粘结长度对AFRP-混凝土界面粘结性能的影响

钢筋混凝土结构在服役期内,由于材料老化、结构损伤等原因不宜继续承载时,常常采用纤维增强聚合物(FRP)来修复或者加固.纤维粘结加固混凝土技术的基础是纤维-混凝土界面的有效粘结.为了研究不同粘结长度对芳纶纤维(AFRP)-混凝土界面粘结性能的影响,本文设计制作了12个试件,进行界面性能力学试验.分析纤维片材表面应变情况,得到粘结长度对AFRP-混凝土界面剥离承载力、界面局部粘结剪应力的影响,并得出AFRP-混凝土界面有效粘结长度范围.试验结果表明,当纤维布与混凝土界面的粘结长度小于纤维布与混凝土界面的有效粘结长度时,AFRP-混凝土界面剥离承载力会随着AFRP纤维布粘结长度的增长而增大.不同粘结长度下AFRP-混凝土界面的表面应变情况、界面局部粘结剪应力情况相似.通过试验数据的回归分析,得到AFRP-混凝土界面剥离承载力修正模型和有效粘结长度修正模型.     

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。     

芳纶纤维加固钢筋混凝土梁界面粘结应力分析

本文根据弹性梁理论和部分组合截面假定,并且考虑了钢筋混凝土梁和芳纶纤维剪切变形的影响,对两点集中加裁情况下的芳纶纤维加固钢筋混凝土梁的界面粘结剪应力和正应力进行了推导分析,由纤维端部边界条件得出了两种应力的解析解,根据试验梁的基本参数绘出了界面应力的分布曲线,找到了界面应力的分布规律,由此提出了降低纤维布端部应力集中的方法,可供施工参考使用.     

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.     

AFRP加固混凝土梁柱节点的应变分析

通过5个芳纶布(AFRP)加固钢筋混凝土框架节点和2个未加固节点的抗震性能试验,研究了加固方式对抗震性能的影响、AFRP布的应变变化规律。研究结果表明,采用AFRP加固后的梁柱节点,极限承载力和抗震性能得到了显著改善,核心区域采用X型粘贴纤维布加固方式、用压条来锚固X型粘布是一种非常有效的锚固方式。     

碳纤维加固梁中碳纤维受力计算与相关系数的分析

根据弹性理论和部分组合截面假定,分析碳纤维加固混凝土梁体系,建立微元体粘结界面剪力表达式和碳纤维轴向拉力微分方程,从而推导出碳纤维拉力和粘结界面剪应力解析解的一般形式,提出并探讨碳纤维加固作用系数Kf和端部应力集中系数k,说明碳纤维加固机理及端部应力集中现象与影响因素.结合算例指出,碳纤维轴向拉力和粘结界面剪应力分布不均匀,在端部区段应力集中,应采取措施加强锚固.     

CFRP加固钢筋混凝土梁锚固位置的试验研究

为研究混凝土梁经CFRP加固后界面粘结性能及抗弯承载力,对4根不同锚固位置的试验梁进行加载试验.结果 表明:随着锚固点的增加,试件由CFRP剥离破坏转为拉断破坏;端部锚固和中部锚固比未锚固梁极限承载力提高20.83％,延性系数提高36.84％,CFRP极限强度利用率最高达83.4％;经端部锚固后,CFRP应变范围扩大,界面粘结应力比不锚固时提高32.1％,说明端部锚固可有效降低应力集中现象,充分发挥外部加固材料的强度.     

