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End Region Behavior Of Precast Prestressed Concrete I Girders Employing 07 Inch Diameter Prestressing Strands
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Book Synopsis End-region Behavior of Precast, Prestressed Concrete I-girders Employing 0.7-inch Diameter Prestressing Strands by : Jessica Lauren Salazar
Download or read book End-region Behavior of Precast, Prestressed Concrete I-girders Employing 0.7-inch Diameter Prestressing Strands written by Jessica Lauren Salazar and published by . This book was released on 2016 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pretensioned concrete girders are currently fabricated using 0.5- or 0.6-in. diameter prestressing strands. In recent years, however, it has become of interest to employ larger-diameter 0.7-in. diameter strands to reduce the number of strands and improve the efficiency of pretensioned concrete members. Such a transition requires a considerable initial investment that needs to be justified based on the benefits obtained. Furthermore, the use of 0.7-in. strands would increase the stresses within the end-region of pretensioned elements, which could lead to undesirable cracking and impact the serviceability of the girders. The work presented in this thesis consists of 1) a comprehensive parametric investigation to evaluate the benefits and limitations of using 0.7-in. strands in pretensioned bridge girders, and 2) a full-scale experimental study to investigate the behavior of pretensioned concrete girders with 0.7-in. strands at the time of prestress transfer. The parametric investigation was accomplished by designing thousands of bridge girders with different span lengths, concrete release strengths, and transverse spacings. The results showed that the most noticeable benefit of 0.7-in. strands over 0.6-in. strands was a reduction of up to 35 percent in the number of strands. However, the difference in the total weight of prestressing steel was insignificant. Increasing the release strength of concrete, at least to 7.5 ksi, was found essential to observe benefits in design aspects other than the number of strands. The experimental investigation involved the fabrication of two Tx46 and two Tx70 specimens at the Ferguson Structural Engineering Laboratory. All specimens employed 0.7-in. strands on a 2- by 2-in. grid and the standard detailing currently used for girders with smaller-diameter strands. The observed crack widths in the specimens upon prestress transfer did not exceed those typically observed in Tx-girders with smaller-diameter strands. Therefore, the use of 0.7-in. strands does not seem to trigger a need to modify the end-region detailing in Tx-girders. However, noticeably greater bursting and spalling forces were observed in the end regions of the specimens compared to the demands predicted by AASHTO LRFD provisions. The measured 24-hour transfer length from the specimens also exceeded estimates by AASHTO LRFD and ACI 318-14 provisions.
Book Synopsis Computational Modeling of Prestress Transfer, End-region Cracks and Shear Behavior in Prestressed Concrete I-girders Employing Large-diameter Strands by : Roya Alirezaei Abyaneh
Download or read book Computational Modeling of Prestress Transfer, End-region Cracks and Shear Behavior in Prestressed Concrete I-girders Employing Large-diameter Strands written by Roya Alirezaei Abyaneh and published by . This book was released on 2016 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt: Prestressed concrete girders are commonly fabricated with 0.5-in. (12.7-mm) or 0.6-in. (15.2-mm) diameter prestressing strands. Recent interest in the use of larger (0.7-in. (17.8-mm) diameter) strands has been driven by potential benefits associated with reduction of the required number of strands and fabrication time, or potential increases in the workable range of prestressed concrete girders (i.e., greater capacities and span capabilities). A limited number of experiments on full-scale specimens with 0.7-in. (17.8-mm) diameter strands have shown that the load-carrying capacity and strand transfer length of specimens with 0.7-in. (17.8-mm) diameter strands can be conservatively estimated using existing AASHTO LRFD provisions. However, performance at prestress transfer requires further investigation to ensure that application of the strands with standard 2-in. (50-mm) spacing and conventional concrete release strength does not increase the end-region cracking that is characteristic of prestressed girders. It must be verified that the development of such cracks does not stimulate anchorage-driven or premature shear failures prior to yielding of the shear reinforcement. Previous research lacks in monitoring of reinforcement stresses and evaluation of end-region cracking which has long been a durability concern. A reliable finite element model that captures the behavior of the specimen at prestress transfer with consideration of performance from construction stages, over the course of the service life, and up to the ultimate limit state can provide key insight into the suitability of using of 0.7-in. (17.8-mm) diameter strands. Further, it could serve as an economical tool for the investigation and proposal of efficient end-region reinforcing details to reduce concrete cracking and enhance durability. Finite element analyses of prestressed I-girder end-regions encompassing cracking and long-term creep- and shrinkage-induced damage, especially in girders fabricated with large diameter strands, have been limited. This research program assessed the limitations of 0.7-in. (17.8-mm) diameter strands at prestress transfer up to limit state response and investigated measures for enhancing the serviceability of the girders through finite element analyses using the commercial software, ATENA 3D. The finite element study was complemented with a full-scale experimental program which was used to validate the numerical results. This paper lays out a validated procedure for modeling the construction stages of prestressed girders and load testing. The model was then used as a tool for investigating alternative end-region reinforcement details for improved end-region serviceability. The most promising options are presented for consideration in further experimental studies and future implementation
