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.     

Experimental study on rectangular CFT columns with high-strength concrete

In the 1999 AISC-LRFD, the in-filled concrete strength of concrete-filled tube (CFT) columns is limited to a maximum value of 55 MPa  (N/mm²). That limiting value is raised to 70 MPa in the 2005 AISC-LRFD. This study aims to assess if the LRFD CFT column formulas are applicable to intermediate to long rectangular columns with higher concrete strengths. Twenty four specimens with varying between 29 and 84 MPa were tested. Various formulas and relevant provisions for CFT columns as specified in the major design codes including AISC-LRFD, EC 4, AS-5100, and CSA S16-01 were examined and compared. The design CFT strength (P_u) predicted by the AISC-LRFD formulas and the test results were found to be in good agreement. The higher limiting value of 70 MPa proposed in the 2005 AISC-LRFD appears acceptable. The test results reveal that the 1999 AISC-LRFD design strengths are conservative and tend to penalize these CFT columns with higher concrete strength.     

Influence of concrete strength and length/diameter on the axial capacity of CFT columns

This paper presents an experimental analysis of the confinement effects in steel–concrete composite columns regarding two parameters: concrete compressive strength and column slenderness. Sixteen concrete-filled steel tubular columns with circular cross section were tested under axial loading. The tested columns were filled by concrete with compressive strengths of 30, 60, 80, and 100 MPa, and had length/diameter ratios of 3, 5, 7, and 10. The experimental values of the columns’ ultimate load were compared to the predictions of 4 code provisions: the Brazilian Code NBR 8800:2008, Eurocode 4 (EN 1994-1-1:2004), AINSI/AISC 360:2005, and CAN/CSA S16-01:2001. According to the results, the load capacity of the composite columns increased with increasing concrete strength and decreased with increasing length/diameter ratio. In general, the code provisions were highly accurate in the prediction of column capacity. Among them, the Brazilian Code was the most conservative, while Eurocode 4 presented the values closest to the experimental results.     

偏压钢管混凝土柱承载力计算方法探讨

介绍了国内3个设计规程对偏心受压钢管混凝土构件的设计公式以及理论依据,借助已有的试验参数,采用3个规程分别计算了不同偏心距和长细比下的偏心受压构件承载力,并且与试验结果进行对比。结果表明,对于极限承载力,《钢-混凝土组合结构设计规程》(DL/T 5085-1999)相对偏于安全;但从规范计算值和试验结果的比较结果看,《钢管混凝土结构设计与施工规程》(CECS 28∶90)的计算值与试验值吻合相对较好。     

In-plane strength and design of parabolic arches

In the current AASHTO LRFD, the arch design formula is based on the bilinear interaction relationship between two extreme cases of the axial and the flexural strength. However, this method is not suitable for the design of the shallow arch which may buckle in a symmetric snap-through mode. Also, the use of the constant reduction factor for the design of arches leads to a conservative design. This paper investigates the in-plane buckling strength and design of parabolic arches. Firstly, the thresholds for the different buckling modes of shallow parabolic arches are summarized and boundaries for the deep and shallow arches are reported. The inelastic strengths of parabolic deep arches based on the finite element analyses are then compared with those presented in AASHTO LRFD. From the results, it is found that AASHTO LRFD provides good predictions of buckling strengths for the parabolic arches under only axial compression, while the bilinear interaction relationship provides conservative values for the in-plane strength of parabolic arches due to the use of constant reduction factors that can be applied regardless of loading and boundary conditions. The modified formulas for reduction factors are proposed for various loading and boundary conditions in this study. It is found that modified formulas for reduction factors show good match with the results obtained from finite element analyses.     

Ultimate flexural strengths of plate girders subjected to web local buckling

The ultimate flexural strengths of bisymmetric and monosymmetric I-girders subjected to local bend-buckling in webs have been investigated by nonlinear finite element analysis incorporating post-buckling behaviors. The plate girders fabricated with high performance steel (HPS) and conventional steel were modeled three-dimensionally with thin shell elements and ultimate strength analyses were conducted utilizing versatile nonlinear techniques provided by a commercial finite element analysis (FEA) package program, ABAQUS. The constitutive relationship for both HPS and conventional steel was assumed to be elasto-plastic strain-hardening, and the initial imperfections were considered in the web panels and the residual stresses were imposed on the hypothetical built-up sections. The ultimate flexural strengths of girders with various slenderness of web were evaluated from the nonlinear FEA and compared with values predicted by the specifications in AASHTO LRFD and Eurocode 3. It has been found that the current flexural strength formulas for conventional steel girders from AASHTO LRFD and Eurocode 3 can be extended to application for HPS girders without modification.     

