混凝土弹塑性分析的新模型

针对混凝土弹塑性分析的平面应力问题和空间问题进行了分析,基于等效外力下的变形相同,提出了一个桁架单元新模型,并给出了实例验证,与实体单元的计算结果吻合良好。     

基于固体新单元模型分析理想弹塑性问题

基于一种固体新单元模型来分析固体受外力作用而发生的位移、应力和应变,并将新单元模型推广到理想弹塑性问题,通过具体算例的分析可以发现新单元法的计算精度良好,值得推广。     

弹塑性固体的新单元模型

根据在等效外力下桁架单元与正六面体单元的剪切、受拉、受压的应力应变曲线相同,建立了一个新单元模型,并求解了弹塑性力学的计算问题,其结果与其他方法计算结果吻合良好。     

Q460C高强钢材断裂韧性的弹塑性有限元分析

应用ANSYS软件对Q460C高强钢材标准三点弯试样断裂韧性进行弹塑性数值模拟,验证高强钢材常温下的裂纹敏感性。采用实体单元SOLID95计算刀口张开位移、三向应力分布以及裂纹尖端张开位移CTOD值,表明沿试样厚度方向,CTOD值变化较小,靠近裂纹尖端呈三向拉应力状态,偏离尖端一定距离呈复杂的应力状态,且复杂应力较大限制了裂纹尖端的塑性发展;不考虑低温影响因素时,缺陷对Q460C钢材的影响较大,当裂纹塑性发展后,Q460C钢材表现为较大的缺陷敏感性。     

铁路钢轨钢材三点弯曲试样的弹塑性有限元分析

对铁路钢轨钢材标准三点弯曲试样的弹塑性断裂性能进行了系统研究与分析。通过有限元计算结果与试验结果进行对比,验证了钢轨钢材的脆性破坏特征。采用普通单元和奇异单元的网格计算应力和位移进行了分析。并对裂纹尖端CTOD值进行了计算分析,CTOD值沿试样厚度方向的变化很小,裂纹尖端始终处于三向拉伸应力状态。而三向拉应力状态将使裂纹尖端处的塑性变形受到很大限制,破坏时的塑性变形很小,更容易发生脆性破坏。     

不同强度钢材对钢管拱桁架动力破坏的影响

以跨度为180 m、矢跨比为0.2的三心圆钢管拱桁架结构为研究对象,采用有限元分析软件SAP2000对选用Q345、Q390和Q420三种不同强度钢材的拱桁架进行动力弹塑性分析,分析表明,随着钢材强度的提高,钢管拱桁架用钢量逐渐减少,而其弹塑性界限加速度峰值和破坏界限加速度峰值显著增大,说明采用高强度钢材可显著提高结构的抗震水平。     

广州市文学创作中心工程静力弹塑性分析

广州市文学创作中心工程采用了跨度为36m的双跨混凝土桁架作为主要受力构件.本文对该大跨度桁架结构进行了罕遇地震作用下的静力弹塑性分析.分析结果表明,该大跨度桁架结构在罕遇地震下具有较好的延性.     

基于土体弹塑性理论的复合桩基附加应力分析

在考虑土的弹塑性及桩土接触特性的基础上,建立了复合桩基三维有限元模型,通过系统计算,绘出了在桩长L、桩径d及桩间距S条件下复合桩基土体附加应力的等值线变化图,对复合桩基附加应力的变化趋势进行了分析.     

钢筋混凝土平面等效桁架模型

针对钢筋混凝土结构有限元分析模型复杂性和难以确定的断裂损伤关系,提出了一种简便的钢筋混凝土有限元模型——平面等效桁架模型。通过RC结构平面应力单元和平面等效桁架单元在同样的节点荷载作用下的位移等效,分析了桁架单元中各桁架杆件的初始等效轴向刚度、等效截面积和等效弹性模量。借鉴有限元求解模式,建立RC平面桁架单元的单元刚度矩阵、应变矩阵和轴力矩阵,进而得出RC平面等效桁架整体式模型和相应的破坏准则。最后,用可视化的VISUAL BASIC语言编制程序计算了Scordelies和Bresler试验梁,理论分析和计算结果表明,对平面应力(应变)问题。用此单元达到简化计算模型,通过一维桁架杆件的开裂或压碎方便模拟构件裂缝的发生和延伸和结构刚度的退化,并有较好的计算精度。     

三维空间桁架弹塑性动力分析

结合实例,采用SAP2000软件分析三维空间桁架结构在竖向地震作用下的受力性能和塑性铰的分布及发展情况,给出空间三维桁架结构的屈服机制,以期为三维空间桁架结构概念设计提供参考。     

A procedure of strain-softening model for elasto-plastic analysis of a circular opening considering elasto-plastic coupling

A simple numerical procedure of strain-softening model for the elasto-plastic analysis of a circular opening is presented by modifying the procedure proposed by Lee and Pietruszczak (2008). The proposed procedure has two advantages over that of Lee and Pietruszczak (2008). One is that the elasto-plastic coupling can be considered, the other is that the equilibrium equation and compatibility equation need not be expressed with respect to the normalized radius. Through MATLAB programming, the accuracy and validity of the proposed procedure are demonstrated through some examples. The influence of elastic modulus and Poisson’s ratio evolution on the distribution of radial displacement and hoop stress, ground response curve (GRC) and plastic radius was investigated, and the results show that, with the decrease of elastic modulus evolutional ratio, the radial displacement, hoop stress and plastic radius all increase. With the increase of Poisson’s ratio evolutional ratio, the radial displacement, hoop stress and plastic radius all decrease. As for influence extent, the evolution of elastic modulus has great influence on the radial displacement; and the evolution of Poisson’s ratio has smaller influence on the radial displacement, both of them have very slight influence on the hoop stress near the excavation face but greater on the hoop stress near the interface of elastic and plastic region. And both of them have very slight influence on the plastic radius.     

