The nonconventional thin-walled arch rib design and its numerical verification of a long span steel arch bridge

Arch bridges have been widely constructed in China owing to their versatile structural configurations and competitive costs. The concept of using high performance prestressed steel wires to withstand the huge horizontal thrust at arch ends has greatly encouraged the engineering practices of large span arch type bridges constructed on soft soil foundations where normally arch structure is an inappropriate selection. However, many technical challenges including the design details, structural behavior and construction method still need to be carefully investigated to ensure the bridge′s safety. As a new practice of such tied arch bridge with nonconventional thin-walled steel box rib and the longest span of this type in the world, this paper presents the innovative design concept and the corresponding studies in regard to its structural behavior compared with conventional single arch design, the shear lag effect of the thin-walled arch rib and its stress distribution via numerical analysis of different finite element models are also investigated. The results show that the current design can reach a very good structural behavior under design load cases, and moreover, provides another very useful engineering practice for long span arch bridge constructed on soft soil foundations.     

Structural behaviour and design of lightweight structural panels using perforated cold-formed thin-walled sections under compression

Cold-formed thin-walled steel sections are widely used as primary loadbearing members in lightweight panels that form walls in residential and other low rise structures. In cold regions, the webs of the steel sections are often perforated to reduce the cold bridging effect in order to increase thermal comfort and reduce energy waste. Perforating the web of a steel section will reduce its loadbearing capacity. This paper presents the results of an experimental and numerical study to investigate the compression behaviour of lightweight structural panels using perforated sections. The primary objective of the tests is to provide experimental data to validate the numerical simulations, which were carried out using the commercial finite element analysis software ABAQUS. The validated FE analysis was used to develop a simple design calculation method to convert a section with perforated web to a section with solid web. In the equivalent solid web, the thickness of the solid web would have the same elastic local buckling strength as the original perforated web with the gross thickness while the thickness of the unperforated flanges remains unchanged. By converting a thin-walled section with perforated web to a solid section with an effective web thickness, the conventional design methods for thin-walled structures can be applied.     

Probabilistic Buckling Analysis of Plates and Shells

For many years, a significant amount of research has been directed towards experimental modelling of thin-walled plates and shells, as well as towards the development of analytical and numerical methods to improve their design against buckling. This paper presents methodologies for probabilistic buckling analysis and reliability assessment of such structural components and examines the link between probabilistic and deterministic studies. In particular, the effect of manufacturing variabilities, such as initial geometric imperfections and residual stresses, on elastoplastic buckling response is investigated through parametric reliability studies of plate panels and cylinders under axial compression.     

Distortional mechanics of restrained steel sections

This paper presents an overview of the mechanics of distortion in members which have restrained thin-walled steel sections. First, the basic features that characterize the distortion of thin-walled sections under compression and/or bending are explained and the generally adopted kinematical assumptions are presented and discussed. On the basis of these assumptions, a simple procedure to build the distortional displacement fields is proposed. Then, two illustrative examples of restrained sections are given and their distortional displacement fields are built. The I-section illustrates the case of a symmetric section having a distortional displacement field with a single d.o.f. The Z-section exemplifies the case of a non symmetric section having a distortional field with two d.o.f. Based on an energy formulation, the equilibrium equation for buckling analysis of simply supported thin-walled members is derived. For two illustrative examples, the distortional displacement field is used to obtain distortional analytical formulae. Finally, some results (buckling loads and moments) were determined and validated by means of comparison with fully numerical obtained from finite strip analysis.     

Energy absorption of axially compressed thin-walled square tubes with patterns

The paper suggests the introduction of patterns to the surface of conventional thin-walled square tubes to improve the energy absorption capacity under axial compressive loads. A quasi-static axial crushing analysis has been conducted numerically by the nonlinear explicit finite element code LS-DYNA. Two types of patterns constructed using the basic pyramid elements were introduced. Type A pattern was aimed at triggering the extensional mode for relatively thin square tubes whereas type B pattern was intended to develop new collapse mode capable of absorbing more energy during collapse. A total of 30 tubes with a length of 120 mm, thickness 1.2 mm and widths of 40 or 60 mm were simulated. Numerical results showed that all tubes with type A patterns developed the extensional collapse mode instead of the symmetric collapse mode and absorbed about 15–32.5% more energy than conventional thin-walled square tubes with a mass increase less than 5%. Meanwhile, a new collapse mode named octagonal collapse mode was observed for tubes with type B pattern and the energy absorption of tubes developing this mode increased by 54–93% compared with the conventional tube. The influence of various configurations of the patterns on the deformation and energy absorption of the tubes was also discussed. The paper opens up a new avenue in design of high energy absorption components.     

