Comparisons of honeycomb sandwich and foam-filled cylindrical columns under axial crushing loads

For the conventional thin-walled energy absorber, the energy dissipation during a collision is concentrated in relatively narrow zones. This means that a great deal of material does not participate in the plastic deformation or enter the large plastic deformation stage. To expand the plastic deformation zones and improve the energy absorption efficiency, the authors presented a new type of honeycomb sandwich circular column. This innovative energy absorber is a composite structure composed of two circular aluminum tubes filled with core shaped as a large-cell honeycomb lattice. In this paper, six different honeycomb sandwich circular columns were investigated numerically. Comparisons of the interaction effect between tubes and filler, the deformation modes and the energy absorption abilities of these columns were conducted. The results were as following. The kagome sandwich column had the best energy absorption capability, followed by the columns sandwiched with triangle, hexagon lattices. In addition, foam-filled columns with different adhesive conditions were also simulated and compared with the honeycomb sandwich columns. It was found that increasing the adhesive strength improved the energy absorption and changed the deformation mode of the foam-filled columns. Furthermore, comparison showed that the honeycomb sandwich columns had higher specific energy absorption capability than the foam-filled tubes except for the strong bonded case. The kagome sandwich column performed best in crashworthiness, followed by triangle sandwich column.     

Tests on concrete filled double-skin (CHS outer and SHS inner) composite short columns under axial compression

This paper presents stub columns tests on concrete-filled double skin sandwich tubes (CFDT) constructed using cold-formed steel tubes. The annulus is filled with micro high-strength concrete having compressive cylinder strength of 64 MPa. The outer skin is made of circular hollow sections (CHS), while the inner skin is made of square hollow sections (SHS). Eight different section sizes were used for the outer skin with diameter-to-thickness ratio ranging from 19 to 55. Three section sizes were chosen for the inner skin with width-to-thickness ratio in the range of 20 to 26. The CFDT construction was found to have significant increase in strength, ductility and energy absorption over the outer jacket. A simplified formula is derived to determine the compressive capacity of CFDT and compared against the current design rules. The proposed formula was found in good agreement with experimental results. This paper also verifies the yield slenderness limit (λ_ey) of 82 specified in AS 4100 for cold-formed CHS stub columns.     

塑-钢管混凝土短柱力学性能的试验研究

在复式钢管混凝土短柱和塑管混凝土短柱的研究基础上,提出一种新型的组合柱：实心塑—钢管混凝土短柱,即以塑管来取代复式钢管混凝土短柱的外钢管而形成的承压构件。通过改变内钢管的径厚比、外塑管的厚度以及混凝土的强度等级来研究该新型组合柱的基本力学性能,同时还研究了FRP的加固方式对组合柱承载能力的影响,包括组合柱在轴向荷载作用下的宏观变形特征、破坏模式以及荷载和纵向应变的关系。     

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.     

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.     

Seismic behavior and shear strength of tubed RC short columns

Reinforced concrete (RC) short columns are vulnerable to brittle shear failure during an earthquake. The objective of this research is to evaluate the performance enhancement of RC short columns tubed with circular or square tubes. Eight short columns were tested under combined constant axial load and cyclic lateral load. The tested specimens included three circular tubed RC (CTRC) columns and three square tubed RC (STRC) columns. Two common RC short columns including one circular RC column and one square RC column were also tested as control specimens. The test results indicated that common RC short columns suffered brittle shear failure with little ductility, while the ductility of tubed RC short columns was excellent due to the effective confinement of the outer thin tube to the core concrete. The lateral load strength of CTRC short columns increases with the increasing of axial load ratio, while the axial load ratio has little effect on the plastic deformation capacity of CTRC short columns. The shear strength increases with increasing of axial load ratio, while the plastic deformation capacity decreases with increasing of axial load ratio for STRC short columns. A circular tube prevents the core concrete from shear failure more effectively than a square tube for the tubed RC short columns. A modified ACI design method is adopted to calculate the nominal shear strength of STRC columns as well as CTRC columns based on the test and analysis results.     

Experimental behavior of concrete filled double steel tubular (CFDST) members under low velocity drop weight impact

Thirty-one tests under low velocity drop weight impact were carried out to examine the residual failure modes and the time history of the impact forces, global deformations and strains of concrete filled double steel tubular (CFDST) members in this paper. The parameters varied in the testing program include the column type (straight and tapered), the boundary conditions (simply supported and fixed), the axial load level and the impact energy. The results showed that all CFDST members behaved in a ductile manner and the residual deformation consisted of local deformation at the impact section, as well as the overall bending deformation. Compared to hollow double steel tubes, the CFDST members under the same applied impact energy demonstrate superior impact behavior in terms of higher energy absorbed, smaller global deformation and local deformation due to the interaction of the sandwich concrete and double skin steel tubes. The influence of key parameters on the dynamic resistance ability of CFDST is discussed.     

