基于柔度法与截面轴力弯矩屈服面本构的梁柱单元

基于截面层次的梁柱单元能兼顾计算精度与效率,但现有截面上的本构模型不能准确反映轴力存在与变化对弯矩的影响,且柔度法在构建梁柱单元中未发挥优势,为此提出了基于截面轴力与弯矩屈服面本构和柔度法的梁柱单元模型。首先,根据截面组合思想构建截面上轴力与弯矩的屈服面;然后,依托柔度法和塑性理论进行单元状态和截面状态确定;最后,利用提出的单元进行平面钢框架的动力弹塑性分析。结果表明,所选用的基于截面轴力弯矩屈服面的本构能很好考虑轴力存在及变化对弯矩的影响;相对于刚度法,使用一个由柔度法构建的单元就足够描述一个梁-柱构件,其计算精度接近基于柔度法的纤维单元模型。     

钢框架翼缘削弱型和扩翼型节点受力性能研究

采用翼缘削弱型节点及扩翼型节点可以使塑性铰外移,缓解梁柱节点连接处应力集中,避免在焊接热影响区发生脆性破坏.针对削弱型节点、扩翼型和普通刚性节点进行了数值分析,结果表明:削弱型节点由于梁翼缘削弱,导致节点承载力降低,扩翼型节点增加了梁端翼缘板宽度,承载力高于削弱型节点和普通刚性节点.通过计算模型分析了节点的设计参数,并给出节点设计参数取值范围,为钢框架节点抗震设计提供理论分析依据.     

有应力史差非匀质截面轴心受压杆的性能研究

对有应力史差、非匀质、非线弹性的轴心受压构件进行了理论分析和试验研究，初步揭示了此类构件的受力特点．理论分析和试验表明：此类构件截面承载力不是各部分材料承载力的简单叠加；承载力和截面破坏控制点因截面上材料的本构关系的变化和应力史差而发生改变．     

变截面高层框筒结构的矩阵传递法

以连续化数学模型和能量变分原理导出的变截面高层框简结构的微分方程组为基础；根据变截面框简结构的截面沿高度为阶形变化的特点，以每个相同截面的层作为一个计算单元，每个单元由微分方程组导出其单元矩阵、截面矩阵和传递矩阵。进而采用传递矩阵法进行分析。此法概念清楚，计算简单．并以算例说明其应用。     

应力波在变截面体中的传播特性

对应力波在变截面体中的传播特性进行了理论研究和数值分析。以杆中一维纵波波动理论和谐波分析法为基础，研究截面变化所导致的应力波的波形弥散和波幅变化。推导了与截面变化相关的应力波演化因子，并对由于截面变化所造成的几何弥散等二维效应进行了分析，同时计算了变截面体的几何特征参数和截面变化等因素影响应力波演化规律的特点。     

Cross Sections in the Three-Body Problem

In Dynamical Systems, Birkhoff gave a clear formulation of a cross section, suggested a possible generalization to cross sections with boundary, and raised the question of whether or not such cross sections exist in the three-body problem. In this work, we explicitly develop Birkhoff's notion of a generalized cross section, formulate homological necessary conditions for the existence of a cross section or generalized cross section, and show that these conditions are not satisfied in the three-body problem.     

The effect of member spacing upon the base pressure distributions recorded on perpendicular flat plates

Conclusions The experimental results presented in this note have provided a comparison between the flow induced pressure distributions associated with non-connecting perpendicular flat plates and similar configurations composed of circular cylinders and square section bars.With regard to the upstream plate, the pressure distributions were found to closely resemble those associated with perpendicular cylinders and, therefore, it is suggested that similar spacing related flow regimes exist. In this respect, at separation distances below three section depths trailing vortices are generated in proximity to the centre of the geometry, whereas at spacings in excess of three section depths the conditions become quasi two-dimensional along the whole span.In the case of the downstream plate, the results at spacings of four section depths and below are similar to those on the downstream perpendicular bar, which is subjected to a horseshoe vortex flow regime over a comparable range of spacings. However, at spacings greater than four section depths the conditions appear to be unique to this section geometry.     