Tests on block shear of coped beams with a welded end connection

An experimental study of block shear of coped beams with a welded clip angle connection is presented in this paper. Twelve full-scale coped steel I-beam tests were conducted. The test parameters included the web block aspect ratio (height to width ratio of the web block connected to the clip angle) and the connection rotational stiffness. Out of the 12 test specimens, eight test specimens failed in block shear of the connection, namely, tensile fracture of the block width (the web underneath the clip angle) and shear yielding of the block height (the web along the vertical side of the clip angle). Two test specimens failed by local web buckling at the cope, one test specimen failed in the welds and the remaining one did not fail due to the limited capacity of the loading jack.The test results showed that in general the block shear capacity of the test specimens increased with increasing web block aspect ratio and increasing connection rotational stiffness. The current design specifications (AISC-LRFD, CAN/CSA-S16-09, CAN/CSA-S16-01, BS EN 1993-1-8-2005, BS5950-1:2000, and AIJ-1990) provide conservative estimates of the block shear capacity of the test specimens except for the specimen that had the smallest connection rotational stiffness. It should be noted that none of the design equations evaluated in this programme consider the influence of the web block aspect ratio and the connection rotational stiffness.     

Ultimate capacity of battened columns composed of four equal slender angles

Cold-formed steel structural members play a great role in modern steel structures due to their high strength and light weight. The behavior and strength of battened column members composed of slender angle sections are mainly governed by local buckling of angle legs or torsional buckling of the angle between batten plates. Moreover, local buckling depends on the interaction between the width–thickness ratio of angle leg, overall slenderness ratio of angle between batten plates and overall slenderness of column. Theoretical study has been carried out by a nonlinear material and geometrical finite element model. Numerous cases of slender battened column sections having different width–thickness angle leg ratios, overall slenderness ratios between batten plates and overall slenderness ratios are chosen in this study. Complete ultimate strength curves are drawn and different failure modes are studied by taking different member lengths, which produce local or torsional buckling of single angles between batten plates or overall buckling of the member. Empirical equations for the effect of shear deformation factor and the ultimate axial load capacities of members formed of battened slender angle sections are proposed. Strengths of axially loaded battened members predicted using finite element as well as the proposed empirical equations is compared with the design strengths obtained using North American and European codes. It is concluded that the design strengths predicted by North American and European codes are generally conservative, and these design rules have been shown to be reliable using reliability analysis.     

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.     

恒定轴压力下Q690高性能钢管抗弯性能的试验研究

为研究国家电网输电塔中高强钢焊接中厚板圆管压弯稳定相关性,考虑长细比30、45和60,径厚比(D0/t)为31.25、50.00和58.33,以壁厚为6,8 mm国产Q690高性能钢板制作了5组15根焊接圆管试件,并对其进行恒定轴压力下的抗弯性能试验。记录各试件加载过程中变形现象,得到了试件的弯矩-轴向变形曲线。根据试验结果分析试件的承载力、失稳破坏模式和破坏状态等力学性能,并采用中国及美国相关行业规范公式对压弯承载力进行验算对比。结果显示:失稳破坏类型主要取决于钢管试件径厚比和长细比,随长细比减小或径厚比增大,构件破坏类型由整体失稳转化为局部失稳;失稳状态关键在于径厚比,随径厚比减小,破坏状态由弹性转化为弹塑性;所有规范设计公式均偏于保守,验证了相关规范压弯设计公式和稳定系数取值用于指导工程设计的可行性和合理性。     

Nonlinear analysis of concrete-filled steel SHS and RHS columns

This paper presents an accurate nonlinear finite element model for the behaviour and design of axially loaded concrete-filled square hollow section (SHS) and rectangular hollow section (RHS) steel tube columns. The nonlinear material models for confined concrete and steel tubes were carefully modeled in the finite element analysis. The column strengths and load-axial shortening curves were evaluated. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to investigate the effects of different concrete strengths and cross-section geometries on the strength and behaviour of concrete-filled SHS and RHS steel tube columns. The study was conducted over a wide range of concrete cube strengths ranged from 30 to 110 MPa. The overall depth of the steel tube-to-plate thickness ratio ranged from 10 to 40 covering compact SHS and RHS steel tube sections. The column strengths predicted from the finite element analysis were compared with the design strengths calculated using the American, Australian and European specifications. Based on the results obtained from the parametric study, it is found that the design strengths calculated using the American Specifications and Australian Standards are conservative, while the design strengths calculated using the European Code are accurate, except for the concrete-filled RHS compact steel tube columns having the overall depth of the steel tube-to-plate thickness ratio of 40.     

