Static and transient response of rectangular plates

Static and transient analysis of composite plates is presented using a recently proposed shear deformation theory. The dynamic response is obtained by employing the numerical time integration scheme due to Newmark. The results obtained by using the classical plate theory (CPT) and the Mindlintype shear deformation theory (SDT) are compared with those obtained by using the proposed theory. The comparison studies reveal that the linear stress distribution, as assumed in CPT and SDT, differs considerably from the predicted nonlinear distribution of the proposed theory.     

Assessment of shell theories for the static analysis of cross-ply laminated circular cylindrical shells

This paper examines the accuracy of classical shell theories (CST) according to Flugge, Sanders, Love and Donnell, with respect to the recently available three-dimensional elasticity solution, for cross-ply laminated circular cylindrical shells under static loads. Further, a study has also been made to examine to what extent incorporation of first order shear deformation (FSDT), in aforementioned shell theories, improves the results. In general, all the basic equations (for both CST and FSDT), of aforementioned shell theories, have been presented in a unified form using tracer coefficients. A Navier type solution has been used to analyse both a simply supported circular cylindrical shell of revolution and an all round simply supported circular cylindrical shell panel. A parametric study has been carried out keeping in view the lamination schemes and geometrical parameters of the shell. From the detailed comparisons of the results it has been shown that (i) Donnell's theory (CST and FSDT) could be in error for certain lamination schemes and geometrical parameters and (ii) improved results for stresses and displacements could be obtained by incorporating shear deformation on more accurate theory like Flugge (CST).     

Analysis of shearing effect on tunnel induced by load transfer along longitudinal direction

In order to analyze the behavior of load transfer mechanism of shield-constructed tunnel in longitudinal direction, tunnel is modeled as the cylindrical shell within elastic foundation (CSEF). By applying the theory of elastic cylindrical shell (ECS) with considering shear deformation and assumed displacement functions of trigonometric series, the distribution of stress and deformation in tunnel lining is obtained. In the solution, the stiffness of tunnel lining is decomposed into two components of circumferential and radial stiffness. The effects of both components on the behavior of deformation and internal forces of tunnel lining are discussed in details. By using the proposed solution, more reasonable results on the behavior of tunnel lining are obtained, e.g bending moment in tunnel cross section becomes smaller with the increase of the circumferential shear stiffness. The analytical results are verified by the results of 3D FEM analysis and field measured data. In accordance with the proposed analytical method, the tunnel lining in soft ground should be designed via considering the following aspects: (i) three dimensional effect of tunnel lining; (ii) relatively weaker shear stiffness in radial direction, and (iii) increase the circumferential shear resistance between rings.     

Developing an element free method for higher order shear deformation analysis of plates

A procedure is presented to eliminate transverse shear locking in analysis of laminated composite plates using Element Free Galerkin (EFG) method based on higher-order transverse shear deformation theory (HSDT). In the procedure, derivatives of the transverse displacement are introduced as independent variables. Thus, a formulation requiring C⁰ continuity shape functions for approximation is proposed for higher-order transverse shear deformation analysis of plates. Shear locking is avoided considering reduced integration for shear stiffness matrix; a method which is implemented in FEM. Moving Least Squares (MLS) method is utilized for shape functions and the penalty method is implemented to impose approximate boundary conditions. The present solutions are verified with other higher-order shear deformable studies. Moreover, a comparison between the present solutions with those obtained by EFG procedure based on First-order transverse Shear Deformation Theory (FSDT) is performed.     

基于简化修正压力场理论的钢筋混凝土柱荷载-变形分析

基于简化修正压力场理论对钢筋混凝土柱抗剪机理进行了分析,并考虑核心混凝土膨胀对箍筋抗剪承载力贡献的影响,计算了骨料咬合作用及受压区的抗剪承载力贡献,获得受拉区和受压区的抗剪强度,从而建立箍筋屈服后柱构件抗剪强度计算方法;结合传统截面纤维分析法,同时引入弯曲变形、剪切变形及滑移变形3种变形分量,在箍筋屈服前对柱构件进行抗弯分析,最终得出压弯剪作用下钢筋混凝土柱荷载-变形曲线,并与所收集的15个钢筋混凝土柱低周反复试验结果进行了对比。研究结果表明:采用该方法计算的荷载-变形曲线与试验骨架曲线吻合较好,对发生弯曲破坏、弯剪破坏及剪切破坏3种不同破坏类型的钢筋混凝土柱均有较好的分析效果,可用于压弯剪作用下钢筋混凝土柱的荷载-变形分析。     