Book Synopsis End-region Behavior and Shear Strength of Pretensioned Concrete Girders Employing 0.7-in. Diameter Strands by : Hossein Yousefpour
Download or read book End-region Behavior and Shear Strength of Pretensioned Concrete Girders Employing 0.7-in. Diameter Strands written by Hossein Yousefpour and published by . This book was released on 2018 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Performance of Precast, Prestressed Concrete I-girders Employing 0.7-in. Diameter Prestressing Strands Under Shear-critical Loading Conditions by : Alex Tyler Katz
Download or read book Performance of Precast, Prestressed Concrete I-girders Employing 0.7-in. Diameter Prestressing Strands Under Shear-critical Loading Conditions written by Alex Tyler Katz and published by . This book was released on 2016 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt: The majority of precast, pretensioned concrete elements are currently fabricated using 0.5- or 0.6-in. diameter prestressing strands. However, in recent years, potential benefits such as reduced fabrication costs and extended span capabilities have led to an interest in using larger-diameter 0.7-in. strands in the pretensioning industry. Such an increase in the diameter of strands might impact the shear strength of pretensioned girders due to the possibility of atypical failure modes that are not considered in current design provisions. An experimental program was conducted to study the effects of using 0.7-in. prestressing strands on the performance of precast, prestressed concrete I-girders under shear-critical loading conditions. Four full-scale pretensioned Texas bulb-tee girders (Tx-girders) employing 0.7-in. strands were fabricated and tested at Ferguson Structural Engineering Laboratory at the University of Texas at Austin. The mild steel reinforcement in the specimens was detailed according to standard drawings by the Texas Department of Transportation for girders employing 0.6-in. strands. The test program investigated the shear failure in girders with different concrete release strengths, overall member depths, shear span-to-depth ratios, and strand patterns. Analysis of the results revealed clear signs of atypical shear failure mechanisms in all specimens. Considerable strand slip was recorded at both ends of the specimens prior to peak load. In three of the specimens, the shear failure resulted in prominent horizontal cracks at the interface between the web and the bottom flange. However, all specimens demonstrated significant diagonal cracking prior to failure. Yielding of the stirrups was also confirmed in all specimens, indicating a shear-tension failure. The capacities of all specimens were conservatively estimated using the general procedure in AASHTO LRFD Bridge Design Specifications and the detailed method in ACI 318-14. The findings of this study reveal no concerns regarding the performance of existing design provisions in predicting the shear strength of Tx-girders that employ 0.7-in. diameter prestressing strands.
Book Synopsis Nonlinear Analysis of Pretensioned Bridge Girder Ends to Understand and Control Cracking at Prestress Release by :
Download or read book Nonlinear Analysis of Pretensioned Bridge Girder Ends to Understand and Control Cracking at Prestress Release written by and published by . This book was released on 2012 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hundreds of prestressed concrete girders are used each year for building bridges. Prestressed concrete girders are preferred due to their effective span to depth ratios, and higher durability characteristics. The prestress transfer from the prestressing strands to concrete takes place at the girder ends. Characteristic cracks form in this end region during or immediately after detensioning. These cracks are more severe for the heavily prestressed deep bulb tee girders with thin webs, creating durability concerns. The problem can be structurally hazardous if cracks form paths for corrosion agents to reach the steel strands. Cracks in the bottom flange closer to the strands can easily form such paths. This research primarily focused on the analyses of nonlinear prestressed girder end regions to understand and recommend control methods for girder end cracking. The behavior of the pretensioned girder ends was simulated using nonlinear finite element analysis. The accuracy of the models was ensured by including the concrete nonlinearity, strain softening and stress redistribution upon cracking. The finite element modeling techniques were verified by test data. The principal tensile strain patterns correlating with cracking were used to explain the reasons behind each type of crack. Potential solutions to control end cracking were examined via finite element models. The impact of end zone reinforcement pattern, debonding of strands, strand cutting order, draped strand pattern, and lifting of the girder on the cracks were evaluated. The reduction in principal tensile strains associated with cracking was quantified for each crack control method. The analysis results showed that debonding strands can effectively control cracking. Other methods improve the end zone strains however are not sufficient to eliminate cracking alone. Combining the solutions involving debonding, extra reinforcing in the web, and a controlled sequence of strand detensioning should lead to elimination of end cracking.
