Nonlinear analysis of concrete-filled thin-walled steel box columns with local buckling effects

Local buckling of steel plates reduces the ultimate loads of concrete-filled thin-walled steel box columns under axial compression. The effects of local buckling have not been considered in advanced analysis methods that lead to the overestimates of the ultimate loads of composite columns and frames. This paper presents a nonlinear fiber element analysis method for predicting the ultimate strengths and behavior of short concrete-filled thin-walled steel box columns with local buckling effects. The fiber element method considers nonlinear constitutive models for confined concrete and structural steel. Effective width formulas for steel plates with geometric imperfections and residual stresses are incorporated in the fiber element analysis program to account for local buckling effects. The progressive local and post-local buckling is simulated by gradually redistributing the normal stresses within the steel plates. Two performance indices are proposed for evaluating the section and ductility performance of concrete-filled steel box columns. The computational technique developed is used to investigate the effects of the width-to-thickness ratios and concrete compressive strengths on the ultimate strength and ductility of concrete-filled steel box columns. It is demonstrated that the nonlinear fiber element method developed predicts well the ultimate loads and behavior of concrete-filled thin-walled steel box columns and can be implemented in advanced analysis programs for the nonlinear analysis of composite frames.     

Local buckling of steel plates in rectangular CFT columns with binding bars

This paper presents a theoretical study on the elastic local buckling of steel plates in rectangular concrete-filled steel tubular (CFT) columns with binding bars under axial compression. It is assumed that the unloaded edges of the steel plate are elastically restrained against rotation, whereas the loaded edges are clamped. Based on the energy method, the formulas for elastic local buckling strength of the steel plate in rectangular CFT columns under axial compression are derived, which are calibrated with the experimental results. Then the formulas are employed to study the elastic local buckling of steel plates in rectangular CFT columns with binding bars under axial compression. It is shown that the binding bars can increase the local buckling coefficient, which results in improvement of the capacity of the steel plate to resist local buckling. Finally, appropriate spacing of binding bars, appropriate limitation for aspect ratio and corresponding appropriate limitation for width-thickness ratio are suggested for rectangular CFT columns with binding bars under axial compression.     

矩形钢管混凝土壁板的屈曲后强度

为研究矩形钢管混凝土壁板的屈曲后强度,根据平板的弹塑性屈曲理论并考虑残余应力的影响,确定了板件发生塑性屈曲、弹塑性屈曲和弹性屈曲的正则化界限宽厚比。采用试验验证的有限元模型进行了宽厚比为20～150、钢材屈服强度为275～960 MPa的矩形钢管混凝土壁板局部屈曲分析,以界限宽厚比为控制点,根据有限元结果拟合出了矩形钢管混凝土壁板的有效宽度计算式。研究结果表明：弹性屈曲板件的屈曲后强度提高程度显著高于弹塑性屈曲板件;屈曲后强度的提高程度与钢材屈服强度无明显相关性;与无面外约束钢板相比,混凝土的单侧约束作用可使板件的屈曲后强度普遍提高约50%;提出的矩形钢管混凝土壁板的正则化界限宽厚比和有效宽度计算式与试验结果吻合较好,有效宽度试验值比所提公式计算值平均增大7.2%,标准差为0.091。     

Post-buckling strength of rectangular concrete-filled steel tube panels

为研究矩形钢管混凝土壁板的屈曲后强度，根据平板的弹塑性屈曲理论并考虑残余应力的影响，确定了板件发生塑性屈曲、弹塑性屈曲和弹性屈曲的正则化界限宽厚比。采用试验验证的有限元模型进行了宽厚比为20~150、钢材屈服强度为275~960 MPa的矩形钢管混凝土壁板局部屈曲分析，以界限宽厚比为控制点，根据有限元结果拟合出了矩形钢管混凝土壁板的有效宽度计算式。研究结果表明：弹性屈曲板件的屈曲后强度提高程度显著高于弹塑性屈曲板件；屈曲后强度的提高程度与钢材屈服强度无明显相关性；与无面外约束钢板相比，混凝土的单侧约束作用可使板件的屈曲后强度普遍提高约50%；提出的矩形钢管混凝土壁板的正则化界限宽厚比和有效宽度计算式与试验结果吻合较好，有效宽度试验值比所提公式计算值平均增大7.2%，标准差为0.091。     