冷弯型钢受压构件的LRFD抗力系数

目前,冷弯型钢抗压构件的LRFD抗力系数取值为0.85,该文旨在研究该系数能否增大。数据库中包含675组同中心荷载柱的试验数据,包含平口卷边C截面、平口卷边Z截面、帽形截面和角形截面以及开孔构件。采用美国钢铁协会标准和直接强度法计算每个试样的强度。直接强度法的计算结果更加精确,其在计算部分有效截面柱的强度时尤为精确。采用一阶二次矩法计算的LRFD抗力系数,与美国钢铁协会标准和直接强度法的规定相符。对于柱的两种破坏情况,达到畸变屈曲极限状态而破坏和由于整体失稳或局部-整体失稳相互作用而破坏,前者的计算结果更为精确。单角钢柱的试验强度与计算强度的比值有很大变化,随着整体长细比的增加,计算结果逐渐变得极为保守。     

HRB600钢筋混凝土短柱轴压性能试验研究

通过对6根HRB600钢筋、1根HRB500钢筋混凝土短柱和2根素混凝土短柱进行轴心受压试验,分析不同配筋率、混凝土强度、钢筋强度、长细比对钢筋混凝土柱轴压性能的影响,提出HRB600钢筋的抗压强度设计值,分析GB 50010-2010《混凝土结构设计规范》中关于轴心受压承载力计算公式的适用性。研究结果表明:随着纵筋配筋率、钢筋强度和混凝土强度的提高,轴压短柱的峰值荷载增大;轴压短柱峰值应变随混凝土强度提高而减小,随钢筋强度提高而略有增大,纵筋配筋率和长细比对峰值应变影响较小;HRB600钢筋抗压强度设计值取为500 MPa,HRB600钢筋混凝土短柱与普通钢筋混凝土短柱的受力性能相似,轴心受压承载力可以按照GB 50010-2010《混凝土结构设计规范》中规定的受压承载力公式进行计算,具有足够的安全储备。     

Structural behaviour of stainless steel stub column under axial compression: a FE study

This paper presents a Finite Element (FE) study on Lean Duplex Stainless Steel stub column with built-up sections subjected to pure axial compression with column web spacing varied at different position across the column flanges. The thicknesses of the steel sections were from 2 to 7 mm to encompass a range of section slenderness. The aim is to study and compare the strength and deformation capacities as well as the failure modes of the built-up stub columns. The FE results have been compared with the un-factored design strengths predicted through EN1993-1-4 (2006)?+?A1 (2015) and ASCE8-02 standards, Continuous Strength Method (CSM) and Direct Strength Method (DSM). The results showed that the design rules generally under predict the bearing capacities of the specimens. It’s been observed that the CSM method offers improved mean resistance and reduced scatter for both classes of cross-sections (i.e. slender and stocky sections) compared to the EN1993-1-4 (2006)?+?A1 (2015) and ASCE 8-02 design rules which are known to be conservative for stocky cross-sections.     

薄腹工字形截面轴压构件有效面积计算方法比较

对各国规范以及Winter公式关于工字形截面构件有效宽度的计算公式进行简要介绍,并采用各国规范方法和有限元数值模拟对腹板不同宽厚比和构件不同长细比的工字形截面轴压构件有效面积进行计算和分析。结果表明:《门式刚架轻型房屋钢结构技术规程》(CECS102:2002)在腹板宽厚比较大时有效面积过于保守,《钢结构设计规范》(GB50017—2003)、欧洲规范(E3-1.5:2006)对于长细比较大构件有效面积过于保守,《冷弯薄壁型钢结构技术规范》(GB50018—2002)、美国规范(AISC:2005)以及Winter公式与数值结果吻合较好,且有一定的安全度,建议对于薄腹工字形截面轴压构件有效面积可采用《冷弯薄壁型钢结构技术规范》(GB50018—2002)计算方法进行计算。     

