Browsing by Subject "Anchorage"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Analytical and Experimental Assessment of an AASHTO I-girder Type I Prestressed with AFRP Tendons(2014-12-12) Cummings, Wesley DavidCorrosion induced deterioration is one of the main reason for repair and rehabilitation programs in conventional steel reinforced concrete bridge decks. Of all bridges in the United States, over 50 percent are constructed of conventional reinforced or prestressed concrete (NACE, 2013), where one in three bridges are considered structurally deficient or functionally obsolete due to corrosion of the steel reinforcement. According to NACE International (2013) the annual cost of corrosion-related maintenance for highway bridges in the U.S. is estimated at $13.6 billion. Over the past couple of decades, fiber reinforced polymer (FRP) bars have been noted by researchers and engineers as a corrosion-resistant alternative for either conventional reinforcing steel or prestressing strands. High strength-to-weight ratio, corrosion resistance, ease in placement of the bars and accelerated implementation due to light weight are the special characteristics that make these bars an appealing alternative. Up to this end, extensive research has been conducted on the structural performance of FRP reinforced concrete beams and slabs; however, less attention has been paid to FRP reinforced concrete bridge girders in composite action with the bridge deck. Accounting for the effect of composite action between the bridge girder and deck can significantly impact the structural performance of the girder including the load and deformation capacities as well as the failure mode. Therefore, separate tests of the FRP concrete beams and slabs may not be sufficient to study the structural behavior and to provide design guidelines for engineers. This thesis presents the experimental and analytical investigations on structural performance of a full-scale AASHTO I-girder Type I, reinforced and prestressed with aramid fiber reinforced polymer (AFRP) bars, where the bridge girder is composite with the deck. The major objectives of this research were to develop a reliable prestressing anchorage system, examine the constructability of the full-scale specimen, study the load and deformation capacities, determine whether or not the design criteria per AASHTO LRFD were met, and improve the performance of the specimen by adjusting the prestressing layout. The specimen was constructed at a prestressing plant in San Marcos, Texas and tested at the High Bay Structural and Material Testing Laboratory on the campus of Texas A&M University. The cross-section of the bridge girder was composed of self-consolidating concrete with a total of 24 prestressed and 8 non-prestressed AFRP bars. The bridge deck consisted of a 203 mm (8 in.) conventional steel reinforced concrete slab. A flexure test was conducted to determine the moment-curvature relationship, flexure load capacity, and failure mode. The test was conducted as a simply supported, four point bending test in order to create a region of constant moment at the center of the beam. Two shear tests were conducted to determine the shear capacity, failure mode, maximum strain in the web, and moment-curvature relationship. The shear tests were conducted as a simply supported, three point bending test with varying load placement. The results of these tests were compared to a similar study which investigated the structural performance of a conventional steel reinforced AASHTO I-girder Type I with topping deck (Trejo et al. 2008). The specimen was also analyzed analytically to determine the effect on performance of varying the prestressing ratio of the separate layers in the bottom flange of the girder. The goal of this analysis was to determine an optimal prestressing layout to improve the performance at the ultimate state, while still satisfying serviceability limits. The prestressing ratio of the layers were varied from 0 to 50 percent in 5 percent increments to study the moment and curvature at both the cracking and ultimate states, along with the available compressive stress due to prestressing at the bottom of the girder. The results of this research confirms that the experimental specimen showed adequate strength and deformation capacities, satisfying the AASHTO LRFD design criteria. Additionally, the experimental specimen showed significantly greater cracking when compared to the conventional steel reinforced specimen, which is an early warning of impending failure. It was also determined that reducing the prestressing ratio of the AFRP bars in the lower layers improves the ductility of the specimen. The moment capacity can also be improved depending on the prestressing layout. However, reducing the prestressing ratio of the bottom layers causes the cracking moment and available compressive stress at the bottom of the girder to diminish. In order to compensate for this loss, the non-prestressed bars in the web can be prestressed. The optimal prestressing layout features the bottom three layers of the specimen prestressed to 35, 40, and 45 percent of their ultimate capacity, and two of the three layers of middle bars prestressed to 50 percent of their ultimate capacity.Item Anchorage-controlled shear capacity of prestressed concrete bridge girders(2012-05) Langefeld, David Philip; Bayrak, Oguzhan, 1969-; Ghannoum, WassimAs 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.Item Evaluation of corrosion resistance of new and upcoming post-tensioning materials