冷弯薄壁型钢双肢拼合构件轴压承载力研究

目前我国相关规范对冷弯薄壁型钢组合截面构件的承载力设计方法比较粗略。基于已有的卷边槽形截面构件和由其组成的组合箱形截面构件的轴心受压承载力试验研究结果,通过有限元模拟和理论分析研究了此类构件拼合前后的受力性能的差异。分析了安装误差和连接件间距对拼合构件承载力的影响。提出了针对组合箱形和工字形截面构件的轴心受压承载力设计方法。研究表明,组合箱形截面构件的整体屈曲和畸变屈曲承载力较单肢截面构件有一定提高,而组合工字形截面构件仅整体屈曲承载力有一定提高。设计承载力与试验结果的比较表明,所提出的建议设计方法基本合理,可为相关规范的编制提供参考。     

曲线形钢管混凝土(CCFST)组合构件轴压试验

描述了一系列曲线形钢管混凝土(CCFST)组合构件的轴压试验。对20个试件(其中包含18个CCFST组合构件和2个曲线形中空截面钢管柱)进行了试验,研究组合构件中管件形状(圆形和方形)、初始曲率(βr,0%～7.4%)、名义长细比(λn,9.9～18.9)、截面形式(2种主要构件、3种主要构件和4种主要构件)以及支撑形式(板条和绳状)等因素对其性能的影响。试验结果表明:CCFST组合构件试样的极限强度和刚度随着βr或λn的增加而降低。板条和绳状支撑组合构件的承载力和失效模式不同。给出利用等效长细比计算轴压下CCFST组合构件极限强度的简单方法。     

四肢拼合冷弯薄壁型钢截面立柱轴压性能试验研究及数值分析

对不同长细比的8根四肢拼合冷弯薄壁型钢截面立柱的轴压性能进行试验研究,在试验研究的基础上建立考虑材料、几何和接触非线性的有限元模型,并通过对试验试件的数值模拟,验证有限元方法的正确性。采用数值方法分析长细比、连接螺钉间距、截面翼缘宽厚比对四肢拼合冷弯薄壁型钢截面立柱轴压性能的影响。结果表明:试件最终破坏均呈现局部屈曲和畸变屈曲的破坏模式;四肢拼合冷弯薄壁型钢截面立柱的轴压性能具有"1×4≥4"的拼合效应;随着长细比的增大,四肢拼合立柱的最大承载力和刚度逐渐降低;当螺钉间距在150～450mm之间变化时,四肢拼合立柱的最大承载力和刚度变化不大;减小四肢拼合立柱截面的翼缘宽厚比,可以显著提高其最大承载力。     

冷弯箱形组合截面长细比的计算

根据AISIS100-2007规范D1.2对由2种截面组成的受压构件(其屈曲模式与连接处剪力大小有关)的有关规定,其抗压承载力必然降低,应用修正长细比(KL/r)m替代原长细比KL/r。修正长细比考虑了连接焊缝间距及组件最小回转半径的影响。基于D1.2截面规定,必须确定焊接箱形组合构件承载力的降低程度。进行了48组试验,研究不同焊缝间距下(100～900mm),刚性及柔性端约束时,由2个C形截面组成的箱形截面受压构件的性能。试件长度为900mm,截面尺寸为100mm×100mm。其中24个试件厚度为1.5mm,其余试件厚度均为2.0mm。试验表明:除焊缝间距为900mm及柔性端约束条件下,极限抗压承载力总体上都没有降低,AISIS100-2007中考虑的极限承载力降低不适用于这些杆件。     

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.     

Evaluation of the slenderness ratio in built-up cold-formed box sections

According to section D1.2 of AISI S100-2007 for compression members composed of two sections in contact whose buckling mode involves shear forces in the connectors, a reduction must be made, KL/r must be replaced by (KL/r)_m. This new modified slenderness ratio takes into account the connection weld spacing and the minimum radius of gyration of an individual shape in the built-up member. Under the provisions of section D1.2 a reduction in load capacity must be made for built-up welded box members, which are the subject of this study. An experimental investigation on 48 samples was addressed to determine the comparative behaviour under compression load of box sections composed of two C-section members in contact by seam welds with different weld spacings (ranging from 100 to 900 mm). The studs were tested simulating rigid and flexible end support conditions. The length of the samples was 900 mm with a cross-section of 100 mm×100 mm. The base material thickness was 1.5 mm (gauge 16) for 24 samples and 2.0 mm (gauge 14) for the rest. The testing done on the samples did not show a statistical reduction in the ultimate compression load capacity for these members except for a weld spacing of 900 mm and a flexible end support condition. The reduction considered in AISI S100-2007is not applicable to determine the ultimate load capacity for the rest of the members.     