设计规范中钢混无腹筋梁受剪承载力计算公式对比分析

为了比较《混凝土结构设计规范》（GB50010—2010）和《公路钢筋混凝土及预应力混凝土桥涵设计规范》（JTGD62—2004）中受剪承载力计算公式的异同,分析了国内外528根跨高比不小于5的无腹筋梁剪切试验数据,得出当梁的有效高度大于600mm或纵筋率小于1．5％时,《混凝土结构设计规范》（GB50010—2010）预测结果偏于不安全。《混凝土结构设计规范》（GB50010—2010）预测结果离散型大,而《公路钢筋混凝土及预应力混凝土桥涵设计规范》（JTGD62—2004）预测结果相对保守。     

Deterministic and reliability analysis of prestressed concrete bridge girders: comparison of the Chinese, Hong Kong and AASHTO LRFD Codes

This paper compares the prestressing requirements and reliability indices of prestressed concrete bridge girders designed using three codes: the Chinese Code, the Hong Kong Code and the AASHTO LRFD Code. Typical post-tensioned concrete girders of spans ranging from 25 to 40 m are considered. Deterministic analysis indicates that the service limit state governs the design according to the Chinese Code and the AASHTO LRFD Code. However for the Hong Kong Code, only those with longer spans are controlled by the service limit state. The actual number of strands needed by the AASHTO LRFD Code is quite close to that needed by the Chinese Code, while that required by the Hong Kong Code is about 18–33% higher than that required by the AASHTO LRFD Code. Disparity between reliability indices for flexural capacity based on the requirements of the service and strength limit states exists in all three codes. However, the disparity does not follow the same trends as that of the required number of strands for service and strength limit states in the three codes. In addition, the reliability index for flexural capacity according to the requirements of the service limit state is always higher than that of the strength limit state in the three codes. The actual reliability indices for flexural capacity of the girders considered according to the three codes, which are governed by the service limit state, are close to one another.     

In-plane buckling behavior of slender parabolic concrete-filled steel tubular arches with fixed ends

现有规范采用“等效梁柱法”计算长细比不超过80的钢管混凝土拱的平面内稳定承载力,而实际工程中有近20%拱桥拱肋长细比超过上述限值,即大长细比钢管混凝土拱。因此,利用ABAQUS建立了有限元分析模型,在基于现有试验数据验证模型可靠性的基础上,对大长细比抛物线形钢管混凝土无铰拱在竖向均布荷载作用下的平面内稳定性能进行了分析,研究了长细比、矢跨比、含钢率、混凝土强度和钢材强度对拱肋平面内稳定承载力的影响;基于参数分析结果,对现有平面内整体稳定系数公式进行修正,提出了大长细比抛物线形钢管混凝土拱平面内稳定承载力设计公式。结果表明：拱肋稳定承载力随长细比增大显著降低,随矢跨比和含钢率增加近似线性提高。其中,矢跨比对大长细比拱肋影响更为显著,而含钢率对采用高强钢的拱肋影响更大;所提出的设计公式计算结果与有限元分析结果吻合良好,有限元分析结果与公式预测结果比值的均值为1.02~1.08,标准差为0.039~0.051,变异系数为3.74%~4.72%。     

Behaviour of normal and high strength concrete-filled compact steel tube circular stub columns

This paper presents the behaviour and design of axially loaded concrete-filled steel tube circular stub columns. The study was conducted over a wide range of concrete cube strengths ranging from 30 to 110 MPa. The external diameter of the steel tube-to-plate thickness (D/t) ratio ranged from 15 to 80 covering compact steel tube sections. An accurate finite element model was developed to carry out the analysis. Accurate nonlinear material models for confined concrete and steel tubes were used. The column strengths and load-axial shortening curves were evaluated. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to investigate the effects of different concrete strengths and cross-section geometries on the strength and behaviour of concrete-filled compact steel tube circular stub columns. The column strengths predicted from the finite element analysis were compared with the design strengths calculated using the American, Australian and European specifications. Based on the results of the parametric study, it is found that the design strengths given by the American Specifications and Australian Standards are conservative, while those of the European Code are generally unconservative. Reliability analysis was performed to evaluate the current composite column design rules.