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| Author | : Michael G. Oliva |
| Publisher | : |
| Total Pages | : 134 |
| Release | : 2011 |
| Genre | : Concrete bridges |
| ISBN | : |
| Author | : |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2012 |
| Genre | : |
| ISBN | : |
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.
| Author | : FIB – International Federation for Structural Concrete |
| Publisher | : FIB - Féd. Int. du Béton |
| Total Pages | : 1312 |
| Release | : 2018-08-01 |
| Genre | : Technology & Engineering |
| ISBN | : 8001064018 |
| Author | : Emre Kizilarslan |
| Publisher | : |
| Total Pages | : 202 |
| Release | : 2016 |
| Genre | : |
| ISBN | : |
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.
| Author | : Roya Alirezaei Abyaneh |
| Publisher | : |
| Total Pages | : 190 |
| Release | : 2016 |
| Genre | : |
| ISBN | : |
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
| Author | : Maher K. Tadros |
| Publisher | : Transportation Research Board |
| Total Pages | : 76 |
| Release | : 2010 |
| Genre | : Technology & Engineering |
| ISBN | : 0309118352 |
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.
| Author | : |
| Publisher | : |
| Total Pages | : 170 |
| Release | : 1994 |
| Genre | : Bridges |
| ISBN | : |
| Author | : Sanjay Chaudhury |
| Publisher | : |
| Total Pages | : 304 |
| Release | : 2004 |
| Genre | : Bridges |
| ISBN | : |
"The speed of construction has become the key issue for bridges. This is especially true in cold regions like Alaska, where you face a very short summer season. The speed of construction can be expedited by connections. As there are advantages in connections there are also disadvantages. One of the primary advantages of the connectors is that it makes the load transfer mechanism very efficient. However everything comes for a price. Maintenance of connections is very difficult. Routine inspections are to be made to ensure proper functioning of the system. This becomes a very important factor in Alaska where extreme winter conditions exists. Another issue is that the current connector design is based on an empirical approach. A rational design method is needed. In this study an effort has been made to find the presence of ISD on the live load distribution factor for single lane loading. Using ABAQUS CAE, 3D finite element (FE) models have been developed and analyzed with different parameters. By varying the parameters, different distribution factors corresponding to the reaction, strains (flexure and shear) as well as the forces originating from the connectors are evaluated and compared. This paper provides a basis for future connector design"--Leave iv.
| Author | : W.T. Marshall |
| Publisher | : |
| Total Pages | : 19 |
| Release | : 1962 |
| Genre | : |
| ISBN | : |
| Author | : William Thomas Marshall |
| Publisher | : |
| Total Pages | : 19 |
| Release | : 1962 |
| Genre | : Prestressed concrete beams |
| ISBN | : |
