Large bending of pipes

The computer model developed has been used successfully for studying the large pipe-bending problem frequently encountered in offshore structural engineering. The pipe-soil interaction is modelled by using the Coulomb friction law. The modified finite element approach coupled with a modified tangent stiffness procedure is used to handle the nonlinearities (geometric and material, etc.) in the problem. The material nonlinearity has been considered both by the plastic-hinge method and by an elastic-plastic method. Before studying the practical problems, sufficient check problems were analysed and a good agreement was found between theoretically exact solutions and the results obtained from the developed computer model.     

Instability of a cylindrical shell under three-point bending

The instability of a cylindrical shell under three point bending is considered. The problem has application to the industrial pipe ram bending process. The loading is idealized as a set of pads of uniform radial pressure in the regions of die-shell contact. A theoretical solution for the smallest buckling load is developed, using the Donnell and Sanders linearized stability equations. A finite element solution is also presented. The paper concludes with a discussion of results, from the two methods.     

Numerical solution of curved pipes submitted to in-plane loading conditions

An alternative formulation to current meshes dealing with finite shell elements is presented to solve the problem of stress analysis of curved pipes subjected to in-plane bending forces. The solution is based on finite curved elements, where displacements are defined from a total set of trigonometric functions or a fifth-order polynomial, combined with Fourier series. Global shell displacements are achieved through the one associated with curved arch bending and the other referred to the toroidal thin-walled shell distortion. Beam-type displacement and in-plane rotation are uncoupled and separately formulated, using trigonometric shape functions, as in Timoshenko or Mindlin beam theory. To build up the solution, a simple deformation model was adopted, based on the semi-membrane concept of the doubly curved shells behaviour. Several studies are presented and compared with experimental and numerical analyses reported by other authors.     

Fabrication of unsymmetrical curved plate girders by cold bending

A proprietary cold bending method was recently developed for the fabrication of the steel girders in the Miami Metromover. In an earlier paper, the authors developed a simplified analysis for this system that could be used for curving symmetrical girders. This paper extends this analysis to unsymmetrical girders typically used in bridge construction where the top flange is smaller than the bottom flange. Guidelines are proposed that set limits on the maximum load and permanent residual strains that develop during the curving operation to ensure they are within acceptable norms. These are integrated in a standardized procedure based on actual practice. A comprehensive numerical example is included to illustrate this procedure. This uses design aids specially developed to simplify calculations in the steel shop.     

Experimental and numerical investigation of masonry under three-point bending (in-plane)

The aim of this study is to investigate the failure and post-peak behaviour of masonry panels with low bond strength mortar under three-point bending (TPB) both experimentally and numerically. Full-scale masonry panels with two different mortar strengths were tested under TPB. The material parameters were obtained from compression, TPB and shear tests on bricks and brick–mortar interfaces. The experimental results are detailed. Adopted for the numerical study was a micro-model finite element formulation in which masonry is modelled using expanded brick units with zero thickness brick–mortar interfaces. The simulation of the masonry TPB tests compared well with the experimental results. Investigations were the crack propagation through the masonry and the effects of dilatancy on the post peak response.     

低碳钢线割裂缝三点弯曲梁的阻裂电测过程分析

为探寻低碳钢三点弯曲试样断裂过程与承载能力,分别对不同尺寸的带裂缝试件进行加载试验,并对其中的典型试件进行应变片电测跟踪测试,得到了一系列关系曲线,其中有载荷与加载点位移关系曲线,中性层位置随载荷变化曲线,塑性段卸载再加载关系曲线等;且计算了各试件失稳时的应力强度因子．同时测量了该试样的塑性变形,并结合黏聚裂纹应力强度因子计算式与断裂准则,得到计算此材料结构承载力的理论值,并与试验值进行对比,两者比较符合．     

四种不同形式的弹性悬索静力解答

首先回顾了悬索静力分析的研究历史,收集整理了国际上常用的不同坐标系下的两种解答及国内近年来推导的不同坐标系下的两种解答,通过同种坐标下国内、外解答的一致性和不同坐标系下国际上流行的两种解答一致性的证明,表明该四种解答是一致的,建议使用竖坐标轴正方向向上的解答,用国际上的相应解答建立悬索分析的有限元方法,用本文作者推导的解答进行索的设计与计算。     

Numerical analysis of elastic-plastic bending of curved beams with thin-walled cross-section

It is well known that, when a curved beam is subject to bending, the shape of its cross-section is flattened and collapse occurs as the rigidity is reduced. It is important for design to determine the nonlinear behavior of such beams. This paper describes the elastic-plastic large deformation analysis of a curved beam with a thin-walled cross-section by the finite element method. The analytical formulation is developed by extending the kinematic work hardening model proposed by Ziegler. Several representative cases are computed.     

