CFRP加固RC梁的抗疲劳与防腐蚀效用

总结分析了腐蚀混凝土梁用FRP片材加固后的疲劳特性.共10根梁试件,其中1个梁未加固未腐蚀作为标准梁;3个梁进行腐蚀但未加固;3个腐蚀梁用GFRP布U型加固;3个梁受拉区用CFRP布进行抗弯加固,同时用GFRP布U型固定.当纵筋腐蚀到5.5%后,用FRP加固.FRP加固后,一些梁立即进行疲劳试验使其破坏,一些梁再进行第二次腐蚀以研究CFRP加固对梁抗腐蚀耐久性的影响.腐蚀坑使钢筋疲劳寿命明显下降.用U型FRP包裹RC梁不能明显改善梁的疲劳性能;但用CFRP加固梁受拉区,可显著提高梁的疲劳性能.预应力加固降低了梁中纵筋应力幅,疲劳寿命随预应力水平的增大而提高,预应力加固使梁的疲劳寿命明显提高.     

RC结构表层嵌入FRP加固技术研究概述

纤维增强聚合物在混凝土结构加固中应用的越来越多,本文首先介绍了纤维增强聚合物(Fiber Reinforced Polymer,简称FRP)的性能,然后分别从混凝土结构外贴和表层嵌粘FRP应用实践、FRP与混凝土粘结性能、单一和混杂FRP加固混凝土结构性能和加固构件非线性有限元分析等方面,说明了目前混凝土结构嵌粘FRP的研究现状,混杂FRP加固技术既经济又有效,具有较大的研究意义。     

FRP锚钉锚固长度对FRP加固混凝土构件拉拔性能影响的试验研究

FRP锚钉是能有效阻止FRP加固混凝土构件界面剥离的前沿方法.为了测定FRP锚钉的不同锚固长度对FRP加固混凝土构件粘结性能的影响,采用拉拔试验,参照ACI规范的试验方法,测定了不同锚固长度下FRP加固混凝土构件的拉拔荷载.试验用不安装锚钉的控制试件和安装了15 mm、30 mm、45 mm三组FRP锚钉的试验试件,结果发现,锚固长度不同,FRP加固混凝土构件的破坏模式也各不相同,主要表现为混凝土内部浅层剥离、混凝土锥形破坏、混凝土锥形破坏联合锚钉部分拉拔破坏、混凝土浅层剥离联合锚钉断裂破坏以及FRP加固层内部浅层剥离联合部分混凝土浅层剥离破坏;FRP锚钉的锚固长度越长,加固试件的粘结性能越好;混凝土圆柱体抗压强度设计为30 MPa时,FRP锚钉的锚固长度应不得小于30 mm.试验结论可以为FRP锚钉的设计制作提供参考.     

外贴FRP加固钢筋混凝土梁抗弯疲劳性能研究进展

纤维增强复合材料(Fiber Reinforced Polymer,简称"FRP")因其轻质、高强、抗疲劳性能好等优点被广泛用于加固工程中。在疲劳荷载作用下,外贴FRP加固钢筋混凝土梁中的各材料性能以及FRP-混凝土界面粘结性能不断劣化,既有损伤不断累积,从而大大降低了加固梁的使用安全性。本文从试验研究、数值模拟以及理论分析三方面对外贴FRP加固钢筋混凝土梁的抗弯疲劳性能研究进行了详细总结,并对FRP-混凝土粘结界面和锈蚀钢筋混凝土加固梁的疲劳性能进行了介绍,分析了现有研究中存在的不足,并为今后的研究方向提出一些建议。     

增强筋混凝土梁受弯疲劳研究进展

本文总结了国内外学者对混凝土、钢筋、FRP筋的材料疲劳性能、破坏准则、损伤模型的研究,论述了由各材料组成的梁构件的疲劳受力过程、破坏形态、刚度退化、挠度增长规律,分析了FRP筋部分代替钢筋的混凝土梁的疲劳性能的特点,并探讨增强筋混凝土梁的疲劳性能的发展空间与研究价值。     

