筋增强ECC梁弯曲性能试验研究

为研究碳纤维增强树脂复合材料(Carbon fiber reinforced polymer,CFRP)筋/超高韧性纤维增强水泥基复合材料(Engineered cementitious composite,ECC)梁的抗弯性能,对3根CFRP筋/ECC梁、1根玻璃纤维增强树脂复合材料(Glass fiber reinforced polymer,GFRP)筋/梁和1根CFRP筋混凝土梁进行了四点弯曲试验,分析了配筋率、纤维增强树脂复合材料(Fiber reinforced polymer,FRP)筋类型和基体类型对梁抗弯性能的影响。试验结果表明:CFRP筋/ECC梁与GFRP筋/ECC梁和CFRP筋混凝土梁类似,均经历了弹性阶段、带裂缝工作阶段和破坏阶段;配筋率对CFRP筋/ECC梁的受弯性能影响较大。随着配筋率的增加,CFRP筋/ECC梁的承载能力不断提高,延性性能逐渐减弱;ECC材料优异的应变硬化能力和受压延性,使得CFRP筋/ECC梁的极限承载能力和变形能力均优于CFRP筋混凝土梁;由于ECC材料多裂缝开裂能力,CFRP筋/ECC梁开裂后,纵筋表面应变分布比CFRP筋混凝土梁更均匀; 由于聚乙烯醇(Polyvinyl alcohol,PVA)纤维的桥联作用,CFRP筋/ECC梁破坏时,其表面出现了大量的细密裂缝,且能保持较好的完整性和自复位能力;正常使用阶段,CFRP筋/ECC梁的最大弯曲裂缝宽度均小于CFRP筋混凝土梁。最后,根据试验结果,建立了基于等效应力图的CFRP筋/ECC梁弯曲承载力简化计算模型,确定模型中的相关系数。由简化模型计算的极限承载力与试验结果具有较好的相关性。      

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.     

钢筋-GFRP筋增强混凝土梁的疲劳力学性能

钢筋-玻璃纤维增强树脂复合材料(GFRP)筋增强混凝土(RC)梁设计结合了钢筋和GFRP筋的优点,可以提高构件承载力,同时改善纯纤维增强复合材料(FRP)筋构件使用性能存在的问题,但是关于其疲劳性能的研究十分有限。因此,本论文进行了7根钢筋-GFRP筋增强RC梁的疲劳试验,研究参数包括疲劳荷载幅、有效配筋率、配筋面积比。结果表明,钢筋-GFRP筋增强RC梁疲劳破坏始于钢筋的疲劳断裂,钢筋疲劳断口光滑平整,显著区别于静力拉伸破坏断口。疲劳加载过程中,截面平截面假定仍然满足。疲劳荷载幅对疲劳寿命有显著影响,随着疲劳荷载幅的增大,梁中钢筋、GFRP筋和混凝土应力和应力幅均随之增大,疲劳寿命减小。增大有效配筋率,跨中挠度和最大裂缝宽度均减小,正常使用性能改善。配筋面积比(Af/As)的增加不利于构件抵抗疲劳荷载,Af/As由0.25增大到2.0,疲劳寿命从36.6万次降低到8.3万次。对比了各种疲劳挠度计算公式,CEB-FIP 2010规范的预测结果较好,误差范围在7%以内,推荐作为钢筋-GFRP筋增强RC梁疲劳挠度的计算公式。     

超高性能混凝土梁正截面受弯承载力理论研究

基于64组超高性能混凝土（ultra high performance concrete, UHPC）抗压性能试验数据,分别建立了峰值压应变ε₀、立方体抗压强度f_cu与轴心抗压强度f_c之间的关系以及弹性模量E_c与立方体抗压强度f_cu的关系;基于复合材料力学,建立了受拉区UHPC等效拉应力;基于平截面假定,建立了UHPC梁正截面受弯承载力计算公式,推导了受压区等效矩形应力图形参数、计算公式,并结合UHPC受压本构确定等效矩形应力图形参数。通过28根试验梁的相关数据,验证UHPC梁正截面受弯承载力计算公式及等效矩形应力图形参数取值的可行性。研究结果表明,等效矩形应力图形参数取值较为合理,梁正截面受弯承载力计算值与试验值吻合良好。     

