Experimental investigation of concrete-filled cold-formed high strength stainless steel tube columns

This paper presents an experimental investigation of concrete-filled cold-formed high strength stainless steel tube columns. The high strength stainless steel tubes had a yield stress and tensile strength up to 536 and 961 MPa, respectively. The behaviour of the columns was investigated using different concrete cylinder strengths varied from 40 to 80 MPa. A series of tests was performed to investigate the effects of the shape of the stainless steel tube, plate thickness and concrete strength on the behaviour and strength of concrete-filled high strength stainless steel tube columns. The high strength stainless steel tubes were cold-rolled into square and rectangular hollow sections. The depth-to-plate thickness ratio of the tube sections varied from 25.7 for compact sections to 55.8 for relatively slender sections. The columns had different lengths so the length-to-depth ratio generally remained at a constant value of 3. The concrete-filled high strength stainless steel tube specimens were subjected to uniform axial compression. The column strengths, load-axial strain relationships and failure modes of the columns were presented. The test strengths were compared with the design strengths calculated using the American specifications and Australian/New Zealand standards that consider the effect of local buckling using an effective width concept in the calculation of the stainless steel tube column strengths. Based on the test results, design recommendations were proposed for concrete-filled high strength stainless steel tube columns.     

FE modelling and fire resistance design of concrete filled double skin tubular columns

Concrete filled double skin tubular columns (CFDST) have excellent structural behaviour. They have been used as transmission towers and have potential to be used as building columns and bridge piers. Performance of the CFDST columns under ambient temperature has been well studied, whereas fire resistance of such columns is still a major concern. A summary of a series of fire tests on CFDST columns conducted by the authors is briefly presented in the paper. A finite element numerical model is developed to analyse the fire behaviour of CFDST columns, namely thermal and structural responses under fire exposure. The model is verified by the test results and then used to perform parametric analyses. Parameters which have significant effect on the fire behaviour of CFDST columns are identified. Based on the parametric studies, suggestions on the fire resistance design of such columns are made. Practical design tables are derived for the fire resistance design of some typical CFDST columns.     

Research on cold-formed steel columns

The paper summarises research on cold-formed steel columns performed by the author. Cold-formed steel members are either cold-rolled or brake-pressed into structural shapes. As a result, cold-formed steel open sections are usually singly-point- or non-symmetric. The most common types of singly-symmetric sections are channel and angle. The research focused on cold-formed steel open sections, such as plain and lipped channels, channels with simple and complex edge stiffeners as well as plain and lipped angles, and unequal angles. In addition, cold-formed steel built-up closed sections with intermediate stiffeners were investigated. Both experimental and numerical investigations into the strength and behaviour of cold-formed steel columns were conducted. The column strengths obtained from these investigations were compared with the design strengths obtained using various international standards for cold-formed steel structures. Furthermore, the behaviour and design of cold-formed steel lipped channel columns at elevated temperatures were also investigated. The paper also summarises the design recommendations for cold-formed steel columns.     

Load capacity of cold-formed column members of lipped channel cross-section with perforations subjected to compression loading – Part I: FE simulation and test results

An investigation was carried out into the influence of perforations of various shapes on the buckling behaviour of cold-formed column members of lipped channel cross-section. A finite element analysis using ANSYS, an experimental investigation, and design code predictions using the AISI Specification, British Standards (BS) and EU Standards, are employed to determine the buckling load capacity. An experimental investigation of the buckling behaviour of flat and fixed ended columns is presented, and the findings from this are used to validate finite element results, and compare with design code predictions. The numerical results of load vs. displacement behaviour are shown to be in good agreement with those reported from the tests. It is shown that the ultimate failure load of the lipped channels under compression varies greatly with the presence of perforations.     

