Bond performance of polystyrene aggregate concrete (PAC) reinforced with glass-fibre-reinforced polymer (GFRP) bars

This paper concerns the bond performance of GFRP bars in polystyrene aggregate concrete (PAC) by the proposed concentric pullout test. Identical specimens reinforced with mild steel bars were used for comparison. The bond performance including the mode of failure and bond strength was studied with varying polystyrene aggregate content, concrete strength, embedment length, shape and surface treatment of the bars. Empirical formulae were developed for the estimation of development length on the basis of the pullout test results. The bond development length (_ld)$(l_{\mathrm{d}})$ determined according to ACI Building Code was used for comparison.     

GFRP筋活性粉末混凝土梁受力性能试验研究

为了研究GFRP筋活性粉末混凝土梁的受力性能,对8根梁进行三分点加载试验,获得了试验梁的开裂弯矩、极限弯矩以及各级荷载作用下的变形及裂缝分布与开展。试验结果表明：活性粉末混凝土试验梁纯弯区段开裂应变 (750×10-6) 约为普通混凝土梁的7倍,开裂弯矩及截面塑性系数计算应考虑纵向受拉GFRP筋的有利影响。GFRP筋活性粉末混凝土梁正截面受弯破坏形式可分为纵向受拉GFRP筋被拉断而受压边缘活性粉末混凝土未被压碎的受拉破坏,受压边缘活性粉末混凝土被压碎(5500×10-6)而纵向受拉GFRP筋未被拉断的受压破坏,以及纵向受拉GFRP筋被拉断的同时受压边缘活性粉末混凝土被压碎的界限破坏等三种。对于受压破坏可按拉区应力为0.25倍活性粉末混凝土抗拉强度来考虑拉应力对正截面受弯承载力的贡献。对于受拉破坏则基于材料应力-应变关系通过数值积分迭代计算正截面受弯承载力。刚度及裂缝宽度计算的关键是合理计算使用阶段GFRP筋的拉应力,在计算GFRP筋拉应力时所用弯矩应为外荷载弯矩减去拉区活性粉末混凝土拉应力合力对压区合力点的弯矩。图9表12参10     

Flexural and shear capacities of concrete beams reinforced with GFRP bars

This paper reports test results of 12 concrete beams reinforced with glass fibre-reinforced polymer (GFRP) bars subjected to a four point loading system. All test specimens had no transverse shear nor compression reinforcement and were classified into two groups according to the concrete compressive strength. The main parameters investigated in each group were the beam depth and amount of GFRP reinforcement. Two modes of failure were observed, namely flexural and shear. The flexural failure is mainly occurred due to tensile rupture of GFRP bars either within the mid-span region or under the applied point load. The shear failure is initiated by a major diagonal crack within the beam shear span. This diagonal crack extended horizontally at the level of the GFRP bars indicating bond failure.Simplified methods for estimating the flexural and shear capacities of beams tested are presented. The flexural capacity is estimated based on the compatibility of strains and equilibrium of forces. Comparisons between the flexural capacity obtained from the theoretical analysis and that experimentally measured in the current investigation and elsewhere show good agreement. To predict the shear capacity of the beams tested, four methods recently proposed in the literature for GFRP-reinforced concrete beams are used. These methods have been developed by modifying the ACI 318-99 shear capacity formula for steel-reinforced concrete beams to account for the difference in the axial stiffness of GFRP and steel bars. It has been shown that the theoretical predictions of the shear capacity obtained from these methods are inconsistent and further research needs to be carried out in order to establish a rational method for the shear capacity calculation of GFRP-reinforced concrete beams.     

碳纤维筋表层嵌贴加固钢筋混凝土梁受弯性能试验研究

通过对4根内嵌碳纤维筋加固钢筋混凝土梁试验研究,在保证嵌入碳纤维筋锚同长度的前提下,尝试采用不同位置的嵌入方式,对不同部位嵌入对承载力提高的影响进行分析,并对嵌入式FRP筋承载力进行理论分析和承载力提高计算,提出了抗弯承载力增强计算方法.结果表明试验取得了较好的吻合效果.     

