复合砂浆钢筋网加固抗弯RC梁的非线性分析

复合砂浆钢筋网薄层加固是一种有效的加固方法,能够显著地提高钢筋混凝土梁的抗弯承载力、变形能力以及抗裂性能。以8根复合砂浆钢筋网加固RC梁的试验研究结果为参考,通过非线性有限元分析广泛地研究了加固梁纵向配筋率、配箍特征值、梁高宽比对极限荷载提高幅度的影响,并初步分析了少筋梁和超筋梁加固后的荷载-跨中挠度曲线的变化规律。根据分析和试验结果,通过等效假定给出了复合砂浆钢筋网加固RC梁的极限承载力计算公式和抗弯刚度计算公式。     

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。     

钢丝网复合砂浆加固混凝土受弯构件非线性分析

对用钢丝网复合砂浆加固的钢筋混凝土梁进行了正截面抗弯试验研究。试验包括16根用钢丝网加固的梁和两根未加固的对比梁,采用U形三面的加固方式(钢丝网复合砂浆包裹了梁的受拉面及两个侧面)。试验中对比了加固与未加固构件的裂缝开展情况、跨中挠度以及极限荷载。试验结果表明,钢丝网复合砂浆薄层可以明显地提高钢筋混凝土梁的抗弯承载力,提高抗裂性能,增强构件的抗弯刚度。理论部分采用非线性的方法得到加固构件的荷载-挠度曲线,与试验结果比较,有较好的吻合。     

预应力FRP加固工程结构技术研究进展

围绕国内外预应力FRP加固技术的研究现状以及最新进展,从预应力FRP加固混凝土结构、预应力FRP加固钢结构、预应力FRP加固中关键技术的研究等方面进行了综述。试验研究表明：预应力FRP加固混凝土能显著提高构件的开裂荷载、屈服荷载和极限荷载,改善受弯构件在长期荷载的力学性能,提高构件的疲劳寿命;预应力CFRP加固钢梁后,其屈服荷载和极限荷载相对于对比梁都有明显的提高,其提高的程度随着预应力CFRP的用量和预应力水平的提高而增大;预应力CFRP加固对钢梁的刚度提高作用也比较明显,对低强度的钢材,提高效果更明显;采用预应力FRP加固工程结构的关键问题在于预应力的施加体系、预应力控制值、预应力损失和端部的锚固。     

重复荷载下高延性混凝土加固受损混凝土无腹筋梁受弯性能试验研究

通过不同高延性混凝土(HDC)加固厚度,对10根受损严重的钢筋混凝土无腹筋梁采用HDC进行加固,并进行了重复荷载作用下正截面受弯试验,研究了不同厚度的HDC对受损无腹筋梁的受弯承载力以及变形性能的影响。试验梁采用三面U形加固方式,试验过程中观察加固梁的裂缝分布形态、荷载-位移曲线等试验变化情况。试验结果表明,采用HDC加固钢筋混凝土梁,会使梁的破坏形态由脆性破坏向延性破坏转变,加固梁的承载力、延性和耗能能力都得到显著提高。与HDC加固层厚度为0的梁相比,加固厚度为1 cm、1.5 cm和2 cm的梁,承载力分别提高了19.8%、32.7%以及46.3%,而残余变形值分别减少了8.96%、13.3%和20.47%。根据加载试验得出的试验结果,以及通过将受压区曲线应力图形等效为矩形应力图形的方法,推导出了简单实用的不同HDC厚度加固受损混凝土无腹筋梁在重复荷载下的极限承载公式,且计算值和试验值吻合较好。     

U型箍加固锈蚀RC梁的抗弯性能试验研究及数值分析

为研究U型箍加固和二次锈蚀对锈蚀RC梁力学性能的影响,该文通过设计7片试验梁,分析构件的应变规律、变形特征、破坏机理等,并采用ABAQUS有限元软件进行了数值模拟,探讨U型箍加固厚度与加固位置对加固梁性能的影响。结果表明,试验梁跨中截面应变满足平截面假定,中和轴高度大致符合这个规律:锈蚀梁以及锈蚀加固再锈蚀梁的中和轴高度均要大于加固锈蚀梁的高度;荷载增大到一定时,U型箍的锚固作用开始发挥作用;加载中后期,同侧三片U型箍分担的剪力存在不均匀性;腐蚀不均匀导致两端的U型箍应变增长规律有差异;加固梁、加固锈蚀梁的裂缝更稀疏,裂缝趋向于跨中区域分布,斜裂缝逐渐变得不明显; U型箍加固梁的开裂荷载与极限荷载有所提高,塑性特征更为明显,主要呈现为弯剪破坏;二次锈蚀和不均匀性会改变构件变形发展,影响梁的破坏形态。数值模拟的极限荷载、极限荷载对应的挠度以及能量吸收值与试验结果的误差分别在4.22%、9.7%、9.9%范围以内,设置3 mm的加固厚度对提高承载力较为适宜,U型箍布置在梁端位置可更好地提高构件的强度和刚度。     