拉筋接触方式对高轴压比钢管混凝土柱抗震性能影响试验研究

高轴压比下的钢管混凝土柱抗震性能较差,端部拉筋能够有效提高钢管混凝土柱的抗震能力,但拉筋与钢管壁焊接施工困难,不利于工程应用。为了研究拉筋笼与钢管壁间接触方式对钢管混凝土柱整体抗震性能的影响,通过对2个圆形和4个方形截面高轴压比端部带拉筋的钢管混凝土柱进行水平低周往复荷载作用下的试验研究,分析不同接触方式对其破坏形态、滞回耗能能力、骨架曲线、弹性刚度、承载力、延性系数、刚度退化和残余变形率的影响规律。结果表明：拉筋笼与钢管内壁焊接能够加强拉筋和钢管对混凝土的约束作用,从而增加构件的整体刚度。同时,塑性铰处钢管鼓曲幅值与局部屈曲长度明显降低,因此获得了更高的弹性刚度、承载力和滞回耗能能力;外径尺寸和其他设计参数相同时,常用拉筋笼约束方式下方钢管混凝土柱比圆钢管混凝土柱具有更大的抗弯刚度、承载力和塑性耗能能力,且破坏时始终表现为塑性压铰,而带拉筋圆钢管混凝土柱在破坏后往往由塑性压铰转变为拉铰。     

波纹管圆柱定型模板施工技术

中兴通讯南京研发中心1号楼圆柱施工中,采用了直径相同的高密度聚乙烯双壁波纹管作为模板,该模板内壁光滑、强度高、重量轻,外壁呈现环波纹状结构,增加了管材的刚度,且不易变形;采用两个半圆组拼,减少了拼缝,可提高混凝土拆模后的成型质量.波纹管模板价格远低于同类型的定型钢模板,且施工方便,可取得较好的经济效益.     

Theoretical prediction and numerical simulation of multi-cell square thin-walled structures

The axial crushing of square multi-cell columns were studied analytically and numerically. Based on the Super Folding Element theory, a theoretical solution for the mean crushing force of multi-cell sections were derived by dividing the profile into 3 parts: corner, crisscross, and T-shape. Numerical simulations of square multi-cell sections subjected to dynamic axial crushing were conducted and an enhancement coefficient was introduced to account for the inertia effects for aluminum alloy AA6060 T4. The analytical solutions show an excellent agreement with the numerical results. It was found that the crisscross part was the most efficient component for energy absorption and the energy absorption efficiency of a single-cell column can be increased by 50% when the section was divided into 3×3 cells. Finally, the proposed method was extended to analyze the plateau stress of square cell honeycomb subjected to out-plane axial crushing and to some extent validate the mechanical insensitivity of honeycomb to cell size.     

Plastic mechanism analysis of concrete-filled double-skin (SHS inner and SHS outer) stub columns

A plastic mechanism to predict the collapse behaviour of concrete-filled double-skin stub columns is developed and analysed in this paper. Both outer and inner tubes are square hollow sections (SHS). In the analysis, the inner tube is treated the same way as that used in previous research on empty SHS stub columns. New mechanism models are developed for the outer tubes. The effect of local buckling in the outer tube is also studied. The concrete model adopted in this paper considers the effect of confinement of the concrete induced by the double skin tubes. It also considers the strength degradation of concrete for large deformation analysis. It has been found that the effect of local buckling on the collapse curve of the outer tube can be ignored. The concrete model including confinement and strength degradation should be used in order to simulate the collapse behaviour, especially for thin outer tubes. Good agreement was achieved between the plastic mechanism analysis and experimental results.     

Optimization of the foam-filled aluminum tubes for crush box application

Axial impact crush tests on empty and foam-filled square aluminum tubes have been performed. Furthermore, in order to find more details about the crush processes, finite element simulations of the experiments have been done. In terms of finding more efficient and lighter crush absorber and achieving maximum energy absorption, multidesign optimization (MDO) technique has been applied for optimizing the square rectangular tubes. Based on practical requirements the optimum tube geometry, which absorbs maximum energy and has a minimum weight, has been determined. Results of previous work indicated that using high density honeycomb for filling the tubes will results more energy absorption but the weight efficiency has been lost [Zarei HR, Kröger M. Optimum honeycomb filled crash absorber design. Mater Des 2007;29:193–204]. Therefore, a comprehensive study has been performed in order to find out the crush behavior of tube filled with foam with different densities. The MDO procedure has been implemented to find an optimum filled tube that absorbed the same energy as an optimum empty tube can absorb.     

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.     

Collapsible impact energy absorbers: an overview

This paper reviews the common shapes of collapsible energy absorbers and the different modes of deformation of the most common ones. Common shapes include circular tubes, square tubes, frusta, struts, honeycombs, and sandwich plates. Common modes of deformation for circular tubes include axial crushing, lateral indentation, lateral flattening, inversion and splitting. Non-collapsible systems, such as lead extrusions or tube expansions, are considered to be beyond the scope of this review.     