单箱三室箱梁剪力滞效应的试验研究

为开展单箱三室箱梁剪力滞效应的试验研究,制作了有机玻璃简支箱梁模型,对试验模型进行了分级加载。对该试验箱梁进行集中加载,分别作用于跨中截面四腹板上方、两对称边腹板上方和两对称中腹板上方。采用DH3816应变采集仪测得跨中及四分之一跨截面各关键点应变值,用百分表测得箱梁各关键截面挠度值。测量得到的截面应力分布规律验证了箱梁截面剪力滞效应的存在。对该有机玻璃简支箱梁,利用有限元方法和模型试验方法,研究了3种集中力工况下截面的剪力滞分布规律。结果表明,集中力作用下单箱三室箱梁各翼板间存在明显的剪力滞效应,且荷载的横向作用位置对箱梁截面剪力滞效应影响较大。     

冷弯薄壁槽形截面钢柱的优化设计

求解冷弯开口薄壁截面短柱的极限承载力是一个板组结构的大挠度弹塑性分析问题，板件之间相互作用和纵向面内加载方式对其局部屈曲后性能和稳定极限承载力有很大的影响。本文应用大挠度弹塑性有限条分析方法系统地研究了冷弯薄壁槽形截面柱的极限承载能力和它们的优化性能，并对荷载偏心距为常数和位移梯度为常数的两种加载条件下的薄壁开口短柱局部屈曲后性能和极限承载力进行了对比分析和探讨。     

陡倾滑面滑坡锯齿形抗滑桩力学性能研究

陡倾滑面滑坡推力竖向分力显著,基于滑坡推力水平假定与普通抗滑桩相互作用不充分这一问题,建立锯齿形抗滑桩结构。依据梯形分布滑坡推力的假设,推导了受荷段内力计算公式,采用Winkler弹性地基理论推导了锚固段内力计算公式,并开展锯齿形抗滑桩的力学性能研究。分析表明,(1)随着滑面倾角的增加,锯齿形抗滑桩的受荷段、锚固段的弯矩、剪力以及侧应力均减小,内力减小幅度随之增大;(2)滑面倾角在20°～40°时,随着滑面倾角的增加,锚固段的理论最小长度在逐渐增加,40°时锚固段的长度为4.2 m达到最大值,且该长度仅占整个桩长35%,远小于按现行规范取得的锚固段长度最大值(1/2总桩长),桩侧摩阻力就可以完全满足竖向力学平衡;(3)将锯齿形抗滑桩与普通抗滑桩内力对比,受荷段和锚固段的弯矩减小34%、剪力减小36%及桩侧应力减小幅度大于30%,力学性能良好。     

考虑约束扭转的薄壁梁单元刚度矩阵

推导了薄壁空间梁单元刚度矩阵 ,考虑了双向弯曲及截面约束扭转对杆件轴向变形的影响 ;计算了截面的翘曲变形 ,以及二次剪应力对翘曲变形的影响 ,可适用于任意截面 (包括开口、闭口和混合剖面 )的薄壁杆件。计算结果表明 ,考虑约束扭转的薄壁梁单元刚度矩阵有相当好的精确度 ,可以用于薄壁杆件的静动力分析。     

On the cross section of minimum stress concentration in the Saint-Venant theory of torsion

A lower bound is derived for the maximum stress in the torsion of cylindrical solids of simply-connected cross section. This bound, which is expressed in terms of the applied torque and the cross-sectional area, is isoperimetric in that it coincides with the maximum stress when the cross section is circular. It confirms the notion that given the applied torque and the area of the cross section, the least maximum stress occurs when the section is circular. Related isoperimetric upper bounds are derived for the minimum value of the stress at boundary points.     

Average absorption coefficient for optically thin media

Modifications are considered of the mean Planck absorption coefficient for a section of an absorbing medium adjacent to a source section, taking into account temperature inequalities of blackbody radiation and the absorption cross section of the medium, as well as the effect of the length of the section, which is small. Equations are presented for an analogous coefficient determining self-absorption of radiation by the gas.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, Vol. 11, No. 1, pp. 12–15, January–February, 1970.     

