高温作用后GFRP筋与海水珊瑚混凝土粘结性能试验研究

为了研究高温后玻璃纤维增强树脂复合材料(GFRP)筋与海水珊瑚混凝土的残余粘结性能,对54个GFRP筋珊瑚混凝土试件及钢筋珊瑚混凝土对比试件进行了高温作用后的中心拔出试验,最高温度为350℃,混凝土强度等级考虑C20～C30。观察了高温后试件的表观变化及粘结破坏形态,获取了各试件的粘结-滑移曲线、粘结强度、粘结刚度和峰值滑移量,分析了不同温度、GFRP筋直径、海水珊瑚混凝土强度等因素对高温后GFRP筋与海水珊瑚混凝土粘结性能的影响。基于烧失率和XRD分析,剖析了GFRP筋海水珊瑚混凝土的高温劣化机制。最后,提出高温后GFRP筋与珊瑚混凝土的剩余粘结强度计算式和粘结-滑移本构模型。研究结果表明：高温作用后,尽管GFRP筋与珊瑚混凝土的粘结破坏形态与常温相似,GFRP筋的碳化和珊瑚混凝土的分解使得二者界面发生显著劣化;随着温度的提高,GFRP筋与珊瑚混凝土的粘结强度逐渐降低,峰值滑移量增大;GFRP筋直径越小,高温后的剩余粘结强度和剩余粘结刚度越小;珊瑚混凝土强度等级越高,剩余粘结刚度越大,峰值滑移量越小。所提出的高温后GFRP筋与珊瑚混凝土剩余粘结强度和粘结-滑移本构关系计算结果与试验结...     

GFRP筋的拉伸性能劣化对其与海水海砂混凝土粘结性能的影响

研究了玻璃纤维增强树脂基复合材料(Glass fiber reinforced polymer,GFRP)筋的拉伸性能劣化对其与海水海砂混凝土(Seawater sea-sand concrete,SSC)粘结性能的影响。采用10 mm直径的GFRP筋,测试了3种不同温度下模拟SSC孔溶液中GFRP筋的拉伸强度随其浸泡时间的变化规律;并通过拉拔试验测试了经上述劣化后GFRP筋和SSC界面的粘结性能,分析了界面的破坏形态、粘结-滑移曲线特征及粘结强度的变化规律。试验结果表明：随着模拟SSC孔溶液中浸泡时间的增加,GFRP筋的拉伸强度逐渐降低。与未经浸泡的GFRP筋相比,在23℃、40℃和60℃下浸泡3个月后的GFRP筋的拉伸强度分别降低25%、29%和48%。GFRP筋的拉伸性能劣化会导致其与SSC界面的粘结强度下降。与未经浸泡的GFRP筋相比,在23℃、40℃和60℃下浸泡3个月后的GFRP筋与SSC的界面强度分别下降了8%、19%和38%。     

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。      

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。      

FRP筋/珊瑚混凝土柱轴心受压承载力

对8根塑料纤维增强树脂复合材料(FRP)筋/珊瑚混凝土轴心受压柱和1根钢筋/珊瑚混凝土轴心受压柱进行了承载能力试验,试验参数包括配筋率、箍筋间距、长细比和筋材种类。结果表明:相同配筋率下,FRP筋/珊瑚混凝土柱和钢筋/珊瑚混凝土柱的破坏机制不同,但受力性能良好;相同构件尺寸下,增大纵筋直径导致纵筋与混凝土保护层的黏结性能降低;减小箍筋间距有利于提高构件的延性;长细比越大的构件承载力越低。然后,基于筋材压缩性能试验的数据分析及参考文献的对比探讨,建议碳纤维增强树脂复合材料(CFRP)筋名义屈服强度取值为0.34f_y(f_y为筋材的极限抗压强度),对应的理论值与试验结果相近,从而提出适用于CFRP筋/珊瑚混凝土柱的理论计算,为工程实践提供参考依据。      

