国内外对FRP筋与混凝土粘结性能研究现状

根据国内外关于FRP筋混凝土粘结性能的试验研究成果。介绍了FRP筋混凝土粘结滑移性能的研究发展和现状,讨论了FRP筋与混凝土粘结性能研究的思路     

FRP筋增强混凝土受弯构件研究

概述国内外FRP筋增强混凝土受弯构件在试验、理论、工程应用及规范编制方面的研究成果,总结FRP筋材的耐久性、混凝土强度、FRP筋直径、表明形式和温度等因素对FRP筋与混凝土界面粘结滑移性能的影响,阐述FRP筋混凝土受弯构件的力学性能试验和数值分析方法,指出目前FRP筋混凝土受弯构件需要进一步研究的问题。     

FRP筋与混凝土粘结滑移性能的试验研究

通过对埋入混凝土一定深度的螺纹FRP筋的对称拉拔试验,研究了FRP筋与混凝土间界面的粘结滑移及界面应力传递机理,分析了自FRP筋加载端至自由端界面粘结滑移的发展、传递过程,探讨了FRP筋沿埋入深度方向的界面剪应力变化及界面粘结滑移的破坏特征。本文研究结果表明,FRP筋与混凝土界面剪应力及FRP筋滑移自FRP筋加载端至自由端逐步传递,滑移量逐渐减小;FRP筋混凝土与钢筋混凝土滑移破坏有着本质的区别,钢筋混凝土产生滑移时主要是混凝土撕裂和压碎,而FRP筋混凝土滑移破坏是以筋肋削弱或剪切破坏为主要特征。     

FRP筋与混凝土粘结性能的研究进展

对国内外FRP筋与混凝土粘结性能的最新研究进展进行了简要综述,着重针对其粘结机理和影响因素进行分析归纳,总结了现有FRP筋与混凝土粘结滑移本构关系模型和理论分析方法,并对现有研究的不足提出了建议。     

考虑粘结滑移本构关系的FRP筋锚固长度

在FRP筋混凝土拉拔试件微分单元受力分析的基础上,考虑FRP筋混凝土粘结本构关系,推导了随不同位置变化的滑移、FRP筋拉应力和粘结应力理论公式。根据这些理论公式进而得到了最小锚固长度的计算公式,并通过算例进行分析。研究表明,对于FRP筋混凝土构件在正常使用极限状态下,在粘结-滑移本构关系上建立起来的FRP筋锚固长度的限值是满足设计要求的。另外,在此基础上建立的FRP筋锚固长度是针对试件实际的粘结滑移关系,对于表面不同类型、不同组成成分的FRP筋均能较好地确定其最小锚固长度,这对FRP筋混凝土结构构件的设计具有一定的指导作用。     

FRP筋与混凝土粘结性能的试验研究

进行了28个纤维聚合物(FRP)筋拔出粘结试验,试验变量为FRP筋种类、FRP筋直径、混凝土强度和粘结长度,拔出试验记录了拔出荷载、FRP筋加载端滑移、破坏现象。FRP筋破坏形式是表面脱落和筋断裂,而混凝土未出现明显破坏。随着FRP筋的种类、直径、粘结长度不同,粘结强度变化范围是7.96~41.80MPa,粘结强度随着粘结长度、直径增加而减少,与混凝土强度无关。     

FRP筋混凝土结构抗震性能的研究现状综述

随着对FRP筋材料受力性能研究的深入,采用FRP筋替代钢筋和预应力筋运用于混凝土结构中,用来提高钢筋混凝土结构受力性能有着广泛的应用前景。但是FRP筋具有弹性模量低和破坏时脆性大等特点,限制了其在震区结构工程中的应用。文章主要介绍了FRP筋混凝土结构的粘结性能,并总结了国内外关于FRP筋混凝土柱、剪力墙和框架混凝土结构抗震性能的研究成果,并提出了今后研究的方向。     

纤维塑料筋混凝土结构的系列研究

彻底解决钢筋锈蚀问题的一个有效办法是采用纤维塑料筋(即FRP筋),1995年我们在国内首先开展了FRP筋混凝土结构的系列研究,取得了阶段性的研究成果:①研制生产国内首批FRP螺纹筋;②对FRP筋在不同环境介质中的粘结锚固性能进行研究;③对FRP筋普通混凝土梁的受力性能和设计理论进行研究;④研制新型FRP筋预应力锚具;⑤对预应力FRP筋混凝土粱的受力性能和设计理论进行研究等.本文重点介绍以上几方面的研究工作,并对今后FRP筋混凝土结构的发展趋势作了展望.     

