Durability of Low-Carbon Structures

考虑到大气中二氧化碳含量增加的危险，加拿大政府在巴黎COP21会议上承诺向低碳经济转型。公路桥是加拿大基础设施的重要组成部分，这些结构的可持续性，包括它们的碳足迹，都需要得到解决。作为一种生物基材料，木材是唯一低碳的主要结构材料。目前用于木材的连接可能很昂贵，并且限制了木材在桥梁中的使用。木材设计中最重要的发展之一是高强度，长长度（高达1.5米），自攻螺钉（STS）的可用性。STS可以提供简单，经济有效的连接，即使是大型木材元件。然而，为了使STS安全有效地用于公路桥梁，必须充分了解其在经历数百万次车辆荷载循环（称为“疲劳”）后的性能。提出的研究重点是自攻螺钉连接的高周疲劳性能。这项工作将包括实验测试和理论建模。重点将放在“接口”和“连接”两个层面上。界面规模工作将检查嵌入木材中的单个螺钉，并了解该界面如何随着重复加载而变化。“连接”规模工作将检查连接全尺寸木材部件的典型连接，并了解这些连接在重复载荷下的行为。疲劳测试可能需要几天甚至几周才能完成。因此，这项工作的关键部分是开发和验证理论模型，以预测给定参数（施加载荷，螺钉类型，木材类型等）的疲劳性能。工程师可以使用这些模型来预测给定应用中的疲劳性能，而不需要对每个新配置进行昂贵的测试。申请人先前开发了钢、混凝土和纤维增强聚合物（FRP）结构和部件的疲劳模型。然而，木材（像申请人研究的其他低碳材料一样）特别容易受潮，并且在性能上有很大的可变性。因此，该研究将在调整先前开发的疲劳模型以处理这些特征方面开辟新天地。向低碳经济过渡的目标是可能的，但用于建筑环境的传统材料仍然是一个挑战。木材是一种重要的低碳替代品，但现在需要进行基础研究，以便探索其作为公路桥梁材料的全部局限性。申请人进行的研究将为工程师提供关键的指导，而8名HQP培训人员将为将该技术应用于工业提供关键的专业知识。

Given the danger of increasing carbon dioxide levels in the atmosphere, the Canadian government at the Paris COP21 conference committed to transition to a low-carbon economy. Highway bridges are critical pieces of Canada's infrastructure, and the sustainability of these structures, including their carbon footprint, needs to be addressed. As a bio-based material, timber is the only major structural material that is low-carbon.The connections currently used for timber can be expensive and limit the use of timber for bridges. One of the most important developments in timber design has been the availability of high-strength, long length (up to 1.5 metres), self-tapping screws (STS). STS can provide simple, cost-effective connections even for large timber elements. However, in order for STS to be safely and effectively used for highway bridges, their performance after experiencing the millions of cycles of loading due to vehicles (called “fatigue”) must be well understood.The proposed research will focus on the high-cycle fatigue performance of timber connections with self-tapping screws. The work will involve both experimental testing and theoretical modeling. The focus will be at both the “interface” and “connection” scales. The interface scale work will examine a single screw embedded in timber and understanding how this interface changes with repeated loading. The “connection” scale work will examine typical connections connecting full-scale timber components and understanding how these connections behave with repeated loads.Fatigue testing can take days or even weeks to complete. Thus, a critical part of this work is to develop and validate theoretical models that predict the fatigue performance for a given set of parameters (applied loads, type of screws, type of timber, etc.). These models can then be used by engineers to predict the fatigue performance in a given application, rather than needing expensive testing for every new configuration. The applicant has previously developed fatigue models for steel, concrete, and fibre-reinforced polymer (FRP) structures and components. However, timber (like other low-carbon materials the applicant has researched) is particularly susceptible to moisture and has large variability in properties. Thus, the research will be breaking new ground in adapting previously developed fatigue models to deal with these characteristics.The goal of transitioning to a low-carbon economy is possible, but conventional materials used for our built environment continue to be a challenge. Timber is an important low-carbon alternative, but fundamental research is needed now so that its full limits as a material for highway bridges can be explored. The research conducted by the applicant will provide critical guidance for engineers and the eight HQP trained will provide critical expertise in bringing this technology to industry.