CFRP筋与海水海砂混凝土粘结性能试验与机制分析

通过碳纤维增强树脂复合材料(CFRP)筋与海水海砂混凝土的中心及偏心拉拔试验,对比了CFRP筋在不同条件下拔出时的粘结应力及滑移值大小,得到完整的CFRP筋/海水海砂混凝土粘结-滑移曲线,同时分析了CFRP筋在混凝土中发生滑移时会产生的若干破坏模式,在此基础上对粘结-滑移曲线不同受力阶段特点进行了分析。同时,采用正交试验的方式,获得了不同因素对CFRP筋/混凝土粘结强度的影响程度。试验表明,CFRP筋/混凝土粘结力中摩擦力的占比较大,且粘结强度最主要的影响因素是混凝土的强度等级。除了传统拉拔试验中会出现的受力筋拉出破坏和混凝土劈裂破坏外,CFRP筋还会由于自身的外形、工艺及力学性能的影响,发生自身破坏。对不同破坏模式、受力筋外形的三种CFRP筋/海水海砂混凝土粘结-滑移曲线,采用多种理论表达式进行对比,最终得到不同条件下CFRP/海水海砂混凝土的粘结-滑移本构关系表达式。     

BFRP筋与珊瑚混凝土粘结性能试验研究

为研究玄武岩纤维增强复合材料筋(BFRP筋)与珊瑚混凝土的粘结性能,对不同直径(d=8 mm、12 mm)、不同粘结长度(2.5 d、5.0 d与7.5 d)及不同养护环境(标准养护室养护、20±2℃人工海水养护)的共24个BFRP筋与珊瑚混凝土粘结锚固试件进行了中心拉拔试验。结果表明:除直径为12 mm,粘结长度为7.5 d的拉拔试件出现珊瑚混凝土劈裂破坏外,其余试件均为BFRP筋从珊瑚混凝土中拔出破坏,其破坏形态与BFRP筋和普通混凝土粘结破坏形态无明显区别,只是更易发生劈裂破坏。其粘结滑移曲线可分为微滑移阶段、滑移阶段、剥离阶段、下降阶段和残余阶段共5个阶段。其最大平均粘结应力随直径与粘结长度的增加显著减小。标准养护条件下的BFRP筋与珊瑚混凝土的粘结强度明显高于20±2℃人工海水养护下的粘结强度。     

新型碳纤维增强复合材料-钢复合管海水海砂混凝土圆柱轴压试验

为研究原状海水海砂混凝土在复合管混凝土中的应用可行性,提出一种新型由内外壁纤维增强复合材料(FRP)和夹心钢管复合的碳纤维增强复合材料(CFRP)-钢复合管海水海砂混凝土柱结构。对12个新型CFRP-钢复合管海水海砂混凝土圆柱试件进行了轴压试验,研究了CFRP层数和核心混凝土强度等级变化对其轴压性能的影响。试验结果表明,内外壁CFRP的包裹能够有效地提高结构承载力和变形能力;CFRP-钢复合管海水海砂普通混凝土圆柱破坏形态为混凝土压溃,而CFRP-钢复合管海水海砂高强混凝土圆柱破坏形态为剪切破坏;结构的极限应力与CFRP层数、混凝土强度呈正相关,而极限应变随着CFRP层数增加而提高,却随着混凝土强度提高而减小;核心混凝土和钢管对极限应力的贡献随着CFRP层数增加基本不变,且当包裹两层及以上CFRP时,CFRP对试件极限应力的贡献占主导地位。      