Post-buckling behaviour and DSM design of web-stiffened lipped channel columns with distortional and local mode interaction

This paper examines the design and load-carrying capacity of fixed-ended web-stiffened lipped channel columns eroded by mode interaction behaviour combined with distortional and local deformations. Initially, the paper presents the results of an experimental investigation of compressive tests on web-stiffened lipped channel columns fabricated from cold-formed mild steel with a thickness of 1.50 mm, which is aimed at determining their failure load-carrying capacity; the experimental investigation also aims to provide experimental evidence of the occurrence of such coupling phenomena concerning distortional and local modes, namely, local-distortional interaction and distortional-local interactive failures. Then, the paper examines the ultimate strength data of experimental columns, both reported in this paper and collected from the literature, and concludes that the current direct strength method (DSM) provides very unsafe predictions concerning such a detrimental interaction nature. Next, two DSM-based design approaches, namely, the nominal strength against local-distortional (NLD) and distortional-local (NDL) procedures, are presented and evaluated on the basis of all available experimental ultimate strength data. Finally, proposals and design considerations based on the DSM-shape for the thin-walled cold-formed steel sections, which fail in mixed modes of distortional and local buckling, are presented.     

异形柱用于8度抗震设防建筑研究

通过混凝土异形柱框架和异形柱框架 -剪力墙结构的弹塑性时程分析以及总结异形柱和异形柱框架的部分试验成果 ,研究了异形柱用于 8度抗震设防地区房屋建筑的可能性 ,提出了 8度抗震设防建筑采用异形柱的设计建议     

Concrete filled high strength steel box columns for tall buildings: Behaviour and design

This paper presents a study of the behaviour and design of concrete filled high strength steel fabricated box columns for use in tall buildings. The many advantages that can be attributed to the use of high strength steel in concrete filled steel box column constructions are presented and discussed. The paper deals with short composite columns and presents guidelines for plate slenderness and overall column slenderness to eliminate local and overall buckling. A proposed design model is developed to calculate the strength of short columns in bending and compression. A method for constructing the strength interaction diagram is presented. Furthermore, to study the ductility of this form of column construction a cross-sectional analysis computer program was developed to consider the moment-thrust-curvature response of such members. This has been undertaken using mild structural steel and high strength steel. The study also shows that, by the use of the method considered, savings can be made in the base column design of a tall building with a negligible penalty in ductility. Finally, recommendations are given for further research into this new method of column construction, which focuses on future experimental work.     

组合T形截面钢管混凝土柱偏心受压试验研究

在分析各种异形钢管混凝土柱工程应用的基础上,提出组合T形截面钢管混凝土柱。考虑长细比、偏心距等参数的影响,设计制作18个组合T形钢管混凝土柱试件。通过偏心受压试验,对长细比16.0<λ≤28.8的组合T形钢管混凝土柱压弯性能进行研究,考察试件的破坏形态,实测试件的荷载-应变曲线和荷载-柱中挠度曲线,分析各参数对试件偏心受压力学性能的影响。通过试验数据回归分析,参考国内外相关规范,提出组合T形截面钢管混凝土柱偏心受压承载力计算公式。试验结果表明：偏心受压柱均为弯曲失稳破坏,长细比越大,弯曲破坏特征越明显;偏心距越大,试件极限承载力越低。研究表明,组合T形钢管混凝土柱的两个组成部分能很好地协同工作,力学性能较好;所提出的承载力计算公式可供工程设计参考。图10表3参8     

A numerical investigation on the behaviour of concrete-filled steel tubular columns under initial stresses

In the practical construction of concrete-filled steel tubular (CFST) structures, the steel tubes usually have already had some initial stresses before they work together with the core-concrete. The initial stress should affect the behaviour of the whole member. In this paper, a comprehensive numerical investigation is presented on the behaviour of CFST columns under initial stresses by the non-linear finite element method. The investigation includes several parametrical studies such as initial stress ratio, slenderness ratio, eccentricity ratio, etc. Numerical analysis results are verified with published experimental ones. Recommendations on how to consider the effect in design formulae are also suggested.     

