对FRP筋混凝土桥梁面板承载力性能的非线性有限元分析

为了研究FRP筋混凝土梁面板的承载能力,采用了大型商用软件ABAQUS对Sherif EI-Gamal等的钢混桥梁模型进行了数值模拟。将非线性有限元计算结果同试验结果进行对比分析,非线性有限元的计算结果与试验结果吻合良好。基于数值模准确的分析结果,对结构体系中的压缩薄膜效应进行了分析,并开展了一系列的参数学习,包括混凝土强度、支撑梁刚度以及横隔梁。分析结果表明,压缩薄膜效应对FRP筋混凝土桥面板的承载能力有显著的影响。     

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。     

结合压缩薄膜效应对BFRP筋自密实混凝土桥面板工作性能有限元分析

采用非线性有限元方法对英国北爱尔兰Thompson桥中的BFRP筋增强自密实混凝土桥面板进行数值分析,通过对比数值模拟结果和试验结果表明所建立的有限元模型能够较准确地反映BFRP筋增强自密实混凝土桥面板在轮压负载下的工作性能。基于有限元模型的有效性,采用非线性数值模拟对该新型桥面板进行极限承载力和破坏模式进行预测及参数化分析。结果表明,BFRP筋自密实桥面板极限承载力大约为欧洲轮压负载150 k N的6倍(100 t),由于现行桥面板设计规范忽略了压缩薄膜效应的存在而导致桥面板极限承载力设计过于保守,参数化分析发现配筋率和筋材类型对桥面板极限承载力影响不大,而混凝土强度和跨高比是影响桥面板极限承载力的主要因素。     

预应力FRP筋混凝土梁的非线性有限元分析

FRP作为一种新型高性能的结构材料,具有轻质、高强和抗腐蚀等特点,在土木工程中是一种具有发展前景的新型预应力筋用材.本文详细介绍了有限元软件ANSYS对预应力FRP筋混凝土梁的建模过程,并且将分析结果与体内有粘结和体内无粘结预应力FRP筋混凝土试验梁的试验结果进行了比较,验证了模型的可靠性.     

铝合金筋体外预应力加固混凝土梁受力性能研究

铝合金具有轻质高强、延性好、低温脆断敏感性小、耐腐蚀等优点,可用于侵蚀环境及寒冷环境下结构体外预应力加固工程.本文对铝合金筋的材料性能进行试验研究,建立了铝合金筋本构关系模型,应用有限元程序ANSYS对既有体外预应力加固混凝土梁的受力过程进行模拟分析,通过计算结果和试验结果的对比分析验证了有限元分析模型的合理性.根据等截面原则和等强度原则,应用铝合金筋分别替换既有混凝土梁的体外预应力筋,对其进行有限元分析.结果表明,与传统体外预应力加固混凝土梁相比,采用等截面原则加固后的铝合金筋体外预应力混凝土梁,可以在适当提高延性的基础上,部分提高混凝土梁的承载能力;采用等强度原则加固后的铝合金筋体外预应力混凝土梁,可同时显著提高混凝土梁的承载能力和延性.     

钢筋混凝土矩形空心墩柱的FRP约束效应研究

为了正确评价纤维增强复合材料(FRP)约束效应对钢筋混凝土(RC)空心墩柱受力性能的影响,首先采用有限元数值模拟方法,对FRP类型、厚度、幅宽和间距参数影响下约束RC矩形空心柱的轴压荷载、约束混凝土压应变、箍筋和FRP拉应变的变化规律进行研究。基于模拟结果,提出一种考虑FRP布环箍和箍筋共同约束效应的侧向约束压力计算公式,进而建立FRP约束混凝土压应力-应变模型。进一步应用提出的FRP约束混凝土模型评价FRP加固矩形空心桥墩的受力性能,并与试验结果对比,两者吻合较好。     

防腐混凝土梁长期力学性能试验研究(英文)

玻璃钢(FRP)筋防腐混凝土是一种强度高、全方位耐腐蚀的新型工程材料,具有十分广泛的应用前景.本文先对防腐混凝土梁采用四点弯曲试验方法,对FRP筋加强混凝土梁的弯曲长期力学特性进行了试验研究与分析,得到了梁在不同荷载水平作用下的蠕变曲线.结果表明,FRP筋不仅提高了防腐混凝土梁的初始刚度和强度,且明显降低了梁的蠕变变形.最后,运用最小二乘法确定蠕变模型参数,分别建立了防腐混凝土粱和FRP筋加强防腐混凝土梁的弯曲蠕变幂律模型,为估计材料的长期力学性能提供依据,对FRP筋防腐混凝土结构设计具有重要的价值.     

