A study of lateral collapse of square and rectangular metallic tubes

The paper presents an experimental and computational study of rectangular and square tubes made of aluminium and mild steel and subjected to quasi-static transverse loading. Deformed shapes at different stages, load–compression and energy–compression curves have been obtained experimentally. The deformation process was numerically simulated using finite element code FORGE2. The contours of different components of stress and strain rate tensors and nodal velocity have been plotted. Mechanics of deformation process, comparison of experimental and computed results and effect of process parameters on the mode of deformation are presented and discussed.     

Simply supported empty and filled thin-square-tubular beams under central wedge loading

Experiments were performed whereby thin-walled square tubes of different span lengths were simply supported and laterally loaded by a wedge indenter in an Instron machine and under the impact of a drop hammer. The tubes were empty as well as filled with polyurethane foam or wood. The span length seems to greatly influence the mode of deformation. Typical histories of deformation and load–compression curves of empty and filled tubes are presented and the effect of infill material and the rate of loading on energy absorbing characteristics of the tubes is discussed. Based on the mechanics of deformation observed experimentally, an analysis is presented to compute the collapse load as well as the post collapse load–compression curve for the simply supported tubes. The analysis considers the formation of stationary and rolling plastic hinges. The results thus obtained compare well with the experiments.     

方钢管混凝土纯弯构件力学性能及承载力的研究

利用轴压方钢管混凝土中钢和混凝土的应力－应变关系模型，采用数值分析方法对方钢管混凝土纯弯构件进行分析，分析结果和试验结果吻合良好。     

方钢管混凝土压弯构件力学性能及承载力的研究

利用轴压方钢管混凝土中钢和混凝土的应力－应变关系模型，采用数值分析方法对方钢管混凝土压弯构件进行分析，分析结果和试验结果吻合良好。     

A study on mode of collapse of varying wall thickness metallic frusta subjected to axial compression

The present paper deals with experimental and computational analysis of deformation behavior of the aluminum thin-walled frusta subjected to axial compression between two parallel platens. The frustas were having different wall thickness through out their height. The frustas were having semi-apical angles between 7 and 9 with D/t values ranging between 26 and 49. Experiments were performed on a universal testing machine INSTRON. The frusta were tested to identify their modes of collapse and to study the associated energy absorption capacity. In experiments, all the frusta were found to collapse with the formation of an axisymmetric mode of collapse due to development of the associated plastic hinges.A Finite Element computational model of development of the axisymmetric mode of collapse is presented and analyzed, using a non-linear Finite Element code FORGE2. The material of the frustas was idealized as rigid visco-plastic. Experimental and computed results of the deformed shapes and their corresponding load- and energy-compression curves were presented and compared to validate the computational model. Typical contours of equivalent strain, equivalent strain rate, nodal velocity distribution, hoop stress and principal stress are presented to help in predicting the mode of collapse. On the basis of the obtained results development of the axisymmetric mode of collapse has been presented, analyzed and discussed.     

A study of the influence of diameter and wall thickness of cylindrical tubes on their axial collapse

Axial compression experiments on aluminium cylindrical shells of diameter to thickness ratios (D/t) between 11.5 and 31.49 were conducted on a gravity drop hammer set up and Zwick machine. Typical histories of their deformation, variation of shell thickness along the fold length, inner and outer radii, folding parameter and size of fold, load–compression curves, energy absorbing capacity, initial peak load, and mean collapse loads obtained from the experiments are presented. Influence of the D/t values of the shell on their modes of collapse and energy absorption capacities are discussed. The shells are numerically simulated and analysed in detail by using the finite element code FORGE2. The material was modelled as rigid-viscoplastic. The experimental and computed results are compared. Typical contours of equivalent strain, equivalent strain rate, different stress components and velocity distribution are presented. The impact response of the shells is compared with their static response.     

Generalised beam theory to analyse the buckling behaviour of circular cylindrical shells and tubes

A formulation of generalised beam theory (GBT) developed to analyse the elastic buckling behaviour of circular hollow section (CHS) members (cylinders and tubes) is presented in this paper. The main concepts involved in the available GBT are adapted to account for the specific aspects related to cross-section geometry. Taking into consideration the kinematic relations used in the theory of thin shells, the variation of the strain energy is evaluated and the terms are physically interpreted, i.e., they are associated with the geometric properties of the CHS. Besides the set of shell-type deformation modes, the formulation also includes axisymmetric and torsion deformation modes. In order to illustrate the application and capabilities of the formulated GBT, the local and global buckling behaviour of CHS members subjected to (i) compression (columns), (ii) bending (beams), (iii) compression and bending (beam-columns) and (iv) torsion (shafts), is analysed. Moreover, the GBT results are compared with estimates obtained by means of shell finite element analyses and are thoroughly discussed.     

