The measurement of imperfections in cylindrical thin-walled members

The structural behaviour of thin-walled circular cylindrical members has been shown to be imperfection sensitive. However, only little information of the exact nature of imperfections in such members is available. In this paper a method of measuring imperfections in circular cylindrical members is described, the method is simple to implement in a laboratory environment while providing accurate measurements. Numerical methods to process the measurements into three-dimensional imperfection maps are also presented along with an algorithm to distinguish between significant imperfection patterns and measurement ‘noise’. Results from a recent research project where this method has been used illustrate the derivations in this paper.     

A Koiter's perturbation strategy for the imperfection sensitivity analysis of thin-walled structures with residual stresses

This paper suggests a strategy for the imperfection sensitivity analysis of elastic thin-walled structures with notable residual stresses. The analysis is carried out by means of a Koiter's perturbation approach. The concept of imperfection, traditionally associated with geometric and load factors, is extended in this paper to the residual stresses. The strategy is implemented in a FEM code. A comparison of the obtained results allows a discussion on the accuracy and the influence of the different coefficients connected to the asymptotic analysis of the residual stresses.     

Long duration blast loading of cylindrical shell structures with variable fill level

This paper investigates the effect of long-duration blast loads on the structural response of aluminium cylindrical shell structures containing varying fluid levels. A detailed non-linear numerical model comprising remapped Lagrangian analysis examines localised plate buckling and deformation. The relative computational accuracy of an uncoupled numerical model developed in this paper is compared with experimental results obtained at one of the worlds׳ most powerful air blast testing facilities. Evaluating structural response for blast loads with an extended dynamic pressure phase is exceptionally difficult using only Eulerian controlled CFD methods; due to domain constraints incorporating restrictive cell sizes engulfing the target structure before remapping. The further complexity of shock transmission through a structure damped by an internal fluid is examined experimentally. Fibre optic controlled instrumentation and high speed photography provide a vital insight towards coupled flow-field behaviour of the shell structure. Surface mounted pressure gauges on the cylindrical wall accurately record the pressure time history throughout the passage of the shock wave. This paper highlights the key influence on blast response due to varying internal fluid levels and the relative importance pertaining to a conservative design solution for varying operational states. Numerical modelling in this paper demonstrates the robust accuracy achievable for a remapped Lagrangian solution. The routine analytical assumption of uniform drag forces acting on the structural body was shown to be both misleading and inaccurate by comparison. This research will be of direct interest to both practitioners and researchers considering high power explosive blasts from sources such as hydrocarbon vapour cloud ignition.     

Meshfree analysis of dynamic fracture in thin-walled structures

Analysis and reliability assessment of fracturing thin-walled structures is important in engineering science. We focus on numerical analysis of dynamic fracture of thin-walled structures such as pipes and pressure vessels. Instead of using finite element method, we propose meshfree method that has advantages because its higher order continuity and smoothness and its opportunities to model fracture in a simple way. Therefore, connectivity between adjacent nodes are simply removed once fracture criterion is met. The main advantage of our meshfree method is its simplicity and robustness.     

An analytical model for axial crushing of a thin-walled cylindrical shell with a hollow foam core

A thin-walled tube filled with light-weighted foam has wide engineering applications because of its excellent energy absorption capacity. When the structure is axially crushed, the interaction between the tube and foam core plays an important role in its energy absorption performance. Previous theoretical studies so far have largely been concerned with fully in-filled tubes. In this paper, a theoretical model is proposed to predict the axi-symmetric crushing behaviour of such structures but with a partial infill. Using a modified model for shell and considering the volume reduction for the foam core, the mean crushing force is predicted by the energy balance. The proposed formula agrees well with previous results reported in literature. A parametric study is carried out to examine the contribution of foam core plateau stress (σ_f), amount of filling and shell's radius-to-thickness ratio (R/h) on the axial crushing behaviour of the structure. This study can give valuable design guidelines in using thin-walled structures as an energy absorber.     

双曲空腹扁网壳结构稳定性分析

以双曲空腹扁网壳为例,采用有限元软件ANSYS对该类网壳进行稳定性分析,用Block lanczos法分析结构的特征值,同时用弧长法平衡跟踪技术对结构进行几何非线性分析及考虑初始缺陷影响的非线性全过程屈曲分析,并讨论该类网壳结构对初始缺陷的敏感性问题。     

Critical assessment of Eurocode approach to stability of metal cylindrical silos with corrugated walls and vertical stiffeners

The paper deals with stability of steel cylindrical silos composed of corrugated walls and vertical open-sectional stringers. Comprehensive three-dimensional finite element analyses were carried out with perfect slender, semi-slender and squat silos by means of a linear buckling approach. Corrugated walls were simulated as an equivalent orthotropic shell and vertical open-sectional stringers as beam elements. The FE results were compared with the Eurocode approach. In addition, comprehensive FE computations for axially compressed cylindrical shells composed of an orthotropic shell and stringers were carried out. An improvement of standard formulae was proposed.     

