Limit of Width-to-Thickness Ratio of Rectangular Concrete-Filled Steel Tubular Column
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摘要: 钢管混凝土组合结构可以充分发挥混凝土和钢材两种材料的优势,在商业和公共建筑中应用非常广泛。近年来,随着装配式建筑的推广,矩形钢管混凝土柱由于其抗弯性能优良、节点形式多样等优点,在民用建筑中受到越来越多的关注。相比商业和公共建筑,住宅钢结构对建筑室内空间的有效利用(避免“凸梁凸柱”)和经济性(减小用钢量)具有更高的要求,为了满足这些要求,住宅钢结构中的矩形钢管混凝土柱的截面普遍具有较大的高宽比,且板件的宽厚比尽可能大。目前,在住宅钢结构中的矩形钢管混凝土柱的截面高宽比已达3.3左右,远超一般规范的适用范围(不大于2.0)。对于钢管混凝土柱而言,外钢管的局部失稳是其重要的破坏模式之一。当发生局部失稳时,钢管混凝土柱的承载能力将大幅下降,从而对构件的后期剩余承载力产生重要影响。我国规范通过限制钢管壁板件的宽厚比来防止管壁过早发生局部屈曲,但是经过研究发现,我国规范的宽厚比限值与国外部分规范存在差异,同时现有规范的宽厚比限值主要依据对截面高宽比不大于2.0构件的研究,对于住宅钢结构中应用广泛的高宽比大于2.0的宽钢管混凝土柱的适用性需要进一步研究。
通过对矩形钢管混凝土柱轴压性能的有限元分析,对宽钢管混凝土柱的板件宽厚比进行了研究。在用于模拟矩形钢管混凝土构件的约束混凝土本构模型和混凝土塑性损伤模型基础上,引入考虑截面高宽比对约束作用影响的截面高宽比系数,建立了可分析截面高宽比较大情况的矩形钢管混凝土柱有限元模型,并通过与试验结果对比验证了有限元模型的准确性。通过参数分析,考虑截面高宽比、宽厚比、钢材强度和混凝土强度等对矩形钢管混凝土柱极限承载力的影响,分析了宽矩形柱截面宽厚比限值。将分析结果与国内外相关规范关于矩形钢管混凝土柱截面宽厚比限值进行对比。定义归一化的极限承载力系数,并将极限承载能力系数曲线的转折点作为钢管宽厚比限值的确定依据。研究发现:钢材强度和混凝土强度分别与试件极限承载力呈负相关和正相关关系,但截面宽厚比对试件的极限承载力影响更为关键;矩形钢管混凝土板件的宽厚比限值可取50√235/fy, 这一数值与规范EC 4和BS 5400的取值接近,小于GB 50936、CECS 159、GJ/B 4142、DBJ/T 13-51以及AISC 360的限值,更明显小于AIJ和DB/T 29-57的限值。Abstract: Concrete-filled steel tubular(CFST) structures can give full play to the advantages of both concrete and steel materials, and have been widely used in commercial and public buildings. With the implementation of the prefabricated building policy in recent years, CFST columns with rectangular section are getting more and more attention in residential projects due to its advantages of excellent bearing capacity and simple joint structure. Compared with commercial and public buildings. residential steel structures have higher requirements for the effective use of building interior space (avoid " convex beams and columns" ) and economy (reduce the amount of steel used). In order to meet these requirements, the section of the rectangular concrete-filled steel tube column in the residential steel structure generally has a large aspect ratio, and the width to thickness ratio of the plate is as large as possible. Currently, the sectional aspect ratio of rectangular CFST column has reached about 3. 3 in the application of engineering, lager than the common range(no more than 2. 0). The local buckling of steel tubes is the one of the most important failure modes of CFST column, which will cause the significant decrease of bearing capacity of CFST column and affect the residual bearing capacity of the specimens. The limit of width-tothickness ratio is recommended in specifications for preventing the local buckling. Therefore, it is necessary to pay attention to the width-to-thickness ratio of CFST columns. However, there is difference of the limitation of width-to-thickness ratio between Chinese code and foreign codes. Meanwhile, the limit of width / thickness ratio of the existing code is mainly based on the study of the component whose section aspect ratio is not more than 2. 0, and for residential steel structure should be used in a wide range of aspect ratio greater than 2. 0 of the wide applicability of the concrete filled steel tube column need further research.
The limit of sectional width-to-thickness ratio of rectangular CFST column is studied by finite element(FE) analysis. Based on the confined concrete constitutive model and concrete damage plastic(CDP) model, considering the effects of section height to width ratio restraint cross section aspect ratio coefficient. FE model of rectangular CFST column is established for analyzing the members with large aspect ratio. The accuracy of the FE model is verified by comparing with the test. Through the parameter analysis, considering the influence of sectional aspect ratio, width-to-thickness ratio, steel strength and concrete strength on the ultimate bearing capacity of rectangular CFST columns, the limit of sectional width-to-thickness ratio of rectangular CFST columns is analyzed. The limits of sectional width-to-thickness ratio of rectangular CFST column in codes are introduced, and the analysis result is compared with the limit in codes. By defining the normalized ultimate bearing capacity coefficient and taking the turning point of the curve of the ultimate load as the basis to determine the limit of width-to-thickness ratio of the steel tube, it is found that the steel strength and concrete strength are negatively correlated and positively correlated with the ultimate bearing capacity of the specimens, respectively. But effect of section width-to-thickness ratio on the ultimate bearing capacity is more critical. The results show that the limit of width-to-thickness ratio of rectangular CFST columns is about 50√235/fy, which is close to the recommendation values of AIJ, EC4 and BS5400, but obviously smaller than the limits of GB 50936, CECS 159, GJ / B 4142, DBJ / T 13-51 and AISC 360. -
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