腹筋对连续深梁剪切破坏影响的有限元分析

我国现行混凝土结构设计规范关于腹筋对深梁抗剪承载力影响的考虑,主要基于简支深梁的试验数据和计算模型,相关规定对于连续深梁的适用性有待验证。腹筋对连续深梁抗剪性能的影响机理十分复杂,系统的试验研究较少,试验结果比较分散。为了弥补试验研究的不足,采用非线性有限元方法模拟钢筋混凝土连续深梁的受力性能。利用已有的试验数据,验证了基于ATENA软件建立的有限元模型,并以此为基础,对以腹筋配筋率和剪跨比为变量的64根连续深梁进行分析,研究腹筋对连续深梁受剪承载力的影响。有限元分析结果与规范公式和压杆-拉杆模型(STM)及最新提出的三参数机动法(3PKT)的比较表明,中国规范高估了水平腹筋对构件受剪承载力的贡献,STM和3PKT方法也存在各自的不足。     

Bending analysis of functionally graded CNT reinforced doubly curved singly ruled truncated rhombic cone

The bending analysis of functionally graded carbon nanotube (CNT) reinforced doubly curved singly ruled truncated rhombic cone is investigated. In this study, a simple C⁰ isoparametric finite element formulation based on third order shear deformation theory is presented. To characterize the membrane-flexure behavior observed in a CNT reinforced truncated rhombic cone, a displacement field involving higher-order terms in in-plane fields is considered. The proposed kinematics field incorporates for transverse shear deformation and nonlinear variation of the in-plane displacement field through the thickness to predict the overall response of the CNT reinforced truncated rhombic cone in an accurate sense. The material properties of the CNT reinforced truncated rhombic cone are estimated according to the rule of mixture. The present model eliminates the need of shear correction factor and imposed zero-transverse shear strain at upper and lower surface of the truncated rhombic cone. The new feature in present model is simultaneous inclusion of twist curvature in strain field as well as curvature in displacement field that makes it suitable for moderately thick and deep truncated rhombic cone. The proposed new mathematical model is implemented in finite element code written in FORTRAN. The proposed model has been validated with analytical, experimental, and finite element results from the literature. This is first attempt to study bending response of CNT reinforced doubly curved singly ruled truncated rhombic cone. The effect of CNT distribution, boundary condition, loading pattern, and other geometric parameters are also examined.     

Prediction of wheel-soil interaction and performance using the finite element method

In this experimental-analytical study of wheel-soil interaction, a technique based on the finite element method is used for predicting continuous wheel performance and subsoil response behaviour. The evaluation of wheel-soil interaction performance at any degree of slip is performed using energy principles. The analytical technique utilizes experimentally determined wheel-soil particle path as displacement input for load simulation to predict the soil response beneath the wheel.

An incremental loading approach is adopted to satisfy as closely as possible the soil loading path. The solution requires initial conditions which establish the soil at zero energy level (no stress history) and proceeds to stationary wheel positions with wheel-soil penetration equal to its dynamic sinkage. The method of analysis then proceeds to the steady-state wheel travel mode. The predicted drawbar pulls and subsoil behaviour results are presented and shown to compare well with the experimentally measured values.     

Multiphase approach as a generalized homogenization procedure for modelling the macroscopic behaviour of soils reinforced by linear inclusions

This paper examines the possibility of applying a homogenization procedure to soils reinforced by linear inclusions, regarded as elastic periodic composites for which scale effects have to be considered, as shown by the preliminary numerical analysis of two illustrative problems. A so-called multiphase model is developed for this purpose, aimed at improving the classical homogenization method on two decisive points. First, by modelling the reinforced soil at the macroscopic scale as the superposition of two mutually interacting continuous phases, describing the soil and the reinforcement network, respectively. Second, by assuming that the reinforcements display a shear and flexural behaviour, in addition to the axial one, so that the corresponding phase may be described as a micropolar continuum. Its is shown that such a multiphase approach can be interpreted as an extension of the homogenization procedure, making it thus possible to capture the previously mentioned scale effects, provided that the constitutive parameters of the model can be properly identified from the reinforced soil characteristics.     