RC桥墩的FRP延性加固设计方法研究

为了制定经济合理的钢筋混凝土(RC)墩柱的纤维增强复合材料(FRP)抗震延性快速加固方案,提出了基于目标位移延性系数提高指标的FRP抗震延性加固设计方法,并建立了加固墩柱宏观力学性能参数(位移、延性系数)与材料性能参数(FRP约束混凝土极限压应变、FRP配箍率、FRP有效极限抗拉强度、FRP有效极限拉应变)之间的力学计算模型。进一步应用所提出的计算模型,结合有限元数值模拟技术,得到FRP约束圆形和矩形墩柱受力性能的分析结果,并与试验结果进行对比。结果表明,提出的FRP延性加固设计方法可较正确地计算加固RC墩柱的受力性能、FRP片材配箍率或加固厚度,并验证了考虑箍筋和FRP共同约束作用的Seible FRP约束混凝土极限压应变计算模型的合理性。     

FRP筋混凝土结构的研究现状分析

近年来,国内外就FRP筋自身的力学特性以及FRP筋混凝土结构的力学性能开展了大量研究。FRP筋耐久性能、FRP筋与混凝土的粘结机理、FRP筋混凝土梁和柱的受力性能、FRP筋混凝土柱和框架的抗震性能是目前研究的主要方向。现有研究表明:大部分受弯构件中使用FRP筋作为纵向受拉筋能充分发挥其抗拉性能,但结构易发生脆性破坏,现有规范的计算方法不适用于该类构件的计算;FRP筋替代钢筋作为柱中主要受力筋会导致抗压强度和延性不如普通钢筋混凝土柱;纤维改性混凝土能够显著提高FRP筋混凝土构件的延性,FRP筋和钢筋的混合配筋柱的抗震性能要明显优于FRP筋柱。下一步研究中,应建立可靠的FRP材料及构件的耐久性测试和评估方法;改善FRP筋与混凝土,尤其是改性混凝土之间的粘结性能;完善现行规范中FRP筋承载力计算方法;建立FRP筋构件抗震设计体系。     

纤维增强复合材料加固钢筋混凝土梁徐变的研究进展

随着纤维增强复合材料(FRP)对既有建筑物的加固与修复技术的运用越来越广泛,使得被加固或修复构件、结构的使用寿命得到延长,因此FRP与被加固构件一起必然要受到长期荷载的作用。收集了国内外已有的关于FRP加固钢筋混凝土梁(简称RC梁)徐变性能的研究文献,从FRP材料的蠕变研究现状以及FRP加固RC梁徐变性能的研究现状这两个方面进行总结,发现现有的关于FRP加固RC梁徐变性能的研究主要集中在FRP单一材料的蠕变性质,以及直结加固梁的徐变研究,对接近实际工况的加固前有损伤的梁的徐变性能研究较少。     

FRP与混凝土界面粘结性能的试验研究

纤维(FRP)与混凝土的粘结性能是外贴纤维增强聚合物加固钢筋混凝土结构技术的关键问题。采用修正梁模型,对9个外贴FRP条带加固混凝土受弯构件的粘结性能进行了试验研究。分析了FRP应变、局部粘结剪应力发展规律以及沿粘结长度在各级荷载下的分布规律。考察了混凝土强度和FRP粘结长度对粘结强度等粘结性能的影响。验证了FRP有效粘结长度,探讨了有效粘结长度的影响因素,计算得到了局部粘结剪应力滑移关系曲线。通过对试验结果的统计回归分析,提出了局部粘结剪应力滑移本构关系模型以及有效粘结长度计算公式,分析结果与试验结果都吻合较好,可供实际加固改造工程应用及完善相应规范的编制参考。     

FRP加固RC梁研究新进展

混凝土梁(RC梁)作为结构体系中的主要受力构件之一,常因各种原因出现劣损影响到结构安全。FRP材料因其具有轻质、高强、耐腐蚀等特性,已被广泛应用于RC梁的加固工程中。目前,FRP加固RC梁的研究较为深入。本文综述了国内外学者关于FRP加固RC梁的静力性能以及抗火性、抗冲击性的研究现状,分析了现阶段研究存在的问题,提出了对未来研究方向的建议。     

