外包式六边形钢管混凝土柱脚抗震性能及设计方法研究

As the reinforced concrete (external) encased hexagonal concrete-filled steel tubular (HCFST) column (internal) bases (referred to as concrete-encased hexagonal concrete-filled steel tubular column bases in this application) are widely used in high-rise buildings in recent years, the mechanical behavior and design method of such column base structures under cyclic loading are investigated in the present study. Due to the lack of systematic research on the seismic performance of the composite column base, there are no robust design methods for such structures under earthquake loading in current design codes of China and other countries yet. As a result, it is important to carry out research on the seismic performance of the concrete-encased hexagonal concrete-filled steel tubular column base, which will benefit both the theoretical backgrounds and engineering applications. A finite element analysis (FEA) model is established to simulate the full-range response of the composite column base under laterally increasing cyclic loading. Seismic tests are carried out on the column base specimens with different parameters, in which the failure modes and seismic resistance of the composite specimens are analyzed. With the FEA model, the mechanical behavior of the concrete-encased hexagonal concrete-filled steel tubular column base under laterally cyclic loading is studied, including the composite actions of different materials in the composite column base. Parametric study is conducted to evaluate the influences of main parameters, such as the axial loading ratio of the column, steel ratio of the HCFST column, reinforcement ratio of the outer reinforced concrete component, and material properties on the seismic performance of the composite column base. Finally, design methods and construction measures on the seismic design of the concrete-encased hexagonal concrete-filled steel tubular column base are drawn based on the parametric study.

本项目以近年来开始在高层建筑中大量应用的外包钢筋混凝土的六边形钢管混凝土柱脚（以下简称外包式六边形钢管混凝土柱脚）为对象，开展其在往复荷载作用下的工作机理和设计原理研究。以往由于缺乏对该类柱脚结构抗震性能的系统研究，目前国内外相关设计规范中尚未给出其抗震设计方法的规定，因此，深入进行本课题研究具有重要的理论和工程应用价值。本课题拟建立外包式六边形钢管混凝土柱脚在横向往复荷载及柱恒定竖向荷载作用下荷载-变形关系全过程分析的有限元模型，进行该类柱脚在不同参数下抗震性能的典型试验。通过理论和试验研究，明晰外包式六边形钢管混凝土柱脚典型的破坏形态和极限承载力变化规律，分析该类柱脚结构在受力全过程中其各组成材料间的共同工作特点。在系统分析柱轴压比、钢管混凝土含钢率、外包钢筋混凝土配筋率和材料强度等主要参数对该类柱脚抗震性能影响规律的基础上，提出其抗震承载力和刚度计算方法以及抗震构造措施设计条文。

六边形钢管混凝土柱具有良好的力学性能和施工性能，同时其特殊的截面形状使得其能够与其他结构构件以多角度相连，已在实际工程得到推广应用。外包式柱脚具有刚度大，承载力高，施工便捷的特点，具有良好的应用前景，也是六边形钢管混凝土柱可优先采用的柱脚形式。本项目以外包式六边形钢管混凝土柱脚为研究对象，对其抗震性能和抗震设计方法展开了试验、数值和理论研究，所完成的主要工作如下：.1. 进行了外包式六边形钢管混凝土柱脚在恒定轴压力和水平往复荷载作用下的全过程性能试验研究。试验参数包括：柱脚外包段高度、加载角度、柱轴压比、柱截面形式、柱脚类型、柱截面尺寸和栓钉设置。通过试验研究柱脚结构的全过程受力性能，剖析构件整体和外包钢筋混凝土的破坏规律，研究其典型破坏形态，分析了各参数对其破坏形态的影响规律。.2. 建立了外包式六边形钢管混凝土柱脚抗震性能分析的有限元模型。模型综合考虑了材料和界面接触的非线性行为、底板-锚栓构造和外包段底截面裂缝的开裂-闭合行为，利用试验数据对模型精度进行了验证，模型计算结果与试验结果吻合良好。基于经过验证的有限元模型系统分析了外包式柱脚的破坏形态，明确了其破坏机理、传力机制、内力分布情况。系统分析了钢管混凝土柱参数、外露式柱脚参数、外包段参数、柱轴压比、加载角度、栓钉等对柱脚抗震性能的影响。.3. 针对两类典型的压弯破坏形态，提出了外包式六边形钢管混凝土柱脚的抗震设计方法，包括其抗弯承载力计算公式，及外包式柱脚的抗震设计构造措施，给出了外包式柱脚中外包段、外露式柱脚以及栓钉设计要求，为有关技术标准的制订创造了条件。

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