The objective of this research was to evaluate the current design specifications for use on prestressed, High Performance Concrete (HPC) bridge girders. An AASHTO Type IV and modified BT-56 girders were constructed with a 10,000 psi HPC to which a composite 7000 psi HPC deck was cast on top. The composite girders were tested in flexure, with the Type IV being tested to failure. The results of the flexure tests showed that the current AASHTO Specification for cracking moment and ultimate capacity are conservative. In addition to flexural testing, each composite girder was studied with respect to the deck contraction induced girder deflection. Each deck and girder were instrumented with strain gauges and string potentiometes. The results of the study indicated the induced deflections are significantly greater than deflections from the deck dead load, and should be considered to accurately predict bridge deflection.

As part of the ongoing research on shear at the Phil M. Ferguson Structural Engineering Laboratory (FSEL) located at The University of Texas at Austin, the anchorage controlled shear capacity of prestressed concrete bridge girders was in this research studied in two distinct ways, experimentally and analytically. The results of this research are an important step towards improving understanding of strand anchorage related issues. For the experimental program, two full-scale Tx46 prestressed concrete bridge girders were fabricated at FSEL. The Tx46 girders were topped with a concrete, composite deck. Both ends of the two girders were instrumented and tested. For the analytical program, a new Anchorage Evaluation Database (AEDB) was developed, by filtering and expanding the University of Texas Prestressed Concrete Shear Database (UTPCSDB), and then evaluated. The AEDB contained 72 shear tests, of which 25 were anchorage failures and 47 were shear failures. The results and analysis from the experimental and analytical programs generated the following three main conclusions: (1) A reasonable percentage of debonding in Tx Girders does not have a marked impact on girder shear capacity calculated using the 2010 AASHTO LRFD General Procedure. (2) The AASHTO anchorage equation is conservative but not accurate. In other words, this equation cannot be used to accurately differentiate between a shear failure and an anchorage failure. In regards to conservativeness, anchorage failures in AASHTO-type girders may lead to unconservative results with respect to the 2010 AASHTO LRFD General Procedure. (3) The 2010 AASHTO anchorage resistance model and its corresponding equation do not apply to Tx Girders. Because of the Tx Girders' wider bottom flange, cracks do not propagate across the strands as they do in AASHTO-type girders. This fact yields overly conservative results for Tx Girders with respect to AASHTO Equation 5.8.3.5-1. In summary, this research uncovered the short-sided nature of the AASHTO anchorage design method. Given its short-comings, there is an obvious need for a validated, comprehensive, and rational approach to anchorage design that considers strength and serviceability. To appropriately develop this method, additional full-scale experimental testing is needed to expand the AEDB, as currently there are not enough tests to distinguish major, general trends and variables. Any future additional research would be expected to further validate and expand the significant findings that this research has produced and so take the next step toward safer, more-efficient bridge designs. / text

This thesis presents the results of a research project that tested five friction reducing techniques on the bearing ends of precast prestressed concrete bridge girders. The five techniques were the following: an oil coated surface, embedded steel plate with an oil coated surface, embedded steel angle with an oil coated surface, teflon pad, and a wax lubricant.

Corrosion of reinforcing steel is a major cause of damage to bridges in the United States. A possible solution to the corrosion issue is carbon fiber reinforced polymer (CFRP) material. CFRP material has been implemented as flexural reinforcement in many cases, but not as transverse reinforcing. The CFRP material studied in this thesis was NEFMAC grid, which consists of vertical and horizontal CFRP tows that form an 8 in. by 10 in. grid. The use of NEFMAC grid as transverse reinforcing has not been previously investigated. First, the development length of NEFMAC grid was determined. Next, an 18 ft long 19 in. deep beam, modeled after prestressed Bulb-T beams, was created with NEFMAC grid reinforcement. The beam was loaded with a single point load near the support to induce shear failure. Beams were fitted with instrumentation to capture shear cracking data. Shear capacity calculations following four methods were compared to test results. Lastly, a parametric study with strut-and-tie modeling was performed on Precast Bulb-T (PCBT) girders to determine the amount of CFRP grid needed for reinforcement in the anchorage zone. This thesis concludes that NEFMAC grid is a viable shear design option and presents the initial recommendations for design methods. These methods provide a basis for the design of NEFMAC grid shear reinforcing that could be used as a starting point for future testing of full scale specimens. When designing with NEFMAC grid, the full manufacturer's guaranteed strength should be used as it is the average reduced by three standard deviations. AASHTO modified compression field theory provides the best prediction of shear capacity. For anchorage zone design, working stress limits for CFRP grids need to be increased to allow more of the strength to be implemented in design. / Master of Science

