纤维墙元模型在剪力墙结构非线性分析中的应用

钢筋混凝土剪力墙是目前高层与超高层建筑中最主要的抗侧力构件，本文在对已有的微观及宏观计算模型进行比较的基础上，基于纤维模型概念，建立了便于高层剪力墙结构非线性分析应用的纤维墙元模型，即由承受轴力及弯矩的纤维子单元与承受剪切变形的剪切子单元相合成的墙元计算模型；同时，对该模型中剪切子单元高度的取值进行了分析，明确了其物理含义；推导了单元的刚度矩阵，并分别建立了纤维子单元及剪切子单元的骨架曲线及滞回规则。另外，应用该计算单元模型，对一栋40层框架剪力墙结构进行了非线性时程分析，计算结果与相应模型的振动台试验结果进行了对比，比较结果表明两者在结构动力特性，位移响应方面等均吻合较好，验证了该计算单元模型的准确性与有效性，可为推广使用提供参考。     

L形柱在反复荷载作用下的非线性分析

在平截面假定的前提下,将钢筋混凝土L形柱划分为两端弹塑性区、中间为弹性区的三分段杆单元模型。将应用于平面剪力墙的多垂直杆单元模型拓展为空间的多垂直杆单元模型,推导了拓展的多垂直杆单元模型单元刚度矩阵,经静力凝聚为三分段杆单元模型刚度矩阵,该单元模型可用于各种截面形式的钢筋混凝土异形柱、剪力墙墙肢和梁的非线性分析,计算工作量较小。讨论了目前垂直杆的轴向拉压滞回模型,提出了轴向拉压滞回曲线考虑骨架曲线下降段的简化处理方法。最后提供了算例,结果表明本文方法计算的滞回轴线与在反复加载下L形柱的试验结果吻合较好。     

T形短肢剪力墙静力性能有限元仿真分析

利用有限元分析软件ANSYS,首先采用其中三维实体单元SOLID65建立了T形短肢剪力墙有限元分析模型,从弹性到混凝土开裂直至破坏的全过程进行了仿真试验分析。分析了影响短肢剪力墙受力的几种因素:混凝土强度等级、配筋率、轴压比、墙肢截面高厚比对短肢剪力墙承载能力、变形能力及延性的影响,剖析了短肢剪力墙破坏过程及其原因。比较真实的反映了短肢剪力墙在轴压力和逐步加载侧向力共同作用下的响应。试验结果表明:增加混凝土等级和轴压比能提高试件的开裂、屈服和极限荷载,但应综合考虑其与变形能力、延性的关系。截面配筋率具有其特殊性,配筋率在1.4%¹.6%之间时试件的承载能力、变形能力及延性较好。墙肢截面高厚比是不稳定因素但在高厚比为6.5⁷.1时,延性及变形能力较强。     

钢筋混凝土联肢剪力墙的非线性有限元分析

本文推导了一种带转动自由度的四节点狭长矩形墙板单元与一种分层高精度二节点厚梁单元,二者的组合既合理地描述了联肢剪力墙墙体与连梁的连续性,又具有计算精度高,计算量少的特点。为分析钢筋混凝土的非线性,本文采用应变硬化的弹塑性应力应变关系描述受压混凝土及钢筋,用线弹性应力应变关系描述受拉混凝土,混凝土开裂后的非线性现象则以一些经验公式给予反映。算例表明,本文建立的有限元计算模型用于钢筋混凝土联肢剪力墙的加载全过程分析是合理的,并且计算效率高。     

钢板墙-双肢C型钢框架简化模型

采用试验与有限元相结合的方法分析了钢板墙-双肢C型钢框架在低周反复荷载作用下的力学性能。在此基础上提出了一种构造简单、力学性能良好的四拉杆等效模型(FSEM)。通过FSEM模型分析了柱刚度系数、钢板墙高厚比和钢板墙高宽比,并与传统有限元模型结果进行了对比。结果表明,FSEM模型精度较高,静力计算时与传统壳单元模型的误差在10%以内,可以在设计中简化计算。提出了FSEM模型等效拉杆的倾角、截面面积计算公式,并建议该类框架钢板墙高厚比取600~1000,高宽比取0.5~1.0,柱刚度系数取79.6~99.5,为实际工程中的设计计算提供参考。     

高层建筑双肢剪力墙的简化计算

本文由基本假定出发,运用结构力学的单位力法和数学的差分法知识,建立了双肢剪力墙连梁跨中的变形协调条件及连梁跨中剪力的矩阵表达式;并推导出双肢墙顶点水平位移和层间水平位移的计算表达式,该法的计算值与实测值符合较好.     