基于FRP的不配筋混凝土桥面结构工作性能研究

为了提高混凝土桥面板的耐久性和降低维修成本,本次研究建立了一种基于FPR的不配筋混凝土桥面结构体系。该桥面结构合理利用面板内的拱效应作为承载机理,采用GFRP杆件作为横向约束杆件,因此面板本体内不需配置受力筋。以支撑梁、约束杆件间距和加载区位置为结构参数,本文建立了一组1∶3比例缩小的桥面结构试验模型并对其进行了静力加载试验。分析研究桥面结构在轮胎荷载作用下的结构响应,清晰揭示了拱效应对该桥面结构承载性能的作用和影响。基于所建立非线性有限元模型计算结果与试验结果吻合良好,本文采用该数值模型进行了深入的参数分析,研究混凝土强度、拱高以及外置FRP约束杆件配置方式变化对该结构工作性能的影响。     

玄武岩FRP筋混凝土梁抗弯性能试验研究

通过6根玄武岩FRP筋混凝土梁与6根钢筋混凝土梁静力加载对比试验,研究不同纵筋配筋率的玄武岩FRP筋混凝土梁与钢筋混凝土梁的受力性能,分析其承载力变化过程、破坏形态、挠度变形与裂缝发展情况。试验结果表明,玄武岩FRP筋混凝土梁载荷–挠度曲线近似为直线,但仍然具有较好的延性;开裂载荷与极限载荷相比钢筋混凝土梁略低;裂缝宽度在2.5 mm以内,且分布对称均匀,裂缝间距略大于钢筋混凝土梁;玄武岩FRP筋混凝土梁产生的挠度较大,应提高玄武岩FRP筋与混凝土之间的粘结性能,最大限度发挥玄武岩FRP筋抗拉强度高的特点。     

全FRP筋混凝土梁斜截面承载力研究进展

纤维增强复合材料(FRP)作为混凝土结构的新型高性能增强材料,受到了国内外土木工程界的广泛关注。全FRP筋混凝土梁斜截面受剪承载力的计算需要考虑FRP纵筋和FRP箍筋的特殊影响。在大量试验研究的基础上,各国规范均提出了全FRP筋混凝土梁斜截面承载力的计算公式,其中包括中国规范(GB 50608—2010)、日本规范(JSCE 1997)、英国规范(BISE 1999)、意大利规范(CNR-DT 203/2006)、美国规范(ACI 440.1R-06)、加拿大规范(CSA.S 806-12)。用这6种规范所提供的计算模型分别计算33根试验梁的斜截面承载力,并与试验结果作对比,以此评价这些方法的可靠性。     

纤维缠绕压力容器的爆破压力与纤维强度转换率

纤维的强度性能在纤维缠绕压力容器中不可能得到百分之百的发挥。本文结合容器的爆破试验结果和有限元分析结果计算确定纤维强度转化率。     

Modeling the evolution and rupture of stretching pendular liquid bridges

A simplified mathematical model and numerical simulations of the governing Navier–Stokes equations are used to predict the shape evolution, rupture distance, and liquid distribution of stretching pendular liquid bridges between two equal-sized spherical solid particles. In the simplified model, the bridge shape is approximated with a parabola, and it is assumed that the surface tension effects dominate the viscous, inertial, and gravitational effects. For the numerical simulations, a commercial Computational Fluid Dynamics (CFD) software package – FLUENT – is used. The rupture distance predictions obtained with both models are compared with experimental data and a reasonable agreement is found. The results of the numerical investigations show that for simulations with negligible viscous, inertial, and gravitational effects, the rupture distance approaches an asymptotic value, which is close to the value predicted by the simplified model. The bridge profiles predicted using the simplified model and the numerical simulation are compared. It is found that a second-order polynomial appropriately represents the stable bridge shape for particles with identical contact angles; however, for liquid bridges between particles with different contact angles, the numerical simulations of the governing Navier–Stokes equations should be used.     

Experimental and numerical study on a bubbling fluidized bed with wet particles

As liquid bridge between particles acts an important role in the particle system, it is of considerable significance to analyze the flow hydrodynamics of wet particles in fluidized beds, which will improve the reactor design and process optimization. Thus, experimental and numerical investigations on wet particles in a bubbling fluidized bed are conducted in current work. On experimental side, particle image velocimetry (PIV) technology is employed with a designed bubbling fluidized bed. The silicone oil is used in this work because it is nonvolatile and transparent. On numerical side, a modified discrete element method (DEM) numerical method is developed by compositing an additional liquid‐bridge module into the traditional soft‐sphere interaction model. Most of the physical parameters are chosen to correspond to the experimental settings. Good agreements of particle velocity are found between the DEM simulation and PIV measurement. The performance of different liquid contents and superficial gas velocities are examined. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1970–1985, 2016     

Nanoindentation of CVD diamond: comparison of an FE model with analytical and experimental data

This paper describes an experimental procedure for the determination of the hardness and the elastic modulus through nanoindentation of a CVD diamond coating using simple analytical formulae. Such tests, performed with a Berkovich indenter, were simulated by finite element analysis. Through the numerical analysis, it was possible to reproduce the load-penetration depth curves and thus, confirm the validity or correct the property calculations. Results show that the predicted property values can be affected by the assumed material strain hardening. By comparing the numerical values with the experimental results, it is possible to characterise, with sufficient accuracy, the material behaviour.     

