Innovative Design for Sustainable Bridges and Other Structures

提出的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)混合无腐蚀桥梁体系的发展：提出了一种创新的中、短跨度桥梁无腐蚀体系。该系统由预制预应力混凝土桁架梁和现浇或预制甲板板组成。大梁的顶部和底部由玻璃纤维增强聚合物（FRP）空心截面填充混凝土制成的混凝土弦。弦由预制的垂直和对角桁架构件连接，这些构件由混凝土填充玻璃钢管制成。竖向构件主要处于受压状态，采用玻璃钢销钉与弦连接。对角线是张拉的，并通过玻璃钢双头杆连接到弦上。底部弦是用碳纤维FRP线预紧的。玻璃钢中空型材采用长丝缠绕生产。它们和管作为原地模板，限制混凝土的压缩，并提供抗拉和抗剪加固。梁顶索采用短GFRP双头螺柱连接甲板板。在多跨桥梁中，梁可以通过外部碳纤维布筋进行后张，以平衡楼板重量并提供连续性。新系统具有减轻自重和增强耐用性的优点。轻的重量减轻了支架上的负荷，允许更长的跨度，从而减少了基础结构的尺寸和多跨桥梁中支撑墩的数量，从而降低了初始成本。耐久性的提高降低了维修成本，延长了结构的使用寿命。将建立计算机模型来研究桁架梁的优化设计。这样的设计应该产生最轻的梁和最好的性能。这些模型将用于确定不同跨度的最佳梁深和桁架弦的最佳尺寸、预应力量、腹板成员的尺寸以及连接对角线和弦所需的头杆的数量和尺寸。全尺寸的样品将在静态、疲劳和持续载荷下制作和测试，以验证最佳设计。长期目标是为新桥系统的设计和建造制定指导方针和程序。*2)预应力梁端部对强度和耐久性的新增强细节：预制梁的端部通常以端部的形式在短长度上减少深度。末端有缺口的梁经常用于桥梁和停车场结构。由于梁端处深度减小，剪应力较大，因此，端部的设计需要特别考虑。有缺口的两端通常用传统的钢制紧密间隔的箍筋和纵向钢筋进行加固，这需要挂钩和弯曲，甚至焊接板来确保足够的锚固。申请人最近的研究表明，用单头和双头钢钉加固有缺口的端部可以消除堵塞，并在不需要外部锚板的情况下为混凝土提供有效的锚固。桥梁和停车场结构暴露在恶劣的环境中，钢的腐蚀是恶化的主要原因。本项目旨在探讨用FRP头筋代替钢钉加固垂端区的效率，以获得更高的强度和更好的耐久性。对不同布置方式的FRP头筋系列垂端梁进行静载和疲劳试验。将进行分析研究，以制定用FRP头钢筋加固的搭接端设计准则。

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.