考虑约束效应的圆端形钢管混凝土构件承载力计算理论

It’s well-known that the round-ended rectangular concrete-filled steel tubes (CFST) have unique features of mechanics, architectural aesthetics as well as collision-impact resistance which have been usually used as arch rib, main tower and column pier, however currently the regarding theoretical and experimental research is not enough, and the load-bearing capacity calculation theory is not so mature that the equivalent area method is still used without consideration of the confinement effect. Since the circular, round-ended, and rectangular CFSTs has showed the consecutive properties of cross-section shape and restraint effect, the research on round-ended rectangular CFSTs in transition zone deserves the theoretical value on connecting the performances between the circular and rectangular CFSTs. In the project, the comparative researches on the mechanical performance and load-bearing capacity of the round-ended rectangular CFSTs are executed by the axial compression, pure bending and compression-bending experiments of the round-ended rectangular, quasi-rectangular and circular CFST members, and the theoretical correlation between the confinement effect and load-bearing performance is established. Meanwhile, the confined stress distribution of the core concrete is investigated under the effects of the geometrical, physical and loading parameters, and the effective confined region of the concrete core is established. As a result, a refined numerical method is proposed based on strong/weak confinement zone model and the confinement factor. Finally, under the guidance of load-bearing performance continuity principle of the circular, round-ended rectangular, and rectangular CFSTs, the cross-section optimization methods and load-bearing capacity of the round-ended rectangular CFST members are investigated and proposed, which would provide the engineering practices with theoretical and design guidance.

圆端形钢管混凝土构件具有鲜明的力学、建筑美学与防撞抗冲击特点，常作为拱肋、主塔及墩柱，但当前国内外研究滞后于实践，还未形成承载力计算理论，使得设计中只能采用忽略约束效应的折算面积粗糙算法。同时圆端形钢管混凝土的研究具有沟通圆形与矩形钢管混凝土间力学性能的理论价值。因此，探究截面约束效应与构件承载力的关系，形成系统的圆端形钢管混凝土构件设计理论具有重要意义。项目拟通过圆端形、圆形及“拟矩形”钢管混凝土构件轴压、压弯及纯弯性能对比试验，研究圆端形钢管混凝土构件受力性能与承载能力，揭示其约束效应与承载性能的理论关系；研究几何、物理、荷载等参数影响下核心混凝土约束作用机理，建立核心混凝土强/弱“约束区”分区模型和以“约束因子”表征的精细数值方法；进而运用“圆形→圆端形→矩形”钢管混凝土承载性能连续性原理，综合分析并提出圆端形钢管混凝土截面优化方法与构件承载力计算方法，为工程实践提供理论与设计指导。

国内外对圆端形钢管混凝土构件力学性能试验与理论研究不足，未建立起承载力计算理论，导致工程实践中未考虑约束效应对其承载性能的影响。本项目结合约束效应机理、有限单元法、承载力统一计算理论等方法，完成了圆端形钢管混凝土约束分区、轴压/偏压/纯弯力学性能、截面优化理论、钢管加劲措施分析、统一承载力计算公式等方面的研究工作，取得了如下研究成果：（1）进行了圆端形钢管混凝土约束效应工作机理的理论分析，提出了核心混凝土“有效约束区”分区模型，试验研究分析了不同截面参数下变圆心角圆端形钢管混凝土短柱轴压性能，试验研究分析了圆端形钢管混凝土中长柱轴压性能；（2）设计制作了圆端形钢管混凝土柱纯弯和偏压试验，研究分析了圆端形钢管混凝土柱强轴和弱轴截面抗弯机理，分析了圆心角等参数对圆端形钢管混凝土短柱偏压性能的影响规律；（3）为实现圆端形钢管混凝土设计优化，根据轴压和偏压结果，证明了圆心角和截面长宽比及约束效应系数对承载力的耦合影响关系，提出了不同设计参数的最优匹配关系，推导了偏压作用下的试件N-M破坏包络曲线表达式；（4）设计了带约束拉杆和肋板加劲的圆端形钢管混凝土短柱，进行了轴压和纯弯试验，研究分析了两种加劲方式对试件力学性能的影响规律；（5）推导并提出了圆形、圆端形、矩形截面钢管混凝土的轴压统一承载力公式。本项目首次开展了基于约束效应与统一理论对圆端形钢管混凝土构件力学性能研究，并提出了圆端形钢管混凝土截面设计优化方法，推导得出了承载力统一计算公式。项目在圆端形钢管混凝土的力学性能试验方法、试验结果、截面优化、承载力计算理论等方面的研究成果，具有较好的理论与工程实践价值。