HDC加固震损无腹筋混凝土梁受弯性能试验研究

利用高延性混凝土(high ductile concrete, HDC)良好的黏结性能和裂缝控制能力,对19根达到极限承载力的无腹筋混凝土梁进行加固处理,并对其进行四点弯曲性能试验,研究了HDC加固震损混凝土梁受弯的裂缝开展情况、破坏形态、承载力、挠度及应力变化的影响,分析了不同HDC厚度、配筋率对HDC加固震损混凝土梁的受弯性能影响。试验结果表明：利用HDC加固震损混凝土梁的承载能力得到了明显的提高,峰值荷载最高提升89%;破坏后的裂缝较原梁多且发展完全;提高加固层厚度的加固效果要明显优于提高配箍率;开裂荷载及破坏时的极限挠度分别最大提高了250%和189%,延性得到明显改善;最大裂缝没有发生在界面处,新旧混凝土之间黏结非常好,协同工作性能良好。     

高延性混凝土加固钢筋混凝土梁受剪性能试验研究及承载力计算

为研究高延性混凝土(HDC)加固钢筋混凝土梁的受剪性能,该文对7根HDC加固梁及4根未加固梁进行静力试验,研究剪跨比、配箍率、加固层厚度和加固层附加箍筋对钢筋混凝土梁破坏形态、荷载-挠度曲线、受剪承载力以及裂缝的影响。结果表明:采用HDC面层对钢筋混凝土梁进行受剪加固,可以显著提高梁的受剪承载力;HDC面层可以代替部分箍筋的受剪作用,改善钢筋混凝土梁的剪切破坏形态;加固试件在达到极限位移之后,试件的完整性较好,剩余承载力较高。基于试验结果,利用桁架-拱模型,提出了HDC加固钢筋混凝土梁的受剪承载力计算公式,计算值与试验值吻合较好。     

U形CFRP条带混锚加固混凝土梁抗剪试验

为解决纯粘贴U形纤维增强聚合物基复合材料（FRP）加固钢筋混凝土梁中FRP端部容易发生剥离破坏等问题,自主研发了对纤维布条带端部进行自锁锚固的方法和锚板,提出了端锚与粘贴并用的混锚U形条带抗剪加固方法。通过2根未加固梁、1根纯粘贴和2根混锚U形碳纤维增强聚合物基复合材料（CFRP）带抗剪加固梁的对比试验,证实了混锚抗剪加固的有效性：混锚能够对纤维带端部进行可靠锚固,阻止端部剥离破坏的发生,实现纤维拉断破坏,大幅度提高材料强度利用率。混锚加固在抑制混凝土梁斜裂缝开展、延缓箍筋屈服、提高箍筋和CFRP的极限应变以及提高抗剪承载力等多个方面的表现均明显优于纯粘贴加固。     

内嵌预应力螺旋肋钢丝加固混凝土梁抗弯试验研究

提出了一种内嵌预应力螺旋肋钢丝加固混凝土梁的新方法,并通过7根混凝土梁的静力加载试验,对内嵌预应力和非预应力螺旋肋钢丝加固混凝土梁中预应力张拉、受力过程、破坏形态、抗弯承载力、延性和变形情况等进行较为系统的研究。试验结果表明:内嵌预应力螺旋肋钢丝加固混凝土梁能够显著提高被加固梁的开裂荷载、截面刚度、屈服荷载、最大承载力;能有效延迟裂缝的开展,限制裂缝的宽度,提高梁的抗变形能力,改善梁的正常使用状态,充分利用螺旋肋钢丝的高强性能。内嵌预应力螺旋肋钢丝加固技术能较好的解决现有加固方法在材料利用不充分、粘结剥离破坏等方面缺点,是一种高效的加固方法。研究成果为该新型加固技术在工程中应用提供了依据。     