HRB600级钢筋高强混凝土无腹筋梁受剪试验研究

为了解配置HRB600级纵筋的高强混凝土梁受剪性能,以纵筋配筋率、混凝土钢纤维掺量为变化参数,对5根配置HRB600级纵筋的无腹筋梁进行了受剪试验,对比分析了各试验梁的斜截面承载力、荷载-挠度曲线、裂缝宽度和破坏特征。研究结果表明:随着纵筋配筋率的提高,HRB600级钢筋高强混凝土梁的开裂荷载和斜截面极限荷载增大,斜裂缝宽度减小;钢纤维可以有效地提高高强混凝土梁的斜截面开裂荷载,限制斜裂缝的产生与发展;随着钢纤维掺量的增加,高强混凝土梁的受剪承载力增大;使用现行混凝土结构设计规范和纤维混凝土结构技术规程对配置HRB600级纵筋的高强混凝土梁和钢纤维高强混凝土梁的斜截面受剪承载力进行设计计算,其结果是偏于安全的。     

玻璃纤维增强树脂复合材料管-钢筋/混凝土空心构件抗弯性能

为研究玻璃纤维增强树脂复合材料(GFRP)管-钢筋/混凝土空心构件的抗弯性能,编制了受弯构件的非线性分析程序,系统地分析了空心率、配筋率、GFRP管管壁厚度及混凝土强度等级等主要参数对其抗弯性能的影响,并通过试验对所编制的程序进行验证,最后建立适用于GFRP管-钢筋/混凝土空心构件的抗弯承载力计算公式。结果表明:利用编制的受弯构件非线性分析程序与建立的抗弯承载力公式,计算结果与试验结果均吻合较好,抗弯承载力随空心率的减小、配筋率的提高、GFRP管管壁厚度的增加及混凝土强度的增大而增加,空心率对构件抗弯承载力影响最大,其次是配筋率和GFRP管管壁厚度,最后是混凝土强度等级,空心部分半径比在0.25~0.5为宜,可以适当提高配筋率、GFRP管管壁厚度或混凝土强度等级来弥补该空心构件抗弯承载力,研究结论可为该结构在实际应用中提供参考依据。      

Deflections of concrete beams reinforced with FRP bars

The aim of this study is to experimentally and theoretically investigate the flexural behavior of concrete beams reinforced with fiber reinforced polymer (FRP) bars. In this research, three types of experiments were made. First, the tensile properties of FRP and steel bars were tested, then the bond-slip behavior between bars and concrete was tested on standard specimens and, in the end, three series of concrete beams reinforced with GFRP, CFRP and steel bars were tested up to failure. The theoretical model for calculating deflections was developed, which included bond-slip behavior of FRP bars. The theoretical results were compared to the test results of beam deflections, as well to deflection results obtained by theoretical models developed by other authors.     

Performance of glass fiber reinforced plastic bars as a reinforcing material for concrete structures

The increasing use of fiber reinforced plastic (FRP) bars to reinforce concrete structures necessitates the need for either developing a new design code or adopt the current one to account for the engineering characteristics of FRP materials. This paper suggests some modifications to the currently used ACI model for computing flexural strength, service load deflection, and the minimum reinforcement needed to avoid rupturing of the tensile reinforcement. Two series of tests were conducted to check the validity of the suggested modifications. The first series was used to check the validity of the modifications made into the flexural and service load deflection models. The test results of the first series were also analyzed to develop two simple models for computing the service load deflection for beams reinforced with glass FRP (GFRP) bars. The second series was used to check the accuracy of the modification suggested into minimum reinforcement model.Test results of the first series indicate that the flexural capacity of the beams reinforced by GFRP bars can be accurately predicted using the ultimate design theory. They also show that the current ACI model for computing the service load deflection underestimates the actual deflection of these beams. The two suggested models for predicting service load deflection accurately estimated the measured deflection under service load, and the simpler of the two pertains better predictions than those of the models available in the literature. Test results of the second series reveal that there is an excellent agreement between the predicted and recorded behavior of the test specimens, which suggests the validity of the proposed model for calculating the required minimum reinforcement for beams reinforced by GFRP bars.     

混杂纤维增强水泥基复合材料弯曲韧性与纤维增强指数的定量关系

基于掺加CaCO₃晶须的混杂纤维增强水泥基复合材料梁和板四点弯曲试验,提出了确定弯曲韧性指标与纤维增强指数（S）关系的数学公式。S考虑了纤维抗拉强度和机械锚固性能对混杂纤维/水泥复合材料弯拉性能的影响,物理意义明确。公式为二次函数形式,可以反映混杂纤维体系对混杂纤维/水泥复合材料增韧效果,而通过确定二次函数极值,能对纤维配比进行优化。该数学模型对钢-合成纤维和钢-植物纤维增强水泥复合材料均有良好的适用性,且无需考虑基体（水泥砂浆或混凝土）和试件形状（梁或板）。另外,该公式不仅适用于指定挠度处弯曲韧性和等效抗弯强度表征的韧性指标,对ASTM C1018规定的弯曲韧性指标,如I₅、I₁₀、I₃₀和I₅₀等也同样适用。     

