A new shear-flexible FRP-reinforced concrete slab element

In this paper, a simple shear-flexible rectangular layered FRP-reinforced concrete slab element is developed based on Mindlin–Reissner plate theory and Timoshenko’s composite beam functions for nonlinear finite element analysis of FRP-reinforced concrete slabs. The Timoshenko’s composite beam functions are developed for FRP-reinforced concrete slabs based on those for composite laminates. The plane displacement interpolation functions of a quadrilateral isoparametric element with drilling degrees of freedom are employed to describe the membrane effects and the bending effects of the slab element are represented by the rotation functions of the slab element derived from Timoshenko’s composite beam functions. Both geometric nonlinearity and material nonlinearity of the materials are included in the new element. The efficiency of the element for nonlinear finite element analysis of FRP-reinforced concrete slabs is validated by comparing the computed results of two numerical examples with those obtained from lab tests.     

Multiscale finite element modeling of failure process of composite laminates

A multiscale nonlinear finite element modeling technique is developed in this paper to predict the progressive failure process for composite laminates. A micromechanical elastic–plastic bridging constitutive model, which considers the nonlinear material properties of the constituent fiber and matrix materials and their interaction and the damage and failure in fibrous composites at the fiber and matrix level, is proposed to represent the material behavior of fiber-reinforced composite laminates. The micromechanics constitutive model is employed in the macroscale finite element analysis of structural behavior especially progressive failure process of the fiber-reinforced composites based on a 4-node 24-DOF shear-locking free rectangular composite plate element.     

波形钢腹板(钢腹杆)-混凝土组合箱抗扭承载力试验与计算

为研究波形钢腹板（钢腹杆）-混凝土组合箱抗扭特性,进行了构件的抗扭承载力试验,结果表明:混凝土底板首先出现斜向裂缝,裂缝与混凝土主拉应变垂直,顶底板裂缝呈螺旋状开展,裂缝方向与主梁纵轴线约成45°;底板出现宽度较大的主斜裂缝,钢筋受拉屈服,组合箱受扭破坏。采用有限元软件ANSYS对扭转试验构件进行了非线性有限元分析,有限元分析结果与试验结果吻合良好。参照混凝土箱梁的开裂扭矩计算公式,建立了组合箱开裂扭矩的计算公式;应用混凝土箱梁变角度空间桁架理论,根据波形钢腹板（钢腹杆）-混凝土组合箱达到极限扭矩时可能出现三种破坏形式,建立了组合箱极限扭矩的计算公式。通过与试验结果和实桥截面有限元分析结果的比较表明,建立的波形钢腹板（钢腹杆）-混凝土组合箱抗扭承载力简化计算公式具较高精度,最大误差不超过10%,可运用于实桥计算。     

Numerical model for composite structures with experimental confirmation

The paper briefly presents a numerical model for the simulation of composite structures. The main structure is modeled with two‐dimensional plane finite elements. The composite surface is modeled with two‐dimensional interface elements for the continuous connection simulation and modified beam elements for the discrete connection simulation. The applied material model’s primary purpose is the simulation of reinforced concrete structures. It includes the most important nonlinear effects of reinforced concrete behavior: yielding in compression and opening and propagation of cracks in tension, with tensile and shear stiffness of cracked concrete, as well as the nonlinear behavior of reinforced steel. It also includes nonlinear behavior of the composite surface and the connection elements. The model was confirmed in experimental tests of composite concrete Omnia slabs, which are in common usage. The achieved test results were compared with the results obtained through the developed numerical model.     

