CFRP全覆盖胶粘加固含中心裂纹钢板的静力性能

碳纤维增强树脂复合材料(CFRP)加固钢板时,往往只将CFRP粘贴于钢板的局部,容易遭受由于试件偏心和搭接边缘应力集中所产生的剥离应力的影响,而粘贴方式采用全覆盖时能大幅度减小剥离应力。开展了30个CFRP全覆盖胶粘加固带缺陷钢板的轴向拉伸试验,并设置了单向防剥离夹具,研究了胶粘剂类型、缺陷长度和碳纤维板厚度对加固效果及破坏模式的影响。结果表明：CFRP板加固效果显著,试件的抗拉强度明显提高;不同胶粘剂对试件的破坏模式影响较大,由HJY胶制作的试件主要为被粘物的破坏,而SIKA30胶及WSB胶均出现了胶粘剂/钢脱粘的现象;而随着缺陷长度的增加,破坏模式有明显的变化,由CFRP板破坏变为CFRP板、钢板破坏或胶粘剂/钢脱粘,而试件的抗拉强度受胶粘剂类型影响较小,受缺陷的大小影响较大,当缺陷增大时,试件的抗拉强度明显降低;基于内聚力模型对静力力学试验进行了数值模拟;通过有限元分析得知,胶粘剂的破坏是先由缺陷附近破坏,再扩展至两端;而增加CFRP板的厚度能显著提高试件的抗拉强度。     

复合材料或钢板加固 RC梁的板端剥离破坏承载力

 对受拉表面粘贴纤维增强复合材料( Fibre reinforced polymer/ plastic , FRP)或钢板的抗弯加固钢筋混凝土(Reinforced concrete , RC)梁的板端剥离破坏承载力进行了较为细致的研究。在分析关键参数、 试验数据及现 有计算模型的基础上 , 提出了一个简单、 合理的板端剥离破坏承载力计算新模型。该模型首先给出板端位于纯弯 区的弯曲剥离和板端位于弯矩为零或接近于零的主剪区的剪切剥离的承载力计算公式 , 进而采用简洁的相关曲线 确定板端在弯2剪共同作用区的剥离承载力。新模型通过包含未加固梁的抗剪承载力和几个物理意义明确的重要 参数 , 充分反映了抗弯加固梁的剥离破坏机制 , 与试验结果吻合良好 , 使用方便 , 可供制订规范和实际加固工程 设计时参考应用。     

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。     

粘贴片材加固混凝土梁的粘结剪应力分析

在受拉区表面粘贴加强片是加固混凝土梁的一种有效方法。本文在弹性理论的基础上,推导了受任意线性分布荷载作用下的混凝土梁采用粘贴加强片加固时,加强片端部粘结剪应力和最大粘结剪应力的计算公式。本文方法和有限元方法基本吻合。结果表明,最大锚固剪应力不但和粘胶层厚度、弹性模量有关,还和加强片厚度、弹性模量及长度有关。采用本文方法可以对加强片端部最大锚固剪应力进行验算,防止混凝土梁出现局部受拉破坏。本文研究结果将为进一步完善我国有关规范提供重要的参考资料。     

粘贴片材料加固混凝土梁的粘结剪应力分析

在受拉区表面粘贴加强片是加固混凝土梁的一种有效方法。本文在弹性理论的基础上，推导了受任意线性分布荷载作用下的混凝土梁采用粘贴加强片加固时，加强片端部粘结剪应力和最大粘结剪应力的计算公式。本文方法和有限元方法基本吻合。结果表明，最大锚固剪应力不但和粘胶层厚度、弹性模量有关，还和加强片厚度、弹性模量及长度有关。采用本文方法可以对加强片端部最大锚固剪应力进行验算，防止混凝土梁出现局部受拉破坏。本文研究结果将为进一步完善我国有关规范提供重要的参考资料。     

CFRP加固混凝土梁各受力阶段的剥离机理

粘贴碳纤维片加固混凝土梁的试验数据和破坏模式表明,在锚固措施可靠的情况下,界面粘贴失效或基面混凝土剥离是加固混凝土梁的主要早期破坏形态。为研究混凝土梁不同受力阶段对界面粘结失效或混凝土剥离的影响程度,针对实际加固工程中常见的混凝土梁损伤状况并结合室内试验结果,分别研究了粘贴碳纤维片加固完整梁及不同开裂程度梁在不同受力阶段中的界面应力分布与剥离机理,指出了加固梁的开裂或裂缝扩展是导致界面或粘贴基面混凝土剥离的主要原因。最后,结合实际混凝土梁的损伤特点,提出了加固设计施工过程中的注意事项及应采取的技术措施。     