基于长宽比变化的FRP加固混凝土轴压矩形柱的试验研究

制作了16根FRP加固混凝土矩形短柱进行轴压试验,按长宽比值不同分成4组,每组4个构件,其中1个未加固,2个无间隙粘贴FRP环向围束加固,1个有间隙粘贴FRP环向围束加固。通过考虑柱截面长宽比、FRP材料类型、粘贴方式等因素的变化,分析探讨了加固前后柱的承载力、延性、破坏形式等。试验表明,长宽比值在提高柱的极限承载力方面影响较大,而在提高柱的延性方面影响较小。根据试验数据对我国混凝土加固规范推荐的公式进行对比,提出了FRP有间隙粘贴环向围束的强度模型。     

Rheological modeling and finite element simulation of epoxy adhesive creep in FRP-strengthened RC beams

We have shown that a significant creep occurs at the concrete–fiber reinforced polymer (FRP) interface based on double shear long-term test. The primary test parameters were the shear stress to ultimate shear strength ratio, the epoxy curing time before loading as well as the epoxy thickness. The test results showed that when the epoxy curing time before loading was earlier than seven days the shear stress level significantly affected the long-term behavior of epoxy at the interfaces, and in particular the combined effect of high shear stress and thick epoxy adhesive can result in interfacial failure if subjected to high-sustained stresses. In this paper, based on the previous experimental observations, an improved rheological model was developed to simulate the long-term behavior of epoxy adhesive at the concrete–FRP interfaces. Furthermore, the newly developed rheological creep model was incorporated in finite element (FE) modeling of a reinforced concrete (RC) beam strengthened with FRP sheets. The use of rheological model in FE setting provides the opportunity to conduct a parametric investigation on the behavior of RC beams strengthened with FRP. It is demonstrated that creep of epoxy at the concrete–FRP interfaces increases the beam deflection. It is also shown that consideration of creep of epoxy is essential if part or the entire load supported by FRP is to be sustained.     

FRP布加固砌体结构界面粘结性能的研究进展

砌体结构存在着承载力低、抗震能力差等问题,所以对砌体结构的加固尤为重要。近些年在国内外兴起的纤维增强复合材料(简称FRP)以其轻质高强、耐久性好、施工方便等优点为砌体结构的加固提供了新的方向。FRP与砌体间的界面粘结性能是影响加固效果的关键因素之一。总结了国内外学者关于FRP加固砌体结构界面粘结性能的研究现状,通过收集到的试验数据对FRP加固砌体结构的极限承载力计算公式进行了校核,并对今后拟开展的研究工作提出了建议。     

预应力FRP筋混凝土梁疲劳性能研究

FRP筋以其耐腐蚀、抗拉强度高、松弛小等特点,在暴露及恶劣条件下的预应力结构中有非常广阔的前景.目前国内外对预应力FRP筋混凝土结构的静力性能已有较多研究,而对于预应力FRP筋混凝土结构的疲劳性能研究,在国外刚刚起步,在国内则是空白.本文在系统地查阅国外最新研究资料的基础上,对FRP筋的疲劳性能、预应力FRP筋混凝土梁的疲劳性能进行了研究与总结,并对今后的发展趋势作了展望.     

Experimental and analytical investigations of creep of epoxy adhesive at the concrete–FRP interfaces

This paper presents the results of experimental and analytical investigations on the long-term behavior of epoxy at the interface between the concrete and the fiber-reinforced-polymer (FRP). Double shear experiments under sustained service load were performed on nine specimens composed of two concrete blocks connected by FRP sheets bonded to concrete using epoxy. The primary investigation parameters included the ratio of shear stress to ultimate shear strength, the epoxy thickness and the epoxy time-before-loading. Loading was sustained for periods up to nine months. We show that the magnitude of shear stress to ultimate shear strength and the epoxy time-before-loading could be the most critical parameters affecting creep of epoxy at the concrete–FRP interfaces. It was also found that the creep of epoxy can result in failure at the interfaces due to the combined effect of relatively high shear stress to ultimate shear strength and thick epoxy adhesive. This can have an adverse effect on the designed performance of reinforced concrete (RC) structures strengthened with FRP. Based on the experimental observations, rheological models were developed to simulate the long-term behavior of epoxy at the concrete–FRP interfaces. It is shown that the long-term behavior of epoxy at the interfaces can be properly modeled by analytically for both loading and unloading stages.     