不锈钢和CFRP混合配筋预应力混凝土梁的延性和变形性能

由于FRP(fiber-reinforcedpolymer/Plastics)材料直到拉断还表现出线弹性的力学性能,使得采用FRP配筋的混凝土结构延性较差,且已成为这类结构应用中人们所关注的一个主要问题。研究了不锈钢和CFRP(Carbonfiber-reinforcedpolymer/Plastics)混合配筋部分粘结、部分预应力混凝土梁的延性和变形特性。分析时假定这类梁的截面在加载过程中具有3折线的弯矩-曲率关系,而在卸载过程中截面的弯矩-曲率关系假定为线性,据此提出了这类梁受力全过程的非线性分析方法,并以试验结果验证了其适用性。基于能量耗散的观点引入了反映这类梁延性特性的延性指标,并利用所提分析方法对这类梁的延性进行了参数分析。分析结果表明:增加混凝土极限压应变和预应力束的无粘结部分长度可以有效地增加这类梁的变形性能,但对延性的增加却很有限,而且这两个参数对梁延性和变形性能的影响程度还强烈依赖于梁的破坏形态。     

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。     

Failure Behavior and Strength of Composite I-Section Beam with Double Cutouts and Stiffener Reinforcement

This work is carried out to study the influence of double cutouts and stiffener reinforcements on the performance of I-section Carbon Fibre/Epoxy composites beam, including buckling, post-buckling behavior and the ultimate failure. The cantilever I-section beam with two diamond-shaped cutouts in the web and three longitudinal L-shaped stiffeners bonded to one side is subjected to a shear load at free end. Both numerical modelling and Experiment of I-section CFRP beam are performed. In numerical analysis, Tsai-Wu failure criterion is utilized to detect the first-ply-failure load in nonlinear analysis by predicting the load-deflection response. Good agreements are obtained from comparison between the numerical simulations and test results. For the double-hole beam web, the two cutouts show close surface deformation amplitude, which indicates that the stiffeners make the force transformation more effective. Comparing to the numerical result of corresponding beam with single cutout and stiffener reinforcement, the longitudinal stiffeners can not only play a significant role in improving the structural stability (increase about 30%), but also take effects to improve the deformation compatibility of structure. Local buckling happened within the sub-webs partioned by the stiffener and the buckling load is different but close. With post-buckling regime, the two areas show similar deformation characteristic, while the sub-web close to fixed end bears more shear load than the sub-web close to loading end with the increase of normal deformation of structure. The catastrophic failure load is approximate 75.6% higher comparing to buckling load. Results illustrate that the tensile fracture of the fiber is the immediate cause of the ultimate failure of the structure.     

U型FRP加固钢筋混凝土梁受剪剥离性能的有限元分析

采用FRP布对梁进行抗剪加固,可以有效的解决梁因配箍率不足而导致的受剪承载力偏低的问题。根据文献[1]中7根试验梁的参数,针对工程中常用的U型FRP受剪加固形式,建立三维有限元分析模型,采用商业有限元计算软件ANSYS,数值模拟了加载全过程和受剪剥离受力性能,根据试验结果确定了FRP-混凝土界面粘结剥离强度,并建议了合适的裂面剪力传递系数。根据有限元分析结果,作者又进一步研究了U型FRP布的应变分布、分担剪力的贡献、剥离破坏的过程,以及加固量、FRP类型和粘贴面积率对加固梁受剪承载力的影响。在有限元分析的基础上结合试验结果,建议了U型粘贴加固的受剪剥离承载力计算方法。     

Experimental investigations and verification of debonding strain of RHSC continuous beams strengthened in flexure with externally bonded FRPs

Although many in-situ RC beams are of continuous constructions, there has been very little research on the behavior of such beams with external reinforcement. This article presents an experimental program conducted to study the flexural behavior and redistribution of moment of reinforced high strength concrete (RHSC) continuous beams strengthened with carbon and glass-fiber-reinforced polymer (CFRP and GFRP) sheets. The program consists of six RHSC continuous (two-span) beams with overall dimensions equal to 250 × 150 × 6000 mm. One beam was not strengthened and was tested as a control beam. Five beams were strengthened with CFRP and GFRP in flexure along their sagging and hogging regions. The main parameters including type of FRP (GFRP or CFRP), the different ratios of CFRP sheet and effectiveness of end anchorage. The test results showed that the use of GFRP sheet in strengthening of continuous beam reduced loss in ductility and moment redistribution but it did not significantly increase the ultimate strength of them. The use of end anchorage in strengthened continuous beams increased the ultimate strength and moment redistribution. The moment enhancement ratio of the strengthened continuous beams was significantly higher than the ultimate load enhancement ratio in the same beam. Also existing international codes and model such as ACI, fib, JSCE, Teng and Toutanji for prediction of IC debonding strain or stress of strengthened continuous beams are verified. Verifications were carried out based on the test results in this research and the published literature on RC continuous beams strengthened with FRP.     

