Finite Element Analysis of Deep Wide-Flanged Pre-stressed Girders to Understand and Control End Cracking
Author: Oliva, Michael G | Size: 9.48 MB | Format:PDF | Quality:Original preprint | Publisher: University of Wisconsin, Madison | Year: 2011 | pages: 132
Hundreds of prestressed concrete girders are used each year for building bridges in Wisconsin. 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. Potential solutions to control end cracking were examined via finite element models and the impact of each solution on cracking was evaluated. Modifications to reinforcement bar size, debonding ratios, strand cutting sequence and use of draped strand patterns were simulated by the models. The results from different analyses were compared to quantify the success of each method in reducing strains causing girder end cracks. The tension strains leading to cracks of all types were responsive to debonding some of the bottom flange prestressing strands. Bottom flange cracking can be prevented by methodically debonding exterior strands, keeping the draped strands bonded, and evenly distributing the remaining bonded strands over the bottom flange.
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Author: Liu, Min Hummer, Joseph E Rasdorf, William J Hollar, Donna A Parikh, Shalin C Lee, Jiyong Gopinath, Sathyanarayana | Size: 4.17 MB | Format:PDF | Quality:Original preprint | Publisher: North Carolina State University, Raleigh | Year: 2011 | pages: 133
Preliminary engineering (PE) for a highway project encompasses two efforts: planning to minimize the physical, social, and human environmental impacts of projects and engineering design to deliver the best alternative. PE efforts begin years in advance of the project's construction letting, often five years or more. An efficient and accurate method to estimate PE costs would benefit transportation departments. Typically, departments estimate PE costs as a percentage of construction costs disregarding other project-specific parameters. By analyzing 461 North Carolina Department of Transportation bridge projects and 188 roadway projects let between 2001 through 2009, the research team developed statistical models linking variation in PE costs and PE duration with distinctive project parameters. The development of a user interface application aids agency users in executing the models to predict a project's PE cost ratio. Modeling strategies included multiple linear regression, hierarchical linear models, Dirichlet process linear models, and multilevel Dirichlet process linear models (MDPLM). The 461 bridge projects exhibited a mean PE cost ratio of 27.8% (ratio of PE cost over estimated construction cost) and a mean PE duration of 66.1 months. Mean PE cost ratio for the 188 roadway projects was 11.7% with a mean PE duration of 55.1 months. Project parameters utilized in the predictive models included project scope classification such as widening or new location, dimensional variables (project length, structure length, detour length, and number of spans); geographical region; and estimated costs for construction and right of way. The MDPLM minimized the mean absolute prediction error for bridges' PE cost ratio, but interpretation of variable effects and sensitivity is difficult because of the multilevel structure. Regression modeling results are also reported since sensitivity interpretation from them is more direct.
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Posted by: mahyarov - 10-29-2012, 06:55 AM - Forum: Concrete
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Concrete Delivery Time Study
Author: Vruno, Daniel M | Size: 5.09 MB | Format:PDF | Quality:Original preprint | Publisher: American Engineering Testing, Incorporated | Year: 2011 | pages: 177
The concrete industry has been asking the Minnesota Department of Transportation (MnDOT) to lengthen the time allowed to deliver concrete. MnDOT is planning on constructing many small bridge projects that are difficult to reach within the existing 60-minute time limit for air-entrained concrete. This 60-minute time limit could unnecessarily increase the cost to construct these bridges. Although other state departments of transportation (DOTs) do allow longer transit times with the use of retarding admixtures, there are no known studies to verify whether the longer hauling time is detrimental to concrete performance. Also, there may be significant differences in the mix designs and materials that are used by other state DOTs, as well as the environments that the concrete is placed and expected to perform in. The goal of this project was to utilize the results of the testing programs and develop specification guidelines that allow the implementation of chemical admixtures to extend transport and delivery time from the current 60 minutes for air-entrained concrete up to 120 minutes.