高强度钢材箱形柱滞回性能试验研究

为研究Q460高强度钢材箱形柱的抗震性能,对5个足尺试件进行了水平往复加载试验研究,分析了板件宽厚比、轴压比等因素对试件的承载力、破坏模式、耗能能力、变形能力和延性的影响。试验结果表明,Q460高强度钢材箱形柱具有很好的耗能能力和抗震性能,适用于抗震钢框架;除试件HB-1外其他试件本身及其柱脚节点均未发生焊缝开裂,证明设计合理、质量合格的Q460高强度钢材焊缝连接具有足够的承载力和良好的抗震性能;板件宽厚比越大,试件局部屈曲出现得越早,最大荷载对应的位移级越小,达到破坏时的位移级也越小;试件发生局部屈曲的范围及屈曲中心位置相对于试件截面高度的比值依次减小,所有试件最大屈曲位置距固定端0.25B~0.50B（B为等边箱型截面外边长）,塑性区范围距离固定端0.72B~1.06B。根据试验结果,建议在轴压比不大于0.2时,Q460钢材箱形截面压弯构件板件宽厚比限值不应大于30;同时,钢框架柱在进行抗震设计时,其板件宽厚比限值应与轴压比相联系,轴压比越大,板件宽厚比限值应越小。     

Local buckling strength of closed polygon folded section columns

The local buckling behavior of regular polygonal, short length steel columns, fabricated by welding two half sections made of folded steel plates, is described. The polygonal sections are composed of five different section profiles with four to eight sides and each profile having component plates with one to four varied width-to-thickness ratios. A total of 15 specimens are used in the compression test, sustaining uniform compression stress in the fixed end condition. Accurate measurements of welding and cold-forming residual stresses and geometric imperfections were taken prior to testing and are presented in this paper. The test strengths are compared with the current plate buckling code in Japan and with the ECCS recommendations for unstiffened circular cylinders. The empirical design formula based on the test data is also presented to predict the local buckling strength of the polygonal section columns.     

铝合金工形截面短柱轴压局部稳定试验研究

为研究铝合金工形截面轴压构件的局部稳定性能,对15根工程中常用大截面铝合金6061-T6和6063-T5轴压短柱试件进行试验研究,并对12组48个材性试样进行拉伸试验。研究了材料的力学性能、试件的局部几何初始缺陷、变形性能、局部屈曲荷载、轴压承载力等,并将试验结果与各国规范中设计方法计算结果进行对比。试验结果表明：铝合金6061-T6强度与普通钢材相当,但延性较差;铝合金挤压型材的局部几何初始缺陷很小,远小于规范中给定数值;板件宽厚比越大,局部屈曲发生越早,破坏时材料的强度越得不到充分发挥,但是局部屈曲后材料强度仍有较大的提高;翼缘和腹板之间存在相互作用;中国规范、欧洲规范、美国规范和澳大利亚/新西兰规范均低估了试件的轴压承载力,其中美国规范计算结果与试验结果最接近。因此,对于板件宽厚比大的试件,应充分利用其屈曲后强度,各国规范得到的承载力计算结果均较保守。     

Structural behavior of centrally loaded steel columns at elevated temperature

A series of experimental studies is conducted to examine the behavior of SN490 steel column subjected to axial load in the fire condition. This experimental work is aimed at examining the effect of the width-to-thickness ratio of flanges, the slenderness ratio of steel columns and residual stresses on the ultimate strength of an SN490 steel column at a specified temperature. From these studies, it is found that the column strength decreases with the increase of width-to-thickness ratio and slenderness ratio. Column behavior is sensitive to width-to-thickness ratios and the slenderness ratio at temperatures below 550 ^°C. However, the influence of width-to-thickness ratios and the slenderness ratios is not severe when the temperature is higher than 550 ^°C. When the temperature is above 550 ^°C, the column strength deteriorates rapidly. It is also found that the failure mode of steel columns changes from inelastic global buckling at room temperature to inelastic local buckling at elevated temperature, due to the release of residual stress in a fire. Based on the results of this study, local buckling criteria and column strength at specified temperatures are suggested.     

Performance of steel H columns loaded under uniform temperature

This paper presents the experimental results for a series of H steel columns under fire load. The width-to-thickness ratio of steel plates and the slenderness ratios of steel columns are two dominating factors linked to local buckling and global buckling of columns, respectively. To evaluate the influence of these two factors on the structural behavior of steel columns in fire conditions, a series of H steel columns were loaded to their limit states at specified temperature levels. The steady state method has been adopted in order to derive the structural behavior of steel columns at specified temperatures directly.On the basis of the experimental results, it has been found that steel columns with non-compact section are able to reach yield strength at elevated temperature. That is, the width-to-thickness ratio, designed in accordance with current ambient temperature specifications, is capable of preventing brittle failure of steel columns in fire conditions. Depending on the slenderness ratio, the failure of steel columns may change from global buckling at ambient temperature to local buckling at elevated temperature. For plastic section columns with a slenderness ratio greater than 50, column strength drops dramatically to 40% of its strength at ambient temperature. At temperature levels of 500 ^°C, the column retains more than 70% of its ambient temperature strength if the slenderness ratio of the column is less than 50. However, in the case of temperature levels exceeding 500 ^°C, or when the slenderness ratio is greater than 50, column strength drops significantly. On the basis of this study, it is tentatively suggested that 500 ^°C be adopted as the critical temperature for steel members subjected to compression in order to ensure that the column strength keeps higher than 2/3 of the ambient temperature yield strength. The slenderness ratio of steel columns should be limited to 50, so as to prevent brittle failure of steel columns under fire attack.     

