Improving durability of joints of precast decks

在过去几年中，北美基础设施的糟糕状况受到了相当大的关注。曼尼托巴省的许多桥梁建于20世纪50年代至70年代。这些桥梁的使用寿命即将结束，在不久的将来需要更换或修复。美国土木工程师协会报告说，在美国，每天有2亿人次通过正在老化、可能需要更换或加固的桥梁。更换或修复的成本受到完成升级所需时间长度的影响。因此，近年来桥梁加速施工（ABC）实践得到了发展。本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，同时提高结构的安全性和耐久性。预制桥面施工除了能加快施工速度外，还能实现高质量的生产和严格的公差要求。预制结构由于其低渗透性而增加了混凝土的长期耐久性，并且由于预制工厂的受控环境而减少了收缩应变。可采用高性能混凝土（HPC）加入预制面板，以缩短固化时间。因此，HPC在施工缝中的应用越来越多，往往是ABC的一个组成部分。本研究将集中于使用创新的加固方法来生产预制桥面板的耐用接缝。目前在负弯矩区域连接预制桥面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）将用于向接缝中引入小水平的压缩。这将通过延迟和最小化裂缝来改善服务负载性能，也将导致更小的裂缝宽度。frp无腐蚀性，因此接头寿命更长。据报道，FRP筋在预应力过程中毫无征兆地失效。为了减轻使用这种材料的预制工厂可能造成的工作场所伤害，我的研究将集中在开发声发射监测技术，以检测FRP筋在受力过程中的失效。预警系统将用于长期监测FRP筋的受力情况，通过检测和防止FRP筋因受力过大而断裂，并在FRP筋失效前提供预警，提高工人在受力作业中的安全性。本研究的实际结果将对桥梁工程师、基础设施业主和预制承包商有用。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。该研究将为加速使用FRP和预应力混凝土柱的桥梁建设提供数据。加速施工减少了交通中断，减少了施工的总成本，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.