受弯钢构件基于曲率的延性评价指标研究

Curvature-based ductility evaluation index for flexural steel members

钢构件的变形评价是钢结构抗震性能化设计中的重要内容。目前已有标准中通常采用弦转角作为受弯构件的变形评价指标,但该指标主要适用于集中塑性铰模型,且计算时需考虑构件受力与边界条件,应用不便。对于应用日益广泛的分布塑性区模型和纤维模型,曲率更易提取且计算方便,但相关延性评价指标研究尚不充分。以H形截面受弯钢构件为研究对象,提出更易于应用的基于曲率的延性评价指标,即曲率延性系数。通过9个截面等级为S1~S4级的典型试件循环加载试验,以及154个考虑截面翼缘宽厚比、腹板高厚比和截面高宽比等参数的有限元模型,研究了受弯构件在循环荷载作用下,不同因素对曲率延性系数的影响,并通过回归分析提出了曲率延性系数的计算式。根据GB 50017—2017《钢结构设计标准》的受弯构件截面等级分类,确定了各等级截面受弯构件曲率延性系数限值。研究结果表明:截面翼缘宽厚比与腹板高厚比均对构件曲率延性系数产生影响,且两者相互耦合;对截面等级S1~S4的受弯钢构件,采用回归分析提出的曲率延性系数经验计算式得到的计算结果与试验和有限元分析结果均有较高的吻合度;确定的不同截面等级的曲率延性系数限值,可用于弹塑性分析中判断构件的延性需求。

The deformation evaluation of steel members is an important part in the performance-based seismic design of steel structures.For flexural steel members,rotation is generally used as the deformation evaluation index in current standards.However,rotation is mainly suitable for the concentrated plastic hinge models,and must take external force and boundary conditions into account during calculation,which is inconvenient to apply.Curvature is easier to extract and calculate for the increasingly used distributed plastic zone model and fiber model,but the related ductility evaluation indexes are not sufficiently investigated.Due to the above reasons,curvature ductility coefficient,an easierto-apply curvature-based ductility evaluation index,was suggested for H-section flexural steel members.Through 9 representative specimens with section grades of S1-S4,and 154 finite element models considering parameters of flange width-thickness ratio,web height-thickness ratio,and section aspect ratio,the effect of various factors on the curvature ductility coefficient of the member under low cyclic reversed load was investigated.A calculation equation of the curvature ductility coefficient was proposed based on regression analysis.Finally,according to the section grade classification in GB 50017—2017“Standard for design of steel structures”,the limits of the curvature ductility coefficients of flexural members with different section grades were determined.The research results show that both the flange width-to-thickness ratio and the web height-to-thickness ratio of the cross section will affect the curvature ductility coefficient of the flexural members,and the two factors are interdependent.For flexural steel members with cross-section grades of S1-S4,the calculated values of the proposed regression formula of curvature ductility coefficient agree well with the experimental values and finite element simulation values.The limits of curvature ductility coefficients for different cross-sectional grades determined in this paper can provide a basis for evaluating the ductility requirements of flexural steel members in elastic-plastic analysis.