内嵌CFRP板条加固混凝土梁的抗弯性能试验研究

通过6根足尺混凝土梁的抗弯加固试验,对内嵌CFRP板条加固梁的破坏过程、受力性能、截面应变分布和挠度变形规律进行了研究。试验结果表明,内嵌CFRP板条加固梁跨中截面应变分布和挠度变形规律与外贴CFRP加固梁相似,但内嵌加固能有效避免板条的剥离破坏,其抗弯加固性能优于相应的外贴加固梁;预载加固将会降低内嵌板条的加固效果。基于混凝土结构加固理论,并考虑预加荷载的影响,对内嵌CFRP板条加固梁3种弯曲破坏形态(钢筋屈服前混凝土压碎、钢筋屈服后混凝土压碎和钢筋屈服后FRP拉断)下的抗弯承载力进行理论分析,并建立开裂弯矩、屈服弯矩和极限弯矩的计算公式,其计算结果与作者及国内外已有的试验实测值吻合较好,可用于实际工程加固设计。     

高温下GFRP筋和混凝土黏结性能试验研究

通过制备出不同试样,并测试其在高温环境中的黏结强度问题,详细分析了不同工况时GFRP筋与混凝土黏结强度问题,并根据测试数据推导理论模型。研究结果得出:温度对GFRP筋与混凝土黏结效果有很大的影响,随着温度升高,两者之间黏结强度不断降低;温度升高使滑移量增加,并且当温度接近玻化温度点时,滑移量变化出现波动,根据测试数据构建了黏结滑移理论式。     

GFRP筋钢纤维高强轻骨料混凝土梁受弯性能试验研究

完成了9根配GFRP筋和1根配钢筋的高强轻骨料混凝土梁受弯性能试验,观察其破坏过程与破坏形态,分析了纤维掺量、纵筋类型、配筋率及纵筋直径等参数对试件承载能力、弯矩-跨中挠度曲线、裂缝宽度等受弯性能的影响,采用美国ACI 440.1R-15、中国GB 50608—2010和加拿大CSA S806-12、ISIS-M03-07等规范中的建议模型,通过开裂弯矩、承载力、挠度和裂缝宽度等参数评估了各国规范对该类构件的适用性。结果表明：随配筋率的增大,试件破坏模式依次表现为受拉破坏、平衡破坏和受压破坏,受压区破坏面贯穿骨料内部,较为光滑;掺入钢纤维能够有效抑制混凝土裂缝开展,延缓构件刚度退化,使开裂弯矩平均提高51.71%,承载力平均提高22.10%;增大GFRP筋配筋率能够提高构件刚度,但GFRP筋直径变化对试件变形及裂缝宽度无显著影响;GFRP筋梁开裂后刚度退化较配钢筋的对比试件迅速。各国规范计算结果表明：受拉破坏试件承载力计算结果较离散,且均偏于不安全;对于平衡破坏和受压破坏的试件预测结果均偏于保守,有足够安全储备。考虑轻骨料和钢纤维对构件刚度退化规律的影响,修正有效惯性矩并给出建议挠度计算模型,计算结果与试验结果吻合较好。     

表层嵌贴预应力CFRP板条加固钢筋混凝土梁的应力传递行为

表层嵌贴预应力FRP板条加固钢筋混凝土结构技术可充分发挥FRP材料强度,且不需设置永久锚具,具有较大的潜力。以试验得到的嵌贴FRP混凝土粘结滑移关系为基础,建立了嵌贴预应力CFRP板条与混凝土的粘结应力微分方程,并根据边界条件推导了方程的解析解,得到了嵌贴预应力CFRP板条放张后界面粘结应力、CFRP拉伸应力的分析模型。与试验结果的比较表明,该模型得出的界面粘结应力及CFRP拉伸应力与试验结果吻合较好。在此基础上,考虑放张后CFRP混凝土界面不出现剥离的条件,分析了粘结界面能抵抗的最大容许预应力。     

Influence of fibers on flexural behavior and ductility of concrete beams reinforced with GFRP rebars

