Browsing by Subject "Prestressed concrete"
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Item Alternate vertical steel reinforcement in prestressed concrete beams(Texas Tech University, 2001-08) Cedeno-Rosete, RafaelThe Texas Department of Transportation (TxDOT) widely uses prestressed concrete I-beams for constructing bridges. Currently, TxDOT prestressed concrete I-beam standard permits the substitution of an equal area of Welded Wire Fabric (WWF) for the traditional standard steel bars used as the vertical steel reinforcement. However, no details are provided to insure the standardization of this allowed substitution. The common practice is to simply make a one-for-one substitution using deformed wire for each conventional deformed bar. A research project was conducted at Texas Tech University (TTU) to study the behavior of the WWF as a vertical steel reinforcement, specifically the anchorage capacity of the WWF. In addition, alternate vertical steel reinforcement details were proposed using a simplified steel area and an equivalent strength steel area of WWF. The results of this study are reported in this work. WWF consists in deformed wire bars in the transverse direction and plain wires in the longitudinal direction welded at each intersection using an electrical resistance welding procedure to form flat sheets of WWF. These flat sheets of WWF are bent into the desired shapes and placed into position as units. The vertical shear reinforcement must be properly anchored at its ends in order to be capable of developing its fiiU shear design strength. Two longitudinal plain wires welded to each vertical leg on the WWF detail and spaced vertically two inches apart are provided to develop this anchorage behavior. This detail requires that the two longitudinal wires and their welds be capable of properly anchoring the vertical wires. This two cross-wire anchoring detail in the WWF has been used in several other similar applications. However, there are some differences between these similar applications and Texas prestressed I-beam details. One of the main objectives of this research work has been to study the effectiveness of this anchorage detail. The current TxDOT vertical reinforcement detail for I-beams at the ends consists of bars with diameter 1/2 inches (No. 4) spaced at 4 inches, called "R" bars, and bars with diameter 5/8 inches (No. 5) spaced at 4 inches, named "S" bars. Both of these sets of bars must be Grade 60. This project also studied a simplified WWF alternative of reinforcement consisting of using an equivalent wire diameter providing the same steel area. This simplified approach has the advantage of reducing the production cost of the WWF cages, due to the fact that only one wire diameter is needed to be fed during the production process. In addition to this alternative vertical steel reinforcement, another reinforcement proposal was studied. An equal strength substitution was proposed using Grade 80 wires with a smaller area in such a way that the total strength developed by the vertical WWF reinforcement will be the same of the traditional reinforcement using No. 5 and No. 4 bars of Grade 60. This change in policy would allow the use of the higher yield strength common in WWF material, leading to reduced areas of steel and an associated reduction in cost. Finally, with the onset of High Performance Concrete, the strength of concrete possibly used in the TxDOT I-beams has increased from 5,000 psi to 10,000 psL Because of this shift, concrete strength was also another study parameter consider in this research. In order to study the performance of the WWF steel substitution in the particular use of vertical steel reinforcement in the TxDOT I-beams, 14 full-scale tests were conducted at the Texas Tech University (TTU) structural testing laboratory. The concrete strength ranges used were 5,000-7,000 psi for normal concrete strength and 10,000-12,000 psi for high strength concrete. The beams were tested to observe their performance failure load. The results of this study were used to state recommendations about the current TxDOT policies of using WWF as vertical shear reinforcement.Item Analysis of the shear behavior of prestressed concrete spliced girders(2016-08) Al-Tarafany, Dhiaa Mustafa T.; Jirsa, J. O. (James Otis); Bayrak, Oguzhan; Tassoulas, John; Hrynyk, Trevor; Ghannoum, Wassim; Wheat, HarovelImplementation of the spliced girder technology in bridges has been growing in recent years. Increased girder lengths can now be realized by splicing shorter precast segments to produce a long span. The research conducted in this dissertation is focused on an evaluation of spliced girders using a three dimensional finite element analysis. The project consisted of a series of tests that were conducted in two phases. In Phase I, the effect of post-tensioning ducts on the shear behavior and strength of prestressed concrete girders was evaluated. In Phase II, the focus was on the behavior of cast-in-place splice regions between precast segments. Since a limited number of full scale beams could be tested, a three-dimensional advanced finite element program is an effective alternative to expensive tests. The parameters considered were grout to girder concrete strength ratio, splice to girder