Experimental investigations and probabilistic strength prediction of linear welded double lap joints composed of timber

Wood-to-wood bonds obtained by means of friction welding are a relatively new type of connections holding high potential to compete with existing structural adhesives, since a load bearing bond is formed almost instantaneously. This paper addresses the question to which extent welding of wood can be considered for structural joining of load bearing timber elements. For this purpose, experimental investigations in form of tensile-shear tests on welded double-lap joints were carried-out, in which a set of parameters, including overlap length and layer thickness, has been varied. In addition to the experimental analysis, the stress–strain state inside of the connection was determined numerically, taking into account the mechanical complexity of the involved components. It could be concluded that (1) failure of the bond is triggered by a combination of shear and tensile stresses acting in the interface, but also that (2) joint strength is not linearly correlated to stress magnitudes. The mechanical behaviour of the welded interface was characterised by a series of off-axis tests, including its statistical components. The results from this characterisation and the numerical modelling were combined in the framework of a strength prediction routine. Finally, experimental and numerical results are compared, allowing for a validation of the suggested approach.     

Strain‐rate and temperature effects on the deformation of polypropylene and its simulation under monotonic compression and bending

Monotonic compressive loading and bending tests are conducted for solid polypropylene (PP) under constant or time‐varying strain‐rates and temperatures of 10, 25, 40°C. The observed compressive stress‐strain responses under constant conditions have revealed that the inelastic deformation behavior is remarkably dependent on loading rates and temperatures of normal use. The examination of such inelastic behavior has indicated that the strain‐rate effects correspond with the temperature effects based on the concept of time‐temperature equivalence. The viscoplastic constitutive theory based on overstress (VBO) has successfully reproduced the experimental responses with stress‐jumping phenomena using the equivalent time. Four‐point bending tests are performed under monotonic loading and holding for PP beams at three different temperatures. The observed deformation behavior has shown that the Bernoulli‐Euler hypothesis is valid. The VBO model and beam bending theory has generated the basic equations for PP beams, showing an analogy with the uniaxial one. In the numerical analysis, the equations are transformed into nonlinear ordinary differential equations with use of Gaussian quadrature for the spatial integrals. The comparison of numerical and experimental results has suggested some modifications for actually loaded moment taking the effect of deflection and friction into consideration. Finally, the numerical calculation has simulated the experimental time‐histories of curvatures fairly well.     

Numerical and experimental tests on adhesive bond behaviour in timber-glass walls

In order to study the behaviour of a timber-glass wall with an epoxy based adhesive bond under extreme loading conditions, a set of experimental and numerical tests was performed. The experimental part consisted of small-size failure tests, related to an evaluation of the adhesive bond behaviour, as well as of life-size failure test of the timber-glass wall for an evaluation of the performance of the complete composite wall. These experiments were simulated numerically by the nonlinear finite element method, where the adhesive was modelled as a visco-hyperelastic material, and the timber-adhesive adhesion was modelled by a cohesive, elasto-damage traction-separation softening law. The qualitative agreement between the experimental and the numerical results was reasonably good, which indicates that the prediction of the highly nonlinear, inelastic and strain-rate dependent response of the timber-glass walls with an adhesive bond under extreme loading conditions can be estimated reasonably well by the nonlinear finite element method.     

Numerical analysis of neck propagation in polymeric materials. Part 2 – Neck propagation behaviour of poly (butylene terephthalate) mouldings

Abstract

This paper examines the factors controlling the formation and propagation of a neck in poly (butylene terephthalate) (PBT) mouldings under tensile loading. Tensile tests were used to investigate the load–displacement and deformation behaviour of PBT and the accompanying changes in surface temperature. In parallel with this experimental study, a numerical model was developed for the deformation of PBT mouldings and neck formation under tensile loading analysed using finite element analysis (FEA). The calculated numerical results were compared with the experimental data. This work has shown that formation does not occur in PBT immediately after the yield point. Instead, plastic deformation first progresses homogeneously through the testpiece. Neck formation and propagation, accompanied by a rise in temperature, then follow. The load–displacement behaviour calculated using FEA could be approximated to the experimental data by adapting an elastic–plastic model at a stable temperature to the necking behaviour of PBT moulding. Furthermore, the dependence of neck formation on strain rate is related to the plastic instability, as demonstrated by the numerical results, and does not depend upon heating effects.