哑铃型钢管混凝土拱肋极限承载力研究

为了研究哑铃型钢管混凝土拱肋的力学性能,基于统一强度理论和等效梁柱法,考虑中间主应力和材料拉压比的影响,推导了其极限承载力的新公式。采用梁单元建立哑铃型钢管混凝土拱肋的有限元模型,对其受力全过程进行双重非线性分析。将理论分析结果和数值计算结果与相关文献的试验结果进行比较,吻合良好,验证了本文理论分析方法和有限元计算方法的正确性。采用有限元方法,对荷载工况、长细比、矢跨比、截面形式和腹腔混凝土等参数的影响特性进行分析,研究结果表明,荷载工况对哑铃型钢管混凝土拱肋的极限承载力影响显著,荷载越对称、均匀,拱肋的极限承载力越高,竖向变形越小;拱肋的极限承载力随长细比的增大而显著降低,随矢跨比的增大先提高后略有降低;截面形式对拱肋的强度和刚度均有较大影响,而腹腔混凝土对其强度和刚度几乎没有影响。     

离心通风器结构分析

根据某发动机离心通风器6个故障件的破坏形貌测量分析结果及简化模型的光弹性试验和有限元计算结果，建立离心通风器壳体力学模型，并通过应力分析结果对结构进行疲劳分析、探讨失效原因．研究结果指出，由于壳体在油气混合环境中使用，其肋的转接台阶处具有高的应力集中、材料铸造表面粗糙；组织疏松等缺陷，肋的截面尺寸公差太大等多种因素造成零件的寿命降低，较多零件的失效．     

任意边界条件下环肋圆柱壳振动特性的建模与求解

边界条件对环肋圆柱壳的振动特性有重要影响。基于能量法,把环肋看作离散模型,构建了任意边界条件下加环肋圆柱壳的动力学模型。采用一种改进的傅里叶级数作为位移容许函数,通过瑞利里兹程序求解结构的拉格朗日方程,得到环肋圆柱壳的振动模态和频响特性。通过与实验和有限元(FEM)方法的计算结果进行对比,验证了论文方法的准确性,在此基础上分析了环肋偏心方式、截面尺寸、位置分布和边界弹簧刚度等参数对环肋圆柱壳振动特性的影响。     

外框密肋复合墙抗剪机理及承载力计算

在外框密肋复合墙低周反复荷载试验的基础上,对墙体的抗剪机理进行了分析;依据极限平衡理论引入砌体抗剪承载力影响系数和框格承载力影响系数,同时考虑RC框格与填充砌块之间的相互作用;提出了外框密肋复合墙抗剪承载力计算公式;本文公式计算结果与试验结果、有限元数值模拟结果进行了比较。研究表明:本文基于水平薄弱层破坏建立的外框密肋复合墙抗剪公式较传统基于斜截面破坏建立的抗剪公式具有更明确的物理意义;本文公式计算精度较高,与试验结果、有限元数值模拟结果相差不到10%。     

平面弯曲下带加劲肋的T型方管节点极限承载力分析

为得到加劲肋加强T型方管节点承受平面内弯矩作用下极限承载力提高系数ψ的表达式,本文在试验与有限元对比的基础上,用ABAQUS软件进行了参数化分析,并用Origin软件进行了回归分析。结果表明:支管与主管截面宽度之比β=0.4~0.7时,节点的破坏主要是上壁面屈服所致,加劲肋加强T节点极限承载力平均是无加劲肋节点的2.55倍;节点承载力与加劲肋厚度t_w、加劲肋宽度b_w、β皆呈正相关,影响程度为βb_wt_w;加劲肋承载力M_S随加劲肋厚度与主管截面宽度之比τ、加劲肋宽度与主管截面宽度之比η和β的增加而增加,其中三者影响程度大小次序为βητ,提高系数ψ随τ、η的增加而增大,其中η的影响大于τ,β对ψ的影响不大。最后得出了加劲肋加强T型方管节点承受平面内弯矩时极限承载力的计算公式。     

