考虑局部屈曲的矩形钢管混凝土轴压承载力计算方法

基于已有的试验研究与理论分析,给出了矩形钢管混凝土中钢管不出现局部屈曲时的最大宽厚比限值,同时提出大宽厚比下矩形钢管混凝土中考虑钢管屈曲的承载力计算方法。通过回归分析给出了矩形钢管混凝土轴压短柱、轴压中长柱的承载力简化计算公式,简化计算结果和大量试验结果进行对比,用试验结果验证了简化计算结果的正确性。同时,采用CECS、DBJ、EC4、LFRD及AIJ规程计算了矩形钢管混凝土承载力并和试验结果进行对比,对比结果表明:欧洲EC4规程、DBJ规程及简化计算结果与试验结果较为接近,所提出的简化计算公式不仅适用于普通宽厚比下矩形钢管混凝土承载力计算,且适用于大宽厚比下考虑局部屈曲时承载力计算,实现了普通壁厚和薄壁矩形钢管混凝土承载力计算公式的统一。     

矩形钢管混凝土柱管壁局部屈曲性能研究

对矩形钢管混凝土柱钢管壁的局部屈曲性能进行了分析研究。用有限条法计算出了各种应力梯度作用下管壁的局部屈曲临界应力σcr和局部屈曲系数k0 ,并将得到的屈曲系数代入到有效宽度统一法则中 ,得到了保证管壁不发生局部屈曲时板件的宽厚比、高厚比的限值表达式。分析结果与《矩形钢管混凝土结构技术规程》(CECS1 5 9:2 0 0 4)中限值的比较表明 ,规程的规定限值是可靠的     

矩形钢管混凝土横向局部承压强度的试验研究

本文进行了9个矩形钢管混凝土和3个空心矩形钢管的横向局部承压试验。试验的主要参数为局部承压面积和管内混凝土填充长度。试验结果表明,矩形钢管混凝土横向局部承压强度提高系数高于素混凝土局部承压强度提高系数,钢管参与了局部承压,管内混凝土的填充长度也是影响横向局部承压强度的主要因素。在分析横向局部承压机理的基础上,构造了考虑钢管参与工作和混凝土长度影响的局部承压强度计算公式,与J.A.Packer和本文的试验结果相比,均吻合较好,为我国正在编制的《矩形钢管混凝土结构技术规程》中桁架X型受压节点承载力计算提供了参考依据。     

基于壁板屈曲后强度的矩形钢管混凝土偏压承载力计算方法

为了准确计算大宽厚比矩形钢管混凝土短柱偏压承载力,通过有限元方法对非均匀受压单侧约束平板的屈曲性能进行了研究,给出了该类板件的弹性屈曲系数计算公式。以此为基础,结合有效宽度法,提出了基于壁板屈曲后强度的矩形钢管混凝土偏压承载力计算方法。为验证所提计算方法的准确性,建立了大宽厚比钢管混凝土短柱偏压试验数据库,并将该计算方法与各规范的计算方法进行了对比。结果表明:提出的两种大宽厚比矩形钢管混凝土偏压承载力计算方法具有较高的计算精度,计算结果与试验结果吻合良好,其中方法二能够准确地评估构件的偏压承载力,可用于大宽厚比矩形钢管混凝土短柱偏压承载力计算中。     

基于有限条法的偏压下方钢管混凝土柱局部屈曲分析

假定方钢管混凝土偏压柱钢板四边均为固定约束,建立基于有限条法的偏压下方钢管混凝土柱钢板局部屈曲模型。利用所建立模型计算了不同应力梯度下方钢管混凝土偏压柱钢板局部临界屈曲系数,从而得到偏压下方钢管混凝土柱的局部屈曲强度。为了验证模型正确性,对基于所述模型的方钢管混凝土偏压柱钢板局部临界屈曲系数计算值与基于能量变分法公式的计算值进行比较,两者非常吻合。同时,基于本文模型的局部屈曲强度计算值与先前试验结果比较,亦整体吻合良好。从而进一步验证了所述模型的正确性。最后,研究了偏压下方钢管混凝土柱钢板合理的宽厚比限值,给出了不同应力比时方钢管混凝土柱钢板合理的宽厚比限值,以便于工程设计应用。     