Book Synopsis Evaluation and Repair Procedures for Precast/prestressed Concrete Girders with Longitudinal Cracking in the Web by : Maher K. Tadros
Download or read book Evaluation and Repair Procedures for Precast/prestressed Concrete Girders with Longitudinal Cracking in the Web written by Maher K. Tadros and published by . This book was released on 2010 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report establishes a user's manual for the acceptance, repair, or rejection of precast/prestressed concrete girders with longitudinal web cracking. The report also proposes revisions to the AASHTO LRFD Bridge Design Specifications and provides recommendations to develop improved crack control reinforcement details for use in new girders. The material in this report will be of immediate interest to bridge engineers.
Book Synopsis Design of Prestressed Concrete Girders Without End Blocks by : Rafik Y. Itani
Download or read book Design of Prestressed Concrete Girders Without End Blocks written by Rafik Y. Itani and published by . This book was released on 1986 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Development of End-region Cracks in Pretensioned Concrete I-girders Employing 0.7-in. Diameter Strands by : Alistair Thornton Longshaw
Download or read book Development of End-region Cracks in Pretensioned Concrete I-girders Employing 0.7-in. Diameter Strands written by Alistair Thornton Longshaw and published by . This book was released on 2018 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although 0.5- and 0.6-in. diameter strands are commonly used in the prestressing industry, there is a growing interest in the implementation of 0.7-in. diameter strands. However, the greater prestressing force induced poses several potential implications, particularly when the strands are placed on a 2- by 2-in. grid. One such issue is end-region cracking, an occurrence that is common in pretensioned girders, regardless of strand size. These cracks tend to grow in width, length, and number over time due to time-dependent effects such as shrinkage or creep. Additionally, the cracks tend to close under an applied load when placed in a service-state condition. End-region crack widths are often used to evaluate the condition of pretensioned girders, so a thorough understanding of the development of these cracks is essential to applying crack width criteria appropriately. A multifaceted experimental program was conducted at the Ferguson Structural Engineering Laboratory at the University of Texas at Austin. A series of seven Texas bulb-tee girders employing 0.7-in. diameter strands was fabricated, monitored, and load tested under shear-critical conditions. The end-region cracks of three specimens were measured immediately after prestress transfer and monitored for at least 28 days, showing that the crack widths grew significantly over time. This growth corresponded closely with the shrinkage strain measured at midspan of each girder, indicating that shrinkage is the primary cause of end-region crack growth. A significant amount of transverse reinforcement is placed in end-regions to restrict cracks immediately after prestress transfer, but this same reinforcement also provides a large amount of restraint against concrete shrinkage, exacerbating crack growth. End-region cracks were also measured during the shear-critical load test for two specimens. Although they closed in a linear manner, they were not completely closed at an expected service load. At ultimate load, the cracks never closed entirely, as the imperfect concrete surfaces bore against each other shortly after initial diagonal shear cracking. Based on both of these findings, future end-region crack widths can be more accurately predicted from any point in the lifespan of a pretensioned girder, allowing for more appropriate applications of permissible crack width limits.
Book Synopsis Prestress Losses in Pretensioned High-strength Concrete Bridge Girders by : Maher K. Tadros
Download or read book Prestress Losses in Pretensioned High-strength Concrete Bridge Girders written by Maher K. Tadros and published by Transportation Research Board. This book was released on 2003 with total page 73 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The HCM includes three printed volumes (Volumes 1-3) that can be purchased from the Transportation Research Board in print and electronic formats. Volume 4 is a free online resource that supports the rest of the manual. It includes: Supplemental chapters 25-38, providing additional details of the methodologies described in the Volume 1-3 chapters, example problems, and other resources; A technical reference library providing access to a significant portion of the research supporting HCM methods; Two applications guides demonstrating how the HCM can be applied to planning-level analysis and a variety of traffic operations applications; Interpretations, updates, and errata for the HCM (as they are developed);A discussion forum allowing HCM users to ask questions and collaborate on HCM-related matters; and Notifications of chapter updates, active discussions, and more via an optional e-mail notification feature."--Publisher.