after long-term exposure testing(2010-12) McCool, Gregory Edward; Breen, J. E. (John Edward), 1932-; Wood, Sharon L.; Wheat, Harovel G.This thesis focuses on the forensic analysis of ten full-scale post-tensioned beam specimens after four years of aggressive exposure testing. The research was funded by FHWA and TxDOT. Post-tensioned structures have been under scrutiny due to their vulnerability to corrosion damage. Recent corrosion failures have been traced to inadequate materials and construction procedures. The purpose of this research project is to evaluate the corrosion performance of new and upcoming post-tensioning materials and systems and to determine their suitability for preventing durability issues which were found in older structures. The following variables were tested in the full-scale beam specimens: strand type, duct type, duct coupler type, anchorage type, tendon encapsulation. Non-destructive and destructive testing methods for evaluating corrosion damage were examined. Cost analysis of each material was conducted using tendon quantities from a typical post-tensioned bridge for comparison. Galvanized steel ducts performed poorly, showing substantial pitting and area loss. Plastic ducts were intact, but elevated grout chloride levels indicate that moisture was able to enter the ducts at the locations of couplers and grout vents. Strand corrosion was minor and uniform for all the types which were examined, suggesting that chloride traveled the length of the tendons through strand interstices. Stainless steel strands were nearly corrosion-free. Pourback quality was found to protect anchorages more than galvanization of bearing plates. The electrically isolated tendon did not completely prevent strand corrosion, but the system resulted in much lower chloride concentrations along the tendon than the conventional systems.Item Seismic retrofit of RC columns with FRP composites and anchorage system(2015-05) Psaros Andriopoulos, Apostolos; Jirsa, J. O. (James Otis); Hrynyk, TrevorResearch on the use of composite materials in structural applications started more than 30 years ago but still remains active. The challenges that accompany those applications are diverse and seem to increase as the variety of applications grows. There are several fiber-reinforced polymer (FRP) systems that have been introduced through the years for strengthening reinforced concrete (RC) structures. Those systems focus on strengthening of slabs, beams and columns. The present study pertains to seismic retrofit of rectangular RC columns. The typical FRP materials used in structural applications are introduced, as well as, how FRP materials become an integral part of the force-resisting system. In addition, analysis work pertaining to a series of strengthened RC columns was conducted and the results were compared to the experimental data. Moreover, deficiencies of typical material models were highlighted. Design guidelines are discussed and recommendations about current design practices are provided. Finally, research gaps and future research recommendations are identified.Item Seismic retrofit of RC columns with FRP composites and anchorage system(2015-05) Psaros Andriopoulos, Apostolos; Jirsa, J. O. (James Otis); Hrynyk, TrevorResearch on the use of composite materials in structural applications started more than 30 years ago but still remains active. The challenges that accompany those applications are diverse and seem to increase as the variety of applications grows. There are several fiber-reinforced polymer (FRP) systems that have been introduced through the years for strengthening reinforced concrete (RC) structures. Those systems focus on strengthening of slabs, beams and columns. The present study pertains to seismic retrofit of rectangular RC columns. The typical FRP materials used in structural applications are introduced, as well as, how FRP materials become an integral part of the force-resisting system. In addition, analysis work pertaining to a series of strengthened RC columns was conducted and the results were compared to the experimental data. Moreover, deficiencies of typical material models were highlighted. Design guidelines are discussed and recommendations about current design practices are provided. Finally, research gaps and future research recommendations are identified.Item Structural performance of ASR/DEF damaged prestressed concrete trapezoidal box beams with dapped ends(2010-08) Larson, Nancy Anne, 1986-; Bayrak, Oguzhan, 1969-; Jirsa, James O.Across the State of Texas and many other areas of the world, relatively young concrete structures have developed signs of premature concrete deterioration. Large cracks form on the surface of the concrete due to expansive forces from alkali-silica reaction (ASR) and delayed-ettringite formation (DEF). The goal of this project is to assess the effect of ASR/DEF on the trapezoidal box beam bridges in the US 59 corridor and Katy Central Business District (CBD) HOV lanes in Houston, TX. Five dapped-end beams were rejected during the casting process and have been in storage at a local precast yard for nearly fifteen years. These beams have been subject to accelerated deterioration and represent the potential severity of the ongoing ASR/DEF distress within the dapped end regions of the in-service trapezoidal box beams. The results from five load tests, corresponding strut-and-tie models, and forensic investigation are used to provide insights into the relationship between the severity of the deterioration and the capacity margin.