T形RAC短肢剪力墙抗震性能试验与极限承载力分析

通过对4个缩尺比例为1∶2的不同再生粗骨料取代率、不同轴压比的T形再生混凝土(RAC)短肢剪力墙结构模型进行低周反复荷载作用下的抗震性能试验,分析试验所得模型破坏形态、滞回曲线、正负向特征荷载的变化规律。结果表明,T形RAC短肢剪力墙具有良好的抗震性能;同时,随着再生粗骨料取代率的增加,滞回性能等指标逐渐增强,而随着轴压比的增大,各指标逐渐减小。最后,通过试验结果分析,建立了T形RAC短肢剪力墙正截面极限承载力计算公式,并在此基础之上推导了其水平极限承载力计算公式。利用所建公式对4个模型水平极限承载力进行计算,所得结果与试验结果基本吻合,平均误差仅为9.45%。上述结果表明:该公式能够应用于实际T形RAC短肢剪力墙的设计计算之中。     

钢筋混凝土剪力墙单元非线性分析模型及其应用

本文简要评述了几种常见的钢筋混凝土剪力墙非线性宏观单元模型后，着重对多垂直杆剪力墙非线性单元模型的几个重要问题如剪力变形的考虑方法，单元刚度矩阵的形式，垂直拉压杆及剪切弹簧的恢复力模型等进行了探讨与改进，最后给出了一个算例，并与试验结果比较，表明非线性宏观墙单元模型具有较好的计算精度。     

一种新的墙单元

本文提出了一种新的空间墙单元模型，这种墙单元把土建中常用的剪力墙作为它的一种特殊情形．本文基于四边形单元所提出的墙单元在平面内是一块膜，它除面内的两个平动自由度外还具有绕平面转动的自由度；平面外是一块弯曲板．因而它是膜和板的一个组合，它的每个节点具有空间的全部六个自由度．由于考虑了空间墙平面内和平面外的刚度，因此这种新的墙单元能够直接与三维框架的梁、柱单元连接．它也能很容易地处理墙的空间变形。     

高效的三维曲梁单元

三维井眼中延伸数千米的三维细长圆截面钢钻柱应力分析问题是一个复杂的力学问题，通常使用有限元数值分析方法对其进行受力分析。而在进行有限元分析时，现有的圆弧曲粱单元和空间直粱单元在几何上都不能很好地模拟三维曲线形状的钻柱。为了确保计算精度．其单元划分势必不能过大，结果是计算时间长，收敛性差。为了解决这一问题，显然必须构建一种新的较有效的曲梁单元。基于自然坐标系，依据圆截面空间曲粱单元节点有6个自由度——3个线位移和3个角位移，利用包含全部刚体位移模式和常应变的形函数，忽略剪切变形，假设变形后的梁轴线的弯曲曲率改变为线性变化，建立起了保证收敛性的具有12个自由度的有初始曲率和挠率的圆截面空间曲梁的有限元模型。为了证明给出的有限元模型的高效性，分析了几个静态问题，并与现有文献中的解析解或数值结果进行了比较。基于所给出的结果，可望该有限元模型可以作为分析三维空间曲粱结构的有效工具。     

Free vibration of axially loaded thin-walled composite Timoshenko beams

Based on shear-deformable beam theory, free vibration of thin-walled composite Timoshenko beams with arbitrary layups under a constant axial force is presented. This model accounts for all the structural coupling coming from material anisotropy. Governing equations for flexural-torsional-shearing coupled vibrations are derived from Hamilton’s principle. The resulting coupling is referred to as sixfold coupled vibrations. A displacement-based one-dimensional finite element model is developed to solve the problem. Numerical results are obtained for thin-walled composite beams to investigate the effects of shear deformation, axial force, fiber angle, modulus ratio on the natural frequencies, corresponding vibration mode shapes and load–frequency interaction curves.     

A new super convergent thin walled composite beam element for analysis of box beam structures

In this paper, a new composite thin wall beam element of arbitrary cross-section with open or closed contour is developed. The formulation incorporates the effect of elastic coupling, restrained warping, transverse shear deformation associated with thin walled composite structures. A first order shear deformation theory is considered with the beam deformation expressed in terms of axial, spanwise and chordwise bending, corresponding shears and twist. The formulated locking free element uses higher order interpolating polynomial obtained by solving static part of the coupled governing differential equations. The formulated element has super convergent properties as it gives the exact elemental stiffness matrix. Static and free vibration analyses are performed for various beam configuration and compared with experimental and numerical results available in current literature. Good correlation is observed in all cases with extremely small system size. The formulated element is used to study the wave propagation behavior in box beams subjected to high frequency loading such as impact. Simultaneous existence of various propagating modes are graphically captured. Here the effect of transverse shear on wave propagation characteristics in axial and transverse directions are investigated for different ply layup sequences.     