腹板开孔复杂卷边槽钢双肢拼合构件轴压性能试验研究

通过12根腹板开孔复杂卷边槽钢和Σ形复杂卷边槽钢双肢拼合工字形简支轴压构件的轴压试验，研究了构件承载能力、失稳模式和拼合作用。采用有限元软件ANSYS对试验进行了模拟，验证了分析模型准确性。并通过有限元变参数分析研究了孔高、孔宽和孔间距对拼合构件承载力的影响。结果表明：复杂卷边槽钢截面双肢拼合开孔构件的腹板多波失稳现象明显，屈曲发生时两腹板间的相互支撑作用较强；Σ形复杂卷边槽钢截面双肢拼合开孔构件能有效地控制腹板局部屈曲的发生并显著提高短柱、中长柱的承载力；设置腹板加劲肋有助于提高孔洞周围板件变形的约束作用，同时也减弱了两单肢腹板间的相互支撑作用；相同条件下，Σ形复杂卷边槽钢截面双肢拼合开孔构件的轴压承载效率与复杂卷边槽钢截面双肢拼合开孔构件相比，短柱提高了32%，中长柱提高了10%，长柱提高了2%；非加劲截面构件在不同长度下，孔高为腹板高度1/2(69 mm)时构件的稳定承载力较孔高为25 mm时下降约7%；而孔宽、孔间距对上述两类截面构件稳定承载力影响不大；此外，采用直接强度法预测非加劲截面双肢拼合构件的承载力结果偏于保守，而对加劲截面双肢拼合构件则略显不安全。     

Laser welded built-up cold-formed steel beams: Experimental investigations

The results of a research project aimed at designing and development a built-up cold-formed steel beam assembled by laser welding are described in this paper. The research activity was concerned with the evaluation of the applicability of laser welded connections to cold-formed members and with the assessment of the load bearing capacity of the assembled beams. With this aim, both lap-shear and U-tension tests were carried out on laser welds in order to assess the influence on connection strength of different parameters such as the gap between the steel sheets and the zinc coating. Finally, the load bearing capacity of laser welded built-up cold-formed members was investigated by four-point bending tests. Four full-scale prototypes were manufactured with different spacings of connections along the flanges in order to evaluate the effects of weld configuration on the load bearing capacity.     

Curved concrete filled steel tubular (CCFST) built-up members under axial compression: Experiments

A series of tests on curved concrete filled steel tubular (CCFST) built-up members subjected to axial compression is described in this paper. Twenty specimens, including 18 CCFST built-up members and 2 curved hollow tubular built-up columns, were tested to investigate the influence of variations in the tube shape (circular and square), initial curvature ratio (β_r, from 0 to 7.4%), nominal slenderness ratio (λ_n, from 9.9 to 18.9), section pattern (two main components, three main components and four main components), as well as brace pattern (battened and laced) on the performance of such composite built-up members. The experimental results showed that the ultimate strength and stiffness of CCFST built-up specimens decreased with increasing β_r or λ_n. Different load-bearing capacities and failure modes were obtained for the battened and laced built-up members. A simplified method using an equivalent slenderness ratio was suggested to calculate the strength of CCFST built-up members under axial compression.     

冷弯薄壁型钢开口三肢拼合立柱轴压性能试验研究

对18根冷弯薄壁型钢开口三肢拼合立柱的轴压性能进行了试验研究,试件分为A、B两种截面类型：A类由3根冷弯薄壁C型钢拼合而成;B类由2根冷弯薄壁C型钢和1根U型钢拼合而成。得到了各试件的荷载-位移曲线和破坏特征,并将试验结果与中、美两国相关规范“有效宽度法”和“直接强度法”计算结果进行了初步对比分析。研究结果表明：两类截面长柱（LC）系列立柱的破坏特征分别为弯扭屈曲、弯曲屈曲,而中柱（MC）系列立柱A类截面为畸变屈曲、B类截面为畸变屈曲和弯曲屈曲,短柱（SC）系列立柱均为局部屈曲和畸变屈曲。AISI有效宽度法计算结果对于A、B两类截面LC系列立柱偏于安全;对于SC系列立柱则偏不安全;对于MC系列立柱吻合较好。AISI直接强度法计算结果对于A类截面LC和MC系列立柱偏于安全;对于SC系列立柱则偏不安全;对于B类截面立柱直接强度法计算结果与试验结果相差-16-5%~11-2%。《冷弯薄壁型钢结构技术规范》计算结果与试验结果相比,LC系列立柱偏于安全,而MC和SC系列立柱计算结果与试验结果吻合较好,相差分别为 -8.7%~4.7%和 -7.3%~13.7%。     