薄壁方钢管再生混凝土短柱屈曲承载力

钢管再生混凝土结构是近年来发展起来的一种新型结构形式,薄壁方形钢管再生混凝土构件的钢管壁容易产生局部屈曲而使构件承载力降低,而目前的钢管再生混凝土承载力计算公式中均未考虑局部屈曲的影响。本文在考虑核心混凝土对钢管产生径向力作用并假定非载荷边为弹性约束的情况下,采用能量法对钢管进行屈曲性能分析,并推导出屈曲系数计算公式,再在此基础上采用有效宽度法来考虑薄壁方钢管发生局部屈曲对承载力的影响,从而提出薄壁方钢管再生混凝土轴压短柱承载力计算公式,并用试验数据验证其合理性,研究结果表明:弹性约束系数和钢管的横向力对屈曲系数有一定的影响,当构件截面宽厚比较大时,应当考虑钢管局部屈曲对承载力的降低。     

国际期刊导读

1 轴向载荷和压弯作用下矩形钢管混凝土截面承载力 将直接强度法（DSM）用于钢管混凝土（CFT）截面的计算。基于已有的试验结果给出局部屈曲CFT截面的抗压和抗弯强度。欧洲规范EC 4不允许CFT截面使用薄壁型材,而AISC规范允许将钢管的宽厚比限值应用于薄壁型材。考虑薄壁钢管的局部屈曲和钢管约束效应将提高核心混凝土抗压强度,基于直接强度法给出CFT截面抗压和抗弯强度的计算公式。根据建议公式计算得到的承载力与试验结果以及AISC规范和EC 4的计算结果进行比较。同时给出轴向压弯作用下CFT构件强度相互作用的计算公式,并将计算结果与试验结果进行比较。结果表明,抗压、抗弯强度以及强度相互作用的计算公式,用于计算轴向荷载和压弯作用下CFT柱的承载力时,计算结果较为保守。     

矩形钢管混凝土桁架节点应力集中特性试验研究

为研究矩形钢管混凝土桁梁桥节点的疲劳性能,开展两榀矩形钢管混凝土组合桁架节段三点弯曲试验,对试件中的K形节点应力集中系数进行测试和分析,同时,基于试验结果,对既有K形节点应力集中系数计算公式的适用性进行分析。结果表明：相比普通钢筋混凝土桥面板和传统剪力钉的构造措施,采用预应力混凝土桥面板和局部释放剪切作用的剪力钉可提高混凝土桥面板开裂荷载,但是对于桁梁承载力基本没影响;两榀矩形钢管混凝土组合桁架节点腹杆表面热点应力水平基本相当,最大值均发生在受拉腹杆焊趾侧处,由于桥面板和剪力钉构造区别,两榀矩形钢管混凝土组合桁架节点弦杆表面热点应力值不同,最大值分别发生在受拉腹杆焊趾侧处;既有K形节点应力集中系数参数计算公式适用性分析表明,Mang等建议公式计算结果偏危险,Soh等建议公式和CIDECT建议公式计算结果偏保守,Puthli等建议公式计算得到的受拉腹杆最大应力集中系数偏保守,计算得到的受压腹杆和弦杆应力集中系数偏危险,Jiang等所提建议公式计算结果与试验结果吻合最好。     

PBL加劲型矩形钢管混凝土轴压柱局部屈曲性能分析

为研究开孔钢板连接件（PBL）加劲肋对矩形钢管混凝土轴压柱局部屈曲性能的影响,用能量法推导钢管屈曲系数计算公式,引入PBL和加劲肋相对刚度计算式并分析二者对屈曲模式的相互作用关系,讨论了PBL加劲型钢管的极限屈曲模式及其极限屈曲系数、最大相对宽厚比限值。结果表明:PBL加劲肋可明显改善钢管局部稳定性,钢管屈曲系数k随着PBL加劲肋刚度增加而增大,直至达到极限屈曲系数42.68;PBL连接件可减小板件纵向屈曲的波长,而加劲肋的影响作用与之相反;设置PBL加劲肋后,钢管的最大相对宽厚比限值可达184,并且板件屈曲后强度随宽厚比的变化曲线下降趋势减缓,强度值随着PBL刚度增加而逐渐提高。     