This research studies the influence of fibers on flexural behavior and ductility of concrete beams reinforced with GFRP bars. The experimental program included seven beams. The tested beams were divided into four groups. Each of the first three groups consisted of two beams one of normal strength and the other of high strength while the fourth group consisted of one normal strength beam. The first group is the reference group which had no internal fibers. The second group studied the effect of using internal polypropylene fibers in the concrete mix. The third group studied the effect of using internal glass fibers in the concrete mix while the fourth group studied the effect of using internal steel fibers in the concrete mix. The experimental results of tests showed that using GFRP as the main reinforcement for the concrete beams achieves reasonable flexural strength. Also the theoretical results calculated using ACI 440 code showed good agreement with the experimental results with an error of about 20%. The results of the current research indicated that all types of the fibers used improved the ductility of FRP- reinforced concrete beams. It was found that the span-to-experimental service load deflection ratio is relatively high when compared to the usually accepted ratio of about span/250.     

基于可靠度的GFRP筋混凝土梁抗弯承载力设计方法

为解决混凝土结构中的钢筋锈蚀问题,采用玻璃纤维增强复合材料(Glass Fiber-Reinforced Polymer,GFRP)筋替代钢筋是一种行之有效的方法。由于GFRP筋的线弹性力学特性,GFRP筋混凝土(GFRP-RC)梁的弯曲破坏模式为脆性破坏(受拉破坏或受压破坏),钢筋混凝土梁的设计方法将不适用于GFRP-RC梁,因此有必要开展基于可靠度的GFRP-RC梁抗弯承载力设计方法研究。基于已有文献数据,系统收集和整理了相关设计参数的统计信息。在考虑荷载组合、配筋率、材料强度等关键参数影响的基础上,建立了3432根GFRP-RC梁的设计空间。采用Monte Carlo模拟对GFRP-RC梁抗弯承载力极限状态开展了可靠度分析。结果表明：受拉破坏时,根据《纤维增强复合材料建设工程应用技术规范》(GB 50608-2010)设计的梁的可靠指标(β=4.08~4.50)高于脆性破坏的目标可靠指标(βT=3.7);受压破坏时,根据《纤维增强复合材料建设工程应用技术规范》GB 50608-2010设计的梁的可靠指标(β=3.08~3.39)低于βT。基于上述分析,以不同弯曲破坏模式下的梁均达到(βT=3.7)为目标,校准了GFRP筋材料分项系数(γf=1.3),并改进了受压破坏控制截面的GFRP筋极限应力计算公式。     

钢筋再生混凝土梁的受弯性能

基于国内外大量相关研究成果,对钢筋再生混凝土梁的受弯性能进行了较为全面系统的分析,主要包括平截面假定对再生混凝土梁的适用性、钢筋再生混凝土梁的破坏形态、极限承载力、变形、刚度以及裂缝等.研究结果表明,与钢筋普通混凝土梁相比,钢筋再生混凝土的破坏形态、极限承载力基本相同,但是钢筋再生混凝土梁的变形较大,刚度低.同时发现平截面假定也适用于受弯的钢筋再生混凝土梁.     

纤维对GFRP筋与自密实混凝土基体粘结性能影响分析

通过18个中心拉拔试件试验,研究在基体中加入不同纤维(聚丙烯长纤维(PPA)、聚丙烯短纤维(PPB)、钢纤维(SF)以及混杂纤维)对玻璃纤维增强聚合物(GFRP)筋与混凝土基体粘结性能的影响,旨在寻找改善GFRP筋与混凝土基体粘结性能的有效途径。参照德国纤维混凝土标准DBV和国际材料与结构研究试验联合会标准RILEM弯曲韧性评价方法,采用等效抗弯强度和变形能来评价粘结韧性。试验结果表明：与素混凝土（NC）基体相比,GFRP筋与掺入混杂钢纤维与聚丙烯长纤维以及各自单掺基体的粘结强度可提高13%～35%,还可改善粘结韧性;同时,GFRP筋与基体的粘结强度随钢纤维掺量增大而提高。根据试验结果拟合得出粘结滑移曲线上升段的模型参数,计算结果与试验结果吻合良好。图11表6参13     