负载条件下CFRP加固轴心受压钢管短柱受力性能研究

该文以试验、有限元与理论相结合的方法研究CFRP(碳纤维)布加固轴心受压钢管短柱构件;以不同负载百分比、不同CFRP粘贴方式为对比参数,研究了加固后构件的受力性能。主要讨论了对于不同负载程度、CFRP粘贴方式对加固后构件极限承载力和破坏形态的影响。通过试验与有限元数值模拟及参数分析,得到随着负载百分比的增大,加固后构件极限承载力呈下降趋势,在极限状态下,构件的破坏形态主要为端部局部屈曲破坏;在构件端部粘贴CFRP的加固效果优于中部加固效果;随着CFRP加固层数的增大,构件极限承载力随之增大,但增大百分比在达到一定程度后呈现下降趋势;随着构件厚度的增大,负载百分比和CFRP层数对构件承载力的影响呈下降的趋势,通过理论与试验和有限元结果的对比分析,得出采用该文所推导的理论可以用于负载条件下加固构件的承载力计算。     

CFRP布端绕双杆自锁加固混凝土窄梁抗弯试验

为了抵抗粘贴碳纤维增强聚合物基复合材料（CFRP）加固钢筋混凝土结构中常见的剥离破坏,发明了将CFRP布端部以特定方式绕平行双杆实现自锁的方法。鉴于窄梁截面宽度有限,提出将CFRP布贴梁受拉底面布置后,用安装在梁侧面的双L形端锚装置固定双杆,形成侧锚底贴加固方案。完成了5根混凝土强度较低的矩形截面梁四点弯曲试验,其中4根采用上述锚固方式抗弯加固,检验了锚固效果,考察了CFRP布宽度及其沿全长与梁底面是否粘结对加固效果的影响。试验结果表明,采用本文方法进行加固后,端部剥离得以避免,中部剥离即使发生,或在无粘结加固梁受力后期,CFRP布仍能承担较大拉力,因此,极限荷载较对比梁有明显提高。比较而言,CFRP布与梁底有粘结时加固效果更好,CFRP布宽度加大也对提高承载力有益。     

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。     

关于粘钢加固技术应用的探讨

粘钢加固亦称粘贴钢板加固,是将钢板采用高性能的环氧类粘接剂粘结于混凝土构件的表面,使钢板与混凝土形成统一的整体,利用钢板良好的抗拉强度达到增强构件承载能力及刚度的目的。本文主要介绍了粘钢加固技术的原理、特点、应用范围、施工工艺以及工程实例分析。     

Interfacial shear stress concentration in FRP-strengthened beams

This paper reports the results of an experimental programme designed to study the interfacial shear stress concentration at the plate curtailment of reinforced concrete (RC) beams strengthened in flexure with externally bonded carbon fibre-reinforced polymer (CFRP). Specifically, the study looks at the relationship between the CFRP plate thickness and the interfacial shear stress concentration at the plate curtailment, the failure modes of the CFRP-strengthened beams as well as the efficiency of the CFRP external reinforcing system. Comparing the experimental results with existing models' predictions is another objective of this study. The experimental programme included five RC beams 115 mm×150 mm in cross-section and 1500 mm in length. Four of the RC beams were reinforced externally with CFRP plates of different thicknesses. Tests in this study showed that the thickness of CFRP plate affects not only the load-carrying and deflection capacities of the strengthened beam, but also the shear stress concentration at the CFRP/concrete interface and the beam failure mode.     

Modeling of composite/concrete interface of RC beams strengthened with composite laminates

In this paper a finite element model for predicting shear and normal stresses in the adhesive layer of plated reinforced concrete beams has been developed. The numerical results carried out agree with those obtained in previous studies by other authors. It is found that shear stresses and high concentrations of peeling forces are present at the ends of the plates when the composite beam is loaded in flexure. These concentrations can produce premature failure of the strengthened beam because of debonding of the plate or cracking of the concrete cover along the level of internal steel reinforcement. The numerical simulation captures the actual interfacial stresses and, in particular, the maximum values of shear and normal stresses.     

Static strength tests of steel plate strengthened concrete beams

The behaviour of damaged concrete beams strengthened by externally bonded steel plates is experimentally investigated. The study includes an investigation of the mode of failure, including flexural failure and the interface separation of the steel plate. Simply supported beams under monotonically increasing loads are considered exclusively. A total of five plain concrete beams externally reinforced with bonded steel plates were tested under static loads to determine their strength and behaviour. The variables tested were the thickness of the external steel plate, length and location of the interfacial crack, and the degree of surface preparation of the steel plate. In all five beams the thickness of adhesive was kept constant. The results indicate that (i) the behaviour of a damaged open sandwich beam is similar to that of a singly reinforced concrete beam when no debonding occurs between the concrete and the adherent steel plate; (ii) when debonding occurs, the failure is sudden and at loads smaller than for a case where failure is either by yielding of steel or crushing of concrete; (iii) the case with an interfacial crack between the steel and the adhesive is more critical than the case when the interfacial crack is between the adhesive and the concrete; and (iv) the failure load and the mode of failure are dependent on the degree of surface preparation of the steel plate. Analytical investigation to predict the interfacial debonding is summarized, and the results suggest that linear elastic fracture mechanics is suited for predicting the failure load for open sandwich beams which fail by interface debonding.     