矩形高强钢管混凝土壁板弹塑性屈曲及-宽厚比限值解析解

钢管混凝土壁板的局部屈曲可通过限制其宽厚比来避免。为了得到矩形高强钢管混凝土柱壁板的宽厚比限值,将其简化为受混凝土单侧约束板,以薄板的弹塑性局部屈曲理论为基础,采用Bleich近似计算方法和Ramberg Osgood高强钢材本构模型,推导出了受单侧约束板在均布压应力作用下的弹塑性屈曲应力,得到了矩形高强钢管混凝土柱壁板宽厚比限值的解析解。进而采用有限元模型进行了屈服强度为460~960MPa、宽厚比为20~60共计168组矩形高强钢管混凝土轴压构件的有限元模拟,模拟结果与已有的试验结果验证了所提出的宽厚比限值解析解的可靠性。与现行各国相关规范的对比分析表明,所提出的宽厚比限值解析解与欧洲BS EN 1994-1-1的计算结果仅相差3%。建议在设计矩形高强钢管混凝土柱时,壁板的宽厚比限值可偏保守地取本文解析解和BS EN 1994-1-1计算结果的较小值。     

非均匀受压矩形钢管混凝土局部弹性屈曲分析

应用不同的特征函数描述了矩形板在非均匀压力作用下的屈曲形态,解决了采用三角级数为屈曲函数模拟非均匀受压荷载作用下单侧表面约束矩形板件屈曲模态的不对称问题;通过伽辽金法建立屈曲控制方程组,分析了非均匀荷载作用对矩形钢管混凝土构件局部弹性屈曲性能的影响。结果表明:钢管屈曲系数随着不均匀荷载梯度α增加而增大,纯弯作用下（α=2）的板件弹性屈曲荷载特征值约为轴压作用下的6倍;钢板的宽厚比限值随不均匀加载梯度α的增大而增加;非均匀荷载作用下非加载边固支约束板件的屈曲系数明显大于简支约束的板件。     

矩形中空夹层钢管混凝土轴压构件的试验研究

对6根矩形中空夹层钢管混凝土和1根矩形实心钢管混凝土短柱试件进行轴压试验,研究了内外钢管的长宽比对短柱的力学性能的影响。试验结果表明:比较内管相同的试件,外管截面尺寸较大者其轴压承载力略高;比较外管相同的试件,由于混凝土的减少和内管的局部屈曲,轴压承载力随内管的增大略有下降,本次试验中的实心钢管混凝土短柱的轴压承载力略高于中空夹层钢管混凝土短柱。同时用ABAQUS有限元软件对试件轴压全过程进行了模拟,计算结果与试验结果吻合良好。     

加劲肋在大宽厚比方钢管混凝土柱中的应用

当方钢管混凝土柱宽厚比较大时,需要考虑管壁局部屈曲导致的截面部分失效。沿管壁纵向布置加劲肋有助于解决此问题。通过对带加劲肋钢板的屈曲系数k值的变参数分析,得出加劲肋尺寸对k值的影响,并建议选择加劲肋需要满足的两个条件。给出大宽厚比情况下等距布置加劲肋的步骤和验算方法。     

High strength thin-walled rectangular concrete-filled steel tubular slender beam-columns,Part II: Behavior

Experimental and numerical research on full-scale high strength thin-walled rectangular steel slender tubes filled with high strength concrete has not been reported in the literature. In a companion paper, a new numerical model was presented that simulates the nonlinear inelastic behavior of uniaxially loaded high strength thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-columns with local buckling effects. The progressive local and post-local buckling of thin steel tube walls under stress gradients was incorporated in the numerical model. This paper presents the verification of the numerical model developed and its applications to the investigation into the fundamental behavior of high strength thin-walled CFST slender beam-columns. Experimental ultimate strengths and load-deflection responses of CFST slender beam-columns tested by independent researchers are used to verify the accuracy of the numerical model. The verified numerical model is then utilized to investigate the effects of local buckling, column slenderness ratio, depth-to-thickness ratio, loading eccentricity ratio, concrete compressive strengths and steel yield strengths on the behavior of high strength thin-walled CFST slender beam-columns. It is demonstrated that the numerical model is accurate and efficient for determining the behavior of high strength thin-walled CFST slender beam-columns with local buckling effects. Numerical results presented in this study are useful for the development of composite design codes for high strength thin-walled rectangular CFST slender beam-columns.     