Experimental behaviour of concrete-filled stiffened thin-walled steel tubular columns

An experimental study on the structural behaviour of concrete-filled stiffened thin-walled steel tubular columns is presented in this paper. The stiffening was achieved by welding longitudinal stiffeners on the inner surfaces of the steel tubes. Companion tests were also undertaken on 12 unstiffened concrete-filled steel tubular (CFST) columns, with or without steel fibres in the infill concrete. The test results showed that the local buckling of the tubes was effectively delayed by the stiffeners. The plate buckling initially occurred when the maximum load had almost reached for stiffened specimens, thus they had higher serviceability benefits compared to those of unstiffened ones. Some of the existing design codes were used to predict the load-carrying capacities of the tested composite columns.     

Column tests of cold-formed steel non-symmetric lipped angle sections

The geometry of angle sections is simple, but the behaviour and design calculations of angle sections can be quite complicated. Furthermore, lipped angle sections with unequal flange widths form a non-symmetric section and the behaviour of the section is even more complicated than a singly-symmetric angle section with equal flange widths. A test program on cold-formed steel non-symmetric lipped angle columns is presented. The non-symmetric angle sections were brake-pressed from high strength structural steel sheets having nominal yield stresses of 450 and 550 MPa with plate thicknesses of 1.0, 1.5 and 1.9 mm. The material properties of the column specimens were obtained by tensile coupon tests. The behaviour and strengths of cold-formed steel non-symmetric lipped angle columns were investigated. The test strengths are compared with the design strengths calculated using the North American Specification for the design of cold-formed steel structural members. In addition, the current design rules in the North American Specification for cold-formed steel non-symmetric lipped angle columns are assessed using reliability analysis. It is shown that the design strengths are generally quite conservative.     

Q460高强度钢材焊接H形截面弱轴压弯柱承载力试验研究

为了研究高强度钢材中厚板焊接H形截面压弯柱的承载力,采用国产Q460高强度钢材11 mm、21 mm中厚板制作了6个焊接H形截面压弯柱,试件截面自由外伸翼缘板宽厚比分别为7、5、3,长细比分别为40、55、80。通过对Q460低合金高强度钢材的材性测试、3种焊接截面残余应力测试、各试件初始几何缺陷测量及承载力试验,进行了H形截面弱轴压弯构件整体失稳承载力的试验研究,并与采用GB 50017-2003《钢结构设计规范》进行计算的承载力对比;同时以理想弹塑性模型,综合考虑试件初始缺陷建立有限元模型,分析计算其承载力。试验及分析结果表明：Q460低合金高强度钢材具有强度高、塑性性能较好等特点;由实测截面残余应力值得到其分布形式与普通钢材焊接H形截面残余应力分布基本相同;高强度钢材焊接H形截面压弯构件承载力试验值明显高于GB 50017-2003设计公式计算值;文中采用的有限元分析方法可以较准确地计算试件的承载力。研究成果为高强度钢材在实际工程中的应用提供试验参考。     

碳纤维复合材料(CFRP)约束矩形截面混凝土柱应力-应变关系研究

现有对于CFRP约束混凝土圆柱的应力-应变关系的研究已经开展得较为广泛，但对于实际中存在更多的矩形柱而言，其相关研究却非常有限。本文对14根碳纤维（CFRP）约束矩形截面混凝土柱进行了轴压试验，分析了试验现象和受力机理，研究了圆角半径，截面长宽比、外包纤维量对承载性能的影响，给出了试验结果，并基于试验数据验证了Lamand Teng（2003）提出的面向设计的纤维约束混凝土矩形柱应力-应变模型，所得的计算值与试验结果基本吻合，证明了该模型的可靠性，能够满足设计要求。     

低周反复水平荷载作用下分体柱承载力的试验研究

本文通过六根分体柱在高轴压比和低周反复水平荷载作用下的试验研究,在已有分体柱抗震性能及刚度分析的基础上,导出了分体柱的承载力计算模型及实用计算公式,提出了分体柱极限承载力的设计计算方法。     

设置砼构造柱的网状配筋砖墙的抗震性能

通过设置钢筋砼构造柱的网状配筋砖砌体墙的拟动力试验,分析了这种墙体的破坏特征和变形性能,建立了抗震承载力计算公式,为抗震设防地区采用这类墙体的房屋设计提供依据.     