Attempts to improve energy absorption characteristics of circular metal tubes subjected to axial loading

In this paper, experimental investigation of two new structural design solutions with the aim of improving crashworthiness characteristics of cylindrical metal tubes is performed. In the first design method, a rigid steel ring is press-fitted on top of circular aluminum tubes. When this arrangement of dissipating energy is subjected to axial compression, the rigid ring is driven into the cylindrical tube and expands its top area; then, plastic folds start shaping along the rest of the tube length as the compression of the structure continues. In the second design method, wide grooves are cut from the outer surface of steel thick-walled circular tubes. In fact, this method converts thick-walled tubes into several thin-walled tubes of shorter length, being assembled together coaxially. When this energy absorbing device is subjected to axial compression, plastic deformation occurs within the space of each wide groove, and thick portions control and stabilize collapsing of the whole structure. In the present study, several specimens of each developed design methods with various geometric parameters are prepared and compressed quasi-statistically. Also, some ordinary tubes of the same size of these specimens are compressed axially to investigate efficiency of the presented structural solutions in energy absorption applications. Experimental results show the significant efficiency of the presented design methods in improving crashworthiness characteristics and collapse modes of circular tubes under axial loading.     

高温作用后圆钢管混凝土轴压力学性能研究

通过对 13个圆钢管混凝土短试件在恒定高温作用后荷载 -变形关系的试验 ,研究高温作用后钢管混凝土轴压力学性能和强度承载力的变化规律。结果表明 ,高温作用后圆钢管混凝土轴心受压构件仍然具有较好的抗变形性能和较高的后期承载力 ;钢管混凝土剩余强度和弹性模量总体上随温度的升高而降低。利用数值分析方法计算了圆钢管混凝土轴压荷载 -变形关系曲线 ,理论计算结果和试验结果吻合较好 ,在此基础上提出了恒高温作用后钢管混凝土轴压承载力和轴压模量简化计算公式     

纤维缠绕CFRP圆管力学性能的试验研究

采用纤维缠绕成型工艺,设计两种尺寸的CFRP圆管,铺层方式均为[(90°/0°)2]S,对CFRP圆管进行压缩和拉伸试验,着重研究CFRP圆管在这两种受力状态下直至破坏的应力-应变关系,极限强度以及材料宏观破坏模式。试验结果表明:铺层方式为[(90°/0°)2]S的CFRP圆管抗拉极限强度和应变远大于其抗压极限强度和应变,但这两种状态下CFRP圆管的弹性模量大致相当,且破坏模式均为脆性破坏。     

Lateral compression of a square or rectangular tube between two parallel narrow width indenters placed non-orthogonally

Collapse behavior of aluminum tubes of square and rectangular cross-sections, when compressed between two identical narrow width indenters placed symmetrically in parallel alignment, is examined. Experiments were performed wherein the angle between the axes of tube and indenters was varied from 0° to 90°. Load compression curves and deformation histories of typical specimens are presented. The collapse of the tubes was seen to be generally symmetrical, though asymmetries were observed in some tubes. Considering only the symmetrical mode of deformation, an analysis is presented for constructing the load compression curves as well as the shape of the deforming tube. The analysis considers the energy, absorbed in stationary and rolling plastic hinges which are formed in the collapsing tube. Computed results thus obtained compare well with the experiments.     

A method for evaluating the mechanical performance of thin-walled titanium tubes

A method which was developed to compare the stress–strain properties of three types of thin-walled, commercially pure titanium tubes is presented. The tubes were of types intended for use in large heat-exchanger applications and were to be subjected to significant plastic deformation during subsequent assembly processes. It had been anticipated that small differences in chemical composition and tube-drawing treatment would produce quite different characteristics. It is known that the properties of titanium can exhibit considerable degrees of anisotropy, especially for wrought products; although axial properties of the materials could be evaluated using standard test equipment and procedures, a novel testing system had to be designed to allow the circumferential properties to be assessed. Significant differences between tube types were observed and anisotropic material behaviour was apparent.     

Investigation on square concrete filled double-skin steel tube (CFDST) subjected to local bearing force: Experiments

Experimental studies on the behaviour of concrete filled double-skin steel tube (CFDST) subjected to local bearing forces are presented in this paper. Sixteen specimens were prepared and tested with the included angle between bearing member (BM) and compression member of 45° and 90°, whilst both the inner and outer steel tubes of the CFDST specimens are square hollow sections (SHS). The main parameters in the tests were: 1) outside width ratio between BM and compression member: from 0.4 to 0.6; 2) hollow ratio of CFDST: from 0 to 0.6; 3) wall thickness of outer steel tube: 3.05 mm and 3.95 mm; and 4) cross-section of BM: solid and hollow. The failure pattern, load versus deformation curve, bearing capacity and corresponding deformation at bearing capacity of the tested specimens are presented and analyzed. The experimental results show that, while subjected to local bearing forces, CFDST specimens have a high bearing capacity and a good deformation-resistant ability. The calculated bearing capacities of CFDST under local bearing forces using the proposed formulae in the paper are evaluated by comparison with the experimental results.     