Corrosion of reinforcing steel causes shorter life spans in bridges throughout the United States. The use of carbon fiber reinforced polymer (CFRP) materials as the flexural reinforcement in bridge girders has been extensively studied. However, CFRP transverse reinforcement has not been as rigorously investigated, and many studies have focused on CFCC stirrups. The use of C-Grid as an option for transverse reinforcing has not been previously investigated. This thesis concludes that C-Grid is a viable shear design option and presents the initial recommendations for design methods. These methods provide a basis for the design of C-Grid shear reinforcing that could be used as a starting point for future testing of full scale specimens. This testing program first determined the mechanical properties of C-Grid and its development length. Four 18 ft long 19 in. deep beams, modeled after prestressed Bulb-T beams, were created to test the C-Grid, as well as steel and CFCC stirrups. The beams were loaded with a single point load closer to one end to create a larger shear load for a given flexural moment. Overall beam displacement was measured to determine when flexural reinforcement yielding was reached, and beams were fitted with rosettes and instrumentation to capture initiation of shear cracking. Shear capacity calculations following four methods were compared to test results. The design method should follow the AASHTO modified compression field theory with equations for β and θ. The manufacturer's guaranteed strength should be used for design as long as that strength is the average reduced by three standard deviations. Shear crack widths are controlled to a similar size as steel stirrups when using at least two layers of grid. / Master of Science

This research embodied a three-prong approach for directly determining the residual prestress force of prestressed concrete bridge girders. For bridges that have yet to be constructed, outfitting girders with instrumentation is a highly effective means of determining residual prestress force in prestressed concrete bridge girders. This constitutes the first prong. Still, many bridges are constructed without such instrumentation. For these bridges, a destructive technique can be used to directly determine the residual prestress in a prestressed concrete bridge girder. This implies that the girder(s) being tested have already been taken out of service. This constitutes the second prong. For bridges that are anticipated to remain in service that are lacking embedded instrumentation, the development of a non-destructive technique used to estimate the remaining force in the tendons of prestressed bridge girders is extremely important. This constitutes the third prong used to directly determine residual prestress force. The flexural capacity was also determined from field tests and compared to analytical estimates. By design, the code estimates are meant to be conservative. Alternatively, the residual prestress force for in-service members can be determined directly through the non-destructive technique presented in this research. As such, bridge service capacities can be determined directly and do not need to be conservatively estimated. (231 pages)

The Icy Springs Bridge in Coalville, Utah carries 2nd South Street over the Weber River west of Interstate 80. The bridge is owned by Coalville City and was originally constructed in 1965 as a single-span 51-foot long bridge using prestressed concrete double-tee girders. In the fall of 2013 the original bridge was replaced with a new 80-foot long single span bridge using prestressed concrete decked bulb-tee girders. The original girders were salvaged and transported to the Systems, Materials, and Structural Health Lab (SMASH Lab) where a series of tests were performed to determine the total losses in the prestressing of the strands, the flexural and shear capacities of the girders, and the punching shear capacity of the reinforced concrete deck. The results of these tests were compared to the values calculated using methods outlined in the 2012 American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO LRFD) Bridge Design Specifications, the current bridge design code used by most departments of transportation, and a finite element model using the computer program ANSYS. For the shear and punching shear test results, the AASHTO LRFD Bridge Design Specifications was conservative and was able to predict the type of failure that occurred. However, the tested flexural results were below the calculated flexural capacities using the AASHTO LRFD Bridge Design Specifications. A finite element model was created and calibrated to the test results for the various loading and support conditions. The actual tested material properties were compared to the material properties used in the finite element analyses to determine the difference between the actual girders and the theoretical models. Funding for this project was provided by the Utah Transportation Center.

During the fall of 2012, two separate Interstate 15 highway bridges over the 400 South roadway in Orem, Utah were demolished after 50 years of service. Four post-tensioned girders were salvaged from both the north-bound and south-bound bridge. A series of tests was performed with these girders in the System Material And Structural Health Laboratory (SMASH Lab). The girders were tested with different loading criteria to determine the strength and material properties of the girder. The experimental results were compared with the American Association of State Highway and Transportation Officials Load Resistance Factored Design (AASHTO LRFD) Bridge Design Specifications and a finite-element model using ANSYS. The AASHTO LRFD Specification was fairly conservative on predicting capacity and capable of predicting the type of failure that occurred. The ANSYS model was developed and calibrated to model the girder behavior. The concrete properties in the model were significantly adjusted in order to be comparable to the experimental results. Further exploration in ANSYS needs to be done to precisely model the actual behavior of the girder.

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