基于纤维模型的顶底角钢腹板双角钢连接组合梁柱子结构抗倒塌机理分析

为研究不等跨顶底角钢腹板双角钢连接组合梁柱子结构的抗倒塌机理，对一个缩尺比1/3的两跨三柱型梁柱子结构进行了单调静载试验。试验结果表明：压拱机制主要提高了组合梁负弯矩区的受弯承载力，通过增强梁机制可以提升子结构的倒塌抗力，角钢发生断裂后，楼板迅速连结剩余构件形成新的传力路径，悬索机制显著发挥；因短跨组合梁率先发生破坏，子结构效能发挥效率仅为83%。在考虑子结构各部件接触关系及损伤演化的基础上，通过组件法对梁柱连接部件进行合理简化；基于OpenSEES形成高效的数值方法，并基于纤维模型进行参数分析，明确高跨比对子结构抗力的影响。研究结果表明，当高跨比较小梁的高跨比大于1/14，高跨比较大梁退出工作后，剩余结构无法提供更高的抗力，角钢断裂时子结构达到峰值荷载；当梁的高跨比小于1/17，钢筋在小变形阶段进入受拉状态，受压区混凝土与钢筋的应力异向加速混凝土的强度退化，并削弱组合梁受弯承载力；高跨比较大梁主导梁机制的发展，其退出工作后梁机制开始下降；双跨梁的不对称轴力可使压拱机制提前退出工作，有利于悬索机制的形成。

Analysis of anti-collapse mechanism of composite beam-column substructure with top-seat angle with double web angles connection based on fiber beam-column model

To explore the anti-collapse mechanism of composite beam-column substructure with unequal span and a top-seat angle with double web angles connection, a monotonic static load test was carried out on a 1/3 scale specimen with two spans and three columns. The test results show that the compressive arch mechanism mainly improves the flexural capacity of the negative moment region of the composite beam, and the collapse resistance of the substructure is enhanced by strengthening the flexural mechanism. After the angle steel breaks, the composite floor quickly connects the remaining members to form a new force transmission path, and the catenary mechanism is significantly promoted. Because the short span composite beam is first damaged, the energy efficiency of the substructure is only 83%. Considering the contact relationship and damage evolution of each component of the substructure, the component-based method is used to simplify the beam-column connection reasonably. Based on OpenSEES, an efficient numerical method was formed, and the parameter analysis was conducted by it to clarify the influence of the height-to-span ratio on the resistance of the substructure. The results show that the remaining structure cannot provide higher resistance when the height-to-span ratio of the beam with a smaller height span ratio is greater than 1/14. After the beam with a larger height-to-span ratio is out of service, the peak load of the substructure is formed at the fracture of the angle steel. When the height-to-span ratio of the beam is less than 1/17, the tension force of the reinforcement is brought into play prematurely at the small deformation stage. Due to the stress difference between the concrete and the reinforcement in the compression area, the strength degradation of the concrete is accelerated, which weakens the flexural capacity of the composite beam. The development of the beam mechanism is dominated by the beam with a larger height-to-span ratio, and the flexural mechanism begins to decline after it fails. The asymmetric axial force of two-bay beams can make the arch compression mechanism fail in advance, which is conducive to the formation of catenary mechanism.