Spatial hysteretic model and elasto-plastic stiffness of steel columns

By defining yielding function, F, and introducing a so called deformation parameter, R, a simple hysteretic model is proposed between F and R to link 3-dimensional forces acting on a section of a steel column and yielding degree of the section. Based on the hysteretic model proposed and plastic flow laws, the spatial elasto-plastic stiffness equation of steel columns is established. The effectiveness and reliability of the hysteretic model and stiffness equation are verified by experiments through applying the theory to predicting the behavior of 6 specimens of box and H-shaped steel columns subjected to constant vertical loads and repeated and reversed bi-directional horizontal loads. The achievements made in this paper provide the key to problems in the analysis of spatial elasto-plastic responses of steel buildings subjected to earthquakes.     

A new elasto-plastic solution for analysis of underwater tunnels considering strain-dependent permeability

An analytical–numerical solution is proposed in this paper for calculating the mechanical and hydraulic characteristics of underwater tunnels, excavated in an elasto-plastic strain-softening and Hoek–Brown rock material considering strain-dependent permeability. The problem is considered with axial-symmetry condition and thus, the initial stress state is assumed to be hydrostatic. Hydraulic and mechanical differential equations governing the plastic and the elastic rock mass around the tunnel are derived. As the derived equations do not have closed-form solutions, a computer program has been prepared, in order to solve the corresponding equations numerically and to examine the analysis. The results obtained are compared with the results obtained using a commercial finite difference code for investigating the effects of utilised simplifying assumptions. The proposed approach is also used to analyse the response of tunnels under different hydro-mechanical conditions. The results show that the proposed solution can be used for the actual design of underwater tunnels, hydraulically and mechanically.     

用于界面裂纹分析的分段线性弹塑性本构模型(英文)

基于分段线性塑性理论和断裂力学理论 ,提出了一种二维的全量形式和增量形式的粘性裂纹的本构模型。给出了相应的数值试验结果。     

隔震结构的弹塑性反应分析

以某7层隔震框架结构为例,以El-centro波和Taft波为激励,采用动态时程分析对该框架结构进行了罕遇地震作用下的弹塑性反应分析,结果表明采用基础隔震后,能够保证结构在罕遇地震作用下上部结构基本上处于弹性。     

一种基于混合物理论的非饱和岩土类材料的弹塑性损伤模型

在混合物理论的框架内，提出了一个处理饱和与非饱和的岩土类材料变形和强度本构建模的新方法。该方法将多相工程材料看成由两个层次的三种混合物模型组成。针对非饱和岩土类材料的特点，应用该方法，给出了一个具体的弹塑性损伤本构方程，可描述材料性质的劣化过程（即损伤和软化）以及非饱和程度对材料变形强度特性的影响，并编制了专用的有限元程序。作为算例，对常规三轴试件进行了有限元分析，得出了一些具体的结果。     

A new numerical procedure for elasto-plastic analysis of a circular opening excavated in a strain-softening rock mass

A simple numerical procedure for calculating the distribution of stresses and radial displacements around a circular tunnel excavated in a strain-softening Mohr–Coulomb or generalized Hoek–Brown rock mass is proposed. The problem is considered as axisymmetric, i.e. the initial stress state is assumed to be hydrostatic and the rock mass is said to be isotropic. By invoking the finite difference approximation of the equilibrium and compatibility equations, the increments of stresses and strains for each ring, starting from the outmost one for which boundary conditions are known a priori, are calculated in a successive manner. In the proposed approach, the potential plastic zone is divided into a finite number of concentric rings whose thicknesses are determined internally to satisfy the equilibrium equation. For the strain-softening behavior, it is assumed that all the strength parameters are a linear function of deviatoric plastic strain. Several illustrative examples are given to demonstrate the performance of the proposed method. For the brittle–plastic case, the results show a very good agreement with the closed-form solution. For strain-softening cases, the predictions by the proposed method are also in good agreement with the known rigorous numerical solutions. It is shown that the approximate solution converges to the exact solution when the increment of stress for each ring becomes smaller. The influence of the strength parameter ‘a’, appearing in the generalized Hoek–Brown criterion, on the elasto-plastic solutions is examined through the establishment of ground reaction curves and the discussion for the locations of the plastic radii.     

混凝土多轴弹塑性损伤本构模型

建立了混凝土的多轴弹塑性损伤本构模型.考虑到混凝土在受拉和受压荷载作用下的不同破坏机理,将应力张量分解成受拉和受压两部分,定义了塑性屈服函数,从而达到考虑混凝土塑性变形的目的.在连续损伤力学理论的框架内定义了相应的损伤变量,并分别给出了损伤准则,以描述材料的不同损伤过程.对混凝土的单/双轴受拉和单/双轴受压四种加载情形进行了数值计算,并与相关的试验对比,结果验证了模型的正确性及有效性.     

Implementation of total Lagrangian formulation for the elasto-plastic analysis of plane steel frames exposed to fire

In this paper, the co-rotational total Lagrangian forms of finite element formulations are derived to perform elasto-plastic analysis for plane steel frames that either experience increasing external loading at ambient temperature or constant external loading at elevated temperatures. Geometric nonlinearities and thermal-expansion effects are considered. A series of programs were developed based on these formulations. To verify the accuracy and efficiency of the nonlinear finite element programs, numerical benchmark tests were performed, and the results from these tests are in a good agreement with the literature. The effects of the nonlinear terms of the stiffness matrices on the computational results were investigated in detail. It was also demonstrated that the influence of geometric nonlinearities on the incremental steps of the finite element analysis for plane steel frames in the presence of fire is limited.