Book Synopsis Behavior of statically loaded prestressed concrete girders with 0.5 inch diameter debonded strands by : Leslie Gene ZumBrunnen
Download or read book Behavior of statically loaded prestressed concrete girders with 0.5 inch diameter debonded strands written by Leslie Gene ZumBrunnen and published by . This book was released on 1991 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1971 with total page 804 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Prediction of Time-dependent Stresses and Deflections in Prestressed, Concrete Girders by : Bill Davison
Download or read book Prediction of Time-dependent Stresses and Deflections in Prestressed, Concrete Girders written by Bill Davison and published by . This book was released on 2014 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fabricators and contractors need accurate prediction of the camber in precast, prestressed, concrete girders. Large differences in the camber between adjacent girders lead to significant construction difficulties that often have financial and/or legal ramifications. Many factors affect the time-dependent deflections of these girders including; creep and shrinkage of concrete, prestressing relaxation, temperature variations and numerous fabrication conditions. The current models used to predict the deflection history are largely empirical and, although they account approximately for some of the important effects, they do not explicitly consider the interactions among these factors. The goal of this research was to generate a camber prediction algorithm that links the time-dependent constitutive models and explicitly considers the fabrication conditions. This was done by using classical structural analysis techniques and combining them with explicit, time-dependent material models. The analysis was divided into four time phases that encompass a girder's life-span, from fabrication through it service life. These phases are: * Strand jacking: The phase during which the prestressing strands are brought up to their specified jacking stress, * Pre-bonding: The phase during which the prestressing strands are anchored to the abutments in the casting bed, but the strands have not yet bonded to the surrounding concrete, * Post-bonding: The phase during which the concrete has bonded to the strands, but the girder is still resting in the casting bed, and the strands are still restrained by the abutments. * Post-release: The phase during which the prestressing strands have been released from the abutments and the girder is removed from the casting bed. This phase includes the entire service life. In each of these four phases, the boundary conditions are different and the system is analyzed to determine the stresses, deformations and deflected shape. The calculations are necessarily iterative because the constitutive laws for the strand and concrete are time-dependent. The foundation of this analysis method is the proper time-dependent constitutive models. A time-dependent constitutive model was developed for concrete creep using basic Kelvin-Voigt rheological models, modified to include time-dependent parameters. This new model was then calibrated against currently accepted creep models in order to optimize model parameters for a specific girder concrete. For the time-dependent strand relaxation model, the model proposed by Bazant and Yu (2012) was used. Unlike the commonly used Magura model (1964) this model is capable of addressing variable stress loading. It also accounts for the key factors that affect relaxation, including temperature and variations in strain. This model was calibrated against relaxation data. Using these calibrated material constitutive models, the camber prediction algorithm was used to predict the pre-release material stresses as well as the camber history for a girder. The resulting predictions were compared with measured cambers at release and up to ten hours after release. The resulting predictions were reasonable and resulted in expected trends. The predictions also compared favorably with the AASHTO (2012) model for long-term predictions.
Book Synopsis End Zone Design for Alabama Deep Prestressed Girders by : David Burkhalter
Download or read book End Zone Design for Alabama Deep Prestressed Girders written by David Burkhalter and published by . This book was released on 2016 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: Deep prestressed concrete bridge girders are becoming increasingly popular due to their ability to span longer distances and reduce the total cost of bridge projects. However, these girders have frequently been subject to end zone cracking during the transfer of prestress forces despite being designed to current AASHTO specifications. Previously, the Alabama Department of Transportation (ALDOT) has designed deep prestressed girders which can span up to 165 ft. During the fabrication of these girders, crack formations in the end zone were typically noticed. To address this concern, longitudinal reinforcement was added to the end zones. This solution controlled cracking to some extent but could not completely eliminate cracking. An experimental study was conducted to find a practical engineering solution to the problem of end zone cracking, as well as to develop a 78 in. deep prestressed bulb-tee girder design to reach a span length of 180 ft. 3D finite element modeling was used to find three practical alternative end zone modifications to the standard design. The modified designs included a lowered draping angle, partial debonding of the strands, and a combination of the two. Four 54 ft. long specimens, including three with end zone modifications, were fabricated at Hanson Pipe & Precast in Pelham, Alabama, and monitored during the detensioning process. The end zones were instrumented with steel and concrete strain gauges to better understand the complex behavior of girder end zones. External DEMEC instrumentation was also included at the girder ends to measure the transfer length of the strands in each specimen. The specimens were then load tested at the UA Large Scale Structures Laboratory (LSSL) to determine the effects of the modified end zone details on the girder capacity. Based on the study, modified girder end zone details are recommended to ALDOT for implementation.
