Innovative Design for Sustainable Bridges and Other Structures

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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.