拼接式组合扁梁受弯性能分析

本文提出了一种拼接式组合扁梁，对其进行了受弯性能分析．组合扁梁属于内嵌式组合梁，其组成部分较为复杂，传统承载力计算公式偏保守．为便于此类梁的设计，本文在等效应力法的基础上使用等效矩形应力图法，对拼接式组合扁梁的正截面抗弯承载力公式进行推导．使用ABAQUS有限元软件对组合方法公式的准确性进行验证，并与等效应力法公式进行对比，结果表明组合公式得到的数值更为精准．在相同截面高度和用钢量下设计了一个深肋组合扁梁和一个拼接式组合扁梁，并进行了受弯性能对比；同时对不同钢强度和翼缘厚度影响下的拼接式组合扁梁抗弯承载性能进行分析．使用换算截面法对其进行了弹性刚度的计算，并和有限元进行了对比，二者吻合较好，研究结果为拼接式组合扁梁的设计和优化提供了一定参考依据．     

带脱层的复合材料层板屈曲分析中的接触问题

用基于Mindlin板理论的有限元方法进行了带脱层损伤复合材料层板的屈曲载荷分析．为了处理在屈曲模态中上下脱层之间的接触问题，我们提出了一种有效的算法．在这种算法中，首先用一阶灵敏度分析和二次规划方法相结合的选代算法算出接触区域的虚拟力，然后将这种虚拟力转化成一些假想弹簧的刚度系数，并对原始刚度矩阵进行修正．数值算例表明本算法可以有效地克服屈曲模态中上下脱层之间的相互贯穿．同时，还对脱层的大小，形状和位置对屈曲载荷的影响进行了研究．     

横肋波纹钢板-钢管混凝土短柱轴心受压性能研究

横肋波纹钢板-钢管混凝土柱是一种新型钢管混凝土组合柱。为研究其轴心受压性能,本文以径宽比(单肢方钢管截面宽度与组合柱截面宽度的比值)为参数,开展了3根横肋波纹钢板-钢管混凝土短柱和1根普通方钢管混凝土短柱的轴心受压试验。探究了径宽比对各试件破坏模态、荷载-纵向应变曲线、承载力提高系数、延性等的影响,并与普通方钢管混凝土柱作了对比。试验研究结果表明:横肋波纹钢板与方钢管具有良好的变形协调性;相比于普通方钢管混凝土柱,横肋波纹钢板-钢管混凝土组合柱具有良好的轴压性能;随着径宽比的增加,试件的承载力及延性逐渐增大,承载力提高系数逐渐减小。在Mander模型以及有限元参数分析的基础上,建立了横肋波纹钢板-钢管混凝土组合柱轴压承载力计算公式,计算结果表明:计算值偏于安全,可为工程设计提供参考。     

复合板旋转约束刚度推导及箱型结构屈曲分析

基于结构稳定性理论,推导出正交各向异性纤维树脂增强复合材料箱型结构各板连接处旋转约束刚度的近似表达式．与以往的经验公式相比,考虑了材料的正交各向异性和截面尺寸的影响．通过对箱型结构的正交各向异性比、截面属性以及纵横比对旋转约束刚度的影响进行参数研究,验证了旋转约束刚度新公式的精确性和适用范围．通过比较采用不同近似表达式得到的结果与有限元计算结果的对比,表明本文的旋转约束刚度新公式可以更精确地用来计算箱型结构的临界屈曲载荷．     

双材料间界面断裂分析的广义界面层模型

给出了双材料间界面层区域的广义模型，并对承受扭转载荷的界面间硬币形裂纹进行了分析与计算．通过处理奇异积分方程得到了应力强度因子，数值结果给出了材料特性、界面层厚度、尤其是分布特征参数ｋ对应力强度因子的影响．与Ｅｒｄｏｇａｎ界面层模型的结果比较表明，本文的模型更具有一般性．     

等直杆单元切线刚度矩阵的精确分析方法

为了有效完成大型铰接单层网壳结构的后屈曲分析,本文采用对杆单元杆端力函数求导的方法推导出了等直杆单元切线刚度矩阵的精确形式。该切线刚度矩阵不受结构小变形限制,适用于结构产生任意大结点位移情况。以六角星桁架、平面圆拱桁架和大跨K8单层网壳结构为算例,采用广义位移控制法进行非线性后屈曲分析,其中预测子采用本文杆单元切线刚度矩阵。算例分析结果表明,本文杆单元切线刚度矩阵在大型铰接单层网壳结构的非线性后屈曲分析中有很强的预测能力。     