concrete strength ratio, concrete shear key detailing, coupler diameter, duct to web width ratio, shear span to depth ratio, and concrete shrinkage losses. The findings are described in detail. Using the experimental and analytical results, it was found that the grout to concrete strength ratio for grouted ducts should not to be less than 0.3. The effect of increasing the duct diameter to web width ratio from 0.43 to 0.57 was minimal. Splice to girder concrete strength ratio should be greater than 0.6. The addition of a shear key had no effect on the shear capacity of the girder. The coupler diameter in the splice region had no effect on the behavior of the spliced girder for coupler diameter to web width ratio up to 0.55. Including concrete shrinkage in the analysis slightly improved the correlation with observed response.Item Behavior of the cast-in-place splice regions of spliced I-girder bridges(2015-08) Williams, Christopher Scott; Bayrak, Oguzhan, 1969-; Jirsa, J. O. (James Otis); Ghannoum, Wassim M; Hrynyk, Trevor D; Wheat, Harovel GSpliced girder technology continues to attract attention due to its versatility over traditional prestressed concrete highway bridge construction. Relatively limited data is available in the literature, however, for large-scale tests of post-tensioned I-girders, and few studies have examined the behavior of the cast-in-place (CIP) splice regions of post-tensioned spliced girder bridges. In addition to limited knowledge on CIP splice region behavior, a wide variety of splice region details (e.g., splice region length, mild reinforcement details, cross-sectional geometry, etc.) continue to be used in the field. In response to these issues, the research program described in this dissertation was developed to (i) study the strength and serviceability behavior of the CIP splice regions of spliced I-girders, (ii) identify design and detailing practices that have been successfully implemented in CIP splice regions, and (iii) develop design recommendations based on the structural performance of spliced I-girder test specimens. To accomplish these tasks, an industry survey was first conducted to identify the best practices that have been implemented for the splice regions of existing bridges. Splice region details were then selected to be included in large-scale post-tensioned spliced I-girder test specimens. Two tests were conducted to study splice region behavior and evaluate the performance of the chosen details. The failure mechanisms of both test girders were characterized by a shear-compression failure of the web concrete with primary crushing occurring in the vicinity of the top post-tensioning duct. Most significantly, the girders acted essentially as monolithic members in shear at failure. Web crushing extended across much of the test span and was not localized within the splice regions. To supplement the spliced girder tests, a shear-friction experimental program was also conducted to gain a better understanding of the interface shear behavior between precast and CIP concrete surfaces at splice regions. The findings of the shear-friction study are summarized within this dissertation. Based on the results of the splice region research program, design recommendations were developed, including recommended CIP splice region details.Item Camber analysis and design of continuous prestressed concrete beams(Texas Tech University, 1969-05) Horn, Howard RichardNot availableItem Controlling cracking in prestressed concrete panels(2010-05) Foreman, James Michael; Klingner, R. E.; Bayrak, OguzhanPrecast, prestressed concrete panels (PCPs) are used in 85% of bridges in Texas. The goal of this thesis is to reduce collinear cracking (cracks propagating parallel to strands) in PCPs. One way to reduce collinear cracking would be to reduce the initial prestress force. In design, TxDOT conservatively assumes total prestress losses of 45 ksi. Based on eight panel specimens, instrumented and fabricated at two different precast plants in Texas, actual prestress losses were measured as at most 25 ksi. This difference (about 20 ksi) is consistent with a reduction in initial prestress force from 16.1 kips per strand to 14.4 kips per strand. Another way to reduce collinear cracking would be to provide additional transverse reinforcement in the end regions of the panels. By comparing crack spacings and crack widths in current and modified panel specimens, it was found that additional reinforcement consisting of one or two #3 bars placed transverse to strands at panel ends would effectively control collinear cracking in PCPs.Item Effect of new prestress loss estimation procedure on precast, pretensioned bridge girders(2014-05) Garber, David Benjamin; Bayrak, Oguzhan, 1969-The prestress loss estimation provision in the AASHTO LRFD Bridge Design Specifications was recalibrated in 2005 to be more accurate for "high-strength [conventional] concrete." Greater accuracy may imply less conservatism, the result of which may be flexural cracking of beams under service loads. Concern with a potential lack of conservatism and the degree of complexity of these recalibrated prestress loss estimation provisions prompted the investigation to be discussed in this dissertation. The primary objectives of this investigation were: (1) to assess the conservatism and accuracy of the current prestress loss provisions, (2) to identify the benefits and weaknesses of using the AASHTO LRFD 2004 and 2005 prestress loss provisions, and (3) to make recommendations to simplify the current provisions. These objectives were accomplished through (1) the fabrication, conditioning, and testing of 30 field-representative girders, (2) the assembly and analysis of a prestress loss database unmatched in size and diversity when compared with previously assembled databases, and (3) a parametric study investigating the design implications and sensitivity of the current loss provisions. Based on the database evaluation coupled with the experimental results, it was revealed that the use of the AASHTO LRFD 2005 prestress loss provisions resulted in underestimation of the prestress loss in nearly half of all cases. A loss estimation procedure was developed based on the AASHTO LRFD 2005 provisions to greatly simplify the procedure and provide a reasonable level of conservatism.Item Investigation of the cracking problem of short type IV girders(2006-05) Tuchscherer, Robin Garrett; Bayrak, Oguzhan, 1969-A research project was conducted at the Phil M. Ferguson Structural Laboratory at the University of Texas at Austin investigating the allowable tensile stress limits of prestressed concrete. The project was funded by TxDOT after field observations were made of flexural cracking in the end regions of AASHTO Type IV beams at the time of prestress transfer. Girders that exhibited cracking were relatively short in length (20 to 60-ft) with highly eccentric strand configurations resulting in tensile stresses in the range of 6 f 'c to 7.5 c f ' .A thorough review was conducted of the documentation and research relating the tensile and compressive strengths of concrete to one another; followed by the material testing of Type III concrete mixes at a very early-age (less than 24 hours). Seven full-scale AASHTO Type IV beam specimens were fabricated and tested at the Ferguson Laboratory at the University of Texas at Austin. Strains were measured in the end regions of each beam; resulting in 14 separate tests. The purpose of measuring the strains was to validate the assumptions of the mechanics of prestress transfer. Beams with an extreme fiber tensile stress greater than 4.5 c f ' exhibited cracking at the time of release. In addition to the full-scale beam tests, an extensive amount of material data was collected through testing and literature review. Properties measured included the compressive strength, split cylinder tensile strength, flexural tensile strength (modulus of rupture), and the modulus of elasticity. Over 60 cylinders were collected on separate occasions from four precast prestressed beam manufacturers (over 240 total cylinders) and tested between 6 to 24-hours after batching. Also, in combination with the fabrication of each Type IV beam, anywhere from 25 to 72 cylinders were prepared and tested. Cylinders were electronically match-cured, cured next to a curing beam, and cured at the ambient laboratory temperature. Split cylinder and modulus of rupture tests did not accurately represent the tensile strength of concrete in a Type IV beam specimen. Specimens fabricated as part of this study cracked with an applied stress less than half of the strength determined per material tests. Based on the full-scale beam and material tests conducted in this study, it was concluded that limiting the extreme fiber tensile to 4 f 'c will prevent cracking at release.Item Shear behavior of spliced post-tensioned girders(2014-08) Moore, Andrew Michael, 1984-; Bayrak, Oguzhan, 1969-; Ghannoum, Wassim M.By its nature a spliced girder must contain a number of post tensioning tendons throughout its length. The focus of the experimental program described in this dissertation is the evaluation of the strength and serviceability of post-tensioned girders loaded in shear, and, more specifically, how a post-tensioning duct located in the web of a girder affects the shear transfer mechanism of a bulb-tee cross-section. Due to the limited number of tests in the literature conducted on full-scale post-tensioned girders, eleven shear tests were performed on seven prestressed concrete bulb-tee girder specimens. Of these tests, ten were conducted on specimens that contained a post-tensioning duct within their web and additional pretensioning reinforcement in their bottom and top flanges. The remaining shear test was conducted on a control specimen that did not have a post-tensioning tendon but contained the same pretensioning reinforcement as the post-tensioned girder specimens. The behavioral characteristics of these eleven test specimens at service level shear forces and at their ultimate shear strengths were evaluated in regards to five primary experimental variables: (i) the presence of a post-tensioning duct, (ii) post-tensioning duct material (plastic or steel), (iii) web-width, (iv) duct diameter, and (v) the transverse reinforcement ratio. The findings of this experimental study are described in detail within this dissertation, but can be summarized by the following two points. (i) No differences were observed in the ultimate or service level shear behavior in girders