混杂CFRP/GFRP筋HPC梁的非线性梁壳组合单元研究

对于混杂CFRP/GFRP筋高性能混凝土（HPC）梁, 研究一种新的三维非线性梁壳组合单元, 对HPC梁进行了全过程分析。引入实体退化壳单元理论, 利用空间梁单元模拟预应力CFRP筋, 并根据CFRP筋单元节点线位移和转角位移的协调性, 推导CFRP筋单元对梁壳组合单元刚度矩阵的贡献, 同时对GFRP筋和HPC梁采用分层壳单元模拟。并运用Jiang屈服准则、 Madrid强化准则等描述混凝土的材料非线性, 提出一种新的非线性梁壳组合单元, 研制相应的三维非线性计算程序。计算结果与试验数据吻合良好, 说明本文构造的非线性梁壳组合单元的正确性和研制程序的可靠性, 以及混凝土材料非线性描述的合理性; 采用组合单元能准确模拟CFRP筋的几何构形, 能综合考虑其拉压弯剪性能, 利于全面地反映配筋对结构的增强作用。      

Post-yield behavior of fixed steel beams encased in concrete with plastic rotation capability under monotonic loads

Flexural strength calculated based on only curvature at sections shows some inconsistencies at large strains compared with nonlinear finite element analyses which considered damaged concrete plasticity. The prediction of the post-yield behavior of steel–concrete composite structures has been a complex issue, rendering analytically inaccurate prediction of the post-yield deflection of composite beams when plastic flows were not considered. The accurate prediction of the post-yield deformation of composite steel beams encased in structural concrete should account for the strain based on plastic rotation. The plastic rotation is influenced by the inelastic energy dissipation. The post-yield behavior of steel–concrete composite structures is affected by the inclination of diagonal cracks of concrete, and the stiffening effect of concrete tension between cracks. Plastic strain occurring in the steel section also contributes to in-elastic behavior of composite structures. The aim of this study was to idealize plastic flow of steel beams encased in structural concrete at fixed foundation. Plastic flows were calculated by non-linear finite element analysis including the consideration of concrete plasticity. The post-yield deflection was, then, predicted in a manner reflecting plastic deformation. The proposed idealization agreed well with numerical data obtained by means of nonlinear finite element analysis, providing a simplified but reliable procedure for practicing engineers designing composite structures in the inelastic region.     

钢筋混凝土梁的非线性分析

本文采用考虑剪切变形的 Timoshenko 梁理论,利用分层有限元法对钢筋混凝土梁进行非线性分析。在分析中,提出了一种在迭代过程中逐次逼近中性轴的办法。在材料模型方面,考虑了混凝土拉伸时的开裂、开裂后的骨料咬合及拉伸加强效应,钢筋暗销作用等,另外,对于混凝土压缩时延性性质,则首次采用了非均匀强化塑性理论来描述。与别的方法相比,本文的方法具有计算量少,数据准备简单等优点。     

Large amplitude free vibration of a shear deformable laminated composite parabolic plate with parabolically orthotropic plies

The large amplitude free vibration of a laminated composite parabolic plate with parabolically orthotropic plies is investigated for the first time. The effects of out-of-plane shear deformations, rotary inertia, and geometrical nonlinearity are taken into account. The geometry of the plate is described, and the analysis performed in the parabolic coordinate system. The problem is solved numerically using a new parabolic hierarchical finite element. The nonlinear equations of free motion are mapped from the time domain into the frequency domain using the harmonic balance method. The resultant nonlinear equations are solved iteratively using the linearized updated mode method. Results for the fundamental linear and nonlinear frequencies are obtained for symmetric and antisymmetric laminates with clamped and simply supported edges. Comparisons are made with the finite element method for clamped and free isotropic parabolic plates and show excellent agreement. The aspect ratio, thickness ratio, moduli ratio, number of plies, layup sequence, and boundary conditions are shown to affect the hardening behavior.     

Experimental and nonlinear finite element studies of RC beams strengthened with FRP plates

This paper presents a joint experimental–analytical investigation aimed at studying the brittle failure modes of RC members strengthened in flexure by FRP plates. Both midspan and plate end failure modes are studied. The finite element analyses are based on nonlinear fracture mechanics. The model considered the actual crack pattern observed in the tests by using a smeared and an interface crack model. This paper shows how concrete cracking, adhesive behavior, plate length, width and stiffness affect the failure mechanisms. The numerical and experimental results show that debonding and concrete cover splitting failure modes occur always by crack propagation inside the concrete.     