Analysis of Cracks and Deformations in a Full Scale Reinforced Concrete Beam Using a Digital Image Correlation Technique

This paper deals with the use of a digital image correlation technique for the determination of the actual mechanical behaviour of a full scale reinforced concrete beam after 25 years of service in a severe industrial environment. The objective is to investigate the influence of the service conditions on the cracking process and the flexural behaviour of the beam. For this purpose, one beam is removed from the existing structure before being tested in four point bending in laboratory. Displacement fields derived from digital images captured during five loading cycles are analysed in terms of crack detection and measurement, beam deflection and curvature. Owing to its good resolution, the method proves suitable for early crack detection and measurement. A comparison between experimental results and theoretical values derived from Eurocode 2 design code in the serviceability state suggests the existence of a longitudinal compressive force in the beam. A complementary analysis confirms the validity of this hypothesis. It is concluded that the cracking and the flexural behaviour of the tested beam are significantly affected by the existence of an initial compressive stress, which is possibly resulting from a swelling of the concrete due to long term exposure to wet atmosphere and elevated temperature.     

以DIASS程序为基础的饱和土与防护结构相互作用动力分析研究

介绍了新开发的防护结构动力有限元分析程序DIASS系统。该系统装有空爆冲击波荷载数值自动生成器,并可将基础土壤模拟为饱和多孔介质模型,采取多重子结构技术进行结构与土体相互作用的动力分析。文中利用该程序系统进行数值试验,给出若干初步结论。     

A thermodynamic finite-strain model for pseudoelastic shape memory alloys

A thermodynamic finite-strain model describing the pseudoelastic response of shape memory alloys is proposed. The model is based on a self-consistent Eulerian theory of finite deformations using the logarithmic rate. Purely elastic material response is derived from a hyperelastic potential. The mass fraction of martensite is introduced as internal state variable to indicate the thermomechanical state of the phase transforming material. The evolution of martensite is governed by a kinetic law which is derived from the Helmholtz free energy of the two-phase solid and takes the heat generated during phase transition into account. The material model is implemented into a finite element code in an updated Lagrangian scheme and calibrated to experimental data. Simulations under different loading conditions illustrate the characteristics of the model.     

复合地基承载特性的弹塑性分析

对桩及承台采用线弹性有限元模型,对承台下桩周土采用弹塑性有限元模型,对群桩以外的土体采用线弹性无限元模型,在桩土接触面上设置接触面单元,利用三维弹塑性有限元对桩%D土%D承台相互作用进行了分析。得出了如下结论 :承台下桩顶反力总体表现出角桩最大,边桩次之,中桩最小的分布规律,随着作用在承台上的荷载增大,桩顶反力趋于均匀分布,承台下桩侧摩阻力是由桩端向桩顶逐渐发展的,承台对桩上部侧摩擦阻力存在“削弱作用”。为了验证本文方法的可行性,对承台下有九桩的情况进行了静载试验,将试验结果与本文计算结果进行了比较。     

Nonlinear transient response of strain rate dependent composite laminated plates using multiscale simulation

The effects of strain rate dependency and inelasticity on the transient responses of composite laminated plates are investigated. A micromechanics model which accounts for the transverse shear stress effect, the effect of strain rate dependency and the effect of inelasticity is used for analyzing the mechanical responses of the fiber and matrix constituents. The accuracy of the micromechanics model under transverse shear loading is verified by comparing the results with those obtained using a general purpose finite element code. A higher order laminated plate theory is extended to capture the inelastic deformations of the composite plate and is implemented using the finite element technique. A complete micro–macro numerical procedure is developed to model the strain rate dependent behavior of inelastic composite laminates by implementing the micromechanics model into the finite element model. Parametric studies of the transient responses of composite plates are conduced. The effects of geometry, ply stacking sequence, material models, boundary conditions and loadings are investigated. The results show that the strain rate dependency and inelasticity influence the transient responses of composite plates via two significantly different mechanisms.     

