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

北美绝大多数建筑都是住宅。轻型木结构建筑是首选在这个地区，由于成本低，材料的可用性和易于施工。典型的轻型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型木结构的脆弱性，由此造成的破坏是经济损失的主要来源。例如，1992年安德鲁飓风造成的200亿至250亿美元经济损失中，轻型木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组件的故障造成的。在这些事件中，风流过屋顶产生类似于飞机机翼的升力。由此产生的屋顶上举力的增加导致屋顶锚固的失效，并且一旦屋顶失效，墙壁在顶部变得横向无支撑，并且抵抗风荷载的能力较小。这反过来又导致墙壁倒塌，整个建筑物倒塌。因此，这种故障往往是造成生命损失的原因，在风暴中，这就需要改善的行为轻框木结构下的隆起负荷。本研究的主要目的是评估技术和经济可行性的原型，以提高屋顶的抗拔能力受到强风。该系统是一种网的形式，可以在屋顶上铸造并锚定在地面上，防止屋顶在强风事件期间在关键节点处失败。建议的系统提供了一个替代的负载路径到地面的上举力，减少了对结构内的薄弱，钉连接的需求。该研究项目描述了所需的数值和实验工作，以评估拟议的改造系统在增加房屋屋顶的抗拔能力方面的能力，并优化系统组件，将原型转换为商业系统，可以成功地引入目标市场，并易于业主应用。

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.