钢管混凝土平面框架子结构抗连续倒塌精细有限元分析

竖向关键构件失效后，结构的抗倒塌能力主要以失效柱上部钢梁的梁机制和悬链线机制为主。选取"两跨三柱"型钢管混凝土平面框架子结构形式为研究对象，采用精细有限元法细致剖析竖向荷载全过程作用下平面框架的倒塌全过程，分析中柱竖向位移与承载力的全过程曲线特征，研究不同几何和物理参数对框架的抗力曲线的影响规律。结果表明:中柱承载力P-竖向位移Δ曲线分为四个阶段:梁机制阶段、转换机制阶段、悬链线机制阶段、破坏阶段。综合抗力指标和位移延性指标可以看出，钢梁翼缘厚度和钢管含钢率对该类结构的抗连续倒塌影响较为显著，工程实际设计和应用中应予重视。

REFINED FINITE ELEMENT ANALYSIS OF PROGRESSIVE COLLAPSE OF PLANAR FRAMES WITH CONCRETE-FILLED STEEL TUBULAR COLUMNS

The capacity of concrete filled steel tubular (CFST) structures against progressive collapse are determined by the beam mechanism and catenary action of the steel beams connected with the damaged key column which is destroyed by extreme loads. This paper presents a finite element (FE) model of a planar frame with CFST columns based on refined finite element analysis to study the progressive collapse resistance. The whole collapse failure modes and the stress distribution revealed the resistance mechanism of the planar frame during the process of progressive collapse. The relationship between the load-carrying capacity (P) versus vertical displacement (Δ) was analyzed in the FE model. The influence of different geometric and physical parameters on the collapse-resisting capacity of the frames were also studied. The results showed that the P-Δ relationship curves contain four stages during the whole collapse, i.e., beam mechanism, transformation mechanism, catenary action and failure phase. The steel beam flange thickness and the steel ratio of tube have significant influence on the collapse-resisting capacity of CFST structures based on the resistance index and displacement ductility index. Attentions should be paid in practical engineering designs and applications.