Thin-walled structures and related optimization problems

The present paper deals with specific methods for optimal design of thin-walled structures and with the problem of optimal design for serviceability and ultimate limit state. A brief classification of structural optimization is given first, followed by a general formulation of the optimal design problem for thin-walled structures and by a discussion of the design models involved. Specific solution techniques which have been found to be suited for structural optimization and selected applications are presented.     

Effects of wall thickness and geometric shape on thin-walled parts structural performance

This paper investigates the effects of wall thickness and geometric shape of thin-walled structures on their performance during structural analysis. Two automotive thin-walled parts, a front joint panel from a vehicle front structure and a tailgate panel from a truck pickup box were involved in this study. Three types of analyses static analysis, impact analysis, and modal analysis were performed separately on each model to find out the influences of different wall thicknesses on both models’ structural performance. Effects of geometric shape of the models on the analysis results were also discussed. The outcomes of this study provide a solid background for the design of lightweight vehicle architectures to meet the impending energy challenge and will also benefit other industrial sectors such as shipbuilding and aircraft industry.     

Multiobjective crashworthiness optimization of multi-cornered thin-walled sheet metal members

Plastic deformation of structures absorbs substantial kinetic energy when impact occurs. Therefore, energy-absorbing components have been extensively used in structural designs to intentionally absorb a large portion of crash energy. On the other hand, high peak crushing force, especially with regard to mean crushing force, may lead to a certain extent and indicate the risk of structural integrity. Thus, maximizing energy absorption and minimizing peak to mean force ratio by seeking for the optimal design of these components are of great significance. Along with this analysis, the collapse behavior of square, hexagonal, and octagonal cross-sections as the baseline for designing a newly introduced 12-edge section for stable collapse with high energy absorption capacity was characterized. Inherent dissipation of the energy from severe deformations at the corners of a section under axial collapse formed the basis of this study, in which multi-cornered thin-walled sections was focused on. Sampling designs of the sections using design of experiments (DOE) based on Taguchi method along with CAE simulations was performed to evaluate the responses over a range of steels grades starting from low end mild steels to high end strength. The optimization process with the target of maximizing both specific energy absorption (SEA) and crush force efficiency (CFE), as the ratio of mean crushing load to peak load, was carried out by nonlinear finite element analysis through LS-DYNA. Based on single-objective and multi-objective optimizations, it was found that octagonal and 12-edge sections had the best crashworthiness performance in terms of maximum SEA and CFE.     

A fire resistance design method for thin-walled steel studs in wall panel constructions exposed to parametric fires

This paper investigates the applicability of a simple fire resistance design method for axially loaded thin-walled steel studs in wall panel assemblies when exposed to parametric fires from one side. The simple method includes calculations of cross-section temperatures and ultimate load carrying capacities at elevated temperatures. The simplified calculation method for heat transfer in the cross-section is based on dividing the cross-section into a number of segments. The thermal properties of these layers are based on weighted averages of the thermal properties of the components contained within. The structural capacity calculation method is based on the Direct Strength Method. Results from the design method are compared with the results from Finite Element simulations for heat transfer and structural analysis (236 models). The calculation results are in good agreement with the simulation results and the proposed method may be used in performance-based fire engineering design of such construction.     

Sustainability in highrise building design and construction

This paper presents a review of the recent literature on sustainability in construction and design with a focus on highrise buildings. The paper is divided into the following main sections: energy consumption, environmental effects and green practices for highrise buildings. A number of concepts in sustainable design are reviewed including passive solar design, renewable energy resources, cogeneration and tri‐generations, embodied energy reduction, net zero energy building, carbon emission reduction, envelope environment quality, green materials, efficient mechanical design and innovative structural systems. Their applications in a dozen signature and iconic structures are described. In order to achieve net zero energy in a new highrise building, first, multiple green solutions need to be evaluated using two categorical solutions: passive solar and envelop environment design and renewable energy resources along with efficient energy generators. Next, a robust optimization algorithm should be used to select the optimum set of solutions. This is worth pursuing in future sustainable design of highrise buildings because they are massive and complex structures with many components. Copyright © 2016 John Wiley & Sons, Ltd.     

Ratcheting behaviour of elasto-plastic thin-walled pipes under internal pressure and subjected to cyclic axial loading

The present paper is concerned with the analysis of the ratcheting behaviour of elasto-plastic thin-walled pipes under internal pressure and subjected to cyclic axial loading. Understanding the behaviour of this kind of structure at different load levels is of critical importance in a range of engineering applications such as in the design of structural components of power and chemical reactors. Depending on the kinematic hardening, the pipe may exhibit a ratcheting behaviour in the circumferential direction, which leads to a progressive accumulation of deformation. Many different constitutive theories have been proposed to model the kinematic hardening under such kind of loading history. The present paper presents a simple local criterion to indicate whether or not the pipe may exhibit a progressive accumulation of deformation. Such criterion is independent of the choice of the evolution law adopted for the backstress tensor. As an example, a semi-analytic approach using a mixed nonlinear kinematic/isotropic hardening model is proposed to be used in a preliminary analysis of this kind of structure.     

