Bond performance of fiber reinforced polymer rebars in different casting positions

In the last two decades, fiber reinforced polymer (FRP) rebars have become attractive to civil engineers, due to their corrosion resistance and high strength‐to‐weight ratio. To take advantage of such properties, many research studies have been carried out on the mechanical and physical properties of FRP rebars in concrete, and critical issues have been discovered regarding the bond behavior of FRP rebars. In this study, an effort was made to investigate the effects of FRP rebar types, locations and concrete casting positions on the bond performance of FRP rebars embedded in concrete members. Experimental investigations were conducted using a total of 63 specimens, with seven types of reinforcing bars, and three different casting positions. According to the test results, the bond performance of FRP reinforced concrete was greatly influenced by FRP type and surface condition; while vertical casting showed higher bond strength than horizontal casting. In addition, the bond strength reduction ratio of FRP rebars cast in the horizontal direction was smaller than that of steel bars. POLYM. COMPOS., 37:2098–2108, 2016. © 2015 Society of Plastics Engineers     

Bond performance of FRP rebars with various surface deformations in reinforced concrete

One of the methods used to overcome the corrosion problem associated with steel rebars in reinforced concrete is the application of reinforced polymer (FRP) rebars. Bonding between the rebar and concrete is one of the major factors affecting the mechanical behavior of the structures. In this study, FRP rebars with four different surface configurations and geometries were constructed and their bonding to concrete was examined. These include a pultruded rod with a smooth surface (RO), externally wound FRP rib on the pultruded rod (RT), pultruded rod with sand sprayed on the surface (RS), and a combination of the last two configurations (RTS). Bonding strength of the rebars to concrete was assessed using pull‐out test at the embedment lengths of 12 and 18 cm. Results showed that the increase in surface roughness of the rebars and hence a greater inter‐mechanical locking, plays a major role in their bonding strength to concrete. RO rebar showed the lowest bonding strength to the concrete followed by the RT rebar. Bonding strength to concrete in the latter type was entirely controlled by the adhesion strength of the externally wound FRP rib to the pultruded core. RTS rebars with embedment length of 12 cm showed greater adhesion to the concrete, where as, in samples with embedment length of 18 cm, RTS and RS rebars showed close results. In all the tests conducted, delaminating of the surface texture was the major failure mode. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

纤维塑料筋粘结强度的研究

纤维塑料筋与混凝土的粘结强度大小直接关系到构件的承载能力、裂缝开展及其它性能等。基于41个碳纤维塑料筋的拉拔试验,并综合分析其它文献的结果,对纤维塑料筋与混凝土的粘结机理、破坏机理和粘结强度进行了较为深入的研究。同时对纤维塑料筋与水泥浆和环氧树脂的粘结强度也进行了探讨。     

玄武岩纤维增强塑料筋混凝土黏结性能的梁式试验研究

设计制作了14个玄武岩纤维增强塑料筋（BFRP筋）混凝土梁式试件和2个钢筋混凝土梁式试件,通过梁式试验分析了影响BFRP筋混凝土黏结性能的主要因素。结果表明,（1）BFRP筋的受力过程可分为微滑移段、正常滑移段、加速滑移段和下降段;（2）当BFRP筋的锚固长度相同时,随着混凝土强度的提高,黏结强度随之增大;（3）当混凝土强度相同时,随着BFRP筋锚固长度的增加,黏结强度明显减小,并且试件的破坏模式也发生了改变;（4）BFRP筋直径的大小对黏结强度的影响不明显;（5）当筋直径、锚固长度和混凝土强度相同时,BFRP筋混凝土的黏结强度与钢筋混凝土基本相当;（6）BFRP筋的外形对BFRP筋混凝土的黏结性能有着较大的影响。     

Bond strength of steel deformed rebars embedded in artificial lightweight aggregate concrete

The recycling of industrial waste such as bottom ash from furnaces is an important issue in construction industry, since it enables reduction in construction cost and has beneficial effect on the environment. In this study, we have investigated the bond characteristics of steel deformed bars embedded in artificial lightweight aggregate concrete which is manufactured from bottom ash. A pullout test was performed on 144 lightweight aggregate concrete specimens to measure the bond strengths. In this test, the parameters included the compressive strength of the concrete and embedment length of rebar. The pullout load vs. slip responses and modes of failure of the specimens were identified during the test. A bond strength equation for lightweight concrete is formulated by performing a regression analysis on the test results and compared with the predictions by the existing equations such as ACI 408, Orangun’s, and Darwin’s. The comparison shows that the existing bond strength equations cannot be directly applied to the design of lightweight concrete structures and the proposed equation is able to provide a more accurate estimation of the bond strength of lightweight concrete than the existing equations.     