冷弯薄壁型钢四肢拼合立柱轴压承载力设计方法

建立了考虑材料、几何和接触非线性的有限元模型,在对冷弯薄壁型钢四肢拼舍截面立柱的轴压性能试验试件进行模拟分析,验证有限元方法正确性的基础上,对考虑长细比、截面翼缘宽厚比等因素的一系列试件进行了数值分析,并得到其轴压承载力.在相关规范“有效宽度法”和“直接强度法”的基础上,提出了冷弯薄壁型钢四肢拼合截面立柱轴压承载力的设...     

Behavior of concrete-filled double skin steel tubular columns with octagon section under axial compression

Based on some conclusions of two kinds of concrete-filled double skin steel tube (CFDSST) members with circular or square sections, a new kind of CFDSST with octagonal section, where the outer tube has an octagonal section and the inner tube has a circular section, is proposed in this paper. Behaviors of the CFDSST members with octagon section subjected to axial compression are investigated, and some curves of load-strain of steel tubes and confined concrete and the bearing capacity of members are obtained. It is indicated that the bearing capacity of the columns with octagonal section is larger than that with square section and is smaller than that with circular section, and the bearing capacity of members is related to the ratio of the straight side to the bevelled one. Based on the proper stress-strain relationship, a couple of numerical analyses are made using the finite element software named ANSYS. Finally, a simplified formula is proposed in the paper, and the numerical results agree well with the experimental results and the mathematical solutions. The results are valuable for engineers. __________ Translated from China Civil Engineering Journal, 2007, 40(2): 33–38 [译自: 土木工程学报]     

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.     

Investigation on slenderness ratios of built-up compression members

This study provides a direct experimental verification of the AISC slenderness ratio formulas for built-up compressive members. The comparison on various code-specified slenderness ratios or provisions, which used in the AISC-ASD, AISC-LRFD, AS-4100, and CSA S16-01, are presented. The 0.75 rule, which states that the slenderness ratio of component element of built-up member should not exceed three-fourths times the governing slenderness ratio of built-up member, seems justified according to the tests. The governing slenderness ratio of built-up member could be either the modified or the unmodified one — as specified in the AISC Specifications. The test results indicate that the built-up members with component slenderness ratio of 0.75 to 1.0 times the governing slenderness ratio (modified or unmodified) could also furnish a quite encouraging design outcome. The use of separation ratio (α) in built-up compression members results in the decrease of design strength when compared to one with no use of separation ratio.     

Axial load capacity of cold-formed steel built-up stub columns

This paper aims to investigate the axial load capacity of innovative cold-formed steel (CFS) built-up stub columns. Four innovative CFS built up section is presented in this paper. Each section is composed of combination of more than two elements as follows: channels, channels with lip, Sigma section and/or plates. The elements of each section are assembled together by using self tapping screws. The concentric axial load capacity of each of the four sections was investigated numerically by using finite element (FE) model using ABAQUS program. The FE model was verified against previous test data. The FE model was used to study different parameters that affect the load capacities of the innovative CFS built-up stub columns, these parameters are: columns profile, steel thickness, steel grade and longitudinal spacing between screws (fasteners), cross sectional area. The axial load capacities obtained from FE models are compared with the perdition of the Effective width (EW) method (available in Eurocode, Egyptian code, American and Australian standards) and direct strength (DS) method (Available in American and Australian standards).     