Benchmark symplectic solutions for bending of corner-supported rectangular thin plates

This work presents the first ever analytical solutions for bending of a rectangular, thin plate supported only at its four corners. This breakthrough analysis employs a new symplectic elasticity approach that extends beyond the limitation of the classical plate bending methods such as Timoshenko's method, Navier method, Levy method and the polynomial approximation analysis of Lee and Ballesteros (Int J Mech Sci 1960;2:206). The classical methods are, in fact, special cases of this symplectic approach in the real eigenvalue regime for wavenumber with at least one pair of opposite sides of plates simply supported. For plate problems that do not fall into this category, the classical methods fail to yield any analytical solutions, but the symplectic approach does because in these cases the plate bending problems enter the complex eigenvalue regime for wavenumber. Another distinctive feature of this new approach is its necessity to pose an eigenvalue problem even for plate bending. In short, this innovative approach establishes the relationship between eigenvalue problem and bending. The novelty of this approach lies in the use of the Hamiltonian principle in a symplectic geometry space to derive a Hamiltonian system and a full state vector. The free boundaries with corner supports are dealt with using the variational principle. Analytical bending modes are then derived by expansion of eigenfunctions. The solutions are compared with other known (approximate) results and numerical finite element solutions but some of the results are not in agreement. Because the analytical bending moment and shear force solutions thus derived fulfill all natural and geometric boundary conditions, it leaves ample room for authentication of the benchmarks in the future. In addition, the twisting moment at the corners satisfies the condition for static bending equilibrium, in which the finite element solutions fail.     

Elasto-plastic response of orthotropic pipes under bending, pressure and axial force

An elasto-plastic analysis of circular thin-walled pipes in the non-buckled configuration subjected to bending moment, pressure and axial loads is presented. Plastic stress-strain relationships based on Drucker's postulates, Hill's yield criterion and the deformation theory are utilized. The analysis includes orthotropic behaviour with the assumption of a linear strain-hardening material. Results are presented for both isotropic and orthotropic materials.     

滑移效应对型钢混凝土梁弹性抗弯强度的影响

指出了由于滑移效应的影响,型钢混凝土梁的抗弯承载力有所降低,采用弹性分析理论,考虑型钢和混凝土交接面滑移影响,建立了考虑滑移效应的弹性抗弯强度计算公式,以提高型钢混凝土梁弹性抗弯强度计算的准确性。     

Dynamic elastic instability of long circular cylindrical shells under pure bending

The present paper studies the responses and instabilities of long circular cylindrical shells subjected to dynamic pure bending. The dynamic instability characteristics of the shells subjected to a sudden step bending load of infinite duration are explored. Analysis is performed using nonlinear finite element numerical methods. Critical dynamic moments are determined through the use of Budiansky and Routh's stability criterion. Numerical predictions for the dynamic instability are compared with those static results given earlier by Brazier. The effects of shell geometry on the dynamic stability of the shells are shown. It is found that the dominating factor to affect the shell stability is the ovalization of the shell cross-section in the centre of the shell.     