Book Synopsis Behavior of End Zone of Precast/pretensioned Concrete Bridge Girders by : Nipon Jongpitaksseel
Download or read book Behavior of End Zone of Precast/pretensioned Concrete Bridge Girders written by Nipon Jongpitaksseel and published by . This book was released on 2003 with total page 278 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Investigation of the Effects of End Region Deterioration in Precast, Prestressed Concrete Bridge Girders by : Darion Timothy Mayhorn
Download or read book Investigation of the Effects of End Region Deterioration in Precast, Prestressed Concrete Bridge Girders written by Darion Timothy Mayhorn and published by . This book was released on 2016 with total page 376 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Behavior of Prestressed Concrete Bridge Girders by : Franklin B. Angomas
Download or read book Behavior of Prestressed Concrete Bridge Girders written by Franklin B. Angomas and published by . This book was released on 2009 with total page 109 pages. Available in PDF, EPUB and Kindle. Book excerpt: For this research, prestress losses were monitored in six HPC bridge girders. These measured losses were compared to predicted losses according to four sources. Prestress loss predictive methods considered for this research were: 1- AASHTO LRFD 2004, 2- AASHTO LRFD 2004 Refined, 3- AASHTO LRFD 2007, and 4- AASHTO LRFD Lump Sum method. On the other hand, the camber prediction methods used in the present research were: 1- Time dependent method described in NCHRP Report 496, 2- PCI multiplier method, and 3- Improved PCI Multiplier method. For the purpose of this research, long-term prestress losses were monitored in select girders from Bridge 669 located near Farmington, Utah. Bridge 669 is a three-span prestress concrete girder bridge. The three spans have lengths of 132.2, 108.5, and 82.2 feet long, respectively. Eleven AASHTO Type VI precast prestressed girders were used to support the deck in each span. The deflection of several girders from a three-span, prestressed, precast concrete girder bridge was monitored for 3 years. Fifteen bridge girders were fabricated for the three span-bridge. Ten girders from the exterior spans had span length of 80 feet, and five girders from the middle span had span length of 137 feet. From the results of this research, in both the 82- and 132-foot-long, the AASHTO LRFD 2004 Refined Method does a better job predicting the prestress loss and it can be concluded that all the prediction methods do a better job predicting the loss for the larger girders. The Lump Sum method predicted very accurately the long term prestress loss for the 132-foot-long girders.
Author :FIB – International Federation for Structural Concrete Publisher :FIB - Féd. Int. du Béton ISBN 13 :2940643008 Total Pages :2322 pages Book Rating :4.9/5 (46 download)
Book Synopsis CONCRETE Innovations in Materials, Design and Structures by : FIB – International Federation for Structural Concrete
Download or read book CONCRETE Innovations in Materials, Design and Structures written by FIB – International Federation for Structural Concrete and published by FIB - Féd. Int. du Béton. This book was released on 2019-05-27 with total page 2322 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Proceedings contains the papers of the fib Symposium “CONCRETE Innovations in Materials, Design and Structures”, which was held in May 2019 in Kraków, Poland. This annual symposium was co-organised by the Cracow University of Technology. The topics covered include Analysis and Design, Sustainability, Durability, Structures, Materials, and Prefabrication. The fib, Fédération internationale du béton, is a not-for-profit association formed by 45 national member groups and approximately 1000 corporate and individual members. The fib’s mission is to develop at an international level the study of scientific and practical matters capable of advancing the technical, economic, aesthetic and environmental performance of concrete construction. The fib, was formed in 1998 by the merger of the Euro-International Committee for Concrete (the CEB) and the International Federation for Prestressing (the FIP). These predecessor organizations existed independently since 1953 and 1952, respectively.
