Horizontal Shear/Composite Action Testing Program Proposal Outline 2/16/04 Objectives The objective of this research centers around several important questions introduced during the design of a recent arch bridge. The main issue addressed is the composite action between the girders and the deck slab. The first main questions involves cross beams that connect between two main longitudinal girders: “How much does the horizontal shear reinforcement in the cross beams contribute to the composite action between the main girders and the deck slab?” The answer to this question has very important implications for the design of bridges with a limited number of girder lines and cross beams. An arch bridge system is a good example of this type of bridge. The second main question involves the spacing of the horizontal shear reinforcement: “What is the maximum spacing of horizontal shear reinforcement?” Currently, both the AASHTO and the ACI codes specify a maximum shear connector spacing of 2 feet. This is generally thought to be very small and not necessary. Maximum spacing requirements between horizontal shear connectors needs to be investigated and, if warranted, updated. A larger spacing will result in the development of new bridge construction systems utilizing full depth precast deck panels placed between the shear connectors. Consequently, construction time and risk will be reduced, and the life of the bridge will be increased. Problem Statements 1. On a typical multi-girder stringer bridge, shear connectors running the length of each girder resist horizontal interface shear and create composite action between the girders and the deck slab. Naturally, in the case of having fewer girders such as arch bridges or cable stayed bridges, there are significantly fewer connectors to resist the shear force. Therefore, creating sufficient composite action between the girders and the deck becomes a much more critical design issue. This is a typical of an arch bridge or any other bridge relying heavily on two exterior girders (see Figure 1). Figure 1 – Typical multi-girder stringer bridge with and without the interior girders removed. How much of the deck is acting compositely with each girder (see Figure 2)? Often, cross beams connect these two exterior girders. Will adding shear connectors to these cross beams help resist the horizontal interface shear? If so, how much? Figure 2 – How much of the deck is acting compositely with the girders? 2. Currently, the maximum shear connector spacing per AASHTO LRFD is 2 ft. This maximum allowable spacing is a significant limiting factor for the use of precast deck panels. What is the maximum connector spacing that would still achieve full composite action. An increased connector spacing (8 ft if possible) would make the use of precast deck panels much more feasible (see Figure 3). Figure 3 – An increased connector spacing would make the use of precast deck panels much more feasible. Testing Program In order to answer the questions in problem statement one, the following testing program is proposed: Two large steel TSS sections will be connected with smaller TSS sections acting as cross beams. The small TSS sections will be welded to the sides of the larger longitudinal girders. The specimen will be simply supported at each end of the longitudinal girders. This is to simulate the bridge situation described in problem statement one. Studs will then be placed only on the cross beams. A deck will be cast over the entire specimen (see Figure 4). A point load will be applied at the center of the deck. Strategically placed strain gauges will provide information on how much of the deck is acting compositely with the longitudinal beams. Figure 4 – Test setup to answer questions in problem statement 1. In order to answer the questions in problem statement 2, the following testing program is proposed: A deck will be cast over a simply supported TSS section. Four different specimens will be created with: 1) studs at 2’, 2) studs at 4’, 3) studs at 6’, and 4) studs at 8’ (see Figure 5). Strategically located strain gauges will tell us for each spacing how much of the deck is acting compositely with the TSS section. Figure 5 – Test setup to answer questions in problem statement 2.
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