A refined finite element method for bending analysis of laminated plates integrated with piezoelectric fiber-reinforced composite actuators

This research presents a finite element formulation based on four-variable refined plate theory for bending analysis of cross-ply and angle-ply laminated composite plates integrated with a piezoelectric fiber-reinforced composite actuator under electromechanical loading. The four-variable refined plate theory is a simple and efficient higher-order shear deformation theory, which predicts parabolic variation of transverse shear stresses across the plate thickness and satisfies zero traction conditions on the plate free surfaces. The weak form of governing equations is derived using the principle of minimum potential energy, and a 4-node non-conforming rectangular plate element with 8 degrees of freedom per node is introduced for discretizing the domain. Several benchmark problems are solved by the developed MATLAB code and the obtained results are compared with those from exact and other numerical solutions, showing good agreement.     

Non-linear finite element analysis of flexible risers in presence of buoyancy force and seabed interaction boundary condition

A non-linear finite element static analysis for flexible risers with large displacements is presented using a four-node pipe elbow element with 24 degrees of freedom. A pipe–soil interaction model is used to identify seabed boundary condition. The effects of buoyancy force as well as steady-state current loading are considered in the finite element solution for riser structures response. In fact considering buoyancy force among with current loading and seabed interaction boundary condition in this paper leads to a particular formulation. The resulting formulation has been implemented in a finite element code which is subsequently used to model and analyze some typical riser configurations. The results of some sample solutions are given to illustrate the accuracy and capability of the formulation.     

The Finite Element Analysis of Interaction Problem Through Water,Soil, Balloon and Pile

This paper presents the finite element analysis of an interaction problem involving water, soil, balloon and pile. A building with friction piles is considered, and balloons are introduced to the top of piles. To control the vertical displacement of the building, water is injected into or removed from the balloons. The two-dimensional incompressible Navier-Stokes equation is introduced, and the ALE (Arbitrary Lagrangian Eulerian) method is applied to the water flow analysis. The FS (Fractional Step) method is also applied in the finite element formulation. The soil, which is assumed as a linear elastic body, is subjected to the deformation analysis. The balloon and pile are assumed as a linear elastic truss and a rigid frame, and the deformation analysis is also performed. All the components are discretized by the finite element method in space and are interactively solved by taking into account continuity conditions of traction and displacement.     

二维有限区域饱和软土Biot固结的数值模拟

针对二维有限矩形区域饱和软土固结问题,选取四种不同边界条件组合,利用数值模拟方法研究了在上表面剪切载荷作用下土体沉降变形的特征和规律。结果表明:在剪切载荷单独作用下,土体位移以水平位移为主,同时竖向位移也客观存在。这反映了土体固结过程中流固耦合的物理现象。土层最终变形量(沉降和水平位移)由剪切载荷与土体物性决定,与边界透水性无关;边界条件对土体的变形模式有着决定性影响。剪切载荷作用、法向载荷作用及二者联合作用的计算结果对比表明:虽然软土Biot固结是复杂的流固耦合过程,但在这个过程中载荷叠加原理依然成立。     

土工格栅加强下有砟铁路道床动力特性的离散元-有限元耦合分析

本文提出了一种可用于分析土工格栅与道砟颗粒间相互作用的离散元-有限元耦合方法。道砟颗粒采用镶嵌单元模拟,土工格栅采用梁单元计算,并在接触面上实现了离散元和有限元域间力学参数的传递。通过循环载荷作用下的计算,对比分析了土工格栅对道砟颗粒的加固性能。通过加筋后道砟颗粒的直剪试验进一步揭示了土工格栅加固作用的内在机理。结果表明：土工格栅可有效地降低有砟道床横向位移以及顶部沉降量,加筋后道砟材料的内聚力和摩擦角都有所提高。由此可见,土工格栅能够增加道砟颗粒间的自锁作用,提高道砟材料的强度,并有效地阻止剪切带从上部道砟箱向下部道砟箱贯穿。     

