预应力正交胶合木剪力墙结构体系抗震机理与可靠度性能

Cross laminated timber (CLT) is featured by its high stiffness and strength, and similar mechanical properties can be obtained in the two orthogonal directions for such engineered wood product. CLT panels are particularly suitable for shear walls in multi-story applications. However, when subjected to earthquakes, CLT shear walls normally have excessive stiffness and strength degradation which is caused by the concentrated damage in the wall connectors. Such mechanism always leads to a brittle failure mode in the wood near the connection region, even though most of the CLT wall panel is still undamaged. In order to avoid such failure mode (i.e. stiff panel with brittle connection), a kind of post-tensioned CLT shear wall system is proposed in this project. Post-tension tendon is employed to increase the lateral load resisting capacity and to minimize the residual deformation. Moreover, novel connectors will be developed for the proposed post-tensioned CLT shear wall system. This project will provide a comprehensive investigation into the seismic behavior of the post-tensioned CLT shear wall system. Pseudo static tests on full-scale wall specimens will be conducted to clarify the influence of prestress effect on the lateral load resisting mechanism of the shear wall system, and the interaction between the prestress effect and the energy dissipation mechanism within the shear wall system will be revealed. Nonlinear finite element model will be developed, and seismic reliability and failure probabilities of such structural system will be evaluated with the consideration into various uncertainties. This project will make significant scientific contributions for understanding the seismic behavior and failure mechanism of post-tensioned CLT shear wall structural system. It will also contribute to the development and utilization of novel seismic resistant timber structures in China.

正交胶合木是一种强度很高、趋于正交方向同性的工程木产品，其剪力墙整体性好、承载力大。然而，侧向力作用下正交胶合木剪力墙的破坏多集中在墙体与楼板或墙体间的连接中，且极易发生以局部木材劈裂为主的脆性破坏，致使其承载性能严重退化，而墙体中大部分木材的强度远未充分发挥。为避免上述“弱连接、强构件”的破坏模式，提出在墙体中贯穿预应力筋来提高其抗侧性能，并配以同预应力墙体侧向变形相协调的连接节点。本项目拟通过试验和理论分析阐明预应力效应对墙体力学性态的影响机理和墙体破坏机理；通过试验研究预应力剪力墙耗能型连接的滞回特性，阐明预应力效应和耗能效应的协同工作机理；继而，基于数值模拟揭示地震作用下结构响应的变化规律，并结合可靠度分析阐明各种不确定性对结构失效概率的影响。本项目对揭示预应力正交胶合木剪力墙结构体系的工作原理和破坏机理有十分重要的科学意义，对构建新型木结构抗震体系有重要工程应用价值。

预应力正交胶合木（cross-laminated timber, CLT）剪力墙结构体系抗侧力性能好、自恢复性能优，改善了传统CLT剪力墙“弱节点”的破坏模式，满足了在高烈度地震区域建造多高层木结构的需要。为了解析该类结构体系的抗震机理及地震可靠度，对预应力CLT剪力墙结构体系开展了系统的试验及理论研究。基于拟静力试验研究了预应力CLT剪力墙的抗侧力性能，阐明了预应力钢绞线的内力损失规律；基于建立的预应力CLT剪力墙模型开展参数分析，明确了相关参数对墙体抗侧力性能的影响规律。开发了适用于CLT墙体的角钢连接件、抗拔件和耗能件，测试了上述节点的力学性能及耗能能力；研究了角钢连接件在竖向拉力与水平剪力间的耦合受力机理，建立了可预估拉剪耦合效应的节点模型。基于直接位移设计法设计了多幢预应力CLT剪力墙结构体系，基于经校对的结构体系模型，分析了其层间位移角限值；结合易损性理论分析了结构体系抗震性能，阐明了余震作用对关键动力响应参数的影响规律，评价了结构震后损伤并提出了耗能件种类的优选方案。分别采用易损性理论和响应面法分析了预应力CLT剪力墙结构的地震可靠度，定量计算了多遇、设防、罕遇地震性能水准下结构的地震可靠指数。研究结果表明：相较于普通CLT剪力墙，预应力CLT剪力墙的抗侧力性能显著提高，设置耗能件能够一定程度上提高预应力墙体的耗能能力；角钢连接件所受恒定竖向拉力的增长将削弱其水平抗剪承载力，经强化设计后其抗剪承载力将显著提升；直接位移设计法较适用于预应力CLT剪力墙结构的抗震设计，多遇、设防、罕遇地震性能水准下建议的结构最大层间位移角限值分别为1/145，1/70和1/45；预应力CLT剪力墙结构的震后残余位移角非常小，余震作用对结构最大层间位移角几乎没有影响。基于响应面法得到的可靠度指标要稍小于基于易损性理论得到的可靠度指标，可基于各自特点选取合适的可靠度分析方法。课题研究为预应力CLT剪力墙结构体系的工程应用奠定了基础，对于倡导绿色低碳建筑、促进多高层建筑抗震技术发展，都有着重要意义。