The influence of the in-plane warping on the behavior of thin-walled beams

The paper presents a theoretical study of the importance of the in-plane deformation on the structural behavior of thin-walled isotropic and composite beams which are subjected to bending and torsional moments. To separate the effects of the out-of-plane warping and the in-plane warping, the overall solution methodology is based on a generic combination of two complementary “inner” and “outer” solutions. The inner model is based on numerical optimization tools which are employed to determine the in-plane deformation that will ensure a stationary (minimum) state of the total potential energy. The outer model performs global solution for cross-sections that are rigid in their own plane but includes the out-of-plane warping. The overall solution is capable of determining the influence of the in-plane warping on any existing approximate numerical scheme that do not include this deformation component. The results correlate well with known analytic solutions for isotropic tubes under pure bending. A parametric study of the relative importance of the in-plane warping as a function of the geometry and the loading parameters in rectangular thin-walled isotropic and composite beams is also presented along with some buckling considerations.     

结构分析软件中的二次分析探讨

在结构分析中,有很多需要利用前一次的计算结果来确定下一次的计算参数以进行二次分析的情况,据此提出了结构二次分析的理念,二次分析的结果才是工程真正可用的计算结果。结合常用结构分析软件,从结构整体分析、具体结构类型和结构构件三个层次详细阐述了在结构分析中需要进行二次分析的原因和依据,并对具体设计给出了操作性强的实用方法,以期对今后更准确地利用结构分析软件进行结构设计提供一些有益的借鉴。     

Performance-based analysis of concrete-filled steel tubular beam-columns, Part I: Theory and algorithms

This paper presents a performance-based analysis (PBA) technique based on fiber element formulations for the nonlinear analysis and performance-based design of thin-walled concrete-filled steel tubular (CFST) beam-columns with local buckling effects. Geometric imperfections, residual stresses and strain hardening of steel tubes and confined concrete models are considered in the PBA technique. Initial local buckling and effective strength/width formulas are incorporated in the PBA program to account for local buckling effects. The progressive local buckling of a thin-walled steel tube filled with concrete is simulated by gradually redistributing normal stresses within the steel tube walls. Performance indices are proposed to quantify the section, axial ductility and curvature ductility performance of thin-walled CFST beam-columns under axial load and biaxial bending. Efficient secant algorithms are developed to iterate the depth and orientation of the neutral axis in a thin-walled CFST beam-column section to satisfy equilibrium conditions. The analysis algorithms for thin-walled CFST beam-columns under axial load and uni- and biaxial bending are presented. The PBA program can efficiently generate axial load-strain curves, moment-curvature curves and axial load-moment strength interaction diagrams for thin-walled CFST beam-columns under biaxial loads. The proposed PBA technique allows the designer to analyze and design thin-walled CFST beam-columns made of compact or non-compact steel tubes with any strength grades and normal and high-strength concrete. The verification and applications of the PBA program are given in a companion paper.     

Cyclic responses of thin-walled structural steel members subjected to three-dimensional loading

This paper presents an experimental investigation of the cyclic responses of thin-walled structural steel members under an earthquake-induced, coupled three-dimensional load. Nine thin-walled structural steel members were tested under various load combinations to investigate the correlation among bending, axial load and torsion. Bending capacities of tested members were compared to distinguish the effects of torsion, axial load and their combination in affecting a member's bending performance. Test results show that members' bending strength is reduced when axial load is applied. Further reduction in member performance is exhibited when coupled torsion and axial load are both present; this reduction demonstrates the necessity for including torsion in calculating a member's bending strength when buildings are designed to be earthquake-resistant.     

轴压下薄壁管断裂的可能性分析

在车辆的防撞设计中薄壁管作为耗能构件被广泛采用,轴压力是防撞部位承受的最典型荷载之一。为了减轻重量,薄壁管采用轻质材料诸如高强度钢材、铝和镁制成。然而,这些轻质材料中的大多数与传统的钢材相比更脆且易断裂。由于材料的应力、应变状态通常被作为判断其构造断裂点的依据,故对薄壁管的三轴应力分布和时程及其等效应变进行了有限元模拟。分析结果显示,三轴应力和等效应变沿着管长波动,方形薄壁管的断裂更可能发生在边缘而非其他位置。对于相同的轴压冲击,当初始冲击速度在6～24m/s变化时,方形薄壁管内部的应力、应变变化不大。对影响应力、应变状态的参数,包括横截面角的形状、壁厚和横截面形状分别进行研究。所得结果可为薄壁管的设计及轻质材料力学性能的试验特性研究提供参考。     

