FRP-混凝土界面剥离破坏过程并行数值模拟

FRP-混凝土界面粘结性能和抗拉裂能力是外贴FRP片材加固混凝土结构技术的关键问题。基于FRP与混凝土界面面内剪切试验的结果,采用材料真实破裂过程三维并行分析(RFPA3D-Parallel)系统,对FRP-混凝土界面的粘结性能进行了三维并行数值模拟研究。数值试验再现了FRP-混凝土构件的三维破裂过程演化过程,清晰地反映了拉伸载荷作用下FRP-混凝土构件界面剥离破坏的规律,FRP-混凝土界面剥离破坏是一个细观损伤不断产生和宏观裂缝形成的渐进过程,可通过监测FRP-混凝土结构损伤演化过程的声发射来揭示FRP-混凝土结构在外载荷作用下的损伤程度。FRP片材在加载过程中的变形剥离破坏过程大致可以划分为四个阶段：(1)弹性变形阶段;(2)弹性软化阶段;(3)弹性软化剥离阶段;(4)软化剥离阶段。本文的数值计算表明RFPA3D-Parallel并行数值模拟方法为FRP片材-混凝土界面剥离破坏过程和机理研究提供了一个很好的途径,同时也为研究FRP-混凝土工程结构等的损伤断裂机理提供了一个新的分析手段,这对于土木建筑工程中FRP-混凝土结构的工程设计施工、损伤断裂控制及混凝土结构加固等研究无疑具有重要的理论指导和实践意义。     

Predicting the Capacity of RC Beams Strengthened in Shear with Side-Bonded FRP Reinforcements Using Artificial Neural Networks

The application of artificial neural network (ANN) to predict the shear capacity of reinforced concrete (RC) beams retrofitted in shear by means of side-bonded fiber-reinforced polymer (FRP) is investigated in this paper. An extensive literature review has been carried out. In addition, ten shear deficient RC beams with different carbon fiber-reinforced polymer (CFRP) configurations were tested and added as data to the collected data. It was aimed to build an efficient and practical ANN model with parameters which can easily be obtained without any calculation and/or experimental investigation. The results are compared with the design guideline equations that emerge as predictions of the FRP contribution using the trained neural networks: these are in good agreement with the experimental results and better than those calculated from the theoretical guideline equations. Based on ANN results, a parametric study has been carried out to study the importance of different influencing parameters on the FRP contribution. Thereafter, a new simple expression is proposed for determining the contribution of externally bonded side-bonded FRP. Accordingly, the suggested design formula is capable of predicting the experimental FRP satisfactorily so that it can be admitted as an alternative to the existing guideline equations within the range of parameters covered in the study.     

Nonlinear stability of timber column strengthened with fiber reinforced polymer

By taking into account the effect of the bi-modulus for tension and compression of the fiber reinforced polymer (FRP) sheet in the reinforcement layer, a general mathematical model for the nonlinear bending of a slender timber beam strengthened with the FRP sheet is established under the hypothesis of the large deflection deformation of the beam. Nonlinear governing equations of the second order effect of the beam bending are derived. The nonlinear stability of a simply-supported slender timber column strengthened with the FRP sheet is then investigated. An expression of the critical load of the simply-supported FRP-strengthened timber beam is obtained. The existence of postbuckling solution of the timber column is proved theoretically, and an asymptotic analytical solution of the postbuckling state in the vicinity of the critical load is obtained using the perturbation method. Parameters are studied showing that the FRP reinforcement layer has great influence on the critical load of the timber column, and has little influence on the dimensionless postbuckling state.     

ANALYTICAL ANALYSIS OF INTERFACIAL STRESSES IN FRP-RC HYBRID BEAMS WITH TIME-DEPENDENT DEFORMATIONS OF RC BEAM

In this paper, the effect of time-dependent deformations (such as shrinkage and creep) on the interfacial stresses between an RC beam and FRP plate is presented. For this end, a closed-form solution for such stresses in externally FRP plated RC beams including creep and shrinkage effects is presented. The developed model is formulated to predict the interfacial stresses at time ‘t’, in which the RC beams have been already subjected to 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 the RC beam and the FRP panel. Contrary to some existing studies, the assumption that both RC beam and FRP panel have the same curvature is not used in the present investigation. This research is helpful for the understanding on mechanical behavior of the interface and design of the FRP-RC hybrid structures.     