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Damage Detection and Repair Methods for GFRP Bridge Decks
Author: Asencio, Rafael Brown, Jeff R | Size: 8.50 MB | Format:PDF | Quality:Original preprint | Publisher: University of Florida, Gainesville | Year: 2011 | pages: 193
Glass fiber-reinforced polymer (GFRP) decks are being considered for use as a replacement for worn steel grid bridge decks due to their high strength-to-weight ratio and fast installation time. In this research, two nondestructive evaluation techniques were considered for use in evaluating in-service GFRP bridge decks for damage: acoustic emissions (AE) and infrared thermography (IRT). Three different commercially available deck systems were tested in positive and negative bending test setups. The testing consisted of loading each specimen sequentially with service, then ultimate, then service level loads, which provided AE data for both undamaged and damaged deck specimens. Damage was induced on the specimens by loading them to their ultimate capacity. The specimens generally exhibited linear elastic behavior up to failure. AE feature data were evaluated using intensity analysis and recovery ratio analysis (RRA). The recovery ratio analysis was adapted from calm ratio analysis, which is based on the Kaiser effect. RRA provided clear distinction between damaged and undamaged decks in all three specimens. Evaluation criteria based on this method are proposed. A modified form of RRA was then used on data collected during a bridge load test of the Hillsboro canal bridge in Belle Glade, Florida.. Initial IRT work required finite element simulation of the heat transfer process to determine optimal heating and data acquisition parameters that were used to inspect GFRP bridge decks in the laboratory. Experimental testing was performed in a laboratory setting on damaged and undamaged GFRP bridge deck specimens from three different manufacturers. IRT evaluation focused on identifying damage in the specimens that had been loaded to their ultimate flexural strength. It was demonstrated that IRT successfully identified features of two types of GFRP bridge decks and that severe delamination/debonding could be detected under ideal circumstances. Additional research is needed to improve detection of severe damage, including methods to reduce the interference of surface imperfections, such as non-uniform heating, which are inherent to the GFRP bridge decks examined in the current study.
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This project was sponsored through the Wisconsin Highway Research Program and its Structure Technical Oversight Committee. The objective of this research was to develop a guide for the analysis of construction loads with and without traffic live loads on permanent bridge structures, including construction of new bridges and rehabilitation of existing bridges. The research also developed specification language indicating the responsibilities of all parties involved to address loads and ensure that structures are not overstressed.
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Deterioration of J-Bar Reinforcement in Abutments and Piers
Author: Harries, Kent | Size: 4.56 MB | Format:PDF | Quality:Original preprint | Publisher: University of Pittsburgh | Year: 2011 | pages: 73
Deterioration and necking of J-bars has been reportedly observed at the interface of the footing and stem wall during the demolition of older retaining walls and bridge abutments. Similar deterioration has been reportedly observed between the pier column and footing. Any decrease in the area of steel at these interfaces may result in foundation instability, and hamper efforts to rehabilitate or preserve existing foundations. The objective of this project was to determine the extent and nature of deterioration and/or necking of J-bars in existing bridge structures. This must be understood in order to identify existing structures having the potential for or existence of deteriorated J-bars. Once at-risk structures were identified, methods to identify and validate deterioration and remedial measures, details, and methodologies were developed to address affected structures.
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Posted by: mahyarov - 10-29-2012, 06:46 AM - Forum: Concrete
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Manual for Design, Construction, and Maintenance of Orthotropic Steel Deck Bridges
Author: Anderson, Darryl DiBrito, Bill | Size: 2.77 MB | Format:PDF | Quality:Original preprint | Publisher: Anderson Engineering and Surveying, Incorporated | Year: 2012 | pages: 60
The Oregon Department of Transportation (ODOT) has experienced early age cracking of newly placed high performance concrete (HPC) bridge decks. The silica fume contained in the HPC requires immediate and proper curing application after placement to avoid early age cracks. Many construction contractors do not consistently apply adequate curing procedures, and project sites may not have easy access to water. This problem led ODOT to investigate a self-curing admixture (SCA) for bridge deck concrete mixes. The SCA reduces wet curing requirements by counteracting to some degree water loss due to evaporation. An admixture in place of wet curing that allows HPC bridge deck concrete to cure properly without early age cracking and without decreasing other performance requirements would provide another option for contractors. The study showed that concrete with the SCA after a 3-day wet cure can produce similar results to standard HPC concrete with a 14-day wet cure. However, the concrete additives in the concrete must be compatible with the SCA.