CFRP筋-高强钢筋/高强混凝土柱的抗震性能

为了研究高强钢筋和碳纤维增强树脂复合材料(CFRP)混合配筋/高强混凝土柱的抗震性能,对CFRP筋-高强钢筋混合配筋的高强混凝土柱进行了低周反复荷载试验和有限元分析,研究了CFRP筋的粘结条件、不同轴压比以及高强混凝土种类等参数对其抗震性能的影响。结果表明:所有的高强混合配筋高强混凝土柱均发生延性破坏;在相同条件下,高强混合配筋混凝土中分别添加了钢纤维活性粉末和钢纤维后,表现出更好的耗能能力和延性;有粘结CFRP筋混合配筋高强混凝土柱比无粘结CFRP筋混合配筋柱的变形能力和承载力分别提高了9.6%和17.1%,但是延性系数降低了22.5%;在延性破坏的条件下,随着轴压比的增加,CFRP筋-高强钢筋混合配筋柱的屈服强度和极限强度明显增大,极限位移和耗能能力也逐渐减小;高强钢筋和CFRP筋配筋率越高,高强混合配筋柱的极限承载力和变形能力越大。      

FRP配筋海水珊瑚骨料混凝土材料及构件力学性能研究进展

为解决钢筋锈蚀和资源短缺问题,具有轻质高强、耐腐蚀特点的纤维增强聚合物(FRP)筋以及与普通骨料力学性能相近的珊瑚骨料成为近年来人们研究的新材料。本文从FRP与珊瑚骨料的材料特性及珊瑚骨料混凝土力学性能、FRP筋与珊瑚骨料混凝土黏结性能以及耐久性、FRP筋海水珊瑚骨料混凝土梁、柱构件的受力性能三个方面,对国内外相关研究进行对比分析,归纳出现有研究成果,认为FRP筋与珊瑚骨料混凝土有较好的协调工作性,并且可以有效增强珊瑚骨料混凝土结构的性能。此外总结出目前FRP筋、珊瑚骨料等材料的局限性以及FRP珊瑚骨料混凝土构件使用性能、耐久性能和设计方法研究还存在的不足,为FRP筋海水珊瑚骨料混凝土这种新型结构的继续研究提供参考。     

GFRP筋与自密实混凝土黏结性能的试验研究

为了研究玻璃纤维增强树脂复合材料(GFRP)筋与自密实混凝土(SCC)的黏结性能,制作了66个GFRP/SCC试件进行中心拉拔试验,研究SCC混凝土保护层厚度、GFRP筋直径和黏结长度以及SCC中添加纤维种类等因素对两者黏结性能的影响,并对试件的破坏形式进行分析。结果表明:试件主要出现了三种破坏形式,即劈裂破坏、拔出破坏、拔出带缝破坏;通过电镜扫描发现SCC浇筑方向对GFRP筋与SCC黏结界面的结构有一定影响,GFRP筋上部界面与SCC黏结更紧密。当SCC保护层厚度由4D增大至7D时,黏结强度提高了约44.05%;当GFRP筋黏结长度由5D增大至15D时,黏结强度降低了约65.43%;当GFRP筋直径由12 mm增大至16 mm时,黏结强度降低了约22.57%;SCC中添加聚丙烯纤维、钢纤维、聚丙烯纤维+钢纤维的试件黏结强度比不添加纤维的试件黏结强度分别提高12.80%、15.16%、15.09%。可以通过适当增加SCC保护层厚度、在SCC中添加纤维等措施来提高GFRP/SCC试件的黏结强度。      

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.     

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.     

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.     