containing plastic grouted ducts when compared to those containing steel grouted ducts and (ii) The current procedure of reducing the effective web width to account for the presence of a post-tensioning duct is ineffective because it addresses the incorrect shear transfer mechanism. A method that correctly addresses the reduction in shear strength due to the presence of a post-tensioning duct was developed and verified using the tests performed during this experimental program and tests reported in the literature.Item Shear database for prestressed concrete members(2011-05) Nakamura, Eisuke; Bayrak, Oguzhan, 1969-; Jirsa, James O.Development of shear databases attracted a great deal of attention in the shear research community within the last decade. Although a few shear databases have already been developed by several research groups, there is no comprehensive shear database that is focused on prestressed concrete members. This thesis aims to develop a shear database for prestressed concrete members with an intensive literature review. This literature review resulted in a database that contained a total of 1,696 tests reported in North America, Japan, and Europe from 1954 to 2010. The database was used to evaluate shear design provisions available in North America, Japan, and Europe. The variations in measured versus calculated shear strength using twelve shear design equations were analyzed. The analysis results indicated that design expressions based on the Modified Compression Filed Theory (MCFT) produced the best performance to estimate the shear strength of prestressed concrete members with sufficient shear reinforcement. The MCFT-based design expressions, however, provided unconservative strength estimations for members that failed in shear but exhibited signs of horizontal shear damage and/or anchorage zone distress. The ACI 318-08 detailed method was found to be less conservative than the MCFT-based design expressions. Additionally, on the basis of a careful examination of test results included in the database, a new limit for the minimum shear reinforcement was proposed. The database was also used to investigate the shear behavior of prestressed concrete members. This investigation revealed that there was no evidence of size effect in the shear strength of prestressed concrete members with sufficient shear reinforcement. Additionally, it was found that prestress force and shear reinforcement increased the shear strength although there was an upper limit on the effectiveness of shear reinforcement.Item Short-term and time-dependent stresses in precast network arches(2015-08) Yousefpoursadatmahalleh, Hossein; Helwig, Todd Aaron, 1965-; Bayrak, Oguzhan, 1969-; Jirsa, James O; Williamson, Eric B; Mear, Mark EDue to their structural efficiency and architectural elegance, concrete arches have long been used in bridge applications. However, the construction of concrete arches requires significant temporary supporting structures, which prevent their widespread use in modern bridges. A relatively new form of arch bridges is the network arch, in which a dense arrangement of inclined hangers is used. Network arches are subjected to considerably smaller bending moments and deflections than traditional arches and are therefore suitable for modern, accelerated construction methods in which the arches are fabricated off-site and then transported to the bridge location. However, service-level stresses, which play a critical role in the performance of the structure, are relatively unknown for concrete network arches and have not been sufficiently investigated in the previous research on concrete arches. The primary objective of this dissertation is to improve the understanding of short-term and time-dependent stresses in concrete arches, and more specifically, concrete network arches. The research presented herein includes extensive field monitoring of the West 7th Street Bridge in Fort Worth, Texas, which is the first precast network arch bridge and probably the first concrete network arch bridge in the world. The bridge consists of twelve identically designed concrete network arches that were precast and post-tensioned before they were transported to the bridge site and erected. A series of vibrating wire gages were embedded in the arches and were monitored throughout the construction and for a few months after the bridge was opened to traffic. The obtained data were processed, and structural response parameters were evaluated to support the safe construction of the innovative arches, identify their short-term and time-dependent structural behavior, and verify the modeling assumptions. The variability of stresses among the arches was also used to assess the reliability of stress calculations. The results of this study provide valuable insight into the elastic, thermal, and time-dependent behavior of concrete arches in general and concrete network arches in particular. The knowledge gained in this investigation also has broader applications towards understanding the behavior of indeterminate prestressed concrete structures that are subjected to variable boundary conditions and thermal and time-dependent effects.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.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.