基于Layerwise理论的共固化粘弹阻尼复合材料动特性分析

共固化粘弹性复合材料兼具结构承载和阻尼减振功能。针对传统的混合单元法在应用于粘弹性夹层复合材料结构阻尼性能分析时存在着前处理困难、计算规模大、精度低以及难以考虑正交各向异性铺层自身损耗能力的缺点,推导了一种基于Layerwise离散层理论的四节点四边形复合材料层合板单元,并利用直接复特征值解法建立了共固化粘弹性复合材料结构的阻尼性能分析方法。将该方法应用于不同的阻尼结构,分析结果与文献中已公开结果和混合单元法的计算结果进行了对比验证。结果表明,基于离散层理论的层合板单元具有计算精度高、前处理建模简单和计算规模小的优点,可有效应用于复杂共固化粘弹性复合材料结构的阻尼性能分析和设计。     

Nonlinear finite element modeling of concrete deep beams with openings strengthened with externally-bonded composites

This paper aims to develop 3D nonlinear finite element (FE) models for reinforced concrete (RC) deep beams containing web openings and strengthened in shear with carbon fiber reinforced polymer (CFRP) composite sheets. The web openings interrupted the natural load path either fully or partially. The FE models adopted realistic materials constitutive laws that account for the nonlinear behavior of materials. In the FE models, solid elements for concrete, multi-layer shell elements for CFRP and link elements for steel reinforcement were used to simulate the physical models. Special interface elements were implemented in the FE models to simulate the interfacial bond behavior between the concrete and CFRP composites. A comparison between the FE results and experimental data published in the literature demonstrated the validity of the computational models in capturing the structural response for both unstrengthened and CFRP-strengthened deep beams with openings. The developed FE models can serve as a numerical platform for performance prediction of RC deep beams with openings strengthened in shear with CFRP composites.     

钢筋混凝土楼板火灾反应数值计算模型

基于退化壳原理,考虑火灾下板壳截面的不均匀温度场分布而引入分层模型,同时在每分层上考虑材料在不同温度下的热力弹塑性本构关系,建立了火灾下钢筋混凝土板壳结构的有限元数值计算模型。另外,通过全拉格朗日方法考虑了大位移的几何非线性影响。最后通过一钢筋混凝土板在高温下的试验进行了验证,并分析了配筋率和保护层厚度的影响。结果表明:提出的火灾下钢筋混凝土壳单元数值计算模型的计算结果与试验结果吻合较好,可以用来分析火灾下钢筋混凝土框架结构楼板的反应。     

采用通用有限元程序的弥散裂缝模型和分层壳单元模拟钢筋混凝土构件裂缝宽度

该文基于弥散裂缝模型,采用通用有限元程序的分层壳单元计算钢筋混凝土构件裂缝宽度的方法。讨论了理论基础,Bazant和Oh提出的经典裂缝带理论主要针对素混凝土构件,严重的局部化效应导致显著的网格依赖性,而将裂缝带理论拓展到工程常用的配筋混凝土构件时,由于多裂缝分布发展的特点,裂缝带宽应修改为平均裂缝间距而使计算结果与网格无关。在理论基础讨论的基础上,给出了采用通用有限元程序的弥散裂缝模型和分层壳单元计算钢筋混凝土构件裂缝宽度的计算流程,其中,平均裂缝间距将有限元分析中的“应变”概念和工程设计中的“裂缝宽度”概念紧密联系起来,是计算流程中最关键的参数。以某承受负弯矩的简支组合梁混凝土板开裂分析为例,验证并讨论了网格相关性、大软化模量导致数值收敛困难的应对策略、平均裂缝间距的决定性作用等重要问题。     

Prediction of the postbuckling response of composite airframe panels including ply failure