Comparative analysis of deformations and tension-stiffening in concrete beams reinforced with GFRP or steel bars and fibers

Present research experimentally and theoretically investigates deformations and tension-stiffening in concrete beams with different types of reinforcement. The paper reports test results of eight beams reinforced with glass fiber reinforced polymer (GFRP) or steel bars, combined with steel fibers. For given uniform reinforcement ratio, different number and distribution of bars was assumed in the section. Experimental curvatures were checked against the predictions by design codes (Eurocode 2, ACI 318 and the new Russian code SP 52-101) and recommendations (Italian CNR-DT 203 and American ACI 440). The study examined capability of different code techniques to predict deformations of beams with varying reinforcement characteristics. It has been shown that distribution of reinforcement had a significant influence on the prediction accuracy. In a more elaborate analysis, the tension-stiffening effect was investigated using an inverse technique earlier developed by the authors. Stress–strain tension-stiffening relationships were obtained for each of the beams using the test moment–curvature diagrams. Unlike the common practice, the analysis took into account the shrinkage effect which was different for steel and GFRP reinforced elements. To verify adequacy of the obtained results of constitutive modeling, the derived tension-stiffening relationships were implemented into finite element simulation as material laws for tensile concrete. It was shown that the above inverse approach offers an alternative and versatile tool for constitutive modeling.     

Performance of reinforced concrete beams strengthened by hybrid FRP laminates

In the last two decades, the use of advanced composite materials such as Fiber Reinforced Polymers (FRP) in strengthening reinforced concrete (RC) structural elements has been increasing. Research and design guidelines concluded that externally bonded FRP could increase the capacity of RC elements efficiently. However, the linear stress–strain characteristics of FRP up to failure and lack of yield plateau have a negative impact on the overall ductility of the strengthened RC elements. Use of hybrid FRP laminates, which consist of a combination of either carbon and glass fibers, or glass and aramid fibers, changes the behaviour of the material to a non-linear behaviour. This paper aims to study the performance of reinforced concrete beams strengthened by hybrid FRP laminates.

This paper presents an experimental program conducted to study the behaviour of RC beams strengthened with hybrid fiber reinforced polymer (HFRP) laminates. The program consists of a total of twelve T-beams with overall dimensions equal to 460 × 300 × 3250 mm. The beams were tested under cyclic loading up to failure to examine its flexural behaviour. Different reinforcement ratios, fiber directions, locations and combinations of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) laminates were attached to the beams to determine the best strengthening scheme. Different percentages of steel reinforcement were also used. An analytical model based on the stress–strain characteristics of concrete, steel and FRP was adopted. Recommendations and design guidelines of RC beams strengthened by FRP and HFRP laminates are introduced.     

全玻璃纤维增强树脂筋混凝土电缆排管的抗弯试验

提出了采用全玻璃纤维增强树脂基复合材料（GFRP）筋混凝土电缆排管代替传统的钢筋混凝土电缆排管,该结构形式具有减少能耗的优点。通过对小尺寸和足尺GFRP筋混凝土电缆排管试件进行抗弯性能试验,研究其抗弯能力、变形及破坏特征等。试验结果表明,GFRP筋混凝土电缆排管具有与普通钢筋混凝土梁相似的力学特征,以混凝土开裂为分界点,位移-荷载曲线表现为双线性,排管侧面拉应力分布不均匀,部分区域出现了较高拉应力。提出了GFRP筋混凝土电缆排管的抗弯设计计算方法,理论计算结果与试验测试结果较为吻合。     

配筋聚乙烯醇纤维增强水泥复合材料梁的曲率延性

聚乙烯醇纤维增强水泥（Polyvinyl alcohol fiber reinforced cement,PVA/C）复合材料具有优越的受拉应变硬化特性,可显著提高结构的变形能力。本文以PVA纤维体积分数和受拉钢筋配筋率为研究参数,对6根配筋PVA/C梁和2根普通混凝土梁（RC）进行四点弯曲试验,并对其曲率延性进行了试验研究和理论分析。试验研究表明:配筋PVA/C梁的荷载-挠度（P-δ）关系曲线所包围的面积是C梁的1.64~2.43倍,证明配筋PVA/C梁有较好的持荷变形能力;在PVA纤维体积分数一定的情况下,试验梁的曲率延性系数随受拉钢筋配筋率的增大而减小;在受拉钢筋配筋率一定的情况下,配筋PVA/C梁的曲率延性系数是C梁的1.56~2.02倍,证明掺入PVA纤维显著提高了试验梁的延性。建立了配筋PVA/C梁曲率延性系数的计算公式,并分析了PVA纤维体积分数对受压区高度系数和曲率延性系数的影响,试验结果与计算结果吻合较好。