Browsing by Subject "Horizontal shear"
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Item A Systematic Investigation of Shear Connections Between Full-Depth Precast Panels and Precast Prestressed Bridge Girders(2010-07-14) Brey, Robert W.Full-depth precast panels are used in concrete bridges to provide several benefits such as faster construction, lower cost and reduced constructional hazard. However, one construction drawback is that connectors are required to transmit horizontal shear across the interface between the girder and deck. Shear connector performance is characterized by a series of experiments performed on part of a bridge system that mimics a full-depth precast deck on concrete girder with a pocket-connector-haunch system. Following initial breakaway of the adhesive bond within the haunch region, the specimens slide with frictional resistance provided by the clamping force of the anchor bolt. This leads to bolt yield with an observed sliding friction coefficient of 0.8 (+/- 20%) with lower values occurring at higher displacements. It is concluded that for a viable connector system to be developed a key feature is to have sufficient stirrups in the neighborhood of the anchor bolt to form a non-contact splice and to ensure the high pull-out force can be sustained without leading to premature beam failure. The successful implementation of a full-depth precast deck-panel system requires the use of a viable design methodology that properly accounts for system behavior. The design of a deck-haunch-girder system uses a truss modeling approach to design for the shear forces created by service loading. The truss model approach is considered more suitable for a concrete member due to the premise that the member will be substantially cracked at an ultimate limit state and that traditional beam theory does not account for the decreased ability of shear stresses to transfer across open cracks. Experimental results from Chapter II, such as the friction coefficient mu, are used along with a previously developed crack angle model to layout the geometry of the truss within a deck-panel span. Design solutions are presented utilizing the Rock Creek Bridge in Parker County, Texas as an example structure.Item Structural performance of Texas U-beams at prestress transfer and under shear-critical loads(2011-08) Hovell, Catherine Grace, 1983-; Wood, Sharon L.; Bayrak, Oguzhan, 1969-; Jirsa, James O.; Williamson, Eric B.; Ezekoye, Ofodike A.The Texas U-Beam standard designs were released in the 1990’s and have been used increasingly in bridges across the state since. While prototypes of the 54-in. deep prestressed concrete beam were built during the design phase, no full-scale load tests were performed. This study of the U-Beam had five goals: (i) determine the magnitude and location of stresses induced in reinforcing bars in the end region of the beam at prestress transfer, (ii) measure concrete curing temperatures in square and skewed end blocks, (iii) establish the vertical shear capacity of the standard section, (iv) evaluate interaction between behavior at prestress transfer and performance under shear-critical loads, and (v) identify design and detailing improvements and make recommendations. Eight full-scale Texas U54 prestressed concrete beams were fabricated to achieve these goals. Load testing of the first four of these beams revealed a critical weakness along the bottom flange-to-web interface of the beam. The weakness caused failures that occurred at loads well below the calculated shear capacity. Given the horizontal sliding observed, the failure mode was called horizontal shear. The next two beams were fabricated to test three modifications to the end-region design, two of which were deemed successful. The final two beam sections tested contained the recommended new standard reinforcement and concrete geometry. A method to evaluate the horizontal shear demand on and capacity of the bottom flange-to-web interface of prestressed concrete beams was developed. The calculations were formulated using the theories of beam bending and shear friction. This method was calibrated and verified using the U-Beam test data, a series of small-scale specimens, and results of shear tests in the literature. Stresses induced in reinforcing bars at prestress transfer met expectations set by existing codified equations. No modifications to the current U-Beam standard design are needed to manage these stresses. The induced stresses did not influence vertical shear behavior, and no interaction between the two is believed to exist for U-Beams. This dissertation contains the specifics of the beams tested and the data collected, and provides the details of recommended changes to the Texas U-Beam standard drawings.