Analysis of longitudinal shear behaviour for composite steel and concrete slabs

The strength of composite slabs depends mainly on the strength of contact between the steel sheeting and concrete. In the article a method of analyses for strength of the horizontal section of the composite slabs based on the theory of built-up bars, which gives one an opportunity to assess strength and the rigidity of contact is presented. The proposed method evaluates the influence of both plastic deformations of the concrete layer and cracks in the concrete on the rigidity of this layer and of the whole slab as well. Performed investigations in deformations and strength of the contact between steel sheeting and concrete allowed one to explore the behaviour of the contact from the start of loading up to the failure. During contact testing, influence of pre-compression forces on deformations and strength of the contact were investigated. The strength of horizontal section in 6 fragments of composite slab with ‘Holorib’ type profiled steel sheeting was investigated experimentally. In tests the thickness of concrete layer of the slab and concrete strength varied. Theoretical calculations for the strength of a horizontal section of experimental slabs were made in this investigation. Calculations were performed according to the method proposed by us with the application of the method of built-up bars. In calculations, rigidity of the contact between steel profiled sheeting and concrete as well as equivalent rigidity of a concrete layer with cracks were evaluated. Experimental and theoretical results of the strength of the horizontal section in composite slabs were compared. Comparison of results revealed that their agreement was sufficiently good.     

双向偏压钢筋混凝土异形构件截面分析的简化方法

为便于双向偏压作用下异形钢筋混凝土构件截面分析,本文提出了新的简便可行的截面积分方法。该方法将截面混凝土划分成若干三角块,用高斯积分法求每个三角块的刚度,之后所有三角块刚度求和得到截面混凝土的刚度。用该方法对异形(L、T、十形)截面进行了极限承载力分析,分析结果与试验数据吻合很好。还分析了荷载角、轴压比、配筋率和混凝土强度等因素对双向偏压作用下的L形截面承载力的影响。     

钢桁架约束混凝土组合柱约束机理及截面曲率分析

钢桁架(ST)约束混凝土组合柱具有良好的力学性能及抗震性能,且其截面形式能够有效提高内部钢材的利用率.基于已进行的轴向力学性能试验,对ST约束混凝土的约束机理进行详细分析,建立有效约束力计算模型、承载力计算模型以及本构模型.进行ST约束混凝土组合柱低周反复荷载试验研究,在试验研究的基础上,建立组合柱的截面弯矩-曲率分析...     

Numerical analysis of pultruded GFRP box girders supporting adhesively-bonded concrete deck in flexure

This paper presents the modeling of pultruded glass fiber reinforced polymer (GFRP) box girders consisting of built-up hat-shape sections and flat plates. The study addresses the effect of a thin concrete deck adhesively bonded to the top GFRP plate on flexural performance, as well as the behavior under positive and negative bending that simulates continuous girders. A three-dimensional finite element (FE) approach is proposed to predict the behavior of the GFRP system, including experimental validation. The efficacy of the girders is compared with other metallic box girders: carbon steel and corrosion-resistant metals, namely, stainless steel and aluminum. Failure is generally due to debonding of the concrete deck, and as such, the ultimate strength is not affected much by the girder material used. The study examines the single girder behavior as well as girder-group systems, to assess load distribution. It is shown that the AASHTO LRFD approach for load distribution can reasonably be used for the proposed girder systems. Design recommendations as to material selection are addressed to better use the girder system.     

Flexural strength of cold-formed steel built-up box sections

Presented in this paper is a study involving finite element analysis to investigate the flexural strength of built-up box sections which have been extensively used in residential and commercial construction in North America. In the North American Specification for the Design of Cold-Formed Steel Structural Members [CSA, North American specification for the design of cold-formed steel structural members, S136, Canadian Standard Association, 2002], there is no guideline or design equation to calculate the flexural strength of this type of section. Both the Lightweight Steel Framing Design Manual [CSA, Supplement 2004 to the North American specification for the design of cold-formed steel structural members, S136, Canadian Standard Association, 2004] and Cold-Formed Steel Framing Design Guide [AISI, Cold-formed steel framing design guide", American Iron and Steel Institute, 1st ed., 2002, 2nd ed., 2007] have recommended that the flexural strength and moment of inertia of the built-up sections to be taken as the sum of the two components based on deflection compatibility of the components. However, this design approximation has yet to be justified by experimental or numerical study especially for the cases of eccentric and concentric loading. In this study, the proposed finite element model of the built-up box sections was validated with the experimental tests carried out by Beshara and Lawson [Beshara B, Lawson TJ. Built-up girder screw connection variation flexural tests, Internal Report, Dietrich Design Group, 2002]. The flexural strengths obtained from the finite element analysis were then compared with the nominal strength evaluated based on the current design method in order to assess its suitability. Parametric studies were carried out for more than 30 specimens to identify factors affecting the flexural strength of cold-formed steel built-up box sections. A recommendation is made for current design practice of evaluating the flexural strength of the box section when subjected to eccentric loading.