Innovative Design for Sustainable Bridges and Other Structures

该研究旨在为混凝土桥梁和建筑结构的可持续性能提供创新设计。重点将放在两个项目上： 1)混合型无腐蚀桥梁系统的开发：提出了一种适用于中短跨度桥梁的创新无腐蚀系统。该系统由预制预应力混凝土桁架梁和现浇或预制桥面板组成。梁的顶部和底部混凝土弦杆由玻璃纤维增强聚合物（FRP）空心截面制成，填充混凝土。弦杆通过由GFRP管混凝土制成的预制垂直和斜向桁架构件连接。竖向构件以受压为主，采用GFRP销钉与弦杆连接。斜杆受拉，并通过GFRP双头钢筋与弦杆连接。下弦杆采用碳纤维增强塑料束预紧。玻璃钢空心型材采用纤维缠绕成型。它们和管作为原地模板，限制混凝土的压力，并提供拉伸和剪切钢筋。短GFRP双头螺柱用于主梁上弦杆，以连接到桥面板。主梁可以通过外部CFRP筋进行后张，以平衡板的重量，并在多跨桥梁中提供连续性。新系统具有减轻自重和增强耐久性的优点。重量轻减少了支架上的负载，并允许更长的跨度，从而减少了多跨桥梁中的下部结构尺寸和支撑墩的数量，从而降低了初始成本。耐久性的提高降低了维护成本，延长了结构的使用寿命。将开发计算机模型来研究桁架梁的优化设计。这样的设计应导致最轻的梁具有最佳的性能。这些模型将用于确定不同跨度的最佳主梁深度、桁架弦杆的最佳尺寸、预应力量、腹杆尺寸以及连接对角线和弦杆所需的带头钢筋的数量和尺寸。为了验证最佳设计，将在静态、疲劳和持续载荷下制造和测试全尺寸样本。长期目标是为新桥梁系统的设计和施工制定指导方针和程序。 2)预制梁端部的新型加固细节，以提高强度和耐久性：预制梁的端部通常在短长度上以端部形式减少深度。端部有缺口的梁经常用于桥梁和停车场结构中。由于梁端的深度减小，剪应力很高，因此，设计有缺口的梁端需要特别考虑。典型地，用传统的紧密间隔的钢箍筋和纵向钢筋来加固搭扣端部，这需要钩和弯曲，甚至焊接板来确保足够的锚固。本申请人最近的研究表明，用单头和双头钢螺柱加强搭接端部消除了堵塞，并提供了对混凝土的有效锚固，而不需要外部锚板。桥梁和停车结构暴露在恶劣的环境中，其中钢铁腐蚀是恶化的主要来源。本项目旨在研究用FRP带头钢筋代替钢栓钉加固缺口区域的效率，以获得更高的强度和更好的耐久性。本文将对一系列不同布置形式的FRP带头钢筋混凝土梁进行静载和疲劳试验。将进行分析研究，以制定用FRP带头钢筋加固的搭接端设计指南。

The proposed research aims at providing innovative design for sustainable performance of concrete bridge and building structures. Focus will be placed on two projects: 1) Development of a Hybrid Corrosion-Free Bridge System: An innovative corrosion-free system for short and medium span bridges is proposed. The system consists of precast prestressed concrete truss girders and a cast-in-place or precast deck slab. The girders have top and bottom concrete chords made of glass fibre reinforced polymer (FRP) hollow sections filled with concrete. The chords are connected by precast vertical and diagonal truss members made of concrete-filled GFRP tubes. The vertical members are mainly in compression and connected to the chords using GFRP dowels. The diagonals are in tension and connected to the chords by GFRP double-headed bars. The bottom chord is pretentioned with carbon FRP strands. The FRP hollow sections are produced by filament winding. They and the tubes serve as stay-in-place formwork, confine the concrete in compression, and provide tensile and shear reinforcement. Short GFRP double-headed studs are used in the girders top chords to connect to the deck slab. The girders can be post-tensioned by external CFRP tendons to balance the slab weight and to provide continuity in multi-span bridges. The new system has the advantages of reduced self-weight and enhanced durability. The light weight reduces the load on the supports and allows for longer spans, resulting in reduction in the size of substructure and in the number of supporting piers in multi-span bridges and, hence, reduction in the initial cost. The improved durability reduces the maintenance cost and extends the structure's life span. Computer models will be developed to investigate an optimum design of the truss girder. Such design should result in the lightest girder with best performance. The models will be used to determine the optimum girder depth for different spans and the optimum dimensions of the truss chords, amount of prestressing, size of the web members, and number and size of headed bars needed to connect the diagonals to the chords. Full-scale specimens will be fabricated and tested under static, fatigue, and sustained load in order to verify the optimum design. The long-term objective is to develop guidelines and procedures for design and construction of the new bridge system. 2) Novel Reinforcing Details in Dapped Ends of Precast Girders for Strength and Durability: The ends of precast girders often have reduced depth over short lengths in the form of dapped ends. Girders with dapped ends are frequently used in bridges and parking structures. Because of the reduced depth at the girder ends, the shear stresses are high, and, therefore, design of dapped ends requires special consideration. Dapped ends are typically reinforced with conventional steel closely-spaced stirrups and longitudinal reinforcing bars, which require hooks and bends and even welded plates to ensure sufficient anchorage. Recent research by the applicant has shown that reinforcing dapped ends with single and double headed steel studs eliminates congestion and provides efficient anchorage to concrete without the need for external anchor plates. Bridges and parking structures are exposed to harsh environment in which corrosion of steel is a major source of deterioration. This project aims at investigating the efficiency of reinforcing dapped-end zones with FRP headed bars in lieu of steel studs to achieve higher strength and better durability. Static load and fatigue tests will be conducted on series of dapped-end beams reinforced with FRP headed bars of different layouts. Analytical studies will be carried out to develop guidelines for design of dapped ends reinforced with FRP headed bars.