光圆钢筋与混凝土界面粘结滑移本构模型研究

对配置光圆钢筋的既有混凝土结构进行承载性能评估时,钢筋与混凝土界面粘结性能优劣是评价该类混凝土结构的重要内容.为此,制作了4组光圆钢筋的中心拉拔试件和2组变形钢筋对比试件,选取粘结长度、钢筋表面形式为主要变量对粘结性能进行试验研究,并通过4组铝合金拉拔试件对比分析光圆筋与混凝土界面的粘结机理.研究结果表明:光圆钢筋的粘结强度显著小于变形钢筋的粘结强度,平均约为变形钢筋粘结强度的18.3%;光圆钢筋的粘结强度主要由化学粘着力和界面摩擦力构成,而铝合金的粘结强度则由化学粘着力构成,平均约为光圆钢筋粘结强度的10%;增加粘结长度后,光圆钢筋的粘结强度随之增大,但铝合金筋的粘结强度无明显变化.进一步基于试验结果及理论分析,建立了光圆钢筋与混凝土界面的粘结-滑移本构模型,并通过已有试验数据对建议模型进行了验证,吻合较好.     

土木工程用FRP筋的耐久性研究进展

纤维增强塑料(FRP)筋作为一种钢筋替代材料在土木工程中应用日渐广泛。本文对FRP筋在多种环境条件下的耐久性问题的国内外研究进展进行了综述,重点讨论了温度、湿度、酸、碱、盐溶液等环境作用下FRP筋的耐久性及模拟加速环境作用对FRP筋与混凝土界面粘结性能的影响。结果表明,上述环境作用对FRP筋及其与混凝土界面粘结性能的耐久性都有不同程度的影响。另外,本文还给出Fares E.Tannous等人建立的FRP筋在盐、碱溶液侵蚀作用下的耐久性预测模型,并对今后FRP筋的耐久性研究趋势作了展望。     

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。     

型钢与地聚合物混凝土粘结滑移性能研究

为了研究型钢与地聚合物混凝土之间的粘结滑移规律,对9个型钢地聚合物混凝土柱试件进行推出试验,研究地聚合物混凝土抗压强度、型钢的保护层厚度、型钢的锚固长度以及配箍率四个参数对型钢地聚合物混凝土试件荷载-滑移曲线、破坏形态以及粘结滑移性能的影响。结果表明:试件的荷载-滑移曲线具有相同的发展趋势,可将其划分为无滑移段、荷载上升段、荷载下降段和水平残余段四个阶段;试件的破坏模式为混凝土劈裂破坏,劈裂裂缝从加载端型钢翼缘产生,并向自由端发展;随着地聚合物混凝土抗压强度、型钢的保护层厚度和配箍率的提高,试件的特征粘结强度呈上升趋势;与普通水泥型钢混凝土不同,型钢的锚固长度增大也会使试件的特征粘结强度提高。根据试验结果,建立了特征粘结强度的计算公式,提出了型钢地聚合物混凝土的粘结-滑移本构模型,采用该模型计算得到的型钢地聚合物混凝土粘结-滑移曲线与试验曲线吻合度较高。     

BFRP筋碱激发混凝土粘结性能试验研究与数值模拟

玄武岩纤维增强复合筋(BFRP筋)碱激发混凝土为海洋环境下混凝土的耐久性提供安全保障。在其中心拉拔试验的基础上,采用分离式模型,运用ABAQUS有限元软件进行粘结滑移性能数值模拟与分析。通过试验数据,得出适用于BFRP筋碱激发混凝土的粘结滑移本构模型以及碱激发混凝土的塑性损伤模型,构建了基于非线性弹簧单元的数值模型,试验结果与计算结果吻合程度较好,验证了模型的准确性。试验与模拟结果表明:粘结长度为2.5d、5d(d为BFRP筋直径)的试件均发生筋材拔出破坏,粘结长度为10d的试件均发生劈裂破坏;BFRP筋与碱激发混凝土之间的粘结应力分布并不均匀,随着粘结长度和筋材直径的增大,极限粘结强度逐渐减小;当BFRP筋直径d=12 mm,粘结长度为2.5d、5d和10d的碱激发混凝土试块极限粘结强度分别为13.92 MPa、13.56 MPa和12.60 MPa,较相同粘结长度的普通混凝土试件,其极限粘结强度分别提高6.58%、10.97%和9.76%。     