Stability loss of thin-walled cylindrical tubes, subjected to longitudinal compressive forces and external corrosion

The paper is devoted to investigation of stability loss of thin-walled elastic circular cylindrical pipes subjected to simultaneous action of longitudinal compressive forces and uniform corrosion from outside. The pipe is treated as a thin closed elastic circular cylindrical shell which can be described within Kirchhoff–Love approximation. The critical time of stability loss of the pipe is found, using the upper critical load value for static stability loss of the pipe, not subjected to corrosion, and the law of corrosion rate. Numerical results were obtained for pipes, made from steel and aluminum with different initial wall thickness.     

北京工人体育场开口单层扁薄拱壳罩棚钢结构整体稳定性能研究

北京工人体育场钢结构罩棚为周边设置摩擦摆支座的开口单层扁薄拱壳结构。为提升结构整体稳定性,采用考虑结构整体初始缺陷的4等分杆件模型进行有限元模拟,针对拱壳整体形态、构件截面规格和支座刚度共计3类11个参数进行单变量敏感性分析,评估结构在特征值屈曲分析、弹性和弹塑性全过程分析下的受力性能。分析表明：弹性全过程分析临界系数与特征值屈曲分析临界系数间具有强线性相关性,二者比值平均为0.535;结构塑性折减系数平均值为0.418;拱壳整体形态类参数的敏感性相对较高,其中拱端高差敏感性最高;构件截面规格类参数中,拱肋和外环梁截面规格的敏感性较高,支座刚度的敏感性相对较低。提出了结构整体稳定设计流程,结合特征值屈曲敏感性分析结果、构件承载力富余度和弹塑性全过程分析出铰杆件类型进行综合分析,有助于提高结构整体稳定设计效率。     

杆件截面对单层网壳结构的影响

运用非线性有限元方法，对不同外径、不同壁厚的网壳承载力进行了计算研究，描述了杆件截面对网壳结构稳定性影响和变化的规律，得出了工程设计中杆件截面选择的建议。     

基于薄壁圆柱壳理论的盾构隧道抗震拟静力分析法

为简化盾构隧道抗震分析,在获得深埋盾构隧道周边自由场剪应变和剪应力的基础上,基于弹性薄壁圆柱壳理论,给出了求解深埋盾构隧道水平地震剪切波作用下的附加内力计算公式,并与同等条件等效刚度数值分析方法结果进行了对比。研究表明：滑移和不滑移条件下的拟静力计算结果与相应的数值分析结果具有良好的一致性,说明基于弹性薄壁圆柱壳理论获得的盾构隧道拟静力公式具有良好的合理性。研究还表明：水平地震剪切波作用下,可滑移条件下的附加弯矩和附加剪力分别大于不滑移条件下的附加弯矩和附加剪力,可滑移条件下的附加轴力小于不滑移条件下的附加轴力;附加弯矩和附加轴力呈现反对称分布特性,其最大值通常分布在45°和225°雷达对称轴或135°和315°雷达对称轴上,附加剪力最大值一般分布在0°和180°雷达对称轴上。研究结论对盾构隧道工程抗震设计具有一定的参考价值。     

A new approach for thin-walled member analysis in the framework of GBT

A new approach is illustrated for the cross-sectional analysis to be performed in the context of the Generalised Beam Theory (GBT). The novelty relies in formulating the problem in the spirit of Kantorovich’s semi-variational method, namely using the dynamic modes of an unconstrained planar frame as in-plane deformation modes. Warping is then evaluated from the post-processing of these in-plane modes, thus reversing the strategy of the classical GBT procedure. The new procedure does not require several steps of the classical algorithm for the determination of the conventional modes, in which bending, shear and local modes are evaluated separately, and is applicable indifferently to open, partially-closed and closed sections. The efficiency and ease of use of the method are outlined by means of two examples, aimed to describe the linear–elastic behaviour of thin-walled members.     

Recent advances on postbuckling analyses of thin-walled structures: Beams, frames and cylindrical shells

The lateral postbuckling response of thin-walled structures such as bars and frames with members having steel rolled shapes as well as circular cylindrical shells under axial compression is thoroughly reconsidered. More specifically via a simple and very efficient technique it is found that beams with rolled shapes (symmetric or non symmetric) under uniform bending and axial compression exhibit a stable lateral-torsional secondary path with limited margins of postbuckling strength. New findings for the static and dynamic stability of frames with crooked steel members-due to the presence of residual stresses-are also reported. It is comprehensively established that the coupling effect due to initial crookedness and loading eccentricity may have a beneficial effect on the load-carrying capacity of the frames. Moreover, simple mechanical models are proposed for simulating the buckling mechanism of axially compressed circular cylindrical shells. Very recently Bodner and Rubin proposed an 1-DOF mechanical model whose buckling parameters correlated to those of the shells by using an empirical formula based on experimentally observed shell buckling loads. In the present analysis a new 2-DOF model for the static and dynamic buckling of axially compressed circular cylindrical shells, which can include mode coupling, is presented.     

