Innovative Design for Sustainable Bridges and Other Structures

建议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)复合式无腐蚀桥梁体系的研制：提出了一种适用于中、短跨径桥梁的新型无腐蚀体系。该体系由预制预应力混凝土桁架梁和现浇或预制桥面板组成。梁的顶部和底部的混凝土弦由玻璃纤维增强聚合物(FRP)填充混凝土的空心段制成。弦杆由预制的竖向和斜向桁架构件连接，桁架构件由GFRP管混凝土制成。竖向构件主要受压，并使用GFRP销连接到弦杆上。对角线处于张拉状态，并通过GFRP双头杆连接到弦杆上。最下面的弦杆是用碳素玻璃钢绞线伪装的。玻璃钢空心型材采用纤维缠绕成型。它们和管子充当留在原地的模板，限制混凝土的受压，并提供拉伸和剪切钢筋。梁上弦杆采用短GFRP双头螺栓连接桥面板。在多跨桥梁中，梁可以用外部CFRP筋进行后张法张拉，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。轻质减轻了支座上的荷载，并允许更大的跨度，从而减少了下部结构的尺寸和多跨桥梁中的支承桥墩数量，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。这样的设计应该产生最轻的梁和最好的性能。该模型将用于确定不同跨度的最佳主梁高度和桁架弦杆的最佳尺寸、预应力量、腹板构件的尺寸以及连接对角线和弦杆所需的带头杆件的数量和尺寸。为了验证优化设计，将制作全尺寸试件，并在静态、疲劳和持续载荷下进行测试。长期目标是为新桥梁系统的设计和建造制定指导方针和程序。 2)在预制梁的预制端进行新的加固细节，以提高强度和耐久性：预制梁的端部通常在较短的长度内以预制端的形式降低深度。梁端凹陷是桥梁和停车结构中常用的结构形式。由于梁端的深度减小，剪应力很高，因此，凹端的设计需要特别考虑。有凸起的端部通常用传统的钢质密集箍筋和纵向钢筋加固，这需要弯钩和弯头，甚至需要焊接板来确保足够的锚固力。申请人最近的研究表明，用单头和双头钢钉加固凸缘末端可以消除拥堵，并在不需要外部锚板的情况下提供有效的混凝土锚固。桥梁和停车结构暴露在恶劣的环境中，钢材的腐蚀是恶化的主要来源。本项目旨在研究用FRP头筋代替钢钉加固凸缘端部区域的效率，以获得更高的强度和更好的耐久性。对采用不同布置形式的FRP头筋加固的节点梁进行了静载和疲劳试验。将进行分析研究，以制定用FRP头筋加固的凹形端部设计指南。

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.