碳纤维布加固复合受力钢筋混凝土箱梁抗扭性能的非线性有限元分析

采用有限元方法对碳纤维布加固钢筋混凝土构件进行非线性分析,是对有限的试验研究的有效补充和进一步深入探讨。根据4根碳纤维布加固钢筋混凝土箱梁的试验研究结果,建立了合理的三维有限元模型,对碳纤维布加固钢筋混凝土箱梁在弯剪扭复合受力下的抗扭性能进行了非线性有限元分析。计算得到的扭矩-扭转角关系曲线、钢筋和碳纤维布的应变曲线以及界面粘接单元的恢复力曲线等与试验结果吻合较好,可以较好地模拟碳纤维布加固箱梁的受扭性能。进一步通过对7根数值梁的计算结果分析,提出碳纤维布加固钢筋混凝土箱梁在复合受力下的剪扭相关性符合直线方程。     

Flexural behavior of steel beams strengthened by carbon fiber reinforced polymer plates – Three dimensional finite element simulation

Debonding, as a mode of failure, is one of the major limitations when using externally bonded carbon fiber reinforced polymer (CFRP) plates in strengthening of steel beams. In this work, mode of failure and flexural behavior of both steel and steel–concrete composite beams strengthened by different lengths of CFRP plates were numerically investigated. The effect of both splicing position (at mid-span and near supports) and CFRP plate ends configuration were studied. Three dimensional finite element analysis (3D FEA) was adopted to simulate the nonlinear behavior of these beams loaded under four point bending configuration. The present numerical analysis assisted by previously valuable experimental results found in the literature succeeded to predict the critical CFRP plate length at which, full efficiency of the adhesively bonded plate is achieved.     

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。     

Flexural response predictions of reinforced concrete beams strengthened with prestressed CFRP plates

Existing experimental studies showed that the reinforced concrete (RC) beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates had three possible flexural failure modes (including the compression failure, tension failure and debonding failure) according to the CFRP reinforcement ratio. Theoretical formulas based on the compatibility of strains and equilibrium of forces were presented to predict the nominal flexural strength of strengthened beams under the three failure modes, respectively, and a limitation on the tensile strain level developed in the prestressed CFRP plate was proposed as the debonding failure occurred. In addition, the calculation methods for cracking moment, crack width and deflection of strengthened beams were provided with taking into account the contribution of prestressed CFRP plates. Experimental studies on five RC beams strengthened with prestressed CFRP plates and a nonlinear finite element parametric analysis were carried out to verify the proposed theoretical formulas. The available test results conducted by other researchers were also compared with the predicted values.     

RC beams strengthened with composite material: a limit analysis approach and experimental study

This paper deals with the flexural strengthening of reinforced concrete beams by means of thin carbon fibre reinforced plastic (CFRP) plates. A simplified laminated plate model is used to describe the behaviour of three-layered plate in cylindrical bending which were subjected to third-point line loads. The upper bound theorem of limit analysis is used to approximate the ultimate load capacity for multi-layered plates and identify different collapse mechanisms. A reinforced concrete beam strengthened by CFRP is designed as a three-layered plate. Experimental results are obtained and a comparison with theoretical predictions made.     

Prediction of the behavior of RC Beams Strengthened with FRP Plates

Epoxy-bonding a composite plate to the tension face is an effective technique to repair reinforced concrete beams since it increases their strength and rigidity. In this paper, the structural behavior of reinforced concrete beams with fibre reinforced polymer (FRP) plates is studied numerically. For it, a numerical damage model is used in order to predict their strength, stiffness and failure modes observed in experimental tests taking into account the influence of different variables such as the amount of steel reinforcement, the type and amount of external reinforcement, the plate length, etc. The consideration of concrete cracking and the yielding of the steel rebars allows to predict in a realistic way the behavior of the strengthened beams and especially the debonding failure mode. In that sense both end and midspan debond can be represented since the model is able to reproduce the tension stiffening phenomenon.     

粘结层和预应力对CFRP板加固损伤钢梁抗弯性能的影响

为了对比粘结层和预应力对碳纤维增强聚合物复合材料(CFRP)板加固损伤钢梁抗弯性能的影响,进行了5根H型损伤钢梁的抗弯试验,分析了特征荷载、荷载-挠度曲线、CFRP板应变及其强度利用率的变化。试验结果表明:有粘结和无粘结CFRP板具有相近的加固效果,特征荷载差值小于2%;非预应力CFRP板在正常使用阶段的加固效果很小,而预应力CFRP板加固钢梁的特征荷载比非预应力CFRP板提高了近30%。平截面假定适用于有粘结CFRP板-钢梁复合截面,而不适用于无粘结CFRP板-钢梁复合截面。相比于非预应力CFRP板,对CFRP板施加预应力可以显著提高CFRP板的强度利用率。建立的有限元模型可以较好地预测试件的抗弯性能,增加CFRP板的预应力、厚度和弹性模量可以提高损伤钢梁的抗弯加固效果。