芳纶纤维加固钢筋混凝土梁抗弯性能试验研究

本文根据芳纶纤维加固钢筋混凝土梁和未加固的混凝土参考梁的抗弯性能静载试验研究,分析了芳纶纤维加固钢筋混凝土受弯构件的破坏过程,研究了加固后钢筋混凝土受弯构件正截面的破坏特征、受力特点及影响因素(粘贴层数和配筋率)。结果表明,粘贴芳纶纤维可以明显地增加钢筋混凝土梁的抗弯刚度,有效地提高钢筋混凝土梁的抗弯承载能力和构件的延性,为芳纶纤维应用于土木工程结构加固领域提供了理论依据。     

AFRP加固钢筋混凝土梁抗爆性能数值模拟研究

借助非线性有限元软件ANSYS/LS-DYNA,建立了爆炸荷载下钢筋混凝土(RC)梁以及芳纶纤维增强复合材料(AFRP)加固后RC梁的三维有限元模型,对比分析了RC梁AFRP加固前后的破坏形态及跨中位移峰值。数值模拟结果表明,AFRP布不仅可以改变RC梁在爆炸荷载下的破坏形态,还可以明显改善梁的变形程度,加固后相较于未加固梁跨中位移峰值约减小50.7%。在此基础上,还分析了AFRP加固方式、加固尺寸、加固层数以及FRP材料类型等因素对FRP加固后RC梁抗爆性能的影响。     

玄武岩纤维布与木材粘结-滑移本构关系的试验研究

FRP-木材界面的粘结滑移关系是外贴纤维增强聚合物加固木结构受力分析的基础.对18块贴玄武岩纤维布试件的粘结性能进行试验研究,考察了贴布层数和BFRP粘结长度对粘结性能的影响,分析了BFRP应变和局部粘结剪应力发展及分布规律,计算得到局部粘结应力.滑移关系曲线.通过对试验结果的统计回归分析,基于Popovics模型提出了福杉顺纹方向的局部粘结应力-滑移本构关系模型,该模型与试验结果吻合较好,对于实际加固工程应用和相应规范的完善具有参考价值.     

芳纶纤维加固钢筋混凝土梁抗弯疲劳性能试验研究

本文采用芳纶纤维加固钢筋混凝土梁进行室内疲劳试验,分析了混凝土和钢筋的应变滞回变化规律及加固构件刚度随循环次数的衰减变化规律.试验表明采用芳纶纤维进行加固后,梁的疲劳抗裂性能得到极大改善,有效地延长了损伤混凝土结构的使用寿命,验证了芳纶纤维用于加固承受疲劳荷载结构的可靠性.     

On the Effect of Time-Dependent Deformations on the Interface Behaviour of RC Beams Strengthened by FRP Plates

In this paper, the effect of time-dependent deformations (such as shrinkage and creep) on the interfacial stresses between a concrete beam and a fibre reinforced polymer plate is presented. The analysis given here involves a closed-form solution for such stresses and includes creep and shrinkage effects. The adherend shear deformations have been included in the present theoretical analysis by assuming a parabolic shear stress through the thickness of both concrete beam and fibre reinforced polymer panel. Contrary to some existing studies, the assumption that both the concrete beam and the fibre reinforced polymer panel have the same curvature is not used in this investigation. The influence of creep and shrinkage effect relative to the time of the casting and the time of the loading of the beams is taken into account. Numerical examples of a typical concrete beam strengthened with an externally bonded fibre reinforced polymer plate are discussed with the emphasis on the shear and normal stresses at the edge of the plate.     

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.     

A Theoretical Improved Adhesively Bonded Bi-material Beam Model for FRP–RC Hybrid Beams

In this paper we present an improved bi-material beam theory with adhesive interface, which has been applied to the study of the interfacial behavior in a concrete beam reinforced by an externally bonded fibre reinforced polymer (FRP) plate. The work explicitly considers the interfacial slip effect on the structural performance by including the effect of adherend shear deformations. This new method needs only one differential equation to determine both shear and normal interfacial stress whereas the others solutions in the literature need two differential equations. Compared with previously published analytical results, this one improves the accuracy of predicting the interfacial stresses and the solution is in a closed form. This research is helpful in the understanding of the mechanical behavior of the interface and design of FRP–reinforced concrete (RC) hybrid beams.     