壁式钢管混凝土柱抗震性能试验研究

通过3个截面高宽比为3.0的壁式钢管混凝土柱足尺试件在高轴压比下的低周反复加载试验和有限元分析,研究壁式钢管混凝土柱的破坏模式、滞回行为、承载能力、变形性能和能量耗散能力。结果表明：试件的破坏模式为压弯破坏,破坏区域钢板受压鼓曲、钢管纵向焊缝涨裂、混凝土压溃;试件滞回曲线稳定饱满,无明显捏拢现象;纵向隔板能够约束钢管壁板平面外变形,提高钢板局部屈曲强度;试件破坏时位移延性系数大于3.0,等效黏滞阻尼系数大于0.4,减小钢管壁板宽厚比可有效增加试件耗能能力。设计轴压比为0.54～0.69时,壁式钢管混凝土柱屈服位移角大于0.005rad,极限位移角大于0.02rad,具有良好的变形性能和耗能能力。建立的精细有限元模型可准确预测壁式钢管混凝土柱在恒定轴力和反复水平力下的滞回行为。有限元分析表明,轴压比对壁式钢管混凝土柱的极限位移影响显著,提高含钢率可有效增加其承载力和变形性能。     

双钢板-混凝土组合剪力墙抗震性能试验研究

提出一种新型的配置L形拉结件的双钢板-混凝土组合剪力墙。通过两组共6个双钢板-混凝土组合剪力墙试件的拟静力试验,对此新型组合剪力墙的抗震性能进行了研究。试件改变参数主要为轴压比和连接件间距,在试验的基础上对试件的破坏形态、承载能力、滞回曲线、骨架曲线、刚度退化曲线等进行分析。试验研究表明：L形拉结件的配置既能增强外包钢板对核心内混凝土的约束作用又能抑制外包钢板的屈曲,充分保证了外包钢板和混凝土之间的协同工作,此新型组合剪力墙具有较高的承载力,较好的延性及耗能能力。在达到峰值荷载之前,墙体钢板未发生明显的局部屈曲变形,最终组合剪力墙均因端柱屈曲拉裂而开始破坏;破坏时极限位移角的平均值为1/58;随着距厚比减小,试件的水平承载力和延性系数均显著提高。     

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...     

Experimental study on steel beam–columns composed of slender H-sections under cyclic bending

This paper presents an experimental study of six H-section steel beam–columns with large width-to-thickness ratios subjected to combined constant axial force and cyclic bending moment about the strong-axis. Considering different categories of cross-sections, various width-to-thickness ratios of the flange and web of the specimens were selected, and a reliable structural testing system was employed. The test results showed that, for all the specimens, local buckling was the dominating failure mode. Due to their relatively large width-to-thickness ratios of the flange and web, the H-section specimens exhibited limited resisting strength but certain plastic deformation capacity as well as energy dissipation capacity, encouraging employment of such members in seismic areas. It was also found that the flange width-to-thickness ratio and the axial force ratio have significant effects on the hysteretic behavior. In addition, a modified plastic effective width method for ultimate strength was proposed.     

纵向变厚度钢板焊接工字形截面受压短柱的局部稳定试验研究

纵向变厚度(LP)钢板是一种沿轧制方向具有不同厚度钢板的钢材,可用于优化结构的力学性能和提高材料利用率。为研究其局部稳定性能,设计了6根LP翼缘焊接工字形截面短柱,6根LP腹板焊接工字形截面短柱和4根传统等厚度焊接工字形截面短柱,并进行了轴向受压试验。试验研究中确定板临界屈曲荷载的两个主要屈曲准则,同时分析了破坏模式、荷载-侧向变形曲线、荷载-应变曲线和极限荷载,研究LP短柱的局部屈曲行为,得到试件更容易在LP钢板的薄端发生屈曲破坏。将试验结果与现有等厚度板设计规范计算结果进行比较可得,现有等厚度板的设计规范预测腹板变厚度短柱的极限荷载偏于危险,而对于翼缘变厚度短柱欧规EN 1993-1-5能较为准确预测,但需要进一步的数值模拟去验证,从而进一步提出修正公式或者修正系数来指导设计。     

