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Oguzhan Bayrak - One of the best experts on this subject based on the ideXlab platform.
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Effects of Increasing Allowable Compressive Stress at PreStress Transfer
ACI Structural Journal, 2010Co-Authors: David B. Birrcher, Oguzhan Bayrak, Michael E. KregerAbstract:This paper evaluates the benefits and weaknesses of increasing the Allowable Compressive Stress at preStress transfer in preStressed concrete members. A historical background of the Allowable release Stress in compression is provided. A simple design example is used to quantify potential production and design benefits of increasing the Allowable Stress and the applicability of these benefits is discussed. Test results of 36 pretensioned beams that were subjected to a range of maximum Compressive Stresses at release are reported and analyzed. The results suggest that the Compressive Stress limit at preStress transfer must govern the design of the pretensioned member to achieve significant production or design benefits from increasing the Allowable Stress, but that production and design benefits cannot be maximized simultaneously. The findings indicate that although increasing the Allowable release Stress in compression at midspan of a member to 0.65fci' or 0.70fci' is possible, members subjected to midspan release Stresses in excess of 0.70fci' displayed premature flexural cracking. Before design codes are changed, however, additional testing on full-scale specimens is recommended.
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Accession No. 4. Title and Subtitle Aggregate Distribution Investigation in Box Beams Fabricated with Self Consolidating Concrete
2009Co-Authors: Ro Avendaño, Oguzhan BayrakAbstract:In 2004, the Texas Department of Transportation initiated Project 0-5197 to investigate the feasibility of increasing the Allowable Compressive Stress limit at preStress transfer. Initially, the live load performance of 36 specimens was evaluated by Birrcher and Bayrak (TxDOT Report 5197-1, 2007). Report 5197-4 presents the subsequent research conducted based on recommendations of Birrcher and Bayrak (2007). In this portion of TxDOT Project 0-5197, 45 Type-C beams and 10 4B28 box beams were tested to experimentally determine their cracking load. The Type-C beams were produced in four different fabrication plants using conventionally consolidated concrete. The 10 4B28 box beams were produced in two fabrication plants using concrete mixture designs of both self consolidating concrete as well as conventional concrete (Schnittker and Bayrak, CTR, 2008). After testing the 10 box beams procured in TxDOT Project 0-5197, Schnittker and Bayrak (2008) reported increased amounts of top flange cracking at release, substantially lower modulus of elasticity (along with increased deflections under live loading), slightly higher cambers near 28-days, and lower than expected flexural cracking loads under live loads. The present investigation is carried out in an effort to explain the poo
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Allowable Compressive Stress at PreStress Transfer
2008Co-Authors: Brian Schnittker, Oguzhan BayrakAbstract:In 2004, the Texas Department of Transportation (TxDOT) initiated Project 5197 to investigate the feasibility of increasing the Allowable Compressive Stress limit at preStress transfer. Initially, the live load performance of 36 specimens was evaluated by Birrcher and Bayrak (TxDOT Report 5197-1, 2007). Report 5197-4 presents the subsequent research conducted based on recommendations of Birrcher and Bayrak (2007). In this portion of TxDOT Project 5197, 45 Type-C beams and 10 4B28 box beams were tested to experimentally determine their cracking load. The Type-C beams were produced in four different fabrication plants using conventionally consolidated concrete. The 10 4B28 box beams were produced in two fabrication plants using concrete mixture designs of both self consolidating concrete as well as conventional concrete. For all specimens, measured cracking loads were compared to predicted cracking loads. The data from the 45 Type-C beams and 10 box beams were added to the 36 beams investigated by Birrcher and Bayrak (2007) to compile a comprehensive set of data from 91 specimens. An appropriate maximum Compressive Stress limit was determined from the ability to accurately predict the load at which cracking occurred. As the maximum Compressive Stress at preStress transfer was increased, a decline in cracking load prediction accuracy was observed. For the specimens subjected to high Compressive Stresses at release (greater than 0.65f’ci), the concrete in the pre-compressed tensile zone was subjected to the non-linear inelastic range causing microcracking to occur. This non-linear behavior (due to microcracking) was unaccounted for in preStress losses or standard design equations (P/A±Mc/I). Based on the analysis of the results, an increase of the Allowable Compressive Stress limit at preStress transfer to 0.65f’ci is justified. Additionally, the use of self consolidating concrete with a maximum Compressive Stress of 0.65f’ci is not recommended.