Damage model and damage assessment for single-layer reticulated domes under exterior blast load

Long-span reticulated dome is often considered as a landmark building of a region, so it is very important to investigate the dynamic response and propose the damage assessment method of reticulated dome under blast loading. In this article, a fine finite element model of Kiewitt8 (K8) single-layer reticulated dome was established by using ANSYS/LS-DYNA. The effects of standoff distance, charge weight, rise–span ratio, span, and roof weight on the responses of K8 single-layer reticulated dome were numerically studied. The results showed that the blast-resistant performance of reticulated dome with smaller rise–span ratio and larger span under exterior blast load was more advantageous. Although the blast-resistant capacity of reticulated dome with large span and large roof weight was favorable, the plastic deformations of reticulated dome members were small and the utilization of material was low at failure state. According to the dynamic response characteristics of plentiful K8 single-layer reticulated domes at different damage levels, a damage model of K8 single-layer reticulated dome under exterior blast load was proposed in this article to indicate the damage level and determine the ultimate strength. Besides, a new damage criterion for K8 reticulated dome was also defined. This damage model was defined based on the physical phenomena at different damage levels, which made the strength failure criterion had definite physical meaning. Using the proposed damage criterion and a new search algorithm for pressure and impulse, the pressure–impulse diagrams for the typical K8 reticulated dome were derived from the numerical simulations to evaluate the damage level of reticulated dome under blast loading. Finally, a method to determine the safety standoff distance for reticulated dome under given TNT charge weight was also proposed.     

The Saltwater/Freshwater Regime in the Sedimentary Cover of the Gorleben Salt Dome

Hydrogeological investigations were conducted around the Gorleben salt dome, in the northeastern part of Lower Saxony in Germany, to study the aquifer system in the cover deposits consisting of unconsolidated Quaternary and Tertiary sediments up to 250m thick. An upper freshwater body is underlain here by saline water. The salinity of the water generally increases with depth. Saturated brines are found in the lower aquifer in a subglacial erosion channel above the salt dome. Hydrochemical analyses and geophysical and isotope studies provide information on development history and behaviour of the flow system. Highly saline groundwater formed by subrosion of salt collects in the lower aquifer above the salt dome. It generally flows north through the erosion channel in the direction of the regional flow field and collects in a basin-like aquifer structure north of the dome. The post-Pleistocene groundwater circulation is progressively replacing the Pleistocene brines with Holocene groundwater. Only a small amount of salt water is being transported into the near-surface aquifer.     

Membrane analysis and optimization of submerged domes with allowance for selfweight and skin cover load

This paper is concerned with membrane analysis and optimal design of submerged domes. In addition to hydrostatic pressure, domes are also subjected to selfweight and skin cover load, which are invariably present in these types of structures. Using the membrane theory for thin shells and by adopting a fully stressed design, equations governing the meridional curve of submerged domes are derived with allowance for selfweight and skin cover load. A set of nonlinear differential equations, which correspond to a two-point boundary problem, is solved by the shooting-optimization method. Based on a family of fully stressed designs associated with a given water depth and dome height, the optimal dome shape for minimum weight is determined.     

STABILITY ANALYSIS FOR TANK-ROOF BASED ON RELIABILITY

根据加肋拱顶稳定性校核公式,应用结构可靠度理论,建立了油罐拱顶可靠性分析模型,对拱顶稳定性进行分析计算,以确定油罐拱顶的使用安全性. 运用最小距离法和有限差分法对该模型的可靠度进行求解.结合工程实例,分析了顶板自支承作用、肋板的加强作用在外载荷作用下对拱顶可靠指标的影响规律,拟合出可靠指标与拱顶各参数间数值关系. 通过对现役油罐拱顶稳定性进行可靠性评定,验证了该模型在现役条件下分析拱顶稳定性的可行性.     