Stützen‐Deckenknoten für Schleuderbetonstützen

Column‐Slab Joints for Spun Concrete Columns In this paper joints consisting of high capacity spun concrete columns with reinforcement ratios up to 14,7% and slabs made of normal strength concrete are discussed. The main focus was put on the load transfer from the columns through the concrete slab. In all tests the reinforcement of the columns in the joints was not continuous. For spun concrete columns an optimized solution using a high strength core is presented. The conventional joints and the joints using a high strength core are compared in experimental tests. The results showed that the new joint design is capable of transferring higher loads and reduce the deformations in the slab. On the basis of the experimental data a model was developed, which provides simple design equations for such joints.     

Fire resistance of partially encased steel columns with restrained thermal elongation

The behaviour of composite columns made of partially encased steel sections subjected to fire has been studied numerically by several researchers. Experimental studies are scarce and there are still many phenomena to study. The influence of the axial and rotational restraint on the behaviour of these types of columns subjected to fire is still under research. This paper presents the results of a series of fire resistance tests on these types of columns with restrained thermal elongation. A new experimental set-up, specially conceived for fire resistance tests on building columns, was used for the tests. The experimental set-up was conceived so that the axial and rotational restraint of the columns would be similar to the conditions in a real building. The parameters studied were the load level, the axial and rotational restraint ratios and the slenderness of the column. The main conclusion of this work is that for low load levels the stiffness of the surrounding structure has a major influence on the behaviour of the column subjected to fire. Increasing the stiffness of the surrounding structure led to reductions in the critical times. The same behaviour was not observed for the high load levels.     

Experimental investigation of built-up cold-formed steel section battened columns

This paper presents an experimental investigation on behaviour and design of built-up cold-formed steel section battened columns. The built-up columns were pin-ended and consisted of two cold-formed steel channels placed back-to-back at varied spacing of intersection. The two channels were connected using batten plates, with varying longitudinal spacing. The cold-formed steel channel sections were manufactured by brake-pressing flat strips having a plate thickness of 2 mm. The built-up cold-formed steel section battened columns had different slenderness and geometries but had the same nominal length of 2200 mm. The column strengths, load–axial shortening, load–lateral displacement and load–axial strain relationships were measured in the tests. In addition, the failure modes and deformed shapes at failure were observed in the tests and reported in this paper. Overall, the built-up column tests provided valuable experimental data regarding the column behaviour that compensated the lack of information on this form of construction as well as used to develop nonlinear 3-D finite element models. The column strengths measured experimentally were compared against design strengths calculated using the North American Specification, Australian/New Zealand Standard and European Code for cold-formed steel columns. Generally, it is shown that the specifications were unconservative for the built-up cold-formed steel section battened columns failing mainly by local buckling, while the specifications were conservative for the built-up columns failing mainly by elastic flexural buckling.     

Investigation of insulated FRP-wrapped reinforced concrete columns in fire

Research has demonstrated that fibre-reinforced polymers (FRPs) can be used efficiently and safely in strengthening and rehabilitation of reinforced concrete structures. However, the use of FRPs in buildings has been limited because relatively little is known about the behaviour in fire of reinforced concrete structural members that have been strengthened with FRP systems. This paper presents the recent results of an ongoing experimental study of the fire performance of FRP-wrapped reinforced concrete circular columns. The results of fire tests on two columns are presented, one of which was tested without supplemental fire protection, and one of which was protected by a supplemental fire protection system applied to the exterior of the FRP-strengthening system. The primary objective of these tests was to compare the fire behaviour of the two FRP-wrapped columns and to investigate the effectiveness of the supplemental insulation system. The thermal and structural behaviour of the two columns are discussed. The results show that, although FRP systems are sensitive to high temperatures, satisfactory fire endurance ratings can be achieved for reinforced concrete columns that are strengthened with FRP systems by providing adequate supplemental fire protection. In particular, the insulated FRP-strengthened column in this study was able to resist elevated temperatures during the fire tests for at least 90 min longer than the equivalent uninsulated FRP-strengthened column.