砂土三维多重机构边界面模型

以土的临界状态和边界面塑性理论为基础,引入状态参数,考虑砂土的剪胀特性,提出一个新型三维多重机构边界面模型。模型将复杂的宏观变形行为分解为一个宏观体应变机构和一系列空间分布的虚拟一维微观剪切机构。每个微观剪切机构包含一个微观剪应力–应变关系和一个微观应力–剪胀关系。利用三轴压缩试验中的应力条件,建立典型宏微观参数之间的关系。模型包含13个参数,多数可通过具有明确物理意义的土性参数来确定。通过对砂土三轴压缩试验和空心圆柱扭剪试验结果的数值模拟,表明模型不但能够合理反映在排水或不排水条件下砂土的硬化及软化特性,而且能在不增加任何参数条件下预测应力主轴旋转产生的变形累积特性和应变增量主轴与应力主轴之间的非共轴特性。     

Shear strength prediction of reinforced concrete walls

Most of existing codes ignore the effect of arch action on shear strength of reinforced concrete (RC) walls, and it leads to more conservative results. A new model considering the influence of the truss and arch on shear strength of RC walls is proposed in this paper. The shear strength provided by the truss is obtained by the modified compression field theory, and the shear strength provided by the arch is obtained by the shear deformation coordination between the truss and arch, which has an upper bound value. Experimental data of 78 RC walls failed in shear are collected to evaluate the adequacy of the proposed method by comparing with the models of Hwang and Lee, Wood, ACI 318‐11,, EC8, MCBC‐04, and JGJ 3‐2010, respectively. The results show that the average value and coefficient of variation of the experimental‐to‐calculated strength ratios obtained by the proposed model are 1.01 and 0.23, which shows better accuracy and reliability. Therefore, the proposed model can predict the shear strength of RC walls failed in shear accurately.     

基于结构精细化模拟分析平台的弯剪纤维单元模型

为模拟钢筋混凝土柱在轴力、剪力和弯矩耦合作用下的非线性滞回特性,利用显式中心差分法,建立一种基于显式算法的弯剪纤维单元模型,并引入到结构精细化模拟分析（RSAPS）平台中。该模型基于Timoshenko梁理论,材料模型选用基于修正斜压场理论（MCFT）的二维钢筋混凝土本构模型。应用RSAPS平台分别模拟往复荷载作用下发生弯曲、弯剪和剪切破坏的钢筋混凝土柱的滞回性能,并将分析结果与试验和未考虑剪切变形的纤维单元模型模拟结果进行对比。结果表明：对于发生弯曲破坏的构件,由于剪切变形较小,未考虑剪切变形的纤维单元和弯剪纤维单元均可以较好地模拟构件的滞回性能;而对于发生弯剪破坏和剪切破坏的构件,采用未考虑剪切变形的纤维单元模型,会高估构件的初始刚度和耗能能力,也会高估其受剪承载力;而所提出的弯剪纤维单元模型能较好地模拟构件的刚度和承载力退化,同时,也能较好地模拟滞回曲线中的捏缩现象,模拟结果与试验结果吻合较好。     

中高层开洞剪力墙双肢变形特性分析的正交分解法

开洞剪力墙的双肢变形特性是进行抗震设计所要考虑的重要因素之一。在正交理论的变形分解基础上,实现对开洞剪力墙振型的精细识别,得到了振型相对变形分解图;进而,通过引入双肢系数,给出了开洞剪力墙振型双肢特性的量化判据;由于振型是结构完备的变形基,该方法可为剪力墙的刚度设计提供技术支持。对8层和16层钢筋混凝土开洞剪力墙试验模型的分析表明,在整体小开洞剪力墙和联肢剪力墙中间存在一种中间状态,该状态的剪力墙在横向静力作用下表现出整体变形特性,在水平地震作用下则可能表现为双肢变形特性,对此,在抗震设计中应引起足够的重视。     

Consideration of the problem of shearing and torsion of thin-walled beams with arbitrary cross-section

In structural analysis it is often necessary to determine the geometrical properties of cross-sectional areas. The location of the shear center is of greater importance for a thin-walled cross-section. The purpose of this paper is the computation of the shear center of arbitrary thin-walled cross-sections using the finite element method. The coupling problem of shearing and torsional deformation of thin-walled beams based on Saint Venant's theory is considered. This problem of coupled shearing and torsional deformation was analyzed using the finite element method in which the matrix of shear rigidity and torsional rigidity were determined. The shear center can be obtained by determining the coordinate axes so as to eliminate the nondiagonal terms. Then, applying the stiffness matrix of shear rigidity and torsional rigidity obtained in the above, the stiffness matrix of the space framework elements in which the shear deformation is taken into consideration is developed.     

