竹皮轴压箱形构件整体稳定性能试验研究

基于114个竹皮箱形截面柱进行了轴心受压试验,研究了0.35 mm与0.5 mm两种厚度规格竹皮制作的等边箱形截面柱在不同宽厚比下的整体稳定性能。基于试验结果,分析了竹皮箱形截面柱的失稳破坏形态和整体稳定系数。试验结果表明,箱形截面构件在受荷时同时存在局部失稳与整体弯曲失稳,其中,长细比小于临界长细比的构件在受压时以局部失稳为主,长细比大于临界长细比的构件以整体失稳为主。通过对试验数据分析拟合,计算了两种规格竹皮各3种宽厚比箱形截面构件的临界长细比值,提出了竹皮轴压箱形构件柱子曲线与承载力设计方法,为学生在结构设计竞赛中进行构件截面设计提供科学的理论依据和计算公式。     

7A04高强铝合金L形截面柱轴压整体稳定性能试验研究

为研究高强铝合金轴心受压构件整体稳定性能,对42根7A04高强铝合金L形截面柱进行轴压整体稳定性能试验,其中包含2种截面和7种长细比。对L形截面柱的破坏形态、稳定承载力和荷载-位移曲线进行研究,并将试验结果与GB50429—2007《铝合金结构设计规范》计算结果进行对比。试验中,长细比为80~100的L形截面柱发生弯曲失稳破坏,长细比为30~60的L形截面柱发生弯扭失稳破坏,长细比在30以下的L形截面柱发生局部失稳破坏。研究结果表明:对于宽厚比较大的长柱,GB 50429—2007中过多地考虑了局部稳定的影响,进而低估其承载能力。     

考虑畸变屈曲的冷弯薄壁型钢卷边槽形截面构件设计可靠度分析

基于已有的冷弯薄壁型钢卷边槽形截面构件承载力试验研究结果,对不同牌号冷弯薄壁型钢卷边槽形截面构件考虑畸变屈曲的有效宽度法承载力计算模式不定性进行了分析,并统计了冷弯薄壁型钢强度不定性和几何特性不定性。在此基础上,采用改进一次二阶矩方法,按《冷弯型钢结构技术规范》(修订稿)的抗力分项系数要求,计算了不同牌号冷弯薄壁型钢卷边槽形截面受压构件在不同可能荷载组合下的可靠指标。结果表明:对于LG550、S350、S280冷弯薄壁型钢卷边槽形截面受压构件,按《冷弯型钢结构技术规范》(修订稿)的抗力分项系数计算得到的可靠指标均能满足目标可靠指标的要求,证明了所采用的考虑畸变屈曲的有效宽度法计算构件承载力的适用性。     

激光焊接不锈钢工字形截面中长柱受力性能研究

为研究激光焊接奥氏体不锈钢工字形截面轴心受压中长柱的承载性能,对10根激光焊接不锈钢工字形薄柔截面中长柱进行轴心受压试验研究,结果表明,中长柱的破坏模式均为板件局部屈曲与构件整体弯曲屈曲的相关失稳。同时,基于残余应力试验,验证了已有激光焊接不锈钢工字形截面的残余应力分布模型。基于试验结果验证了有限元模型,对激光焊接不锈钢工字形截面轴心受压中长柱开展参数分析,研究了几何初始缺陷和残余应力对中长柱稳定承载力的影响,结果表明,残余应力是影响中长柱稳定承载力的主要因素。结合试验和有限元计算结果,对CECS 410:2015《不锈钢结构技术规程》中轴心受压构件稳定承载力设计公式的适用性进行评估,并考虑残余应力的影响修正了轴心受压构件整体稳定设计公式的计算系数。采用修正后计算系数的规范公式能准确计算激光焊接不锈钢工字形截面轴心受压构件的稳定承载力。     

G450级冷弯薄壁型钢轴压柱承载力的计算方法探讨

对冷弯薄壁型钢构件承载力的几种计算方法进行了综述,引用了国外的一组试验数据,分别用美国规范(AISI 1996),中国规范(GB 50018-2002),北美规范NAS 2004附录中的直接强度法(DSM)进行了稳定承载力计算。结果表明:直接强度法可以有效地预测G450级冷弯薄壁卷边槽钢轴压柱的稳定承载力,美国规范的计算结果偏于不安全,GB50018-2002对G450级冷弯薄壁卷边槽钢轴压柱进行稳定承载力计算的结果与试验结果相比也偏于不安全,必须进行修正。考虑构件截面板组相关性的影响,修正后的计算结果与试验结果吻合良好且偏于安全,可供修订规范和设计时参考。     