碳纤维布加固钢筋混凝土梁受力性能的试验研究

通过对8根矩形截面钢筋混凝土梁的静力加载试验,研究了抗弯和抗剪两种加固方式对钢筋混凝土梁的破坏形态和力学性能的影响,对比分析了碳纤维加固率、试验梁的状态、混凝土强度对加固效果的影响。结果表明：经碳纤维抗弯哥口抗剪加固后加圉梁相应的力学性能指标值明显提高;混凝土裂缝扩展得到了有效延缓,加固效果明显;抗弯加固后可显著提高混凝土梁的承载力和延性,但提高程度并不与加固率成正比;预裂粱抗弯加固后承载力和延性得到提高,但与其相同加固参数的梁相比,其承载力和延性有所降低;抗剪加固时混凝土强度越高,加固后混凝土梁的承载力和变形能力提高幅度越大,其中混凝土梁的变形能力受混凝土强度的影响较大。最后,对加固梁的极限承载力进行了理论分析与计算,建立了实用的理论计算公式,计算结果与试验结果吻合较好。     

轻质金属点阵夹层板热屈曲临界温度分析

本文针对均匀温度场下四边简支和四边固支金属点阵夹层板的临界热屈曲温度进行了求解和参数影响分析。将点阵夹芯等效为均匀连续体,并且将夹层板的剪切刚度近似为点阵夹芯的抗剪切刚度,忽略夹芯的抗弯刚度且认为夹层板主要由面板来提供抗弯刚度。对于无法获得解析解的四边固支条件,通过对未知变量进行双傅里叶展开的方法求解了Ressiner夹层板模型的临界屈曲温度,理论分析结果与有限元计算结果吻合良好。进一步分析了不同边界条件、点阵胞元构型、点阵材料相对密度、面板厚度等对临界屈曲温度的影响规律。     

Analysis of a high intensity shear zone between overlapping fiber ends in a polymer matrix composite

The formation of high intensity shear zones in a glass fiber reinforced thermoplast is studied numerically. The thermoplast is characterized by a finite strain elastic-viscoplastic constitutive relation and the calculations are carried out using a dynamic finite element program where plane strain conditions are assumed to prevail in the direction of the thickness. Different ratios of the elongation strain and the transverse strain are studied to consider the effect of different levels of stress triaxiality and the effect of these states on the shear zone development and emerging strain and stress concentrations. Comparing a case of embedded infinitely stiff fibers to a case with glass fiber reinforcement shows little difference thus illustrating that the glass fibers act approximately as infinitely stiff. Fiber spacing and fiber width are shown to influence the shear zones and the stress fields that develop as the highly deformed region approaches the limit resulting from network stiffening in the polymer. A simple analysis assuming periodicity is included in order to study the mechanical behaviour of the polymer matrix between fiber ends with long overlap.     

波流场中的桩柱结构地震反应研究

采用理论分析及有限元模拟的方法, 对波流场中桩柱结构的地震动力反应进行了研究. 除考虑波流场作用在桩柱上的波流力和动水压力外, 根据模型试验结果认为还需考虑作用在 桩柱上的涡振横向力. 通过地震作用下波流场中四桩平台的有限元模拟计算, 发现 水中地 震放大了桩柱结构的动力反应; 波流力和涡振横向力共同作用导致桩的相对位移、剪力及弯 矩值大幅提高, 但是对桩身加速度影响较小; 桩底部位易于发生地震破坏.     

不均匀土中有限长桩的横向瞬态波动

将Timoshenko梁模型引入到弹性地基粱中,土体对桩的作用用连续分布的弹簧来模拟,基于回传射线矩阵法,研究了桩顶受到横向冲击荷载作用下有限长桩的横向瞬态波动．经参数分析表明：土体刚度比对上软下硬、上硬下软两层地基中的有限长桩剪力波和弯矩波影响很大;从挠曲波曲线中难以辨别有无软硬夹层．