压电层合梁静动力学分析的高精度梁单元

给出了一个对复合材料压电层合梁进行数值分析的高精度压电层合梁单元。基于Shi三阶剪切变形板理论的位移场和Layer-wise理论的电势场,用力-电耦合的变分原理及Hamilton原理推导了压电层合梁单元列式。采用拟协调元方法推导了一个可显式给出单元刚度矩阵的两节点压电层合梁单元,并应用于压电层合梁的力-电耦合弯曲和自由振动分析。计算结果表明,该梁单元给出的梁挠度和固有频率与解析解吻合良好,并优于其它梁单元的计算结果,说明了本文所给压电层合梁单元的可靠性和准确性。研究结果可为力-电耦合作用下压电层合梁的力学分析提供一个简单、精确且高效的压电层合梁单元。     

A new finite element of spatial thin-walled beams

Based on the theories of Timoshenko＇s beams and Vlasov＇s thin-walled members, a new spatial thin-walled beam element with an interior node is developed. By independently interpolating bending angles and warp, factors such as transverse shear deformation, torsional shear deformation and their Coupling, coupling of flexure and torsion, and second shear stress are considered. According to the generalized variational theory of Hellinger-Reissner, the element stiffness matrix is derived. Examples show that the developed model is accurate and can be applied in the finite element analysis of thinwalled structures.     

Axial-flexural coupled vibration and buckling of composite beams using sinusoidal shear deformation theory

A finite element model based on sinusoidal shear deformation theory is developed to study vibration and buckling analysis of composite beams with arbitrary lay-ups. This theory satisfies the zero traction boundary conditions on the top and bottom surfaces of beam without using shear correction factors. Besides, it has strong similarity with Euler–Bernoulli beam theory in some aspects such as governing equations, boundary conditions, and stress resultant expressions. By using Hamilton’s principle, governing equations of motion are derived. A displacement-based one-dimensional finite element model is developed to solve the problem. Numerical results for cross-ply and angle-ply composite beams are obtained as special cases and are compared with other solutions available in the literature. A variety of parametric studies are conducted to demonstrate the effect of fiber orientation and modulus ratio on the natural frequencies, critical buckling loads, and load-frequency curves as well as corresponding mode shapes of composite beams.     

Geometrical nonlinear analysis of thin-walled composite beams using finite element method based on first order shear deformation theory

Based on a seven-degree-of-freedom shear deformable beam model, a geometrical nonlinear analysis of thin-walled composite beams with arbitrary lay-ups under various types of loads is presented. This model accounts for all the structural coupling coming from both material anisotropy and geometric nonlinearity. The general nonlinear governing equations are derived and solved by means of an incremental Newton–Raphson method. A displacement-based one-dimensional finite element model that accounts for the geometric nonlinearity in the von Kármán sense is developed to solve the problem. Numerical results are obtained for thin-walled composite beam under vertical load to investigate the effects of fiber orientation, geometric nonlinearity, and shear deformation on the axial–flexural–torsional response.     

Static and vibration analysis of functionally graded beams using refined shear deformation theory

Static and vibration analysis of functionally graded beams using refined shear deformation theory is presented. The developed theory, which does not require shear correction factor, accounts for shear deformation effect and coupling coming from the material anisotropy. Governing equations of motion are derived from the Hamilton’s principle. The resulting coupling is referred to as triply coupled axial-flexural response. A two-noded Hermite-cubic element with five degree-of-freedom per node is developed to solve the problem. Numerical results are obtained for functionally graded beams with simply-supported, cantilever-free and clamped-clamped boundary conditions to investigate effects of the power-law exponent and modulus ratio on the displacements, natural frequencies and corresponding mode shapes.     

Contact dynamics of elasto-plastic thin beams simulated via absolute nodal coordinate formulation

Under the frame of multibody dynamics, the contact dynamics of elasto-plastic spatial thin beams is numerically studied by using the spatial thin beam elements of absolute nodal coordinate formulation (ANCF). The inter-nal force of the elasto-plastic spatial thin beam element is derived under the assumption that the plastic strain of the beam element depends only on its longitudinal deformation. A new body-fixed local coordinate system is introduced into the spatial thin beam element of ANCF for efficient con-tact detection in the contact dynamics simulation. The linear isotropic hardening constitutive law is used to describe the elasto-plastic deformation of beam material, and the classical return mapping algorithm is adopted to evaluate the plastic strains. A multi-zone contact approach of thin beams previ-ously proposed by the authors is also introduced to detect the multiple contact zones of beams accurately, and the penalty method is used to compute the normal contact force of thin beams in contact. Four numerical examples are given to demonstrate the applicability and effectiveness of the pro-posed elasto-plastic spatial thin beam element of ANCF for flexible multibody system dynamics.     

Shear deformable finite beam elements for composite box beams

The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated composite box beams is presented by taking into account all the structural couplings coming from the material anisotropy and the shear deformation effects. The current composite beam includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Seven governing equations are derived for the coupled axial-flexural-torsional-shearing buckling based on the principle of minimum total potential energy. Based on the present analytical model, three different types of finite composite beam elements, namely, linear, quadratic and cubic elements are developed to analyze the flexural, torsional, and buckling problems. In order to demonstrate the accuracy and superiority of the beam theory and the finite beam elements developed by this study,numerical solutions are presented and compared with the results obtained by other researchers and the detailed threedimensional analysis results using the shell elements of ABAQUS. Especially, the influences of the modulus ratio and the simplified assumptions in stress–strain relations on the deflection, twisting angle, and critical buckling loads of composite box beams are investigated.