Future design scenarios aim to allow buckling in composite airframe panels. Reliable simulation procedures should be able to capture the postbuckling elastic as well as the inelastic response associated with damage. Damage in composite laminates in terms of ply failure may primarily occur as fiber fracture or matrix cracking. This paper presents a model which is able to capture both geometrical and material nonlinearity. It bases on the finite element formulation of a layered, iso-parametric, quadrilateral shell element which allows for an arbitrary reference surface as well as an arbitrary stacking sequence. Geometrical nonlinearity is accounted for by utilizing Green strains and second Piola–Kirchhoff stresses. Material nonlinearity is considered via a layerwise ideally brittle damage model. The model is applied to a buckling test of a stringer-stiffened composite airframe panel. The numerical results are compared with an experiment proving the applicability of the proposed concept.     

考虑荷载分布的多跨连续钢-再生混凝土组合板长期性能研究

为量化再生粗骨料掺入对多跨连续钢-混凝土组合板长期性能的影响,基于ABAQUS软件建立组合板的非线性热力耦合有限元模型,模型考虑非均匀收缩、非均匀徐变以及混凝土开裂的耦合影响;利用18组足尺试验数据验证模型的可靠性,并对现有规范方法的适用性进行评述;在此基础上,研究不同荷载分布下再生粗骨料取代率对五跨连续组合板长期性能...     

钢板混凝土组合墙轴压受力性能有限元分析

为了研究核电工程中钢板混凝土组合墙的承载能力以及设计参数对承载力的影响,以4个核电工程中钢板混凝土组合墙的轴压试验为基础,采用ABAQUS建立钢板混凝土组合墙的有限元模型,模型中混凝土、钢板和栓钉均采用实体模型模拟,考虑了材料非线性和钢板焊接残余应力等。研究了栓钉的受力机理,模拟了试件中钢板的屈曲变形,分析不同参数如钢板与混凝土的强度、距厚比和含钢量对承载力的影响。分析结果表明:有限元模型计算结果与试验结果吻合较好,栓钉在受力过程中始终处于弹性受力状态,混凝土强度对承载力影响最大,距厚比对钢板的屈曲影响较大,较小的距厚比能保证钢板与混凝土协同工作。     

空间框架结构非线性分析的简化数值方法

钢筋混凝土框架结构正常使用期间是带裂缝工作的,合理的分析方法应考虑因开裂引起的非线性。在杆系结构有限元基础上,根据构件截面广义应力-应变关系,提出了空间框架结构非线性分析的简化数值方法——网格-等效截面法。该方法能考虑材料非线性,混凝土开裂导致构件有效刚度降低,混凝土徐变和加载历程等影响因素。给出了相应的实施步骤,并采用通用有限元软件ANSYS部分功能,自编主体计算程序的混合编程方法编制了程序。通过考题,程序编制方法正确,计算精度满足工程要求。最后,采用程序对荷载和温度作用下某超长框架结构进行了计算。     

Nonlinear Viscoelastic Response of Unidirectional Polymeric Laminated Composite Plates Under Bending Loads

Nonlinear bending analysis of polymeric laminated composite plate is examined considering material nonlinearity for viscoelastic matrix material through a Micro–macro approach. The micromechanical Simplified Unit Cell Method (SUCM) in three-dimensional closed-form solution is used for the overall behavior of the unidirectional composite in any combination of loading conditions. The elastic fibers are transversely isotropic where Schapery single integral equation in multiaxial stress state describes the matrix material by recursive-iterative formulation. The finite difference Dynamic Relaxation (DR) method is utilized to study the bending behavior of Mindlin annular sector plate including geometric nonlinearity under uniform lateral pressure with clamped and hinged edge constraints. The unsymmetrical laminated plate deflection is predicted for different thicknesses and also various pressures in different time steps and they are compared with elastic finite element results. As a main objective, the deflection results of viscoelastic laminated sector plate are obtained for various fiber volume fractions in the composite system.