冷弯薄壁C型钢轴压短柱承载力计算方法的改进

用我国规范有效宽度法求得的冷弯薄壁型钢短柱构件极限承载力高于试验结果,倾向于不安全。所以,通过分析提出,按照《冷弯薄壁型钢结构技术规范》GB50018-2002中的有效宽度法计算组合截面冷弯薄壁型钢受压构件承载力时,可以对计算结果乘以一个修正系数以示其原结果的不安全程度。由于有效宽度法在计算试件极限承载力时存在不安全性,因此本文引入另一种适用于冷弯薄壁型钢构件的计算方法,即直接强度法(Direct Strength Method,DSM)。将直接强度法和有效宽度法计算求得的短柱极限承载力与试验结果进行对比,结果表明,直接强度法的计算结果与试验值更为吻合,为使其结果更加经济、安全,本文提出适用于计算组合截面冷弯薄壁型钢受压构件承载力的直接强度法建议公式。     

卷边C形截面不锈钢柱畸变屈曲直接强度法

为研究轴心受压卷边C形截面不锈钢柱的畸变屈曲承载力,采用ABAQUS软件对不锈钢轴压构件进行了非线性有限元模拟,并通过现有试验验证了有限元模型计算结果的准确性。弹性畸变屈曲荷载是采用直接强度法（DSM）的关键参数,首先研究了边界条件对构件承载力的影响,然后对比分析了现有轴心受压卷边C形截面不锈钢柱畸变屈曲承载力的计算方法与试验结果,发现BECQUE等提出的DSM公式与AISI中的畸变屈曲DSM公式均不能准确地预测卷边C形截面不锈钢构件的畸变屈曲承载力。最后,在大量有限元分析的基础上提出了轴心受压卷边C形截面不锈钢柱畸变屈曲承载力计算公式,并采用现有的试验结果验证了该公式的准确性。     

AISC设计指南中不锈钢结构设计准则的进展

介绍了AISC(美国钢结构协会)设计指南中热轧和焊接不锈钢结构设计准则的进展。不锈钢性能与碳素钢类似的,设计指南仅简要引用了ANSI/AISC 360-10《美国钢结构建筑设计规范》的相关章节。AISC规范中设计准则用于不锈钢时计算结果不保守,给出了与AISC 360中等效表达式类似、适用于不锈钢的特定准则。通过大量构件和连接节点的试验结果对不锈钢设计准则进行了验证。为计算LRFD抗力系数,进行了可靠性分析;结果表明,在多数情况下,碳素钢的抗力系数也适用于不锈钢。     

铝合金结构构件的设计公式及其可靠度研究

对国产铝合金结构进行了一系列试验,包括42个材料拉伸试验、63个轴压构件试验、14个受弯构件试验和45个偏压构件试验;搜集整理了国内已有的试验结果,初步建立起铝合金结构的试验数据库。数据库中包括53条本构关系曲线、205个轴压构件试验点、38个受弯构件试验点和57个偏压构件试验点。采用有限单元法对铝合金结构构件进行了大规模的数值计算,得到了252条轴压构件失稳的稳定系数-正则化长细比曲线、480条弯曲构件弯扭失稳的整体稳定系数-正则化长细比曲线和1920条偏压构件弯曲失稳的相关曲线;并根据数值计算结果拟合出了各类构件的计算公式。最后以试验数据为基础对铝合金结构构件进行了可靠度分析,得出了国产铝合金材料的抗力分项系数,建议了其强度设计值。     