内嵌CFRP筋/片加固木梁受弯性能试验研究

为研究内嵌CFRP筋/片加固木梁的受弯性能,制作5根底面中心内嵌CFRP筋加固试件,3根侧面内嵌CFRP筋加固试件,6根底面中心内嵌CFRP片加固试件以及3根未加固的对比试件,对其进行三分点静载试验。试验参数包括：CFRP筋/片,内嵌位置（底面或侧面）,CFRP筋/片数量（1根或2根）、是否采用附加锚固措施（U形铁钉或CFRP布U形箍）、底面是否粘贴CFRP布等。研究表明,内嵌CFRP筋/片加固试件的受弯承载力较未加固试件明显提高,提高幅度为14%~85%,平均提高39%;破坏位移亦平均提高32%。内嵌CFRP筋加固试件的初始弯曲刚度均大于对比试件,而内嵌CFRP片加固试件由于底面开槽面积较大其初始弯曲刚度未见提高。内嵌CFRP筋加固试件的跨中截面应变随荷载增加仍基本符合平截面假定,而内嵌CFRP片加固木梁的跨中截面应变变化与平截面假定存在一定差距。增加内嵌CFRP筋/片的数量及端部采用U形铁钉锚固措施对提高加固木梁承载力的作用不明显;而在加固木梁底面粘贴一层CFRP布可显著提高其加固效果。     

GFRP筋增强ECC梁的抗弯性能研究

利用玻璃纤维增强聚合物(GFRP)筋取代钢筋作为混凝土结构增强筋可以有效解决侵蚀环境下钢筋锈蚀问题,但存在着延性不足的问题,结构常常呈脆性破坏。研究了GFRP筋高韧性水泥基复合材料(ECC)梁的抗弯性能,并与GFRP筋普通混凝土梁和钢筋混凝土梁进行对比,结果显示GFRP筋ECC梁在抗弯承载力和延性方面均优于GFRP筋普通混凝土梁,并且GFRP筋ECC梁具有类似于钢筋混凝土的塑性破坏特征,不同于GFRP筋普通混凝土梁的脆性破坏。GFRP筋与ECC具有良好的协同工作能力,并且两者均具有优异的耐久性能,因此在海洋工程、冬季撒除冰盐的公路与桥梁工程等领域具有广阔的前景。     

基于准平面假定的内嵌CFRP筋加固宽缺口混凝土梁裂缝分析

为研究内嵌CFRP筋加固的宽缺口混凝土梁的裂缝特性,通过16根内嵌CFRP筋加固的混凝土梁静载试验,详细观测和研究了其开裂和裂缝扩展状况。基于FRP类材料加固混凝土梁应变协调的准平面假定,根据传统的钢筋混凝土裂缝研究理论,在充分考虑CFRP筋的力学贡献的前提下,对内嵌CFRP筋加固的普通混凝土梁、宽缺口混凝土梁的裂缝间距、裂缝宽度和最大裂缝宽度的计算式进行了理论推导。将理论算式的计算结果与试验实测结果进行了比对。研究结果表明：与对比梁相比,内嵌CFRP筋材加固的宽缺口混凝土梁和内嵌CFRP筋加固的普通混凝土梁的开裂裂缝和最大裂缝宽度均有大幅度降低,前者的裂缝宽度降低幅度要小于后者的。两类加固梁的最大裂缝宽度都随着CFRP加固量的增大而减小。裂缝间距、裂缝宽度和最大裂缝宽度的理论算式的计算结果与实测结果吻合较好。4个加固梁试件组的平均开裂裂缝均比对比梁的开裂裂缝宽度减少0.30mm。     