混合配筋钢纤维增强混凝土梁受弯承载力试验及理论计算

为研究玻璃纤维增强聚合物复合材料(GFRP)筋与普通钢筋混合配筋钢纤维增强混凝土(SF/混凝土)梁的受弯性能及其受弯承载力计算方法,在考虑受拉区混凝土抗拉强度的基础上,给出混合配筋SF/混凝土梁的界限配筋率及受弯承载力计算公式;在此基础上设计制作了三种配筋方式的SF/混凝土梁,重点探讨了混合配筋率及筋材面积比(A_f/A_s)对试验梁失效模式和受弯承载力的影响;同时,借助已有相关试验结果,对比分析了混凝土强度对混合配筋SF/混凝土梁受弯性能的影响。试验和对比分析结果表明:混合配筋SF/混凝土梁正截面应变仍符合平截面假定;相同配筋形式下,混合配筋SF/混凝土梁的受弯承载力和跨中挠度随筋材面积比A_f/A_s的增加而增大;单层配筋梁的受弯承载力比双层配筋梁大;合理提高混凝土强度可在充分发挥GFRP筋抗拉作用的同时进一步提高混合配筋SF/混凝土梁的受弯承载力;采用本文给出的界限配筋率公式能有效预测混合配筋SF/混凝土梁的失效模式;梁受弯承载力建议公式的预测值与试验值吻合较好,具有良好的适用性。      

玻璃纤维增强聚合物复合材料筋与工程水泥基复合材料黏结性能

为了研究玻璃纤维增强聚合物（GFRP）复合材料筋和工程水泥基复合材料（ECC）黏结性能的影响因素,对42个GFRP/ECC试件进行了拉拔试验,分析了GFRP复合材料筋表面形式、直径、ECC基体强度及保护层厚度等因素对GFRP复合材料筋与ECC基体黏结性能的影响。结果表明:GFRP/ECC试件的破坏形式主要有拔出破坏、筋剥离剪切破坏、劈裂破坏三种形式。表面带肋GFRP复合材料筋黏结强度比光滑GFRP复合材料筋高约66%;当ECC保护层厚度由1.5D（D为GFRP筋直径）增大至4D时,GFRP/ECC黏结强度提高了约58%;当GFRP复合材料筋直径为12~18 mm时,GFRP/ECC黏结强度随着GFRP复合材料筋直径的增大而降低;ECC强度由33.7 MPa增大至73.3 MPa时,GFRP/ECC黏结强度增大约3倍。增加GFRP复合材料筋表面形式复杂程度,或一定程度上提高ECC基体保护层厚度、提高ECC强度等级,有助于提高GFRP复合材料筋与ECC的黏结强度。      

Ultimate behavior of axially loaded RC wall-like columns confined with GFRP

The assessment of the effectiveness of the fiber reinforced polymer (FRP) confinement on rectangular reinforced concrete (RC) columns with high aspect ratio (wall-like) still represents an unresolved issue. The present paper aims at providing more experimental evidence about the behavior of such members confined with both uni-directional and quadri-directional glass FRP laminates. Particular attention is devoted to issues related to the premature failure of confining fibers experimentally observed in wall-like columns. Test results on nine axially loaded columns are herein presented; emphasis is also given to the analysis of FRP strain profiles along the sides of the cross-section. The analysis of test results highlights that glass FRP (GFRP) confinement could determine significant strength and ductility increases; the discussion of failure modes points out that the failure of GFRP confined wall-like columns is controlled by the shape of the cross-section and occurs at transverse strains in the jacket much lower than those ultimate of the fibers. Theoretical–experimental comparisons are performed using some available models for strength prediction of such members.     

Degradation of bond between FRP and RC beams

Beams and slabs externally reinforced with FRP are often in contact with moisture and temperature cycles that reduce the expected durability of the system. Bond degradation is a frequent cause of premature failure of structural elements and environmental conditions are known to relate to such failures. The study shows the effects of cycles of salt fog, temperature and moisture as well as immersion in salt water on the bending response of beams externally reinforced with GFRP or CFRP, especially on bond between FRP reinforcement and concrete. Temperature cycles (−10 °C; 10 °C) and moisture cycles were associated with failure in the concrete substrate, while salt fog cycles originated failure at the interface concrete–adhesive. Immersion in salt water and salt fog caused considerable degradation of bond between the GFRP strips and concrete. However, immersion did not lower the load carrying capacity of beams, unlike temperature cycles (−10 °C; 10 °C) that caused considerable loss. No significant differences were detected on the behavior of the systems strengthened with GFRP and CFRP, perhaps because the design of the tests impeded failure of the fibres.