Stress resultants plasticity with general closest point projection

In this paper, general closest point projection algorithm is derived for the elastoplastic behavior of a cross-section of a beam finite element. For given section deformations, the section forces (stress resultants) and the section tangent stiffness matrix are obtained as the response for the cross-section. Backward Euler time integration rule is used for the solution of the nonlinear evolution equations. The solution yields the general closest projection algorithm for stress resultants plasticity model. Algorithmic consistent tangent stiffness matrix for the section is derived. Numerical verification of the algorithms in a mixed formulation beam finite element proves the accuracy and robustness of the approach in simulating nonlinear behavior.     

基于拟满应力设计和遗传算法的网架截面优化方法

通过在遗传算法中嵌入拟满应力算子,提出了一种以网架结构杆件截面作为离散变量的优化设计方法,即基于拟满应力设计和遗传算法的网架截面优化方法.分析结果表明,该法能够提高遗传算法的搜索效率和获得全局最优解的可靠性,对于同时有应力和位移约束的网架等空间结构截面优化问题,这种混合算法有较高的效率.     

初始几何缺陷对网壳截面优化结果影响研究

单层网壳结构是缺陷敏感结构,初始几何缺陷不同对"网壳截面优化结果"有显著影响,该文研究了网壳杆件截面取值与缺陷分布、结构极限承载力之间的关系.结果表明:经截面优化设计的网壳结构最不利应力最早并且一直出现在初始几何缺陷较大处;优化寻优结果与初始几何缺陷分布有直接关系,增大缺陷较大处杆件截面能显著提高结构承载力;由于缺陷随机分布,经截面优化设计的网壳结构须校核其在不同缺陷下的稳定承载力以确保结构安全.     

高压下液体微管道流动的摄动分析

应用参数摄动法对可压缩N-S方程进行渐近展开,并取其零阶近似对高压下微管道液体流动特性进行了分析．对任意截面形状和面积的微管道,在等温流动假设下将其截面形状、滑移长度等对解的贡献转化为求解该截面的格林函数,并给出等截面圆形微管道流动的零阶近似解．以此分析可压缩性、黏性以及壁面滑移等因素对高压下液体微管道流动特性的影响,进一步揭示了高压驱动下液体微管道流动偏离经典Hagen-Poiseuille(HP)理论的原因．      

Design Optimization of Connection Section for Concentrated Force Diffusion

In many load carrying thin shell structures, a connection section is arranged to transfer concentrated external forces to its main section. It is very important for the concentrated external forces to diffuse as uniformly as possible. Nevertheless the traditional design of uniform radial rib is not optimized. The present paper studies an integrated optimization procedure for design optimization of connection section. Variance constraint of node forces at the interface between the main section and connection section is firstly proposed as the evaluation criterion of concentrated force diffusion efficiency and introduced into the topology optimization formulation. Afterwards, for improving the manufacturability of the final design the topology optimization results are interpreted and further optimized by size or shape optimization. Two strategies of interpretation are examined. The first strategy is called strategy of making holes, which inserts a number of internal holes of regular geometric features and smooth boundary with B-spline curves in the continuum based on the topology optimization result. In the second strategy, an initial truss-like design is extracted from the characteristic of topology optimization result. Then a further shape and sizing optimization is followed to obtain the final optimal design. An example of design optimization of plane connection section is presented. The effectiveness of the present approach is demonstrated. The respective advantages and disadvantages of the two strategies are discussed.     

自平衡端头载荷问题衰减率的分析与计算

给出了自平衡端头载荷问题应力衰减率分析的一种方法．用边界单元法求得了在端面自平衡载荷作用下，具有椭圆截面和矩形截面的弹性柱体内应力场的最小衰减率。计算结果表明：当椭圆截面的长短轴之比和矩形截面的长宽之比变化时，最小衰减率变化很小．     

黄河下游堤防地质险段研究

由地质作用影响形成的易出险堤段称为地质险段 ,主要包括活断层作用影响形成的堤基易渗漏段、强地震高发区段和地基稳定性差段等。构造节点是识别地质险段的重要的河流地貌标志之一。根据成因 ,本文将黄河下游的地质险段分为三类 ,即新构造险段、沉降险段、断裂复活险段。针对黄河下游堤防地质特征 ,圈定出东坝头、大刘屯—董口黄河南岸和路那里—十里堡黄河南岸地质险段 ,提出了治理的有关措施