玻璃钢渔船结构的特点

介绍了玻璃钢作为造船材料的特点与成型工艺、玻璃钢渔船结构中的板材、骨材以及玻璃钢渔船结构的类型。     

锥头弹丸撞击下FRP层合板的侵彻与穿透的理论研究

 研究了锥头弹丸撞击下FRP层合板的侵彻和穿透性能，在局部化破坏模式假定的基础上改进了Wen提出的能量简化分析模型。改进模型仍假设弹体在侵彻过程中表面所受靶体的平均压力由靶体材料弹塑性变形所引起的静态阻力和速度效应引起的动阻力两部分组成，认为侵彻过程中靶体对弹体的阻力不再是一个常数，而是侵彻速度的函数。并由此推导出了锥头弹丸在侵彻和贯穿过程中的侵彻深度、残余速度和弹道极限速度的公式。理论预测与实验结果符合得很好。     

Finite element analysis of interfacial stresses in FRP–RC hybrid beams

The interfacial stresses in fiber reinforced plastic (FRP)–reinforced concrete (RC) hybrid beams were studied by the finite element method. The mesh sensitivity test shows that the finite element results for interfacial stresses are not sensitive to the finite element mesh. The finite element analysis then is used to calculate the interfacial stress distribution and evaluate the effect of the structural parameters on the interfacial behavior. It is shown that both the normal and shear stresses at the interface are influenced by the material and geometry parameters of the composite beam. This research is helpful for the understanding on mechanical behavior of the interface and design of the FRP–RC hybrid structures.     

超高分子量聚乙烯纤维表面改性的研究进展

超高分子量聚乙烯(UHMWPE)纤维具有诸多优异性能,因此被广泛应用于纤维增强复合材料(FRP)。但是由于UHMWPE纤维表面光滑且无极性基团,与树脂基体粘接性差,可通过纤维表面改性有效提高FRP的界面强度,进而提升材料性能。本文总结了近几年基于化学处理、等离子体处理、电晕放电和辐射引发表面接枝等方法对UHMWPE纤维表面改性的研究进展,并对改性方法的发展进行了展望。     

Geometric and mechanical characterization of ribbed FRP rebars

The paper discusses the advantage of fiber-reinforced polymer (FRP) rebar for application in concrete because of its light weight, high strength, high corrosion resistance and durability. Different options of shaping the wave-like texture of FRP bars for concrete bonding are considered. The diameter measurement problem of ribbed FRP bars is examined, and a proprietary procedure is suggested to determine the equivalent diameter and elastic modulus of ribbed FRP bars. The tensile strength (889–1197 MPa) obtained herein is greater than the longitudinal flexural strength (566–822 MPa), which is due to the ribs, contrary to the case of plain bars. The elastic modulus values obtained (40–61 GPa) are in agreement with the known literature data.     

Peeling behavior and spalling resistance of CFRP sheets bonded to bent concrete surfaces

In this paper, the peeling behavior and the spalling resistance effect of carbon fiber reinforced polymer （CFRP） sheets externally bonded to bent concrete surfaces are firstly investigated experimentally. Twenty one curved specimens and seven plane specimens are studied in the paper, in which curved specimens with bonded CFRP sheets can simulate the concrete spalling in tunnel, culvert, arch bridge etc., whereas plane specimens with bonded CFRP sheets can simulate the concrete spalling in beam bridge, slab bridge and pedestrian bridge. Three kinds of curved specimens with different radii of curvature are chosen by referring to practical tunnel structures, and plane specimens are used for comparison with curved ones. A peeling load is applied on the FRP sheet by loading a circular steel tube placed into the central notch of beam to debond CFRP sheets from the bent concrete surface, meanwhile full-range load-deflection curves are recorded by a MTS 831.10 Elastomer Test System. Based on the experimental results, a theoretical analysis is also conducted for the specimens. Both theoretical and experimental results show that only two material parameters, the interfacial fracture energy of CFRP-concrete interface and the tensile stiffness of CFRP sheets, are needed for describing the interfacial spalling behavior. It is found that the radius of curvature has remarkable influence on peeling load-deflection curves. The test methods and test results given in the paper are helpful and available for reference to the designer of tunnel strengthening.