侧向低速冲击作用下钢管混凝土构件开裂评估模型及影响因素研究

基于落锤冲击试验研究了钢管混凝土构件发生变形、开裂及断裂的受力机理，试验表明，构件在开裂前存在明显的局部响应过程，在冲击位置及支座截面发生局部凹陷和屈曲，临界开裂能量主要由整体变形耗能和局部耗能所决定。结合数值模拟得到了基于冲击质量和冲击速度的开裂评估曲线，从能量角度建立了可以考虑构件局部耗能的开裂评估模型，并研究了冲击位置、混凝土强度、钢管强度、含钢率对开裂评估模型的影响。结果表明：使构件处于临界开裂状态的冲击能量并非一个定值，在冲击速度大、质量小时，构件的局部响应更加明显且局部耗能更多，因此临界开裂能量变大；随着冲击质量增大，开裂评估模型逐渐收敛于水平渐近线，即最小临界开裂能量，根据冲击能量与开裂评估模型的关系可以判断构件的局部损伤及开裂状态；改变冲击位置对构件开裂评估模型的影响较大，增大钢管强度及含钢率可以有效提高构件抵御冲击开裂的性能，但提高混凝土强度对构件开裂状态的影响不明显。

Study on evaluation model and influencing factors for cracking of concrete-filled steel tubular members subjected to lateral low-velocity impact

Based on the drop weight impact tests, the mechanisms of deformation, cracking and fracture for concrete-filled steel tubular (CFST) members are investigated. The experimental results show that the CFST members experience the prominent local response stage before cracking, with the local depression at the impact position and the local buckling at the support section. Hence, the critical cracking energy is mainly determined by the energy dissipations of global deformation and local damage. Based on the numerical simulations, the cracking evaluation curve considering the impact mass and impact velocity is obtained. From the energy viewpoint, the cracking evaluation model considering the local energy dissipation is established, and the effects of impact location, concrete strength, steel strength and steel ratio on the cracking evaluation model are investigated. The research results show that the impact energy which makes the CFST member in critical cracking state is not a constant value. For the case of high impact velocity and low impact mass, the more obvious local response of the CFST member produces more local energy dissipation, and the critical cracking energy increases. With the increase of the impact mass, the cracking evaluation model converges asymptotically to a horizontal line, which corresponds to the minimum critical cracking energy. According to the relationship between the impact energy and the cracking evaluation model, the local damage and cracking state of the CFST member can be evaluated. The change of the impact location may significantly affect the cracking evaluation model. The increases of the steel strength and steel ratio can effectively improve the performance of resisting impact cracking of the CFST members, but the improvement of the concrete strength has little effect on the cracking state of the CFST member.