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effects of increasing the Allowable Compressive Stress at release on the shear strength of preStressed concrete girders
2008Co-Authors: Christopher Heckmann, Oguzhan BayrakAbstract:In recent years, several research projects have been conducted to study the feasibility of increasing the Allowable Compressive Stress in concrete at preStress transfer, currently defined as 0.60f'ci in the AASHTO LRFD Bridge Design Specifications. Increasing the limit would result in many economical and design benefits for the precast concrete industry, such as increased span lengths and faster turnover of beams in Stressing beds. This research study focuses on the effects of increasing the Allowable Compressive Stress at release on the shear strength of preStressed concrete members, a topic which has not yet been explored by past research projects. The current experimental work is funded under Texas Department of Transportation (TxDOT) Project 5197, which initiated in 2004 at the University of Texas at Austin. In the shear performance evaluation, 18 shear tests were performed. In the shear tests, the beams were loaded to fail in web-shear, with a shear span to depth ratio of 2.22. The diagonal cracking shears and shear capacities were experimentally measured for all specimens tested. All test specimens were TxDOT Type-C highway bridge girders (40-inch deep pretensioned I-beams) and were fabricated by three different precast plants in Texas. The Compressive Stress at release for the test specimens ranged from 0.56f'ci to 0.76f'ci. The measured cracking shears and shear capacities were compared to the estimated cracking shears and shear capacities, as calculated using ACI 318-08 and AASHTO LRFD (2007), and the effects of higher release Stresses on shear strength and serviceability were evaluated by examining the conservativeness and accuracy of the predictions. Based on the experimental results summarized in this report, an increase in the Allowable maximum Compressive Stress in concrete in the end regions of preStressed concrete beams at preStress transfer to 0.65f'ci or 0.70f'ci can be justified.
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2. Government 3. Recipient’s Catalog No. Accession No. 4. Title and Subtitle Effects of Increasing the Allowable Compressive Stress at Release on the Shear Strength of PreStressed Concrete Girders
2008Co-Authors: Christopher Heckmann, Oguzhan BayrakAbstract:In recent years, several research projects have been conducted to study the feasibility of increasing the Allowable Compressive Stress in concrete at preStress transfer, currently defined as 0.60f'ci in the AASHTO LRFD Bridge Design Specifications. Increasing the limit would result in many economical and design benefits for the precast concrete industry, such as increased span lengths and faster turnover of beams in Stressing beds. This research study focuses on the effects of increasing the Allowable Compressive Stress at release on the shear strength of preStressed concrete members, a topic which has not yet been explored by past research projects. The current experimental work is funded under TxDOT Project 5197, which initiated in 2004 at the University of Texas at Austin. In the shear performance evaluation, 18 shear tests were performed. In the shear tests, the beams were loaded to fail in web-shear, with a shear span to depth ratio of 2.22. The diagonal cracking shears and shear capacities were experimentally measured for all specimens tested. All test specimens were TxDOT Type-C highway bridge girders (40-inch deep pretensioned I-beams) and were fabricated by three different precast plants in Texas. The Compressive Stress at release for the test specimens ranged from 0.56f'ci to 0.76f'ci. The measured cracking shears and shea
David B. Birrcher - One of the best experts on this subject based on the ideXlab platform.
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Effects of Increasing Allowable Compressive Stress at PreStress Transfer
ACI Structural Journal, 2010Co-Authors: David B. Birrcher, Oguzhan Bayrak, Michael E. KregerAbstract:This paper evaluates the benefits and weaknesses of increasing the Allowable Compressive Stress at preStress transfer in preStressed concrete members. A historical background of the Allowable release Stress in compression is provided. A simple design example is used to quantify potential production and design benefits of increasing the Allowable Stress and the applicability of these benefits is discussed. Test results of 36 pretensioned beams that were subjected to a range of maximum Compressive Stresses at release are reported and analyzed. The results suggest that the Compressive Stress limit at preStress transfer must govern the design of the pretensioned member to achieve significant production or design benefits from increasing the Allowable Stress, but that production and design benefits cannot be maximized simultaneously. The findings indicate that although increasing the Allowable release Stress in compression at midspan of a member to 0.65fci' or 0.70fci' is possible, members subjected to midspan release Stresses in excess of 0.70fci' displayed premature flexural cracking. Before design codes are changed, however, additional testing on full-scale specimens is recommended.