Energy absorption of aluminium alloy circular and square tubes under an axial explosive load

The energy absorption of circular and square aluminium alloy tubes subjected to an axial explosive load, which is transmitted to a tube by a small attached mass, is discussed. Particular attention is paid to the interaction between the inertia of the attached mass and a tube when the importance of the initial compression phase is revealed. The effect of this phase on the mean load, which is characteristic of the energy absorption capacity of structural elements, is demonstrated. The influence of the material models on the prediction of the response of aluminium alloy circular and square tubes is also discussed in relation with the temperature effects caused by the high strain rates. The analysis shows that the material properties play an important role for the formation of the buckling pattern due to the finite duration of the initial compression phase when plastic stress waves at different speeds propagate along a shell.     

Axial crushing analysis of end-capped circular tubes

The paper investigates collapse mechanisms and energy absorption capacity during the axial compression of the end-capped thin-walled circular aluminum tubes which are hollow or filled with polyurethane foam. An experimental technique is used to evaluate the crushing behavior of the circular tubes under compressive quasi-static strain rate. A numerical model is presented based on finite element analysis to simulate the crushing of circular tubes considering nonlinear response due to material behavior, contact boundary conditions and large deformation. The validated model using existing experimental results is used to evaluate the dynamic response in order to determine the dynamic amplification factor relating the quasi-static results to dynamic response. The experimental and numerical results are used to determine energy absorption capacity due to the plastic deformation of thin-wall tube and crushable foam. The performance of end-capped tubes is compared with non-capped tubes and it is found that maximum initial peak load can be controlled and convenient crash protection systems can be obtained using end-capped circular tubes.     

圆型基坑的变形特点及主要影响因素分析

圆形基坑多为应用于特殊场合的超深基坑,上海某圆形基坑的施工监测资料显示,圆形基坑的变形规律与条形基坑差异很大,对圆形基坑的水平位移、土压力监测资料进行了分析,并通过应用中厚壳理论对基坑变形和内力作的有限元模拟,认为圆形基坑以承受环向轴压为主,与主要承受经向弯矩的条形基坑有本质区别。同时,对混凝土轴向受压、槽段间泥浆受压、环向不均匀荷载等主要变形因素也进行了探讨,指出在设计和施工阶段应对不均匀荷载予以密切关注。     

Experimental behavior of circular concrete-filled steel tube stub columns

This paper presented an experimental study on the behavior of circular, concrete-filled, steel tube (CFT) stub columns with self-compacting concrete (SCC) and normal concrete (NC) concentrically loaded in compression to failure. Four measurement methods on the axial deformation of specimens were compared. Seventeen specimens were tested to investigate the effects of concrete strength, notched holes or slots, and different loading conditions on the ultimate capacity and the load-deformation behavior of the columns. The behavior of these stub columns in confinement was discussed.It is concluded that for the specimens with the entire section loaded, strain gauges with different dimensions could record the strains of the steel tubes, and electronic displacement transducers with certain gauge lengths could record the axial displacement. By using higher strength concrete, the specimens with the entire section loaded experienced a significant increase in the ultimate capacity, but their residual capacity after failure is almost constant. However, once the steel tube was notched, the axial compressive stiffness of specimens was reduced; in some cases the ultimate capacity was also reduced, and the steel tube acted more as a transverse confinement than an axial compression component. Eurocode 4 predicted a reasonable capacity for the unnotched CFT stub columns with both SCC and NC if the entire section of the specimen is loaded.     

Time-dependent tests on intact rocks in uniaxial compression

The influence of strain history on rock specimen deformation during multi-level loading and unloading cyclic uniaxial compression creep tests is studied with a creep testing machine. An experimental data processing method for such creep tests is suggested. The correction formulas to determine the rheological model parameters are derived for the case when load relaxation is considered. Creep and relaxation tests under uniaxial compression on four types of rocks are conducted using an electronic hydraulic servo-controlled stiff testing machine. The creep and relaxation laws of the different rocks are compared. The complete stress–strain curves for red sandstone specimens are obtained at nine strain rates from 2.43×10⁻⁶ to 4.38×10⁻³/s. The effects of strain rates on rock strength and limit strain are discussed. Empirical equations to evaluate the strain rate dependence of rock mechanical properties are presented.     

设置钢筋混凝土柱的砖墙体受压时的承载能力

本文通过理论分析和８片墙体试件的试验结果，讨论了设置钢筋混凝土柱的砖墙体受压时的受力机理、变形、裂缝和破坏形态，提出了它受压时承载能力的计算公式和构造措施。     

钢筋混凝土偏压剪扭构件的变形计算方法探讨

本文主要讨论了钢筋混凝土偏压剪扭构件在单调扭矩作用下刚度变化 ,对这种构件的变形进行了理论分析 ,提出了适用的计算公式 ,与已有的试验结果比较 ,符合良好。