蜂窝式可替换塑性铰梁柱节点力学性能

为避免梁柱翼缘相交处的焊缝在地震作用下发生脆性破坏,提出了一种蜂窝式可替换塑性铰节点形式,以实现中震可修的延性设计抗震目标.通过ABAQUS有限元分析软件对7个不同蜂窝式耗能环尺寸的节点模型、1个腹板开圆孔型削弱型节点模型、1个腹板开六边形孔型削弱型节点模型和1个普通梁柱节点模型在同等条件下进行了低周反复加载模拟.分析...     

钢管约束的钢管混凝土短柱轴压性能试验研究

为增强核心混凝土约束作用并改善其力学性能,在钢管混凝土外部增设圆钢管形成钢管约束的钢管混凝土组合柱,以构件类型、内层和外层钢管含钢率及核心混凝土强度等级为参数,设计并完成了14个钢管约束的钢管混凝土短柱和14个钢管混凝土短柱的轴压试验;观察试验现象和不同试件的破坏模式,研究各关键参数对试件轴压力学性能的影响,分析内层和外层钢管应力和应变发展规律,对比分析钢管混凝土和钢管约束的钢管混凝土的承载力和变形性能。研究结果表明:当钢管约束的钢管混凝土套箍系数不小于0.87,可使钢管混凝土柱的剪切脆性破坏转为截面压溃破坏,外观表现为腰鼓形破坏;达到承载力时,外层钢管横向应力可以达到钢材屈服强度,对核心混凝土的约束作用较强;钢管约束的钢管混凝土短柱轴压承载力较含钢率相近的常规钢管混凝土承载力可以提高20%左右,较内部钢管混凝土承载力可提高约70%。基于叠加法和GB 50936—2014《钢管混凝土结构技术规范》,提出两种钢管约束的钢管混凝土轴压承载力计算方法,预测结果与试验结果吻合良好。     

混凝土-粉煤灰砌块砌体剪力墙的试验研究

本文对混凝土-粉煤灰砌块砌体剪力墙进行了试验研究,试件共2榀,其中一榀是有配筋芯柱的。低周反复水平力作用下的试验结果表明,混凝土边柱与粉煤灰砌体能共同工作,受力特点和破坏形态与剪力墙的相同,具有较好的抗震性能。对比两榀试件的试验结果,表明芯柱可显著提高这种砌体剪力墙的承载力和变形能力。     

圆中空夹层钢管混凝土柱轴压工作机理研究

利用有限元软件ABAQUS建模,并对圆中空夹层钢管混凝土轴心受压时的荷载-变形全过程关系曲线进行计算,计算结果与试验结果符合良好。同时,对轴压时荷载-变形全过程中内外钢管和混凝土所承担的荷载及其相互作用力进行分析,并对空心率、名义含钢率和材料强度等因素对相互作用力的影响进行分析。     

Quasi-static axial compression behavior of constraint hexagonal and square-packed empty and aluminum foam-filled aluminum multi-tubes

The axial crushing behavior of empty and Al close-cell foam-filled single Al tubes and Al multi-tube designs (hexagonal and square) were investigated through quasi-static compression testing. The effects of foam filling on the deformation mode and the crushing and average crushing loads of single tubes and multi-tube designs were determined. The foam filling was found to shift the deformation mode of empty single tube and empty multi-tube designs from diamond into concertina. In multi-tube designs the constraint effects and the frictional forces were found to increase the average crushing loads over those of single tubes. It was also found that foam filling induced a higher strengthening coefficient in multi-tube than single tubes. Although foam filling increased the energy absorption in single tubes and multi-tube designs, it was not effective in increasing the specific absorbed energy over that of the empty tubes. However, multi-tube designs were found to be energetically more effective than single tubes at similar foam-filler densities, proving a higher interaction effect in multi-tube designs.     

Energy absorbtion and mean crushing load of thin-walled grooved tubes under axial compression

In the present study, crashworthiness characteristics of thin-walled steel tubes containing annular grooves are studied. For this purpose, the grooves are introduced in the tube to force the plastic deformation to occur at predetermined intervals along the tube. The aims are controlling the buckling mode and predicting energy absorption capacity of the tubes. To do so, circumferential grooves are cut alternately inside and outside of the tubes at predetermined intervals. Quasi-static axial crushing tests are performed and the load-displacement curves are studied. Theoretical formulations are presented for predicting the energy absorption and mean crushing load. It is found a good agreement between the theoretical results and experimental findings. The results indicate that the load-displacement curve and energy absorbed by the axial crushing of tubes could be controlled by the introduction of grooves with different distances. Also, grooves can stabilize the deformation behavior and thus, the proposed method could be a good candidate as a controllable energy absorption element.