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Effects of Increasing the Allowable Compressive Stress at Release of PreStressed Concrete Girders
2007Co-Authors: David B. Birrcher, Oguzhan BayrakAbstract:In this report, the feasibility of increasing the Allowable Compressive Stress limit at preStress transfer of 0.60f'ci is evaluated. For this purpose, the live-load performance and initial camber of pretensioned beams was investigated. Static-load tests were performed on 24 scaled and 12 full-scale specimens that were subjected to a maximum Compressive Stress at release ranging from 0.46f'ci to 0.91f'ci. From the comparison of the measured and predicted cracking loads of these test specimens, an increase of the Allowable Compressive Stress to 0.65f'ci was justified. For the specimens subjected to release Stresses exceeding 0.65f'ci, premature cracking in flexure was detected due to nonlinear deformation at release and associated microcracking. In addition, an initial camber database of information from 223 pretensioned girders was compiled. The data suggested that increasing 0.60f'ci did not affect the ability to accurately estimate initial camber. However, for a given section, higher cambers were detected as the Compressive Stress at release increased. Lastly, a simple technique for improving the initial camber estimates of conventional girders was presented as a feasibility study for future work.
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Accession No. 4. Title and Subtitle Effects of Increasing the Allowable Compressive Stress at Release of PresStressed Concrete Girders
2007Co-Authors: David B. Birrcher, Oguzhan BayrakAbstract:In this report, the feasibility of increasing the Allowable Compressive Stress limit at preStress transfer of 0.60f'ci is evaluated. For this purpose, the live-load performance and initial camber of pretensioned beams was investigated. Static-load tests were performed on 24 scaled and 12 full-scale specimens that were subjected to a maximum Compressive Stress at release ranging from 0.46f'ci to 0.91f'ci. From the comparison of the measured and predicted cracking loads of these test specimens, an increase of the Allowable Compressive Stress to 0.65f'ci was justified. For the specimens subjected to release Stresses exceeding 0.65f'ci, premature cracking in flexure was detected due to nonlinear deformation at release and associated microcracking. In addition, an initial camber database of information from 223 pretensioned girders was compiled. The data suggested that increasing 0.60f'ci did not affect the ability to accurately estimate initial camber. However, for a given section, higher cambers were detected as the Compressive Stress at release increased. Lastly, a simple technique for improving the initial camber estimates of conventional girders was presented as a feasibility study for future work. 17. Key Words Allowable release Stress, Compressive Stress limit, preStress transfer, initial cambe
Christopher Heckmann - One of the best experts on this subject based on the ideXlab platform.
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effects of increasing the Allowable Compressive Stress at release on the shear strength of preStressed concrete girders
2008Co-Authors: Christopher Heckmann, Oguzhan BayrakAbstract:In recent years, several research projects have been conducted to study the feasibility of increasing the Allowable Compressive Stress in concrete at preStress transfer, currently defined as 0.60f'ci in the AASHTO LRFD Bridge Design Specifications. Increasing the limit would result in many economical and design benefits for the precast concrete industry, such as increased span lengths and faster turnover of beams in Stressing beds. This research study focuses on the effects of increasing the Allowable Compressive Stress at release on the shear strength of preStressed concrete members, a topic which has not yet been explored by past research projects. The current experimental work is funded under Texas Department of Transportation (TxDOT) Project 5197, which initiated in 2004 at the University of Texas at Austin. In the shear performance evaluation, 18 shear tests were performed. In the shear tests, the beams were loaded to fail in web-shear, with a shear span to depth ratio of 2.22. The diagonal cracking shears and shear capacities were experimentally measured for all specimens tested. All test specimens were TxDOT Type-C highway bridge girders (40-inch deep pretensioned I-beams) and were fabricated by three different precast plants in Texas. The Compressive Stress at release for the test specimens ranged from 0.56f'ci to 0.76f'ci. The measured cracking shears and shear capacities were compared to the estimated cracking shears and shear capacities, as calculated using ACI 318-08 and AASHTO LRFD (2007), and the effects of higher release Stresses on shear strength and serviceability were evaluated by examining the conservativeness and accuracy of the predictions. Based on the experimental results summarized in this report, an increase in the Allowable maximum Compressive Stress in concrete in the end regions of preStressed concrete beams at preStress transfer to 0.65f'ci or 0.70f'ci can be justified.