FRP筋与混凝土的粘结性能

FRP筋与混凝土之间的粘结性能是FRP筋混凝土结构的关键问题,是能否充分利用FRP筋高强性能的决定性因素。本文分析了FRP混凝土结构的粘结机理以及粘结破坏形式,讨论了影响FRP筋混凝土结构粘结性能的因素,并在最后提出了一些问题及建议。     

新型FRP筋粘结性能研究

基于33个拉拔试件和27个梁式试件的试验结果,对新型FRP筋与不同环境介质(包括混凝土C30、掺纤维与不掺纤维的混凝土C50、R42.5水泥浆以及环氧树脂等)之间的粘结性能进行了较为系统的研究。研究表明,新型FRP筋的粘结强度略低于钢筋;混凝土强度等级对FRP筋的粘结性能影响较大,但是否掺加聚丙烯纤维对其粘结性能影响较小;基于梁式试验的FRP筋粘结强度稍低于基于拉拔试验的FRP筋粘结强度。     

纤维增强塑料筋混凝土粘结滑移本构模型

纤维增强塑料筋与钢筋性能的差异 ,使纤维增强塑料筋混凝土的粘结性能与钢筋混凝土的粘结性能存在明显不同 ,因此 ,研究塑料筋混凝土粘结滑移本构模型 ,对推广塑料筋混凝土结构在工程中的应用具有重要的理论意义和实用价值。在总结国内外已有的纤维增强塑料筋与混凝土粘结滑移本构模型的基础上 ,提出了粘结滑移的连续曲线本构模型。该模型以粘结滑移曲线的三个关键点为基础 ,物理概念明确、光滑连续 ,并与试验结果吻合良好     

HB FRP加固混凝土结构组合界面黏结特性

为揭示HB-FRP(hybrid bonded fiber reinforced polymer)加固混凝土结构多作用组合工作机制,设计了5组黏结作用组合试验.基于实测荷载-滑移关系、应变分布、黏结-滑移关系开展了界面黏结特性研究,提出组合界面黏结-滑移统一模型和黏结荷载表达式.结果表明:HB-FRP加固混凝土组合作用可拆分为FRP黏结混凝土、侧压力和FRP黏结钢板;组合界面的黏结应力发展不同步,FRP板下表面与混凝土的剥离早于FRP板上表面与钢板的剥离,叠合工作时序不同;由侧压力引起的界面摩擦应力随界面应力的发展而增加并趋于稳定;理论模型结果与试验结果具有较好的一致性,可用于计算组合界面的黏结荷载.     

Derivation of the bond–slip characteristics for FRP plated steel members

In order to understand the behaviour of steel members retrofitted using adhesively bonded fibre reinforced polymer (FRP) plates, the bond–slip characteristics of the adhesive joint between the FRP and steel must first be established. This is important so that debonding does not occur whilst the members are in service. Previously, purely empirical research on establishing the bond–slip characteristics involved strain gauging the length of the FRP plate, which can lead to a major scatter of results as well as underestimating the peak shear stress. The subject of this paper is to describe a technique for quantifying the bond–slip characteristics based on a structural mechanics approach and which does not require strain gauging the plate. Two types of pull tests and a partial-interaction numerical model are used to quantify the major characteristics of the bond–slip and two types of adhesive are used to illustrate the approach.     

外贴纤维与混凝土结合面的粘结滑移关系

本文在外贴纤维复合材料(FRP)与混凝土结合面双剪试验中,采用电子散斑干涉技术(ESPI)对FRP-混凝土结合面的变形场进行了测试,重点研究了结合面的粘结滑移关系。试验结果表明,FRP-混凝土结合面的粘结滑移关系曲线的发展过程由非线性上升段和不稳定下降段两部分组成,峰值应力与混凝土强度有关,达到应力峰值时的滑移和极限滑移受混凝土强度和FRP的形式(板或布)等的影响不大。通过结合面滑移刚度衰减规律的分析,本文提出了FRP-混凝土结合面粘结滑移本构关系的基本模式,该模式基于FRP-混凝土结合面的初始(弹性)滑移刚度,力学概念明确。     

Modeling of Tension Stiffening Behavior in FRP‐Strengthened RC Members Based on Rigid Body Spring Networks

Abstract: Allowing for the tension stiffening effects resulting from the bond between steel reinforcement and surrounding concrete leads to effective deformation analysis of reinforced concrete (RC) members when using a nonlinear finite element analysis modeled on the smeared crack concept. Nowadays, externally bonded fiber reinforced polymer (FRP) composites are widely used for strengthening existing RC structures. However, it remains unclear to what extent the tension stiffening of postcracking concrete is quantitatively influenced by the addition of FRP composites, as a result of the bond between the FRP and the concrete substrate. This article presents a discrete model, which is based on rigid body spring networks (RBSN), for investigating the tension stiffening behavior of concrete in FRP‐strengthened RC tensile members. A two‐parameter fracture energy‐based model was deployed to represent the bond‐slip behavior of the FRP‐to‐concrete interface. The reliability of the RBSN model was verified through comparisons with previous test results. Further parametric analysis indicates that the tension stiffening of concrete is hardly influenced by the addition of FRP composites before the yield of steel reinforcement has occurred although concrete crack patterns and crack widths may be influenced by the bond‐slip behavior of the FRP‐to‐concrete interface.     