主管内填混凝土矩形和圆形钢管桁架受弯性能对比试验研究

为研究主管内填混凝土对矩形和圆形钢管桁架结构受弯性能的影响及两者区别,进行了矩形和圆形钢管桁架空管、仅受压主管内填混凝土和拉压主管均内填混凝土三种类型桁架的对比试验研究。试验结果表明:矩形截面桁架均发生节点失效,空管桁架为受压主管侧壁鼓曲破坏,仅受压主管内填混凝土和拉压主管均内填混凝土桁架发生受拉主管顶板的冲剪破坏;圆形截面空管桁架和仅受压主管内填混凝土桁架发生空管节点处的主管侧壁鼓曲破坏,拉压主管均内填混凝土桁架为受拉支管受拉断裂破坏。主管内填混凝土有助于提高主管轴向刚度,提高节点强度和刚度及整体承载力,节点承载力按规范计算结果偏于安全,桁架整体变形计算需考虑节点变形的影响。两种截面空管桁架的承载力及变形差异不明显,主管内填混凝土后,圆形截面桁架的整体和节点承载力比相应矩形截面桁架承载力要高,变形能力更好,且节点变形比例更小。     

Numerical analysis of slender elliptical concrete filled columns under axial compression

This paper presents a non-linear finite element model (FEM) used to predict the behaviour of slender concrete filled steel tubular (CFST) columns with elliptical hollow sections subjected to axial compression. The accuracy of the FEM was validated by comparing the numerical prediction against experimental observation of eighteen elliptical CFST columns which carefully chosen to represent typical sectional sizes and member slenderness. The adaptability to apply the current design rules provided in Eurocode 4 for circular and rectangular CFST columns to elliptical CFST columns were discussed. A parametric study is carried out with various section sizes, lengths and concrete strength in order to cover a wider range of member cross-sections and slenderness which is currently used in practices to examine the important structural behaviour and design parameters, such as column imperfection, non-dimension slenderness and buckling reduction factor, etc. It is concluded that the design rules given in Eurocode 4 for circular and rectangular CFST columns may be adopted to calculate the axial buckling load of elliptical CFST columns although using the imperfection of length/300 specified in the Eurocode 4 might be over-conservative for elliptical CFST columns with lower non-dimensional slenderness.     

Fire behaviour of high strength self-consolidating concrete filled steel tubular stub columns

This paper reports an investigation into the behaviour of high strength SCC (self-consolidating concrete) filled steel tubular stub columns exposed to standard fire. A series of tests were carried out to obtain the temperature distribution, axial deformation, limiting temperature of steel and fire endurance of the SCC filled steel tubular stub columns. In addition, a finite element analysis (FEA) model was proposed and used to simulate the fire behaviour of the columns. In the FEA modeling, a sensitivity study was conducted to determine the concrete fracture energy and the contact property of the steel and concrete interface. The verified FEA model was used to analyse the structural behaviour of the columns under fire exposure, such as strain, stress, the load sharing between the steel tube and concrete and local buckling of the steel tube, to gain an insight into the failure mechanism of the columns.     

Strength of slender concrete filled high strength steel box columns

The use of thin walled steel sections coupled with concrete infill has been used on various building projects with great advantage. The currently available international standards for composite structures are limited to the design of concrete filled steel columns with compact sections. However, there is limited research work in the literature available which is concerned with slender concrete filled thin-walled steel columns. This paper presents a comprehensive experimental study of thin walled steel sections utilising high strength steel of a thin walled nature and filled with normal strength concrete. A numerical model is developed herein in order to study the behaviour of slender concrete filled high strength steel columns incorporating material and geometric non-linearities. For this analysis, the equilibrium of the member is investigated in the deformed state, using the idealised stress–strain relationships for both the steel and concrete materials, considering the elastic and plastic ranges. This paper presents both an experimental and theoretical treatment of coupled local and global buckling of concrete filled high strength steel columns sometimes termed interaction buckling. The experimental results of columns with high strength steel casings conducted herein by the authors are used for comparison. The effect of the confined concrete core is also addressed and the method shows good agreement with the experimental results of concrete filled steel columns with compact sections. The behaviour of concrete filled steel slender columns affected by elastic or inelastic local buckling is also investigated and compared with relevant experimental results. The paper then concludes with a design recommendation for the strength evaluation of slender composite columns using high strength steel plates with thin-walled steel sections, paying particular attention to existing codes of practice so as not to deviate from current design methodologies.