GFRP筋混凝土梁耐火性能计算方法

通过GFRP筋混凝土梁耐火性能的理论分析与有限元计算,提出GFRP筋混凝土结构耐火性能的计算方法。在合理选择GFRP和混凝土材料的热工参数、高温力学参数的基础上,采用有限元分析软件ABAQUS建立三面受火的GFRP筋混凝土梁的高温热力学模型。经与GFRP筋混凝土梁火灾试验结果的对比验证,该高温力学模型具有较高的精确性。对影响GFRP筋混凝土梁高温力学性能的各参数进行有限元分析,结果表明,影响梁耐火性能的主要因素为梁上作用的荷载比、GFRP筋在混凝土截面的位置和受火时间。参考欧洲规范钢筋混凝土抗火性能的设计方法,提出GFRP筋混凝土构件基于力学性能的耐火设计公式。通过混凝土500℃等温线简化受火面积和GFRP筋高温强度等效换算的方式,将火灾下截面的非均匀材料力学性质转变为随受火时间变化的均匀材料,提出了不同受火时刻GFRP筋混凝土受弯构件的承载力计算式。经与有限元分析结果的对比,该计算方法精度较高,可应用于评估不同受火时刻下GFRP筋混凝土的高温承载力。     

粘贴预应力GFRP板-混凝土梁抗剪加固试验研究

先通过预张玻璃钢板(Glass-Fibre-Reinforced-Polymer,简称GFRP)粘贴于混凝土梁受拉面,后在梁侧面用GFRP板进行剪切补强试验;分析了不同侧面贴GFRP方式对加固梁抗剪性能和破坏模式的影响,比较了各试验梁的跨中挠度、力筋和GFRP板应变的关系.试验结果表明,侧面贴GFRP可有效抑制斜裂缝的出现,提高试验梁的抗剪能力,改变其破坏形态,加固效果比较理想.     

Investigation on modeling parameters of concrete beams reinforced with basalt FRP bars

Fiber-reinforced polymer (FRP) bars are widely used as internal reinforcement replacing the conventional steel bars to prevent from corrosion. Among the different types of FRP bars, basalt FRP (BFRP) bars have been used in different structural applications and, herein, three already tested concrete beams reinforced with BFRP bars are analyzed using three-dimensional (3-D) finite element analysis (FEA). The beams were tested in four-point bending. In the FEA the behavior of concrete is simulated using the “Concrete-Damaged Plasticity” model offered in ABAQUS software. The research presented here presents a calibrated model for nonlinear FEA of BFRP concrete beams to predict their response considering both the accuracy and the computational efficiency. The calibration process showed that the concrete model should be regularized using a mesh-dependent characteristic length and material-dependent post-yield fracture and crushing energies to provide accurate mesh-size independent results. FEA results were compared to the test results with regard to failure load and crack patterns. Both the test results and the numerical results were compared to the design predictions of ACI 440.1R-15 and CSA S806-12, where CSA S806-12 seems to overestimate the shear strength for two beams.     

玻璃纤维片材用于加固钢筋混凝土梁抗剪试验研究

本文通过对几根采用玻璃纤维布加固的混凝土梁进行的抗剪试验研究，分析了粘贴层数、预加荷载、粘贴角度、条带粘贴间距等对加固效果的影响。讨论并提出了可用于实际工程的设计公式。     

Flexure strengthening of lightweight reinforced concrete beams using carbon fibre-reinforced polymers

A series of 40 lightweight reinforced concrete (LWRC) beams of 1400 mm length and a rectangular cross section of 150 × 200 mm were cast, strengthened and then tested under four-point bending test to study the effectiveness of using externally applied carbon fibre-reinforced polymer (CFRP) composites as a method of increasing the flexural strength of under-reinforced LWRC beams. Parameters investigated include reinforcement ratio, ρ; ρ = 0.55ρ_b and ρ = 0.27ρ_b, CFRP sheet length; 600, 800 and 1000 mm, CFRP sheet width; beam width and half-beam width. Three types of strengthening schemes were used: jacketing covers the beam from bottom and two sides with total width of 500 mm, sheets at the tension side with width equal to beam width and sheets with width equal to half-beam width. Test results showed a limited increase in ultimate load-carrying capacity accompanied with some reduction in mid-span deflection for the strengthened beams. Among the strengthening schemes investigated, jacketing was the most effective for strength enhancement (about 41%) with respect to control beam; however, it reduced ductility significantly. An analytical model was proposed for predicting the ultimate load-carrying capacity of LWRC beams strengthened with CFRP composites.