冷热循环下纤维混凝土与高强钢筋间粘结强度损伤模型

通过对普通混凝土(PC)、钢纤维混凝土(SFRC)、聚丙烯纤维混凝土(PFRC)与HRB500E钢筋进行冷热循环作用后的中心拉拔试验,研究不同类型混凝土的劣化机理,分析冷热循环对PC、SFRC、PFRC的质量损失、相对动弹性模量以及粘结强度的影响。试验结果表明:冷热循环后,混凝土的质量损失和动弹性模量损失增加,钢筋与混凝土的粘结强度下降;掺入钢纤维、聚丙烯纤维的试件,其粘结强度衰减有所减弱,并且聚丙烯纤维的抑制效果更为明显。结合试验数据,对国内外的Petersen模型、Xu模型和Wu模型进行对比分析,同时考虑冷热循环对相对动弹性模量和相对粘结强度的影响,基于Weibull概率分布理论和强度衰减模型,建立了纤维混凝土与高强钢筋间粘结强度劣化模型,并通过本文数据对其进行了验证,粘结强度实测值与计算值比值的平均值为0.97,标准差为0.07,两者吻合良好,可为冷热环境下纤维混凝土结构耐久性设计提供理论参考。     

FRP筋异强混凝土叠浇梁挠度与延性研究

为提高纤维增强聚合物(FRP)筋异强混凝土叠浇梁的抗弯性能与延性,研究了钢纤维掺量、钢纤维混凝土叠浇层厚度对FRP筋异强混凝土叠浇梁的影响。以钢纤维体积掺量(0%、0.5%、1.0%、1.5%)与钢纤维混凝土叠浇层厚度(0 mm、180 mm、210 mm、300 mm)为变量,对6根FRP筋异强混凝土叠浇梁进行三分点弯曲试验,并对试验梁的破坏过程、破坏形态、裂缝宽度以及跨中挠度进行分析。研究结果表明：钢纤维的掺入改善了FRP筋异强混凝土叠浇梁的受力性能,使其由脆性破坏向延性破坏发展;随着钢纤维掺量、钢纤维混凝土叠浇层厚度的增加,FRP筋异强混凝土叠浇梁的极限承载力提高了9%～33%,抗弯性能提升了4%～21%,延性提升了22%～89%。基于试验与理论分析,建立了钢纤维作用下的FRP筋异强混凝土叠浇梁挠度计算公式与延性评价方法。     

结构混杂GFRP棒拉伸力学性能试验测试

本文提出了一种结构混杂的工艺制造GFRP,以改善材料的脆性,并对其进行了拉伸及破坏试验,试验结果表明,结构混杂GFRP棒的拉伸应力一应变曲线呈现出双线性特征。     

Experimental study on bond behavior between corrosion-cracked reinforced concrete and CFRP sheets

Bond behavior between corrosion damaged reinforced concrete and carbon fiber reinforced concrete polymer (CFRP) sheets was experimentally investigated. Forty ordinary strength concrete blocks (150 × 150 × 200 mm) were reinforced at one side across the 200-mm-dimension using three conventional ?12 mm steel bars at a spacing of (30, 40, and 50 mm) at a concrete clear cover of 15 mm. Thirty blocks were subjected to a cyclic treatment in 3% chloride solution until corrosion initiated and resulted in three different global cracking widths of up to 0.90 mm. Both control and corrosion damaged blocks were attached to CFRP sheets over their steel reinforced zone at bond lengths and widths ranging from (90 to 150 mm) and (50 to 150 mm), respectively, with CFRP bond length-to-bar spacing ratio kept constant at 1/3. Near-end pull-off tests were carried out using a special setup, mounted on a Universal Testing machine. Corrosion cracking caused significant reductions in bond strength, and slippage at ultimate stress at (41 and 68%), respectively. Other bond characteristics such as stress at first slippage, and bond stiffness and toughness were reduced, as well, by as high as (83, 44 and 67%) of those of control specimens, respectively. Corrosion cracks were more detrimental for smaller bond length and width values; especially after first and second corrosion stages, where bond failure was categorized by concrete skin peeling-off.     

不同试验方法对GFRP筋粘结强度的影响研究

基于拉拔和粱式试验，探讨了这两种试验方法对GFRP筋与不同种类混凝土(包括混凝土C30、掺纤维与不掺纤维的混凝土C50等)之间粘结强度的影响。研究表明，梁式试验的GFRP筋粘结强度稍低于拉拔试验的结果；混凝土强度等级以及是否掺加聚丙烯纤维对GFRP筋的粘结强度影响较小。     

Numerical modelling of carbon fibre‐reinforced polymer and hybrid reinforced concrete beams in fire

