Improving durability of joints of precast decks

北美糟糕的基础设施状况在过去几年里受到了相当大的关注。马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，需要在不久的将来更换或修复。美国土木工程师协会报告称，在美国，每天有2亿人次穿越那些正在老化、可能需要更换或加固的桥梁。更换或修复的成本受完成升级所需时间长短的影响。因此，近年来，加速桥梁施工(ABC)实践得到了发展。本研究方案的重点是预制桥梁构件，这是一种在提高结构安全性和耐久性的同时进一步加快施工速度的ABC。预制桥面施工除了加快施工外，还具有实现高质量生产和紧公差的优势。由于混凝土的低渗透性，预制施工提高了混凝土的长期耐久性，并由于预制工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，以缩短养护时间。因此，高性能混凝土在施工缝中的使用越来越多，而且往往是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久接头。目前在负弯矩区域连接预制桥面的方法需要外部后张法，以防止接缝开裂。我的研究提出了解决这一问题的创新方法。纤维增强聚合物(FRP)预应力混凝土棱柱(PCP)将被用来在节点中引入小幅压缩。这将通过延迟和最大限度地减少裂缝来改善使用载荷性能，并将导致更小的裂缝宽度。玻璃钢是无腐蚀性的，因此接头的使用寿命更长。据报道，在预应力过程中，FRP筋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中可能出现的工作场所伤害，我的研究将集中在开发声发射监测技术来检测FRP筋在受力过程中的故障。该预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筋失效之前提供警告，提高工人在受力操作期间的安全。这项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。该研究将为加快采用玻璃钢和预应力混凝土棱柱进行桥梁施工提供依据。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.