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2. Government 3. Recipient’s Catalog No. Accession No. 4. Title and Subtitle Effects of Increasing the Allowable Compressive Stress at Release on the Shear Strength of PreStressed Concrete Girders
2008Co-Authors: Christopher Heckmann, Oguzhan BayrakAbstract:In recent years, several research projects have been conducted to study the feasibility of increasing the Allowable Compressive Stress in concrete at preStress transfer, currently defined as 0.60f'ci in the AASHTO LRFD Bridge Design Specifications. Increasing the limit would result in many economical and design benefits for the precast concrete industry, such as increased span lengths and faster turnover of beams in Stressing beds. This research study focuses on the effects of increasing the Allowable Compressive Stress at release on the shear strength of preStressed concrete members, a topic which has not yet been explored by past research projects. The current experimental work is funded under TxDOT Project 5197, which initiated in 2004 at the University of Texas at Austin. In the shear performance evaluation, 18 shear tests were performed. In the shear tests, the beams were loaded to fail in web-shear, with a shear span to depth ratio of 2.22. The diagonal cracking shears and shear capacities were experimentally measured for all specimens tested. All test specimens were TxDOT Type-C highway bridge girders (40-inch deep pretensioned I-beams) and were fabricated by three different precast plants in Texas. The Compressive Stress at release for the test specimens ranged from 0.56f'ci to 0.76f'ci. The measured cracking shears and shea
Kang Su Kim - One of the best experts on this subject based on the ideXlab platform.
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an experimental study on Allowable Compressive Stress at preStress transfer in pre tensioned concrete members
Journal of the Korea institute for structural maintenance and inspection, 2012Co-Authors: Jeong Yeon Lee, Deuck Hang Lee, Kang Su Kim, Min Kook Park, Sang Chun YoonAbstract:In the previous research, Allowable Compressive Stress was analyzed based on strength theory, in which primary effect factors on the Allowable Compressive Stress, such as eccentricity ratio, section type, section size, preStress and self-weight moment, were considered. As its results, Allowable Compressive Stress equations were proposed. As a series of the previous research, this paper presents an experimental study on the preStress at transfer of pre-tensioned members with different eccentricity ratios. The results shows that ACI318-08 and EC2-02 are unconservative for the members under low eccentricity ratios, and they are conservative for the members under high eccentricity ratios. Compared to the code provisions, the results indicates that the proposed equation reasonably well evaluates the Allowable Compressive Stresses for those with different eccentricity ratios.
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Allowable Compressive Stress of Pre-Tensioned Members with Tee or Inverted Tee Sections at Transfer
Journal of The Korea Concrete Institute, 2011Co-Authors: Deuck Hang Lee, Jeong Yeon Lee, Joo-hyuk Lim, Kang Su KimAbstract:In a previous research performed by the authors, the Allowable Compressive Stress coefficient (K) in pretensioned members with rectangular section at transfer was proposed based on strength design theory. In this study, a subsequent research of an enormous analysis was performed to determine the K factor for Tee and inverted Tee section members, considering the effect of section height (h), section type, amount of tendons (), and eccentricity ratio (e/h). Based on the analysis results, the Allowable Compressive Stress coefficients (K) for Tee and inverted Tee section members at transfer were derived, which limit the maximum Allowable Stresses as 80% and 70% of the Compressive strengths at the time of release for Tee section and inverted Tee section, respectively. And these were larger than the Allowable Stresses specified in domestic and other international codes. In order to verify the proposed equations, they were compared to the test results available in literature and other codes, which showed that the Allowable Stresses in domestic and international codes are unconservative for the cases with low eccentricity ratios while conservative for those with high eccentricity ratios. The proposed equations, however, estimate the Allowable Stresses of the Tee and inverted Tee section members reasonably close to test results.
Matthew Gilbert - One of the best experts on this subject based on the ideXlab platform.
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Optimum structure for a uniform load over multiple spans
Structural and Multidisciplinary Optimization, 2015Co-Authors: Aleksey V. Pichugin, Andrew Tyas, Matthew GilbertAbstract:This paper presents a new half-plane Michell structure that transmits a uniformly distributed load of infinite horizontal extent to a series of equally-spaced pinned supports. A full kinematic description of the structure is obtained for the case when the maximum Allowable tensile Stress is greater than or equal to the Allowable Compressive Stress. Although formal proof of optimality of the solution presented is not yet available, the proposed analytical solution is supported by substantial numerical evidence, involving the solution of problems with in excess of 10 billion potential members. Furthermore, numerical solutions for various combinations of unequal Allowable Stresses suggest the existence of a family of related, simple, and practically relevant structures, which range in form from a Hemp-type arch with vertical hangers to a structure which strongly resembles a cable-stayed bridge.