形状优化的装配式剪切型金属阻尼器力学性能研究

为了解决剪切型金属阻尼器应力集中和焊接区的热应力影响问题，提高其耗能效率，提出一种采用等应力线优化形状的装配式剪切型金属阻尼器。根据弹塑性力学J2理论寻找在一定外力条件下的等应力线，以等应力线同时进入屈服为条件设定剪切型金属阻尼器耗能片形状，并进一步推导了供设计使用的阻尼器初始刚度与承载力的计算式；建立了阻尼器的精细有限元数值模型，以模拟其低周往复加载的力学性能，分析阻尼器的变形模式与耗能能力，并进行了4个阻尼器的拟静力试验研究。试验与数值分析结果表明：提出的阻尼器初始刚度与承载力计算式的计算值与数值分析和试验结果吻合较好；形状优化阻尼器具有良好的低周疲劳性能与稳定的耗能能力；与未优化阻尼器相比，形状优化剪切型金属阻尼器的塑性变形分布更加均匀，最大累积等效塑性应变明显减小；采用全螺栓连接，易于更换。     

筒中筒结构的简化计算

A.Coull用等代筒体法分析框筒结果表明:剪力滞后对框筒变形的影响较小,可以近似地按等代筒体,乘以剪力滞后影响系数来考虑。因此,在筒中筒结构中我们可以将外缘框筒作为具有弯曲及剪切变形的等代筒体,按与只考虑弯曲变形的内筒的形变协调条件,建立微分方程,解出筒中筒结构的侧移计算公式及内外筒的荷载分配计算公式。由此,用顶点位移法可求出筒中筒结构的主振周期及地震力。当作用于外筒上的荷载分布公式确定后,可由此导出应力调整函数S(z)的计算式。利用程序计算器,可方便地求出框筒梁柱中的内力。     

钢结构柱脚抗剪键抗剪承载力计算

为了确定钢结构柱脚抗剪键的抗剪承载力,分别以混凝土应变达到应力峰值应变和极限应变为抗剪屈服承载力和极限承载力的两种极限状态,选取混凝土应力-应变关系接近实际受力情况的非线性弹塑性模型,建立了考虑抗剪键剪切变形的Timoshenko梁平衡微分方程,采用Galerkin法求得抗剪键的变形曲线,进而推导了两种抗剪承载力的理论计算公式,提出了确定抗剪键埋深和截面规格的方法。研究表明：抗剪键的抗剪承载力和理论埋深取决于其材料截面特性及基础混凝土强度。研究同时表明,抗剪键埋深范围内混凝土压力方向不改变,对柱脚底板产生附加弯矩。采用有限元方法对比分析,算例结果验证了理论计算公式的正确性。图7表1参13     

钢箱梁非弹性剪滞建模

对钢箱梁中非弹性剪滞性能进行研究。带翼缘受弯构件中的剪滞效应经常被认为是不均匀的纵向变形和沿翼缘的正应力。弹性剪滞性能被广泛研究并在结构设计中给予考虑,然而对非弹性剪滞涉及较少。带翼缘受弯构件在其极限状态下可能会发生塑性变形,故采用基于最小功的方法来模拟非弹性剪滞性能。在非弹性剪滞模型中,有效模量采用公式表达,泊松比按塑性理论取值。通过两个钢箱梁的试验结果对该分析方法进行验证。经与试验数据对比后表明,所给出的变分法可以精确地得到钢箱梁的塑性正应变分布和变形。     

Longitudinal structural modelling of shield tunnels considering shearing dislocation between segmental rings

Shield tunnels in soft deposits are often subjected to differential settlement and longitudinal structural deformation during long-term operation. Since the shear stiffness in circumferential joints between rings is relatively low, shearing induced dislocation between segmental rings becomes a significant aspect of longitudinal deformation of tunnels. The longitudinal deformation mode comprises both rigid rotation of segmental rings (bending mode) and dislocation between rings (dislocation mode). The existing modelling method is usually based on Euler–Bernoulli beam theory, which only considers the bending effect and ignores the shearing deformation. This paper proposes a new longitudinal structural model to consider the shearing dislocation between rings. In the proposed model, the tunnel is simplified as a homogenous Timoshenko beam, and an equivalent shear stiffness is proposed to consider the influence of joints. Since Timoshenko beam theory considers both flexural deformation and shear deformation of the beam, it can describe the actual deformation mode of a tunnel reasonably. The proposed model is compared with the traditional Euler–Bernoulli beam model based on a field measured longitudinal deformation of a Shanghai metro tunnel. The results indicate that the traditional Euler–Bernoulli model overestimates the longitudinal internal forces of a tunnel. The proposed model based on Timoshenko beam theory predicts a smaller joint opening and a greater dislocation between rings than the Euler–Bernoulli beam model.     