纤维增强塑料板在日本砼结构加固工程中的应用

介绍日本纤维增强塑料(FRP)的基本性能和FRP板用于砼梁、柱和隧道衬砌方面的加固应用情况,简要讨论了该类结构的基本破坏模式,旨在推动FRP在我国砼结构加固工程上的应用。     

FRP环向加固木柱轴心受压性能试验研究

提供了15根FRP环向加固木柱的轴心抗压性能试验数据,详细探讨了受载后试件的工作机理和破坏模式,试件的设计参数为FRP的层数和FRP的类型,分析了各设计参数对加固木柱承载力和峰值应变的影响。试验结果表明,FRP环向加固木柱可提高木柱的抗压承载力,改善木柱的延性。在极限荷载以前,加固木柱的荷载-应变关系曲线基本保持线性变化,在极限荷载以后曲线为近似理想塑性。加固木柱的承载力和峰值应变随加固层数的增加而增加。3层GFRP可提高木柱承载力和峰值应变分别达21.82%和94.95%。试件的极限荷载和轴向应变随环向FRP的弹性模量的增加而增加,但增幅逐渐变缓。加固木柱达到极限荷载时,环向加固层没有出现拉断现象,其环向应变并未达到环向加固层的极限应变,仅为FRP极限拉应变的10%左右。木柱的破坏始于木纤维的弯曲变形,环向FRP可有效约束这种变形的发展,这是改善木柱轴心受压性能的主要原因。所有试件的破坏模式都表现为木柱产生错动变形,被完全压皱破坏。     

Limiting shear creep of epoxy adhesive at the FRP–concrete interface using multi-walled carbon nanotubes

Fiber reinforced polymer (FRP) composites are widely used in structural strengthening and retrofitting due to their high strength-to-weight ratio and non-corrosive properties. However, one of the recently recognized drawbacks of common FRP strengthening systems is the relatively high shear creep deformation of epoxy adhesives when FRP sheets are used to strengthen concrete structures against sustained loads. On the other hand, carbon nanotubes (CNTs) are reported to provide significant enhancement to various mechanical properties when used in epoxy adhesives. This enhancement is attributed to the extraordinary mechanical properties of the CNTs and their ability to bond to epoxy. In this article, we report the results of experimental and analytical investigations conducted to examine shear creep behavior of multi-walled carbon nanotubes (MWCNTs) reinforced epoxy nanocomposite used at the FRP–concrete interface. Double shear tests were performed on FRP sheets bonded to concrete blocks with MWCNTs reinforced epoxy nanocomposite. Various levels of pristine and functionalized MWCNTs by weight were examined including 0.1%, 0.5%, 1.0% and 1.5%. The viscoelastic behavior of MWCNTs reinforced epoxy nanocomposite was simulated with rheological models and the models' parameters were extracted and discussed. The results show the ability of MWCNTs to significantly reduce creep compliance of epoxy at the FRP–concrete interface making it a viable solution if FRP is used to strengthen concrete structures subjected to sustained stress.     

An Investigation of Interfacial Stresses in Reinforced Concrete Beams Using FRP Laminates

Reinforcement of reinforced concrete (RC) beams against bending through utilization of bonded fibre-reinforced plastic (FRP) laminates has been accepted as an effective method of strengthening. In this study, the effects of FRP reinforcement over the parameters of interfacial stresses in reinforced concrete beams were examined both experimentally and numerically. Essentially, the main goal of the study was to investigate quantitatively the behaviour of the RC beams strengthened with adhesively bonded FRP. In order to achieve this goal, an experimental study was initially carried out. Afterwards, the ANSYS® WB finite element program was employed to model and analyze the RC beams externally bonded to FRP. The obtained results are expected to demonstrate the main characteristics of interfacial stress distributions inside beams strengthened with FRP. The evaluation of interfacial stresses provides the basis for understanding the main characteristics in such beams and for developing suitable design rules.