Numerical and experimental study of a new system for retrofitting roofs subjected to extreme wind loading

北美的绝大多数建筑都是住宅。轻型木结构建筑是该地区的首选，因为它的成本低，材料容易获得，而且施工容易。典型的轻型框架木结构遵循建筑规范的要求来确定构件尺寸和连接细节；因此，这些结构不需要进行结构分析和设计。尽管如此，过去的高速风事件暴露了现有住宅轻框木结构的脆弱性，由此造成的破坏是经济损失的主要来源。例如，在1992年安德鲁飓风造成的200-250亿美元的经济损失中，对轻型木结构结构的破坏占了很大一部分，其中约95%的损失是由于屋顶系统部件的故障造成的。在这些活动中，风在屋顶上流动时产生的升力类似于飞机机翼上的升力。由此产生的屋顶上拔力的增加会导致屋顶锚固失效，一旦屋顶失效，顶部的墙就变得横向无支撑，抵抗风荷载的能力降低。这反过来又会导致墙壁倒塌，整个建筑倒塌。因此，这样的故障往往是在风暴期间造成生命损失的原因，这就需要改善轻框架木结构结构在上拔荷载下的性能。这项研究的主要目的是评估所开发的原型的技术和经济可行性，以提高屋顶在强风作用下的上浮能力。这个系统是以一张网的形式存在的，它可以撒在房子的屋顶上，并固定在地面上，防止屋顶在强风事件中的关键节点处坍塌。建议的系统提供了一条通向地面的替代荷载路径，减少了对结构内薄弱的钉子连接的需求。该研究项目描述了所需的数值和实验工作，以评估拟议的改装系统在增加房屋屋顶的抗拔能力方面的能力，以及优化系统组件以将原型转变为能够成功地引入目标市场并便于房主应用的商业系统。

The vast majority of structures in North America are residential. Light-framed wood construction is preferred in this region due to the low cost, the availability of materials and the ease of construction. Typical light-framed wood structures follow the requirements of governing building codes to determine the member sizes and connection details; consequently, structural analysis and design are not needed for these structures. Despite this fact, past high speed wind events have exposed vulnerabilities in existing residential light-framed wood structures, with the resulting damage being a major source of economic loss. For example, the damage to light-framed wood structures which represented a large portion of the US$20-25 billion of economic losses caused by Hurricane Andrew in 1992, with approximately 95% of those losses resulting from failure of components of the roof system. During these events, wind flowing over a roof creates lift similar to that on airplane wings. The resultant increase in the uplift forces on the roof causes failure of the roof anchorage and once the roof has failed, walls become laterally unsupported at the top and have less capacity to resist wind loads. This in turn causes the walls to fail and the whole building to collapse. As a result, such failures are often the cause of loss of life during wind storms, which requires an improvement in the behaviour of light-framed wood structures under uplift loading. The main objective of this research is to assess the technical and economical viabilities of a developed prototype for enhancing the uplift capacity of roofs subjected to strong wind. This system is in the form of a net that can be cast over a house's roof and anchored in the ground preventing roofs from failing at the critical joints during strong wind events. The proposed system provides the uplift forces an alternate load path to the ground, reducing the demand placed on the weak, nailed connections within the structure. This research project describes the numerical and experimental work required to assess the ability of the proposed retrofit system in increasing the uplift capacity of a house's roof and to optimize the system components to transform the prototype into a commercial system that can be successfully introduced to the target market and easily applied by homeowners.