Random response of antisymmetric angle-ply laminated plates

The random response of an antisymmetric angle-ply composite plate subjected to random lateral load on its surface is obtained. The first-order transverse shear deformation theory, involving five coupled partial differential equations, is used. To evaluate the effect of shear deformation, anisotropy and other problem parameters on the response, the numerical results obtained with this theory are compared with the results obtained by the classical plate theory. Significant differences are observed in the two sets of results obtained by the two theories especially for thick plates, thus demonstrating the importance of shear deformations and need for utilization of plate theories which properly account for such deformations.     

考虑腹板剪切变形及滑移的波形钢腹板梁理论模型

在采用栓钉等柔性剪力连接件的波形钢腹板组合梁中,由于波形钢腹板较大的剪切变形及双界面剪切滑移,平截面假定不再适用。为此,通过将波形钢腹板梁的弯曲分解为顶底板整体满足平截面假定的主弯曲和顶底板各自满足平截面假定的次弯曲,引入波形钢腹板的剪切变形协调条件和界面剪切滑移关系,推导了考虑波形钢腹板剪切变形及界面滑移的波形钢腹板梁弹性弯曲微分方程,利用给出的横隔板对次弯曲和滑移的约束边界条件,求得了简支波形钢腹板梁在不同荷载作用下的解析解,并采用有限元分析予以验证。在此基础上,分析了横隔板及滑移对梁体弯曲性能的影响。结果表明：横隔板约束对梁体变形影响很小,但会使其附近梁段顶底板出现应力集中;当界面剪切刚度系数大于0.9时,在高跨比1/20~1/10范围内,考虑滑移与不考虑滑移梁跨中挠度比小于1.05;界面剪切刚度系数越小,横隔板附近梁段顶底板应力集中越严重。     

T形截面短肢剪力墙剪滞效应及其影响

利用变分原理求解T形截面短肢剪力墙的剪力滞系数和构件变形,讨论不同几何参数和荷载形式对剪力滞效应及变形的影响。用有限元法对翼缘板的纵向应力分布情况进行分析,并与初等梁理论及变分原理的计算结果进行比较,揭示了剪力滞效应对构件侧移刚度的影响程度。     

基于颗粒物质热动力学理论的非饱和土热水力耦合模型研究

基于颗粒物质热动力学理论和混合物理论,结合改进的土水特征曲线(SWCC)模型,考虑温度和饱和度变化引发的颗粒层次能量耗散,提出了一个非饱和土的热水力耦合模型。该模型引入颗粒熵和颗粒温度的概念,通过构建热力学恒等式得出非饱和土非弹性变形的本构关系,并通过迁移系数和能量函数模型将非饱和土体的耗散机制与宏观的物理力学行为建立联系。基于该理论模型,研究了非饱和土的热水力耦合问题,通过模拟结果与试验数据的对比,证实了模型的有效性。模拟结果表明,模型具有描述非饱和土在不同温度和吸力下的固结和剪切特性以及非等温条件下的热体应变特性的能力。     

“12·20”深圳滑坡动态模拟

将深圳滑坡堆填渣土近似视为饱和土,考虑快速填筑效应,假定填筑高度在填筑过程中随时间线性增大,由一维固结理论推导出由于快速加载引起的土体内超静孔隙水压力分布,同时根据修正剑桥模型考虑填土剪缩效应对超静孔隙水压力的影响。总孔隙水压力为静水压力、快速加载和剪缩引起的超静孔隙水压力三部分之和,从而由总应力得到余泥渣土失稳时的有效应力,进而由有效内摩擦角得到其剪切强度。再将快速滑出过程看作不排水条件下的破坏,利用推导出的填土不排水强度,采用可以有效模拟超大变形问题的物质点法对深圳滑坡的全过程进行了动态模拟,并研究了滑坡体对建筑物的破坏作用。模拟结果表明该模型能较好解释深圳滑坡中滑动土体高速远程输送特征。