An approach to reliability-based optimization of redundant structures

This paper proposes an optimum design procedure for redundant structures with the constraints on the formation probabilities of structural failure modes. Although there exist numerous failure modes in a large-scale redundant structure, it is found that only a representative group consisting of some dominant failure modes needs to be considered in the optimization process. The proposed procedure introduces such dominant modes step by step from various design stages to keep the total number of the constraints at a minimum level. A branch-and-bound technique is used to identify dominant failure modes in a design state. Some analytical methods are discussed for the calculation of the formation probabilities of failure modes in the optimum design process. A numerical example is given to illustrate the effectiveness of the proposed procedure.     

单层球面网壳结构的风振及其参数分析

大跨度网壳结构日趋多样化、大型化、复杂化．风荷载常常起主要甚至决定性作用，风振动力响应特性研究日益受到关注与重视．目前，网壳结构的抗风设计参数取值方法尚不完善，大多沿用高层或高耸结构设计规范．本文讨论了网壳结构风振响应的时程分析计算方法，并利用节点位移风振系数、单元内力风振系数等概念来衡量网壳结构风振特性．对一类K6—6型单层球面网壳结构进行了包括几何参数、结构参数、阻尼比参数、边界约束参数、平均风速参数等多种工况的风振特性参数影响分析，得出该类单层球面网壳结构在上述各种参数工况下风振系数的变化规律，为单层网壳结构抗风设计、防灾分析提供一定参考．     

网壳结构的整体稳定性分析方法

介绍了壳体结构的四类整体稳定性分析方法,并分别阐述了各类网壳结构整体稳定性分析方法的原理、研究现状及其优缺点,为工程结构分析提供指导,以期提高壳体结构稳定性分析水平。     

A systematic approach towards the structural behaviour of a lightweight deck–side shell system

Lightweight structures are increasingly used for high-speed ships. This paper presents a systematic approach to analyse the structural behaviour of a lightweight deck–side shell system using high strength steel. An analytical model of the deck–side shell system was first given, which includes the effects of stiffeners for the deck and side shell, the support conditions of the centreline girder (CL-girder), the influence of transverse beams, and the interaction between the side shell and the lightweight deck as parts of problems to the solution. By changing several geometric parameters, the sensitivity of both overall and local stress and deflection for the deck–side shell system was investigated. The different geometric parameters analysed comprise the influence for variation in the thickness of the web for transverse beams, longitudinal stiffeners and the CL-girder, the thickness of lower flange for the transverse beam and, the thickness for the panel. Furthermore, the influence of the lightweight deck and loads from the deck above on the side shell, the effects of the side shell and loads from top deck on the deck, the support conditions for the CL-girder, and the influence of deck loads on the eigenmodes were also analysed. By evaluating the results obtained from FE simulation, the support conditions of the CL-girder, the thickness of the panels and the lower flange of the transverse beams were found to be the most relevant parameters affecting both the stress and the deflection distribution of the structure. The dynamic characteristics of the structure were also analysed. The FE analysis concerning buckling of the structure was present. The results enable naval architects and structural engineers to design new extreme lightweight deck structure more reliable and economical. And some suggestions for future research are also given.     

Finite element reliability and sensitivity analysis of structures using the multiplicative dimensional reduction method

Finite element reliability analysis (FERA) has been used to evaluate the reliability of structures. In FERA, approximate methods are commonly used to estimate the mean and variance of the structural response, while its probability distribution is primarily derived based on the Monte Carlo simulation (MCS) method. This paper advances FERA by combining it with the multiplicative dimensional reduction method (M-DRM). The proposed M-DRM allows fairly accurate estimation of the statistical moments, as well as the probability distribution of the structural response. The distribution of the response is obtained using fractional moments, which are calculated from the M-DRM, along with the maximum entropy principle. The variance of the response, based on global sensitivity measures, is obtained as a by-product of the analysis. The proposed approach is integrated with the OpenSees software and is illustrated through examples of nonlinear finite element analyses of reinforced concrete and steel frames. The paper shows that the proposed approach is an accurate and efficient alternative for FERA.     

A new approach to determine the base shear of steel frame structures

Base shear (V) is the maximum lateral force that will occur due to seismic ground motion at the base of a structure. Calculations of base shear depend on a lot of factors such as soil conditions, level of ductility, fundamental period of vibration of the structure, etc. A great number of methodologies have been developed to determine the dynamic responses of individual frameworks. However, there is no well established empirical solution of the dynamic response of the problem due to the base shear of the steel frames. In this study, a formulation based on NN to determine the dynamic response of both braced and unbraced plane steel frames are provided. The presented formulation is a function of number of stories (ns), bays of the frames (nb), and soil types (Z). The training and testing patterns of the proposed NN formulation are obtained from linear Finite Element Analysis (FEA) solution. The NN-based formulation results are compared with the results obtained from numerical and some current design codes. The NN- based formulation results are found to be more accurate.