Some comments on the numerical analysis of plates and thin-walled structures

The paper briefly reviews the theoretical analysis of plates structures that might exhibit multiple ‘loading paths’ and highlights the need for engineers using non-linear numerical modelling to be aware of the multi-mode phenomenon and to ensure that the modelling is set up in such a manner that the various ‘loading paths’ and possible changes of path would be incorporated in the modelling response. The paper presents a simple example of numerical analysis of thin-plate buckling that involves ‘coupled buckling modes’ and provides comments on suitable methods for defining in a simple and straightforward way the numerical modelling that could ensure that results from computer analysis describe the physically correct relationship between applied loadings and deformations of thin-walled structural components.     

Performance-based analysis of concrete-filled steel tubular beam–columns,Part II: Verification and applications

The theory and algorithms of a performance-based analysis (PBA) technique for the nonlinear analysis and performance-based design of thin-walled concrete-filled steel tubular (CFST) beam–columns with local buckling effects were presented in a companion paper. Initial local buckling and effective strength/width formulas for steel plates are incorporated in the PBA program to account for local buckling effects. Performance indices are used in the PBA program to quantify the section, axial ductility and curvature ductility performance of thin-walled CFST beam–columns. This paper presents the verification and applications of the PBA program developed. The axial load–strain curves, ultimate axial loads and moment–curvature curves for thin-walled CFST columns predicted by the PBA program are verified by experimental data. The PBA program is then utilized to investigate the effects of local buckling, depth-to-thickness ratio, concrete compressive strengths, steel yield strengths and axial load levels on the stiffness, strength and ductility performance of thin-walled CFST beam–columns under axial load and biaxial bending. The PBA technique developed is shown to be efficient and accurate and can be used directly in the performance-based design of thin-walled CFST beam–columns and implemented in advanced analysis programs for composite columns and frames.     

High strength thin-walled rectangular concrete-filled steel tubular slender beam-columns,Part II: Behavior

Experimental and numerical research on full-scale high strength thin-walled rectangular steel slender tubes filled with high strength concrete has not been reported in the literature. In a companion paper, a new numerical model was presented that simulates the nonlinear inelastic behavior of uniaxially loaded high strength thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-columns with local buckling effects. The progressive local and post-local buckling of thin steel tube walls under stress gradients was incorporated in the numerical model. This paper presents the verification of the numerical model developed and its applications to the investigation into the fundamental behavior of high strength thin-walled CFST slender beam-columns. Experimental ultimate strengths and load-deflection responses of CFST slender beam-columns tested by independent researchers are used to verify the accuracy of the numerical model. The verified numerical model is then utilized to investigate the effects of local buckling, column slenderness ratio, depth-to-thickness ratio, loading eccentricity ratio, concrete compressive strengths and steel yield strengths on the behavior of high strength thin-walled CFST slender beam-columns. It is demonstrated that the numerical model is accurate and efficient for determining the behavior of high strength thin-walled CFST slender beam-columns with local buckling effects. Numerical results presented in this study are useful for the development of composite design codes for high strength thin-walled rectangular CFST slender beam-columns.     

Biaxially loaded high-strength concrete-filled steel tubular slender beam-columns,Part I: Multiscale simulation

The steel tube walls of a biaxially loaded thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-column may be subjected to compressive stress gradients. Local buckling of the steel tube walls under stress gradients, which significantly reduces the stiffness and strength of a CFST beam-column, needs to be considered in the inelastic analysis of the slender beam-column. Existing numerical models that do not consider local buckling effects may overestimate the ultimate strengths of thin-walled CFST slender beam-columns under biaxial loads. This paper presents a new multiscale numerical model for simulating the structural performance of biaxially loaded high-strength rectangular CFST slender beam-columns accounting for progressive local buckling, initial geometric imperfections, high strength materials and second order effects. The inelastic behavior of column cross-sections is modeled at the mesoscale level using the accurate fiber element method. Macroscale models are developed to simulate the load-deflection responses and strength envelopes of thin-walled CFST slender beam-columns. New computational algorithms based on the Müller's method are developed to iteratively adjust the depth and orientation of the neutral axis and the curvature at the column's ends to obtain nonlinear solutions. Steel and concrete contribution ratios and strength reduction factor are proposed for evaluating the performance of CFST slender beam-columns. Computational algorithms developed are shown to be an accurate and efficient computer simulation and design tool for biaxially loaded high-strength thin-walled CFST slender beam-columns. The verification of the multiscale numerical model and parametric study are presented in a companion paper.