塑性铰区采用高延性混凝土梁变形性能研究

为提高钢筋混凝土(RC)梁的变形能力,考虑在其塑性铰区采用高延性混凝土(HDC)代替普通混凝土。共设计6个剪跨比为3.6的RC梁试件,包含5个塑性铰区采用HDC的试件和1个RC对比试件。考虑HDC区长度、纵筋配筋率以及配筋方式和梁端配箍率的影响,研究试件在低周反复荷载下的滞回特性、变形能力及耗能能力。结果表明:与RC梁相比,塑性铰区采用HDC后,试件的破坏形态由弯剪破坏向弯曲破坏转变,延性和耗能能力均得到显著提高;纵筋配筋率、配筋方式相同时,在梁端塑性铰区采用HDC,试件的位移延性系数和极限位移角分别提高30%和53%,而同时采用HDC和箍筋时分别相应提高33%和76%;梁端局部采用HDC替换混凝土可减少箍筋用量;梁端塑性铰区的HDC长度对试件延性的影响较小。分别计算塑性铰区采用HDC梁在开裂荷载、屈服荷载、峰值荷载、极限荷载时的顶点位移,其计算值与试验值吻合较好。     

弯曲梁柱结构平面外失稳的研究

研究了两节梁组成的弯曲梁在受竖向集中载荷作用下的平面外稳定问题,通过建立每节梁临界状态下弯曲和扭转变形微分方程,根据变形协调关系,得出了一端固定一端悬臂的弯曲梁平面外失稳的特征方程,并以等截面等长度梁构成的弯曲梁为对象,探讨了弯曲梁上拱和上翘对其平面外稳定性的影响,以及抗扭刚度对稳定性的影响。结果表明,同样的载荷作用幅度和梁高度,采用上拱的弯曲梁比直梁具有更高的侧向稳定性,并且存在一个最佳的弯曲角度,而上翘弯曲梁的侧向稳定性要低于直梁的侧向稳定性。当弯曲梁上翘时,增大抗扭刚度可以提高侧向稳定性,弯曲梁上拱时,增大抗扭刚度却会降低其侧向稳定性。     

Shear repair of RC beams using epoxy injection and hybrid external FRP

This experimental study aims at investigating the behavior of reinforced concrete (RC) beams strengthened by unidirectional and hybrid bidirectional fiber-reinforced polymer (FRP) sheets and subjected to cyclic loading. RC beams tested under cycled loading were subsequently repaired using both epoxy injection and external FRP sheets, and then re-tested under monotonic loading. Six RC beam specimens, two of which were control specimens and four were shear deficient, were upgraded with side-bonded FRP sheets in the first phase of the experimental program. In the second phase, three of the damaged beams were repaired using epoxy injection and unidirectional carbon fiber polymer (CFRP) sheets. The repairing method, FRP type, and FRP wrapping scheme were the test variables investigated. Test results show that the repair schemes imparted significant mechanical improvements in terms of ultimate shear capacity and ductility. The simultaneous application of epoxy injection and externally bonded FRP sheets was found to be a highly effective repair technique.     

Effect of steel and synthetic fibers on flexural behavior of high-strength concrete beams reinforced with FRP bars

Six high-strength concrete beam specimens reinforced with fiber-reinforced polymer (FRP) bars were constructed and tested. Three of the beams were reinforced with carbon FRP (CFRP) bars and the other three beams were reinforced with glass FRP (GFRP) bars as flexural reinforcements. Steel fibers and polyolefin synthetic fibers were used as reinforcing discrete fibers. An investigation was performed on the influence of the addition of fibers on load-carrying capacity, cracking response, and ductility. In addition, the test results were compared with the predictions for the ultimate flexural moment. The addition of fibers increased the first-cracking load, ultimate flexural strength, and ductility, and also mitigated the large crack width of the FRP bar-reinforced concrete beams.