Investigation on the fire resistance of fibre‐reinforced polymer (FRP) reinforced concrete (RC) is essential for increased application of FRP bars in the construction industry. Experimental tests for determining the fire resistance of RC elements tend to be expensive and time‐consuming. Although numerical models provide an effective alternative to these tests, their use in case of FRP RC structures is hindered because of the insufficient constitutive laws for FRP bars at elevated temperatures. This paper presents the details of a numerical modelling work that was carried out for simply supported carbon FRP (CFRP) and hybrid (steel‐FRP) bar RC beams at elevated temperatures. Constitutive laws for determining temperature‐dependent strength and stiffness properties of CFRP bars are proposed. Numerical models based on finite element modelling were employed for the rational analysis of beams using the proposed constitutive laws. The behaviour of concrete was simulated by means of a smeared crack model based on the tangent stiffness solution algorithm. The employed numerical models were validated against previous experimental results. The theoretical rebar stresses were calculated in both the FRP and steel bars, and the differences are discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

不同掺合料混凝土与锈蚀钢筋间粘结-滑移力学性能试验研究

采用中心拉拔法对普通混凝土(PC)、水泥基渗透结晶防水混凝土(CCCW)、聚丙烯纤维混凝土(PFRC)与热轧带肋钢筋进行粘结-滑移试验。通过电化学锈蚀方法对钢筋进行加速锈蚀,研究锈蚀后钢筋与混凝土粘结性能。结果表明:在混凝土中引入适量聚丙烯纤维及水泥基渗透结晶防水材料能够显著提升其对钢筋的极限粘结强度,分别提高了20.8%、6.8%;无论是否添加掺合料,钢筋-混凝土拉拔试件的极限粘结力均随着锈蚀率的增大呈线性下降趋势。基于锈蚀构件拉拔试验结果,拟合出不同混凝土的极限粘结强度与锈蚀率计算公式,发现随着锈蚀率的增大,聚丙烯纤维及水泥基渗透结晶防水材料能减缓钢筋-混凝土极限粘结强度下降速度。     

Development of bond strength model for FRP plates using back‐propagation algorithm

For the flexural reinforcement of bridge and building structure, synthetic materials whose dynamic properties are superior and those containing the merit of corrosion‐proof are widely used as the substitute for a steel plate. Since FRP plate has improved bond strength owing to the fibers externally adhering to the plate, many researches regarding the bond strength improvement have been substantially performed. To search out such bond strength improvement, previous researchers had ever examined the bond strength of FRP plate through their experiment by setting up many variables. However, since the experiment for a research on the bond strength takes much of expenditure for setting up the equipment and is time‐consuming, also is difficult to be carried out, it is limitedly conducted. The purpose of this study was to develop the most suitable artificial neural network model by application of various neural network models and algorithm to the data of the bond strength experiment conducted by previous researchers. Many variables were used as input layers against bond strength: depth, width, modulus of elasticity, tensile strength of FRP plate and the compressive strength, tensile strength, and width of concrete. The developed artificial neural network model has been applied back‐propagation, and its error was learned to be converged within the range of 0.001. Besides, the process for the over‐fitting problem has been dissolved by Bayesian technique. The verification on the developed model was executed by comparison with the test results of bond strength made by other previous researchers, which was never been utilized to the learning as yet. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 5119–5127, 2006     

FRP筋和钢筋混合配筋混凝土梁受弯性能数值模拟及理论分析

近年来,FRP筋和钢筋混合配筋混凝土结构已逐渐成为土木工程界的研究热点问题之一。在试验研究基础上,应用有限元分析软件ANSYS建立了GFRP筋和钢筋混合配筋混凝土梁的数值模型,对其抗弯性能进行了有限元分析,提出了FRP筋和钢筋混合配筋混凝土梁名义配筋面积的概念,并结合中国《纤维增强复合材料建设工程应用技术规范》建立理论模型,对混合配筋混凝土梁的抗弯承载力和挠度进行了理论分析。通过与试验结果对比,证明了有限元模型的精确性以及基于《纤维增强复合材料建设工程应用技术规范》提出的理论计算模型对混合配筋混凝土梁的有效指导性。     

An experimental study on the bond strength between reinforcement bars and concrete as a function of concrete cover,strength and corrosion level

The effect of corrosion on the bond strength between reinforcement bars and concrete was studied in a series of experiments. An accelerated corrosion method was used to corrode the reinforcement bars embedded in concrete specimens. Pullout tests were performed to develop an empirical model for the ultimate bond strength by evaluating bond strengths in two different concrete mixes, three concrete cover depths and different mass losses of reinforcement bars after corrosion. Bond-slip relationships for the different corrosion levels were compared. It was found that the relationship between bond strength and concrete strength in uncorroded specimens differed from that of corroded specimens set in high-strength concrete because of brittleness in the corroded specimens, which caused a sudden loss of bond strength. The results revealed that specimens with higher concrete strength levels and corroded reinforcements showed a higher percentage of bond strength degradation due to concrete cracking during the pullout tests.