Finite element analysis of thin GFRC panels reinforced with FRP

Glass fibre reinforced concrete (GFRC) incorporating fibre reinforced polymer (FRP) bar reinforcement is potentially an ideal composite material for the manufacture of thin structural elements due to its superior durability over GFRC containing conventional steel reinforcement. GFRC without any bar reinforcement has only been used for small units and short spans due to its relatively low flexural strength. Until now, no work has been reported on the use of FRP bars in GFRC. The first part of the paper deals with the stress–strain characteristics of GFRC. In the second part the bond strength of GFRC with both steel and FRP reinforcing bars is determined from a series of 24 pullout tests from which the characteristics of the local bond stress–slip response was established. The results show that the bond of FRP bars in GFRC is, in general, better than the bond in normal concrete, and that conventional numerical models can be used to model the behaviour. The last part of the paper investigates the performance of a 3 m span thin GFRC permanent formwork panel, reinforced with FRP, both experimentally and analytically with finite element (FE) analysis. It is concluded that the behaviour of thin GFRC elements incorporating FRP reinforcement can be predicted by FE analysis in which the GFRC stress–strain characteristics and bond characteristics are modelled with robust spring elements.     

Modeling of debonding failure for RC beams strengthened in shear with NSM FRP reinforcement

The shear capacity of reinforced concrete members can be successfully increased using near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement. Tests conducted thus far have shown that failure is often controlled by diagonal tension associated to debonding between the NSM reinforcement and the concrete substrate. In absence of steel stirrups and/or when the spacing of the NSM reinforcement is large, debonding involves separately each of the bars crossed by the critical shear crack. In order for shear strengthening of beams with NSM reinforcement to be safely designed, an analytical model able to encompass the failure mode mentioned above must be developed. This paper presents two possible approaches, a simplified and a more sophisticated one, to predict the FRP contribution to the shear capacity. In the first approach, suitable for immediate design use, an ideally plastic bond–slip behavior of the NSM reinforcement is assumed, which implies a complete redistribution of the bond stresses along the reinforcement at ultimate. The second approach, implemented numerically, accounts for detailed bond–slip modeling of the NSM reinforcement, considering different types of local bond–slip laws calibrated during previous experimental investigations. It also takes advantage of an approach developed by previous researchers to evaluate the interaction between the contributions of steel stirrups and FRP reinforcement to the shear capacity. The paper illustrates the two models and compares their predictions, with the ultimate goal to evaluate whether the first simple model can be used expecting the same safety in predictions of the second model.     

Bond strengthening of lap spliced reinforcement using external FRP jackets: An effective technique for seismic retrofit of rectangular or circular RC columns

Confinement of concrete at the critical hinging regions is one of the most effective means for improving the seismic behavior of reinforced concrete (RC) members. Confinement reduces the bond degradation of the steel reinforcement and limits the concrete damage within the confined zone leading to increased energy absorption and dissipation capacity of the structure. Recent experimental and analytical studies undertaken on the use of FRP composites for seismic upgrading of RC members [FRPRCS08 Proceedings. In: Triantafillou TC, editor. 8th International symposium on fiber-reinforced polymer reinforcement for concrete structures. Patrace, Greece: University of Patrace; July 2007. p. 16–8] have clearly identified the advantages of this technology when compared to conventional strengthening methods. However, unfortunately, no guidelines have yet been developed by code committees for seismic retrofit using FRP composites. This paper provides a synthesis of the results of a series of experimental and analytical studies undertaken in the main part by the writer and in part by other investigators on the use of external FRP jackets for bond strengthening of developed/spliced steel bars in tension and its implications on the static and seismic response of concrete members. Results of the experimental programs are briefly discussed, and design expressions for evaluating the minimum thickness of FRP jacket required for seismic bond strengthening are presented and compared. The accuracy of the design expressions was verified against experimental data. In addition, a generalized model of the local bond stress–slip response of steel bars embedded in FRP confined concrete corresponding to splitting mode of bond failure is described. The model is composed of a monotonic envelope curve and bond degrading curve and can be used for evaluating the seismic behavior of the hinging zones in reinforced concrete members when confined externally with FRP jackets in comparison with the response of unconfined concrete.