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Development Of End Region Cracks In Pretensioned Concrete I Girders Employing 07 In Diameter Strands
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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 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 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 Transportation Research Board. This book was released on 2010 with total page 76 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 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 De-bonding Strands as an Anchorage Zone Crack Control Method for Pretensioned Concrete Bulb-tee Bridge Girders Using Nonlinear Finite Element Analysis by : Emre Kizilarslan
Download or read book De-bonding Strands as an Anchorage Zone Crack Control Method for Pretensioned Concrete Bulb-tee Bridge Girders Using Nonlinear Finite Element Analysis written by Emre Kizilarslan and published by . This book was released on 2016 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt: Wisconsin bulb tee pretensioned concrete girders have being used for bridges. Their effective spans to depth ratios and higher durability have made prestressed concrete girders desirable. However, cracks were observed at the anchorage zones of these girders because of the demand. To satisfy demand, these girders are heavily prestressed. Cracks initiate during detensioning of pretensioned strands and grow more while transporting them to the resting beds. These cracks create durability concerns as cracks lead aggressive salty water to the steel strands, endangering structures' stability. Especially, cracks in the bottom flange closer to the strands are main concerns in this research. This research primarily focused on the analyses of prestressed girder ends with modelling with nonlinear material properties to understand and recommend control methods for girder end cracking. The end zone behavior of the pretensioned girder was modelled using nonlinear material properties. The concrete nonlinearity, strain softening and stress redistribution upon cracking were also included in the behavior and the verification of tests were done by real tests on these girders. Finally, the reasons for cracks were explained by examining the principal tensile strain directions. The results of previous study showed that debonding strands can effectively control cracking. In this thesis, only debonding for cracking control method, therefore, was tested on 72W with 48 strands and 54W with 42 strands WI girders to see the real effect of debonding on anchorage zone cracks. After getting good results from tests and verifying them with Finite Element Analysis models, exact debonding percentages for other girders to eliminate cracks were presented by giving results of FEA models built for each of them.
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 0 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 Finite Element Modeling of Pretensioned Concrete Girders by : Amir A. Arab
Download or read book Finite Element Modeling of Pretensioned Concrete Girders written by Amir A. Arab and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Structural Behavior of Concrete Girders Prestressed with Stainless Steel Strands by : Anwer Al-Kaimakchi
Download or read book Structural Behavior of Concrete Girders Prestressed with Stainless Steel Strands written by Anwer Al-Kaimakchi and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Prestressed concrete is used in structures because of its versatility, adaptability, and durability. Durability of prestressed concrete bridges in extremely aggressive environments is of increasing concern because of corrosion of the carbon steel strands that are typically used for prestressing. Concrete is a permeable material where chloride ions can penetrate through and reach the internal reinforcement and carbon steel strands are highly susceptible to corrosion. Thus, prestressed concrete bridges located in areas with high exposure to environmental factors (e.g., marine environments) deteriorate due to corrosion of carbon steel strands. For example, Florida has a long coastline, with many concrete bridges over coastal water. Among the 12,518 bridges in Florida, 6,303 are prestressed concrete, and almost half of them are older than 40 years. One solution to overcome the early deterioration of coastal bridges is to use corrosion-resistant strands, such as Duplex High-Strength Stainless Steel (HSSS) strands.HSSS strands have high corrosion resistance and are an alternative to carbon steel strands in concrete bridges in extremely aggressive environments. The growing interest in using stainless steel strands has led to the development of the ASTM A1114. In 2020, ASTM A1114 was released as a standard specification for low-relaxation, seven-wire, Grade 240, stainless steel strands for prestressed concrete. Stainless steel is made from different alloys compared to carbon steel, and thus the mechanical properties of stainless steel strands are fundamentally different than those of carbon steel strands. The most significant difference is in the guaranteed ultimate strain: the value for stainless steel strands is only 1.4%. Several departments of transportation (DOTs) have already used or allowed the use of HSSS strands in prestressed piles. As of 2020, a total of 17 projects have used stainless steel strands, a majority of them in piles. Those projects are in areas with high exposure to environmental factors. The use of HSSS strands in flexural members has been hindered by the lack of full-scale test results, structural design approaches, and/or design guidelines. The main concern in using HSSS strands in flexural members is their low ductility. Concrete members prestressed with HSSS strands, if not properly designed, might fail suddenly without adequate warning. There have been no attempts to address this problem in full-scale research studies. The goals of this research project were to investigate the use of HSSS strands in flexural members and to develop design guidelines that could be used by bridge engineers. A total of thirteen (13) 42-ft-long AASHTO Type II girders were designed, fabricated, and tested in flexure or shear. Ten (10) girders were prestressed with HSSS strands, while the other three (3) were prestressed with carbon steel strands and served as control girders. This research program included experimental activities to determine the mechanical and bond strength characteristics, prestress losses, and transfer length of 0.6-in-diameter HSSS strands. Twenty HSSS strands from two spools were tested in direct tension. A stress-strain equation is proposed for the 0.6-in.