Q420等边角钢轴压杆整体稳定性能试验研究

国内大型输电铁塔中已逐步采用Q420高强度角钢。为研究此类高强度等边角钢轴压杆的整体稳定性能,进行了轴压静力试验研究,试验包括60个试件,截面类型选取了在所有热轧角钢截面中板件宽厚比最大的5种。基于试验结果,研究了Q420高强度等边角钢轴心受压柱的失稳破坏形态和极限承载力,通过计算得到其稳定系数,并与现行钢结构设计规范的柱曲线进行了对比,同时分析了板件宽厚比超限对Q420高强度等边角钢轴压柱失稳破坏形态和稳定承载力的影响。结果表明：该类构件以弯扭失稳为主,根据试验实测得到的稳定系数明显高于现行钢结构设计规范所规定的等边角钢所在的b类截面柱曲线,甚至高于a类截面柱曲线。研究为后续的有限元计算和数值参数分析提供了重要的基础数据,为设计方法提供了参考建议。图11表4参17     

Compression tests of high strength cold-formed steel channels with buckling interaction

This paper describes a series of compression tests conducted on cold-formed simple lipped channels and lipped channels with intermediate stiffeners in the flanges and web fabricated from high strength steel plate of thickness 0.6 and 0.8 mm with the nominal yield stress 560 MPa. A range of lengths of lipped channel sections were tested to failure with both ends of the column fixed with a special capping to prevent local failure of column ends and influence from the shift of centroid during testing. The high strength cold-formed steel channel sections of intermediate lengths generally displayed a significant interaction between local and distortional buckling. A noticeable interaction between local and overall buckling was also observed for the long columns. A significant post-buckling strength reserve was shown for those sections that showed interaction between local and distortional or overall buckling. Simple design strength formulas in the Direct Strength Method for the thin-walled cold-formed steel sections failing in the mixed mode of local and distortional buckling have been studied. The strengths predicted by the strength formulas proposed are compared with the test results for verification.     

中美规范关于卷边槽形受弯构件承载力比较分析

新近纳入北美规范NAS 2004的直接强度法对冷弯型钢构件的畸变屈曲要求单独验算,但《冷弯薄壁型钢结构技术规范》(GB 50018-2002)对此还无明确规定。在总结冷弯型钢构件畸变屈曲性能的基础上,对其承载力计算方法给予介绍,由简化模型计算得到的受弯构件的畸变屈曲弹性临界应力中,引入直接强度法计算“规范”(GB 50018-2002)附录中卷边槽形受弯构件的承载力。结果表明,附录中部分截面的受弯承载力由畸变屈曲控制。同时,NAS 2004与“规范”(GB 50018-2002)计算结果的比较表明,“规范”(GB 50018-2002)的计算规定虽安全,但太过保守。因此,提出将翼缘屈曲系数调高至3.0的建议。     

Calculating the global buckling resistance of thin-walled steel members with uniform and non-uniform elevated temperatures under axial compression

This paper develops a method, based on the Direct Strength Method (DSM) global buckling curve, to calculate the global buckling ultimate strength of cold-formed thin-walled (CF-TW) steel members under uniform and non-uniform elevated temperatures. The assessment is carried out by checking the DSM curve-based results with numerical simulation results using the general finite element software ABAQUS. The numerical model has been validated against a series of ambient temperature and fire tests on panels made of two different lipped channel sections tested to their ultimate load carrying capacities at ambient temperature or to their fire resistance at different load levels. The validated numerical model has been used to generate a database of numerical results of load carry capacity of CF-TW members with different uniform and non-uniform temperature distributions in the cross-sections under different boundary and loading conditions and with different dimensions. It is concluded that the DSM global buckling column curve is directly applicable for uniform temperature but a simple modification is required for non-uniform temperature distributions.     

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.     

Application of the Direct Strength Method to local buckling resistance of thin-walled steel members with non-uniform elevated temperatures under axial compression

This paper assesses the applicability of the Direct Strength Method (DSM) to calculating the local buckling ultimate strength of cold-formed thin-walled (CF-TW) steel members with non-uniform elevated temperature distributions in the cross-section. The assessment was carried out by checking the DSM calculation results with numerical simulation results using the general finite element software ABAQUS which was validated against ambient and uniform elevated temperature tests on short lipped channel sections. The validated numerical model was used to generate an extensive database (372 models) of numerical results of load carry capacity of CF-TW members with different uniform and non-uniform temperature distributions in the cross-sections, under different boundary and loading conditions and with different dimensions and lengths. It was concluded that the DSM local buckling curve was directly applicable for columns with uniform temperature distributions in the cross-section. For columns with non-uniform temperature distributions, a modification to the local buckling curve was necessary and this paper has proposed a new curve.     

Application of the Direct Strength Method to local buckling resistance of thin-walled steel members with non-uniform elevated temperatures under axial compression

This paper assesses the applicability of the Direct Strength Method (DSM) to calculating the local buckling ultimate strength of cold-formed thin-walled (CF-TW) steel members with non-uniform elevated temperature distributions in the cross-section. The assessment was carried out by checking the DSM calculation results with numerical simulation results using the general finite element software ABAQUS which was validated against ambient and uniform elevated temperature tests on short lipped channel sections. The validated numerical model was used to generate an extensive database (372 models) of numerical results of load carry capacity of CF-TW members with different uniform and non-uniform temperature distributions in the cross-sections, under different boundary and loading conditions and with different dimensions and lengths. It was concluded that the DSM local buckling curve was directly applicable for columns with uniform temperature distributions in the cross-section. For columns with non-uniform temperature distributions, a modification to the local buckling curve was necessary and this paper has proposed a new curve.     

Compression tests of welded section columns undergoing buckling interaction

This paper describes a series of compression tests performed on welded H-section and channel section columns fabricated from a mild steel plate of thickness 6.0 mm with nominal yield stress of 240 MPa. The ultimate strength and performance of the compression members undergoing nonlinear interaction between local and overall buckling were investigated experimentally and theoretically. The compression tests indicated that the interaction between local and overall buckling had a significant negative effect on the ultimate strength of the thin-walled welded steel section columns. The Direct Strength Method (DSM), which was newly developed and adopted as an alternative to the effective width method for the design of cold-formed steel sections recently by NAS (AISI, 2004), was calibrated by using the test results for application to welded steel sections. This paper confirms that the Direct Strength Method can properly predict the ultimate strength of welded section columns when local buckling and flexural buckling occur simultaneously or nearly simultaneously.     

Direct Strength Method for calculating distortional buckling capacity of cold-formed thin-walled steel columns with uniform and non-uniform elevated temperatures

This paper assesses the applicability of the Direct Strength Method (DSM) to calculating the distortional buckling strength of cold-formed thin-walled (CF-TW) steel members with uniform and non-uniform elevated temperature distributions in the cross-section. The assessment was carried out by checking the DSM calculation results with numerical simulation results using the general finite element software ABAQUS which was further validated against ambient and uniform elevated temperature tests on short lipped channel sections, in addition to the author's previous validation studies for thin-walled steel columns with non-uniform temperature distributions. The validated numerical model has been used to generate an extensive database (453) of numerical results of load carrying capacity of CF-TW members with different uniform and non-uniform temperature distributions in the cross-sections, under different boundary and loading conditions and with different dimensions and lengths. It is concluded that the existing DSM distortional buckling curve for ambient temperature application is also applicable for columns with uniform temperature distributions in the cross-section, but is un-conservative for columns with non-uniform temperature distributions in the cross-section. This paper proposes a modification to the distortional buckling curve to enable DSM to deal with distortional buckling in columns with non-uniform temperature distributions.     

Post-buckling behaviour and direct strength design of lipped channel columns experiencing local/distortional interaction

This paper reports an investigation aimed at developing a Direct Strength Method (DSM) approach to estimate the ultimate strength of lipped channel columns affected by local/distortional buckling mode interaction. Following a brief presentation of a few relevant aspects concerning the shell finite element analysis of the geometrically and materially non-linear behaviour of thin-walled members, one illustrates the methodology adopted to obtain a lipped channel column ultimate load “data bank” intended to be used in the development and assessment of a DSM design approach. Next, the current DSM expressions to predict the load-carrying capacity of columns failing in local and distortional modes are briefly reviewed, devoting special attention to an approach that takes into account the above mode interaction. Then, the results of a parametric study, carried out by means of the code Abaqus, are presented and discussed — this study involves the evaluation of the “exact” ultimate loads of 276 lipped channel columns with various geometries and two boundary conditions (pinned and fixed end supports), all exhibiting local/distortional interaction. Finally, these ultimate strength data are compared with the estimates provided by the available DSM expressions and, on the basis of this comparison, one identifies several features that a DSM approach successfully accounting for local/distortional interaction must incorporate.