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Author: Andrew Michael Moore
Publisher:
ISBN:
Category :
Languages : en
Pages : 500
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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.
Author: Andrew Michael Moore
Publisher:
ISBN:
Category :
Languages : en
Pages : 500
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Book Description
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.
Author: Dhiaa Mustafa T. Al-Tarafany
Publisher:
ISBN:
Category :
Languages : en
Pages : 412
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Book Description
Implementation 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.
Author: Christopher Scott Williams
Publisher:
ISBN:
Category :
Languages : en
Pages : 786
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Spliced 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.
Author: William Leo Gamble
Publisher:
ISBN:
Category : Concrete bridges
Languages : en
Pages : 280
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Tests of two prestressed concrete composite bridge girders which were continuous over two spans are reported. Both were I-section girders with cast-in-place decks, and had spans of about 37 ft (11 m), and were approximately 1/3 scale models of structures spanning 125 ft (38 m). Each girder was constructed from three segments which were joined end-to-end by cast-in-place concrete splices. Modell was post-tensioned after erection of the girders and casting of the deck and splice concrete. The two end segments, each supported on the final abutments and on temporary supports located about 1/3 of the span from the central pier, were pretensioned for their dead loads plus the deck concrete. The central segment, which was supported on the central pier of the structure plus the two temporary supports was precast reinforced concrete, plus a small amount of pre= tensioned reinforcement. Model 2 was externally similar, but was not post-tensioned. The segments were pretensioned for the final moments, and were joined by splicing reinforcing bars which extended into the splice region. Both structures were subjected to a series of loadings to the service load, design ultimate, and high over-load levels. Both had capacities which were significantly higher than the design ultimate values. The capacities were generally predictable on the basis of flexural strength calculations, and shear did not cause major problems. Joint details in Modell lead to difficulties in two tests, and this aspect of the design is discussed in detail.
Author: Gustavo Adolfo Llanos
Publisher:
ISBN:
Category :
Languages : en
Pages :
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ABSTRACT: The objective of this study was to evaluate the behavior of post-tensioned I-girders with end blocks. The beams had two parabolic tendons and two straight that were anchored at each of the ends of the beam. Post-tensioning of the beams was done in the laboratory with the objective of measuring losses due to seating, elastic, creep and shrinkage. Outside of the end block, approximately 3 ft from each end, there was no shear reinforcement. U-bars were used in the top flange to provide composite action between the deck and girder. Without the presence of shear reinforcement loading configurations used short shear span to depth ratios to see if a shear failure would occur. In the field these beams were observed to have no bearing pads and rested directly on concrete. Two post-tensioned beams with the same loading pattern were tested to failure with only the support condition varying, one neoprene and one resting directly on concrete. This was done to see if the stiffness would be affected by the support conditions. A third test was conducted for a shorter shear span to observe the type of failure that would occur. Each girder was instrumented to measure strains, vertical deflections and crack initiation at relevant points. Finally, capacities were predicted using three methods, ACI, AASHTO, and Strut-and-Tie. These predicted values were compared to experimental capacities to observe the disparity between the two.
Author: David Paul Gustafson
Publisher:
ISBN:
Category : Girders
Languages : en
Pages : 350
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Author: Wing Hong Louis Lo
Publisher:
ISBN:
Category :
Languages : en
Pages :
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During the fall of 2012, two separate Interstate 15 highway bridges over the 400 South roadway in Orem, Utah were demolished after 50 years of service. Four post-tensioned girders were salvaged from both the north-bound and south-bound bridge. A series of tests was performed with these girders in the System Material And Structural Health Laboratory (SMASH Lab). The girders were tested with different loading criteria to determine the strength and material properties of the girder. The experimental results were compared with the American Association of State Highway and Transportation Officials Load Resistance Factored Design (AASHTO LRFD) Bridge Design Specifications and a finite-element model using ANSYS. The AASHTO LRFD Specification was fairly conservative on predicting capacity and capable of predicting the type of failure that occurred. The ANSYS model was developed and calibrated to model the girder behavior. The concrete properties in the model were significantly adjusted in order to be comparable to the experimental results. Further exploration in ANSYS needs to be done to precisely model the actual behavior of the girder.
Author: James Oscar Felan
Publisher:
ISBN:
Category :
Languages : en
Pages : 254
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The goal of the splice girder research project 0-6652 funded by the Texas Department of Transportation is to utilize the full potential of splicing prestressed TX girders continuously. The TX girder family of beams is cost effective alone due to their simple, repetitive fabrication, but to truly optimize their potential would be to span several beams together as one continuous unit. The weight and length restrictions allowed by trucks or barges limit the prestressed beam lengths. Therefore, splicing together prestressed beams becomes the solution to the transporting obstacle. As a result, the prestressed girders will be more competitive to other bridge types such as steel I-girders, steel trapezoidal girders, cable-stayed bridges, and concrete segmental bridges. In fact, a prestressed/post-tensioned concrete bridge is preferred over steel designs in highly corrosive environments such as the coast or in snow regions where de-icing chemicals are used. In comparison, to a segmental box girder bridge, the post-tensioned prestressed bridge has reduced complexity due to fewer segments and the number of reduced joints susceptible to corrosion. The issue that arises with splicing prestressed beams is that in the process of connecting them together an opening must be made to install the post-tensioning (PT) steel strands. The openings are created by installing several steel or plastic circular ducts into the web region. Since the post-tensioning results in a reduction of the concrete web region, a modification is necessary to the shear capacity equation. The experimental study performed at the Ferguson Structural Engineering Laboratory consisted of fabricating and testing two full-scale prestressed Tx46 girders. One girder contained a plastic post-tensioning duct with grout and steel strands installed in the web region. The other beam was a standard Tx46 beam fabricated without a duct. Both beams had a reinforced concrete deck installed with an overhang to model an actual bridge section. Furthermore, the purpose of the standard beam was to serve as a direct comparison to the beam with a duct and determine the actual reduction in shear capacity. The research and findings will include the impact of the plastic duct in the Tx46 compared to the control beam. The failure loads of the test specimens will be compared to the current 2012 AASHTO code predictions for shear design. Also, revisions to the AASHTO code will be recommended if necessary. The primary goal of this research was to improve the design and detailing of the skewed end-blocks commonly used in these beams. As U-beams had been in service for several decades without incident, it was anticipated that there would be little need for change in the design, and the findings of the research would involve a slight tweaking to improve the overall performance.
Author: A. I. Fadl
Publisher:
ISBN:
Category : Bridges, Concrete
Languages : en
Pages : 402
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Author:
Publisher:
ISBN:
Category : Precast concrete
Languages : en
Pages : 666
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