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Manual for Design, Construction, and Maintenance of Orthotropic Steel Deck Bridges
Author: Connor, Robert Fisher, John Gatti, Walter Gopalaratnam, Vellore Kozy, Brian Leshko, Brian McQuaid, David L Medlock, Ronald Mertz, Dennis Murphy, Thomas Paterson, Duncan Sorensen, Ove Yadlosky, John | Size: 9.92 MB | Format:PDF | Quality:Original preprint | Publisher: HDR Engineering, Incorporated | Year: 2012 | pages: 291
Precast concrete bridge rail systems offer several advantages over traditional cast-in-place rail designs, including reduced construction time and costs, installation in a wide range of environmental conditions, easier maintenance and repair, improved railing quality, and greater flexibility for aesthetic treatments. The objective of this project was to develop a precast concrete bridge rail system that met the Test Level 4 impact safety standards provided in the American Association for State Highway and Transportation Officials (AASHTO) document entitled Manual for Assessing Safety Hardware (MASH). The design criteria for the new bridge rail system included criteria for barrier geometry, provisions for open and closed rail options, constructability, weight limitations, segment length, design impact loads, connection of barrier segments, and connection to the bridge deck among other factors. The research effort proceeded in several phases. First, the research focused on determining the overall concept for the new bridge rail system in terms of the rail configuration and geometry as well as the required barrier reinforcement. Next, design concepts for the joints connecting adjacent rail segments were designed and subjected to dynamic component testing in order to select a design capable of meeting design criteria for the precast bridge rail system. After selection of an appropriate rail joint, the researchers developed connection details for the attachment of the rail to the bridge deck. Once the design of the various precast bridge rail components was completed, a complete set of computer-aided design (CAD) details for the prototype precast concrete bridge rail system were completed. Following the design effort, recommendations were made regarding the full-scale testing required to implement the new, precast concrete bridge rail system.
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Phase 1 Development of An Aesthetic Precast Concrete Bridge Rail
Author: Rosenbaugh, Scott K Faller, Ronald K Bielenberg, Robert W Sicking, Dean L Reid, John D | Size: 41.66 MB | Format:PDF | Quality:Original preprint | Publisher: University of Nebraska, Lincoln | Year: 2012 | pages: 360
Precast concrete bridge rail systems offer several advantages over traditional cast-in-place rail designs, including reduced construction time and costs, installation in a wide range of environmental conditions, easier maintenance and repair, improved railing quality, and greater flexibility for aesthetic treatments. The objective of this project was to develop a precast concrete bridge rail system that met the Test Level 4 impact safety standards provided in the American Association for State Highway and Transportation Officials (AASHTO) document entitled Manual for Assessing Safety Hardware (MASH). The design criteria for the new bridge rail system included criteria for barrier geometry, provisions for open and closed rail options, constructability, weight limitations, segment length, design impact loads, connection of barrier segments, and connection to the bridge deck among other factors. The research effort proceeded in several phases. First, the research focused on determining the overall concept for the new bridge rail system in terms of the rail configuration and geometry as well as the required barrier reinforcement. Next, design concepts for the joints connecting adjacent rail segments were designed and subjected to dynamic component testing in order to select a design capable of meeting design criteria for the precast bridge rail system. After selection of an appropriate rail joint, the researchers developed connection details for the attachment of the rail to the bridge deck. Once the design of the various precast bridge rail components was completed, a complete set of computer-aided design (CAD) details for the prototype precast concrete bridge rail system were completed. Following the design effort, recommendations were made regarding the full-scale testing required to implement the new, precast concrete bridge rail system.
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This document contains the Appendices A through D for the report Strength and Durability of Near-Surface Mounted CFRP Bars for Shear Strengthening Reinforced Concrete Bridge Girders published in a separate 123-page document.
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