Modeling Variable Density Flow and Solute Transport in Porous Medium: 2. Re‐Evaluation of the Salt Dome Flow Problem

Case 5, Level 1 of the international HYDROCOIN groundwater flow modeling project is an example of idealized flow over a salt dome. The groundwater flow is strongly coupled to solute transport since density variations in this example are large (20%).Several independent teams simulated this problem using different models. Results obtained by different codes can be contradictory. We develop a new numerical model based on the mixed hybrid finite elements approximation for flow, which provides a good approximation of the velocity, and the discontinuous finite elements approximation to solve the advection equation, which gives a good approximation of concentration even when the dispersion tensor is very small. We use the new numerical model to simulate the salt dome flow problem.In this paper we study the effect of molecular diffusion and we compare linear and nonlinear dispersion equations. We show the importance of the discretization of the boundary condition on the extent of recirculation and the final salt distribution. We study also the salt dome flow problem with a more realistic dispersion (very small dispersion tensor). Our results are different to prior works with regard to the magnitude of recirculation and the final concentration distribution. In all cases, we obtain recirculation in the lower part of the domain, even for only dispersive fluxes at the boundary. When the dispersion tensor becomes very small, the magnitude of recirculation is small. Swept forward displacement could be reproduced by using finite difference method to compute the dispersive fluxes instead of mixed hybrid finite elements.     

Numerical Analysis of Axisymmetric Buckling of a Conical Shell under Radial Compression

The nonlinear boundary-value problem of the axisymmetric buckling of a simply supported conical shell (dome) under a radial compressive load applied to the supported edge is formulated for a system of six first-order ordinary differential equations for independent fields of finite displacements and rotations. Multivalued solutions are obtained using the shooting method with specified accuracy. For various values of the loading parameter, bifurcation of the solutions of the problem is studied and a parametric branching diagram is constructed. The buckling modes are obtained for three branches of the solution. Curves of the buckling modes corresponding to three isolated branches of the solution are given.     

Axisymmetric deformation of plates and shells with phase trasformations under thermal cycling

A mathematical formulation is given of nonlinear axisymmetric buckling problems for plates and shells in the two-phase zones of austenite-to-martensite transformation. Numerical solutions of the direct-and inverse-transformation problems are used to construct hysteresis loops for thermomechanically cycled, pressure-loaded circular plates and shallow spherical domes of titanium nickelide (NiTi) alloy. It is shown that dynamic instability of the dome deformation process can occur during transformation under loads notably lower than the upper critical values for the isothermal states of the material outside the transformation zone. A theoretical analysis gives external loads below which the dome remains stable in the thermally cycled material with phase transformations. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 204–210, March–April, 2008.     

地震作用下基于响应敏感性的单层球面网壳冗余度分析方法研究

冗余特性是结构鲁棒性的重要组成部分,也是损伤情况下结构安全性的体现。在地震等动力荷载作用下单层球面网壳结构的倒塌模式由诸多因素决定,其中结构的冗余度是重要的影响因素。为合理评估地震作用下的结构冗余度,本文基于结构响应对单元材料弹性模量的敏感性提出地震作用下的结构构件冗余度评价方法,并对一星型网壳在地震作用下的弹性、弹塑性冗余度进行分析,以验证方法的有效性。结果表明,结构冗余度能够反映构件在结构中的重要性,冗余度值的大小是构件重要性的衡量指标,低冗余度构件是结构的关键构件。利用结构的冗余度分布,可以采取加强低冗余构件的措施,从而实现网壳结构倒塌模式的优化控制。     

葵花型索穹顶结构等效平面桁架静力计算方法

选取n次轴对称葵花型索穹顶结构的1/n,将空间轴对称结构等效为一次超静定平面桁架结构.给出了葵花型索穹顶结构撑杆不在同一径向上的内力和位移处理方法,推导了力法求解约束力的计算公式,提出了小变形时各点位移计算的位移传递矩阵和计算公式.最后,通过一个算例介绍了该方法的计算过程并与有限元计算结果进行了比较,内力和位移误差均在工程设计要求内,验证了方法的正确性和准确性.