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。     

Experimental study of low yield point steel gusset plate connections

Concentrically braced frames have been used widely in the seismic-resistant design of steel building structures. During earthquake excitation, the braces of the concentrically braced frame are subjected to recursive tensile and compressive forces. The compressive strength of the brace is usually less than its tensile strength because of the buckling of the brace, and this may degenerate the seismic resistance capacity of the braced frame. In this reported research, an alternative design concept that adopts the weak gusset plate-strong brace is examined. The gusset plate is designed to yield prior to the buckling of the brace. Low yield point (LYP) steel is selected for the gusset plate. The LYP steel possesses low yield strength and high elongation capacity. A series of experimental studies was carried out to examine the LYP steel gusset plates under cyclic loads. It is found that adding slot-type restrainers (STR) to the LYP steel gusset plate greatly enhances the seismic resistance of the gusset plate. The proposed LYP steel gusset plate with an STR is able to provide similar strengths under tensile and compressive loads. The energy dissipation capacity of the gusset plate is also increased substantially. Based on this study, suggestions are made for the design of LYP gusset plates.     

Experimental study of low-yield-point steel plate shear wall under in-plane load

This paper describes the study of the low-yield-point (LYP) steel plate shear walls under in-plane load. In the LYP steel plate shear wall system, LYP steel was selected for the steel plate wall while the boundary frame was constructed by the high strength structural steel. A series of experimental studies examined the inelastic shear buckling behavior of the LYP steel plate wall under monotonic in-plane load. The effects of width-to-thickness ratio on the shear buckling of LYP steel plates were examined. The stiffness, strength, deformation, and energy dissipation characteristics were investigated by performing cyclic loading tests on the multistorey LYP steel plate shear walls. Excellent deformation and energy dissipation capacity were obtained for all specimens tested. The LYP steel plate shear wall system is able to exceed 5% of storey drift angle under lateral force.     

Seismic behavior of steel plate shear walls with centrally placed circular perforations

The behavior of unstiffened thin steel plate shear walls with circular perforations placed at the center of the infill plates is examined. A shear strength equation is developed for perforated steel plate shear wall with circular perforation at the center. A series of single storey perforated steel plate shear walls with different aspect ratios and different perforation diameters were analyzed to assess the proposed shear strength equation. A comparison between the nonlinear pushover analysis and the proposed equation shows excellent agreement. The proposed shear strength equation is applied for design of boundary columns of one 4-storey and one 6-storey perforated steel plate shear walls. The predicted design forces in the boundary columns for the selected perforated shear walls are compared to the forces obtained from nonlinear seismic analysis. The proposed equation gives very good predictions for the design forces in the boundary columns.     

钢板-砖砌体组合短柱轴心受压性能试验研究与理论分析

为了研究钢板-砖砌体组合柱中对拉螺栓间距、钢板厚度与结构胶侧向黏结力对钢板局部屈曲的影响,对6个钢板-砖砌体组合短柱试件进行轴心受压试验。结果表明,随着钢板厚度的增加、螺栓间距与钢板厚度之比的减小,钢板局部屈曲变形程度相对降低;可见屈曲荷载与极限荷载的比值为70%~85%左右;在有结构胶侧向黏结力作用下,钢板的局部屈曲发展受到一定程度的约束,使得采用应变片读数判断的钢板局部屈曲临界点与钢板发生可见屈曲变形时对应的荷载值可能存在差异。基于试验数据,通过拟合分析得到钢板发生可见屈曲变形时的钢板应力计算模型,提出轴心受压钢板-砖砌体组合柱钢板发生可见屈曲变形时的承载力计算式。通过与试验结果的对比可知,提出的计算方法可以用于指导类似构件的设计。     

均匀受压钢板件的变形能力和承载能力

钢结构塑性设计要求截面组成权件有足够的局部变形能力，以防由机件的局部层曲而降低构件的承载能力，从而满足截面发展塑性或塑性较的需要．本文利用非线性有限元方法，考虑初始几何缺陷和残余应力的影响，对钢结构中常见的四边交承权件和三边支承权件在均匀受压情况下的屈曲性能进行了分析研究，重点分析了权公宽厚比和板件变形能力、板件承载能力的关系．和有关试验结果进行的对比表明：本文提出的公式，略低于试验曲线，可用来确定不同延性要求的权件宽厚地限值．