Improving durability of joints of precast decks

北美基础设施的糟糕状况在过去几年中受到了相当大的关注。马尼托巴的许多桥梁建于20世纪50年代至70年代。这些桥梁的使用寿命即将结束，需要在不久的将来进行更换或修复。美国土木工程师协会报告说，美国每天有2亿人次穿越桥梁，这些桥梁正在恶化，可能需要更换或加固。更换或修复的费用受完成升级所需时间长短的影响。因此，近年来开发了加速桥梁施工（ABC）实践。这项研究计划的重点是桥梁构件的预制，这是一种ABC，将进一步加快施工速度，同时提高结构安全性和耐久性。 除了加快施工速度外，预制桥面板施工还具有实现高质量生产和严格公差的优势。由于混凝土的低渗透性，预制结构提高了混凝土的长期耐久性，并由于预制厂的受控环境而减少了收缩应变。高性能混凝土（HPC）可用于连接预制板，以缩短固化时间。因此，高性能混凝土在施工缝中的使用越来越多，通常是ABC的组成部分。 这项研究将集中在使用创新的加固方法，以生产耐用的接头预制桥面板。目前在负弯矩区连接预制桥面板的方法需要外部后张拉，以防止接缝开裂。我的研究提出了解决问题的创新方法。 纤维增强聚合物（FRP）预应力混凝土棱柱（PCP）将用于在接缝中引入较小的压缩水平。这将通过延迟和最小化开裂来改善使用荷载性能，并且还将导致小得多的裂缝宽度。玻璃钢是非腐蚀性的，因此接头将持续更长时间。 据报道，FRP筋在预应力过程中会在没有警告的情况下失效。为了减少使用这种材料的预制厂可能发生的工伤事故，我的研究将集中在声发射监测技术的发展，以检测FRP筋在应力过程中的故障。该报警系统将用于长期监测FRP筋的应力，并通过检测和防止FRP筋因过度应力而断裂，并在FRP筋失效前发出警告，提高工人在应力操作期间的安全性。 本研究的实际结果将有助于桥梁工程师，基础设施业主和预制承包商。FRP失效预警系统的开发对提高FRP加固和预应力结构的安全性具有很大的潜力。为加快FRP与预应力混凝土棱柱体组合桥梁的建设提供了依据。加速施工减少了交通中断，降低了施工总成本，同时提高了耐久性和结构完整性。

The poor state of North American infrastructure has received considerable attention over the last several years. Many of the bridges in Manitoba were built in the 1950s to 1970s. These bridges are approaching the end of their service lives and will need to be replaced or rehabilitated in the near future. The American Society of Civil Engineers reports that 200 million trips in the United States are taken daily across bridges that are deteriorating and may need replacing or strengthening. The cost of replacement or rehabilitation is impacted by the length of time required to complete the upgrade. As a result, Accelerated Bridge Construction (ABC) practices have been developed in recent years. This research proposal focuses on prefabrication of bridge elements, a type of ABC that will further accelerate construction while improving structural safety and durability. Besides accelerating construction, precast bridge deck construction has the advantage of achieving high quality production with tight tolerances. Precast construction increases the long-term durability of concrete as a result of its low permeability, and reduces shrinkage strains thanks to the controlled environment of a precast plant. High performance concrete (HPC) can be used to join the precast panels to shorten the curing time. Therefore, the use of HPC in construction joints is increasing and is often an integral part of ABC. This research will focus on the use of innovative reinforcement methods to produce durable joints for precast bridge deck panels. The current methods of joining precast bridge decks in negative moment regions requires external post-tensioning, in order to prevent cracking of the joint. My research proposes innovative methods to solve the problem. Fibre-reinforced polymer (FRP) prestressed concrete prisms (PCP) will be used to introduce small levels of compression into the joints. This will improve the service load performance by delaying and minimizing cracking, and also will result in much smaller crack widths. FRPs are non-corrosive, therefore the joints will last longer. FRP tendons have been reported to fail without warning during prestressing. To mitigate possible workplace injuries in precast plants using this material, my research will focus on developing of acoustic emission monitoring technique to detect failures of FRP bars during stressing. The warning system will be used for long-term monitoring of stresses in FRP bars, and improving worker safety during stressing operations by detecting and preventing FRP bar rupture due to overstressing and providing warning before FRP bar failure. The practical findings of this research will be useful for bridge engineers, infrastructure owners, and precast contractors. The development of FRP failure warning system has a large potential for improving safety of FRP-reinforced and prestressed structures. The research will provide data for accelerating bridge construction using FRP and prestressed concrete prisms. Accelerated construction reduces traffic interruptions, and the overall cost of construction while improving durability and structural integrity.