Experimental investigation of bond-slip behavior of aluminum plates adhesively bonded to concrete

The main objective of this investigation is to assess the feasibility of using aluminum alloy (AA) plates as externally bonded strengthening material for reinforced concrete members. Consequently, the main aim of this paper is to experimentally investigate the bond stress-slip behavior of AA plates adhesively bonded to concrete surface. In addition, the effect of different AA surface roughness on the bond stress and bond behavior of AA-concrete interface was also investigated. Twelve specimens with six different surface roughnesses were instrumented and tested under single shear. The tested specimens have two bonded lengths – long bonded lengths (75% of prism length) and short bonded length (30% of prism length). It was observed that the bond shear stress, loading capacity, and failure modes vary with AA surface roughness and bonded length. The load capacity and maximum bond stress increased by 143.6 and 342.6%, respectively, for long bonded length (75%) of randomly grinded AA surface compared with those of normal AA surface. Such increase in load capacity and bond stress demonstrated the potential of using AA as externally bonded strengthening material. In addition, the bond-slip behavior of the AA plates was predicted, with reasonable level of accuracy, using existing bond-slip models that were originally developed for fiber-reinforced polymer materials. However, a more elaborate study is warranted to develop bond stress-slip models, specifically, for AA-concrete interface.     

Interfacial stresses in FRP-plated RC beams: Effect of adherend shear deformations

A recently popular method for retrofitting reinforced concrete (RC) beams is to bond fibre reinforced polymer (FRP) plates to their tensile faces. An important failure mode of such plated beams is the debonding of the FRP plates from the concrete due to high level of stress concentration in the adhesive at the ends of the FRP plate. This paper presents an improved solution for interfacial stresses in a concrete beam bonded with the FRP plate by including the effect of the adherend shear deformations. The analysis is based on the deformation compatibility approach where both the shear and normal stresses are assumed to be invariant across the adhesive layer thickness. In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both the concrete beam and the bonded plate. Numerical results from the present analysis are presented both to demonstrate the advantages of the present solution over existing ones and to illustrate the main characteristics of interfacial stress distributions.     

Influence of elevated temperatures on epoxy adhesive used in CFRP strengthening systems for civil engineering applications

This paper presents experimental investigations about the influence of elevated temperatures on the mechanical behaviour of an epoxy adhesive typically used in carbon fibre reinforced polymer (CFRP) strengthening systems and numerical investigations about the influence of changes underwent by the adhesive on the response of bonded joints between CFRP strips and concrete. The experiments included shear and tensile tests at elevated temperatures (up to 120 °C) on a commercial epoxy adhesive. In both types of tests, the mechanical response of the adhesive at different temperatures was assessed, namely in terms of stress vs. strain curves, stiffness, strength and failure modes. The results obtained highlighted the considerable reduction of both shear and tensile properties with increasing temperatures: at 70 °C the shear and tensile strengths are both reduced to around 15% of the corresponding ambient temperature strengths, while the tensile and shear moduli can be considered negligible. Analytical formulae were fit to the test data, describing the reduction with temperature of the adhesive's tensile and shear properties. In the numerical investigations, three-dimensional finite element models were developed to simulate previous double-lap shear tests performed on concrete blocks strengthened with CFRP strips according to either the externally bonded reinforcement (EBR) or the near surface mounted (NSM) techniques, using the epoxy adhesive characterized in the present study. Two distinct modelling strategies were adopted for the concrete-CFRP bond in order to assess the relative importance of the adhesive distortion and interfacial slippage at the concrete-adhesive-CFRP interfaces in the overall slip between concrete and CFRP: (i) to explicitly simulate the adhesive, considering the mechanical properties determined in the tests and assuming a perfect bond at all interfaces; and, alternatively, (ii) to simulate the CFRP-concrete interaction by means of global bilinear bond-slip laws for different temperatures. Comparison between numerical results and test data allowed quantifying the relative importance of the adhesive distortion and of the interfacial slippage at the bonded interfaces as a function of temperature, providing a better understanding of the contribution of these two mechanisms to the CFRP-concrete bond at elevated temperature. While the former effect is the most relevant at ambient temperature, with elevated temperature the interfacial slippage at the bonded interfaces becomes the most relevant mechanism.