浅谈玻璃热弯炉的构成、种类和常见问题的解决方法

本文介绍了热弯玻璃工艺制作流程及热弯炉的主要分类等,并分析了影响热弯玻璃质量的因素,提出了解决办法。     

连续曲线双箱钢-混组合梁弯扭性能试验研究

为研究连续曲线双箱钢-混组合梁的弯扭性能,以实际工程为背景,以曲线半径和横隔板连接方式为参数,设计了3根1∶10的缩尺模型,并对其进行静力加载试验,研究试验梁跨中截面的荷载-挠度曲线、横向挠度分布和钢梁与混凝土板间的相对滑移规律。结果表明,3根梁的破坏形式一致,均为弯扭破坏,负弯矩区在0.1P;(P;为极限荷载)时就会开裂;极限荷载时,试验梁跨中截面外侧挠度达内侧的1.37倍;试验梁的抗弯刚度和抗扭刚度均随着曲线半径的增大而提高,横隔板连接方式对其弯扭性能影响不大;混凝土板与钢梁结合面切向滑移随着曲线半径的增大而减小,横向栓接试验梁的滑移量小于横向焊接试验梁的;切向滑移量最大值出现在跨度的3/4处,径向滑移量最大值出现在中支点附近处。     

弹性半空间上圆板的弯曲分析

对各向同性弹性半空间地基上薄圆板一般弯曲问题进行了系统的分析.板的挠度、荷载、地基反力及板下地基表面的沉降均被展开为二重Fourier-Bessel级数,这些级数中的待定系数,由板的边界条件、板的控制方程及板-地基的相容条件加以确定,从而将弹性半空间地基与薄圆板的相互作用问题转化为数值积分和代数方程组的求解问题.数值计算表明,该级数解答具有较快的收敛速度.     

The elastic buckling behaviour of a multi-celled panel under almost pure bending

Observations on the elastic buckling behaviour of a riveted thin-walled three-celled panel under almost pure bending are compared with the output from an efficient finite strip microcomputer program. Results from some preliminary studies using simple channel sections and a box section are also given. The agreement was found to be excellent for the simple sections but only fair for the more complex panel. The possible reasons for this are discussed.     

考虑材料不同拉压强度纯弯曲箱梁弹塑性分析

对桥梁工程中常用的薄壁箱梁及其他截面梁纯弯曲进行弹塑性分析,给出了考虑材料拉压屈服强度不同时的塑性极限弯矩计算公式,计算结果表明所推公式具有广泛适用性,方便了薄壁主梁结构弹塑性分析与计算应用。     

Shear and bending flexibility in closed-form moment solutions for continuous beams and bridge structures

Shear deformations can affect final member-end-moments for statically indeterminate continuous beams and frame structures, though for typical civil engineering structures their effect is small and moments can be based on flexural deformations only. When a member is deep relative to span length, however, shear deformations should be considered in the analysis. This can be included in the stiffness method and in a modified form of moment distribution where the carry-over factor is less than one-half due to the added flexibility from shear. In a prior paper the first author presented a new approach for solving statically indeterminate beams and bridge frames, with final end moments given in closed-form expressions. The advantages of this new approach are that no simultaneous equations are required as in the stiffness method, moments are not distributed back and forth as in moment distribution, and manual calculations may be used which give exact results for as many spans as desired. While only flexural deformations were considered in the original paper, this paper presents a closed-form approach that has been modified to include shear deformations. Final expressions are given for continuous beams and bridge frames, providing exact member-end-moments that match results from the stiffness method when shear deformations are included in the analysis.     

曲面建筑幕墙弹性成型法研究

弹性成型法利用材料的弹性,在平板上布置夹持点,通过夹持点的支座对平板施加面外位移,使平板产生弹性变形来形成和保持建筑曲面。这种成型方法的建造成本较低,曲面建筑效果较好,特别是板块接缝的高低差和宽度差较小,具有较好的整体效果。这种成型方法适用于曲面建筑的整个外表皮建造,包括建筑幕墙,建筑屋面和天花。     

螺栓连接曲梁的弯曲应力及螺栓剪力计算

由于螺栓连接曲梁变形是静不定问题,不能简单把螺栓连接曲梁的弯曲变形作为静定问题处理,否则会导致曲梁的弯曲应力及螺栓剪力存在较大的计算误差.因此,按静不定问题研究螺栓连接曲梁的弯曲变形,推导出了曲梁弯曲应力及螺栓剪力的计算公式.算例分析表明,该方法计算结果与有限元方法求解结果非常接近,两种方法计算结果的误差很小;对于螺栓连接曲梁截面弯曲应力及螺栓剪力的计算,应把梁弯曲变形按静不定问题处理更为合理.