高温下内配圆管的方钢管混凝土柱轴压力学性能

为了研究高温下内配圆管的方钢管混凝土柱力学性能，该文在修正高温下核心混凝土材料本构关系的基础上，建立钢管混凝土柱的非线性有限元模型，并利用相关试验实测数据对数值模型进行了验证。基于建立的有限元模型，对不同参数下外方内圆钢管混凝土柱的耐火性能进行分析，阐述了受火过程中圆钢管和混凝土轴向承载力的贡献变化规律，并对火灾下钢管混凝土柱的典型变形曲线进行分析。研究结果表明:钢管混凝土柱的耐火极限可比普通钢管混凝土提高2倍以上；随内钢管直径与外钢管边长比增大，耐火极限先增大后减小；圆钢管的约束效应系数增大，耐火极限明显提高。通过合理设计，复合钢管混凝土柱在不设置防火保护层的情况下，可满足抗火设计规范的耐火需求。

AXIAL PERFORMANCE OF SQUARE CONCRETE-FILLED STEEL TUBE (CFST) COLUMNS REINFORCED BY CIRCULAR STEEL TUBES AT ELEVATED TEMPERATURES

To investigate the mechanical performance of square concrete-filled steel tube (CFST) columns reinforced by circular steel tubes at elevated temperatures, a nonlinear finite element (FE) model of the composite column in fire was established. The model is on the basis of modification for the inner concrete stress-strain relationship of CFST columns at elevated temperatures. Comparison between the measured data and predicted results was carried out to verify the FE model. Based on the verified FE model, the fire resistance performance analysis of composite columns reinforced by circular steel tubes with different parameters was conducted, elaborating the rules of axial bearing capacity of the circular CFST section when the composite columns were exposed to fire. Typical deformation curves were analyzed in this paper. Research results show that:1) the inner circular steel tube could remarkably enforce the fire resistance of composite CFST columns; 2) the fire resistance of the composite columns was two times higher than that of normal CFST columns; 3) the fire resistance increased with the diameter-width ratio of D/B and then reduced; however, the fire resistance increased with the coefficient of confinement effect of circular steel tubes. It is concluded that subject to rational design, the bare CFST column reinforced by circular steel tubes are able to meet the national requirements on fire protection.