-diameter HSSS strands, which satisfied all ASTM A1114 requirements. The minimum and average bond strengths, following ASTM A1081, of six 0.6-in.-diameter HSSS strands were 15.8 kips and 17.9 kips, respectively. The minimum and average experimental ASTM A1081 bond strengths were 23.4% and 19.8% greater than the recommended values by PCI Strand Bond Task Group. The maximum measured transfer length of 0.6-in.-diameter HSSS strands was 21.5 inches, which was less than the value predicted by AASHTO LRFD Bridge Design Specifications' equation for carbon steel strands. Experimental flexural and shear results showed that the post-cracking behavior of girders prestressed with HSSS strands continued to increase up to failure with no discernible plateau. The behavior is attributed to the stress-strain behavior of the HSSS strands. Also, flexural results revealed that, although HSSS strands have low ductility and all composite girders failed due to rupture of strands, the girders exhibited large reserve deflection and strength beyond the cracking load and provided significant and substantial warning through large deflection, as well as well-distributed and extensive flexural cracking, before failure. A non-linear analytical model and an iterative numerical model were developed to predict the flexural behavior of concrete members prestressed with HSSS strands. Although the analytical model gave better predictions, the iterative numerical approach is slightly conservative and is easier to use for design - designers prefer to use an equation type of approach to perform preliminary designs. Numerical equations were developed to calculate the nominal flexural resistance for flexural members prestressed with HSSS strands. The proposed equations are only valid for rectangular sections. In the case of flanged sections, iterative numerical approaches were also introduced. Because HSSS strand is a brittle material, the design must consider the strain capacity of the strand and must be balanced between flexural strength and ductility. Based on the flexural design philosophy for using carbon steel strands in prestressed concrete girders, along with experimentally-observed behaviors and analytical results for concrete members prestressed with HSSS strands, flexural design guidelines were developed for the use of HSSS strands in flexural members. For I-girders, rupture of strands failure mode is recommended by assuring that concrete in the extreme compression fiber reaches considerable inelastic stresses, at least 0.7f_c^'. For slab beams (e.g. Florida Slab Beam), crushing of concrete failure mode is recommended by assuring that the net tensile strain in the HSSS strand is greater than 0.005. The recommended maximum allowable jacking stress and stress immediately prior to transfer are 75% and 70%, respectively. A resistance factor of 0.75 is recommended for both rupture of strand and crushing of concrete failure modes. AASHTO equations conservatively estimated the measured transfer length and prestress losses of 0.6-inches-diameter HSSS strands. The ACI 318-19 and AASHTO LRFD conservatively predicted the shear capacity of concrete girders prestressed with HSSS strands.
Book Synopsis Prestressed Concrete Design and Construction by : Fritz Leonhardt
Download or read book Prestressed Concrete Design and Construction written by Fritz Leonhardt and published by . This book was released on 1980-01-01 with total page 677 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Implementation of 0.7 In. Diameter Strands in Prestressed Concrete Girders by : George Morcous
Download or read book Implementation of 0.7 In. Diameter Strands in Prestressed Concrete Girders written by George Morcous and published by . This book was released on 2013 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Control of Horizontal Cracking in the Ends of Pretensioned Prestressed Concrete Girders by : W.T. Marshall
Download or read book Control of Horizontal Cracking in the Ends of Pretensioned Prestressed Concrete Girders written by W.T. Marshall and published by . This book was released on 1962 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Cable-Stayed Bridges by : Holger Svensson
Download or read book Cable-Stayed Bridges written by Holger Svensson and published by John Wiley & Sons. This book was released on 2013-08-06 with total page 458 pages. Available in PDF, EPUB and Kindle. Book excerpt: The need for large-scale bridges is constantly growing due to the enormous infrastructure development around the world. Since the 1970s many of them have been cable-stayed bridges. In 1975 the largest span length was 404 m, in 1995 it increased to 856 m, and today it is 1104 m. Thus the economically efficient range of cable-stayed bridges is tending to move towards even larger spans, and cable-stayed bridges are increasingly the focus of interest worldwide. This book describes the fundamentals of design analysis, fabrication and construction, in which the author refers to 250 built examples to illustrate all aspects. International or national codes and technical regulations are referred to only as examples, such as bridges that were designed to German DIN, Eurocode, AASHTO, British Standards. The chapters on cables and erection are a major focus of this work as they represent the most important difference from other types of bridges. The examples were chosen from the bridges in which the author was personally involved, or where the consulting engineers, Leonhardt, Andrä and Partners (LAP), participated significantly. Other bridges are included for their special structural characteristics or their record span lengths. The most important design engineers are also presented. Note: The lecture videos which are attached to the print book on DVD are not part of the e-book.
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 Control of Horizontal Cracking in the Ends of Pretensioned Prestressed Concrete Girders by : William Thomas Marshall
Download or read book Control of Horizontal Cracking in the Ends of Pretensioned Prestressed Concrete Girders written by William Thomas Marshall and published by . This book was released on 1962 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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.
Download or read book Final Report written by Patrick J. Kelly and published by . This book was released on 2007 with total page 474 pages. Available in PDF, EPUB and Kindle. Book excerpt:
