Posted by: mahyarov - 10-29-2012, 07:18 AM - Forum: Concrete
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Evaluation of Continuity Detail for Precast Prestressed Girders
Author: Okeil, Ayman M Louisiana State University, Baton Rouge Cai, Steve Chebole, Veeravenkata Hossain, Tanvir | Size: 7.10 MB | Format:PDF | Quality:Original preprint | Publisher: Louisiana State University, Baton Rouge | Year: 2011 | pages: 206
The construction of highway bridges using precast prestressed concrete (PSC) girders is considered one of the most economical construction alternatives because of the advantages they offer (e.g. reducing formwork and rapid construction). Constructing multi-simple span bridges is an easy alternative for precast PSC girder bridges. However, the existence of expansion joints often leads to a host of problems in their vicinity due to drainage leaks and debris accumulation. The maintenance of expansion joints is, therefore, an activity that bridge owners would rather avoid by eliminating these joints by building connections between precast elements that are capable of resisting the forces resulting from establishing continuity. Several continuity details have been used over the years for slab-on-girder bridges with the goal of avoiding the aforementioned maintenance issues and reaping the benefits of continuity without the drawbacks of introducing it in large structures such as bridges (e.g. thermal movements). A new continuity detail is adopted in the John James Audubon Bridge that differs from the current standard detail in Louisiana. The new detail is based on the recommendation of the National Cooperative Highway Research Program (NCHRP) Report 519 [1]. A 96-channel monitoring system was installed to provide information that can be used to assess the performance of the continuity detail. Embedded and surface-mounted sensors of different types were installed to measure strains, temperatures, rotations, and gap openings in critical locations in the monitored segment. Data from about 24 months of monitoring was collected. The data, its processing, and interpretation are presented in this report. Analyses based on NCHRP Report 519 model and finite element models were also conducted to further understand the behavior of the new detail. Results from the analyses were also used to recommend girder age at continuity to meet prespecified design criteria. A live load test was also conducted to assess the performance of the new detail. Recommendations based on the findings of the project are drawn. It can be said that the continuity detail is capable of transferring forces between girder ends. However, girder ends may be subjected to high localized strains, especially due to thermal variation, which can cause cracking. Such cracks are detrimental to the shear strength of PSC girders. Therefore, thermal gradients need to be considered in the design of this detail.
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Self-consolidating concrete (SCC) is a workable yet stable concrete which flows easily and consolidates under its own weight. Its unique properties can substantially reduce the labor required to pour complex or heavily reinforced structural members. Over the past decade, the American precast industry has taken significant strides to adopt SCC in commercial projects, though concern about early-age bond behavior has limited the material’s application in prestressed members. A general need remains for further research on the bond properties of SCC in full-scale prestressed members. The wide array of specimen types and SCC mixture designs utilized in practice further underscores this need. To explore the application of SCC in Illinois bridge construction, the Illinois Department of Transportation (IDOT) and Illinois Center for Transportation (ICT) sponsored a three-phase study investigating the bond behavior of steel strands in pretensioned bridge box and I-girders. In the first phase, 56 pullout tests were conducted to compare the performance of seven-wire strands embedded in SCC to that of strands in normally consolidated concrete (NCC) blocks. In the second phase, transfer lengths of prestressing strands in two 28-ft. SCC hollow box girders and two 48-ft. SCC I-girders were determined experimentally. In the third phase, development lengths of strands in the four girders were determined through a series of iterative flexural tests. This report details the experimental program for the study’s three phases and compares results to current requirements of the American Concrete Institute (ACI) and the American Association of State Highway and Transportation Officials (AASHTO). The results of this study may prove fundamental to the safe application of SCC within the state of Illinois’ prestressed concrete industry.
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Long-term Maintenance Monitoring Demonstration on a Movable Bridge
Author: Gul, Mustafa | Size: 2.50 MB | Format:PDF | Quality:Original preprint | Publisher: University of Central Florida, Orlando | Year: 2011 | pages: 70
The maintenance costs related to movable bridges are considerably higher than those of fixed bridges, mostly because of the complex interaction of the mechanical, electrical and structural components. A malfunction of any component can cause an unexpected failure of bridge operation, which creates problems for both land and maritime traffic. Maintenance processes associated with the operation system and mechanical parts require special expertise. A comprehensive monitoring system was implemented on Sunrise Bridge (Ft. Lauderdale) to track the behavior and condition of several critical mechanical, electrical and structural components. A number of tests and monitoring of the bridge yielded a wide variety of data, which were analyzed in detail with methods developed by the PI and his research team, and the results obtained at the end of the project were reported to FDOT in a detailed report. After the completion of this previous project, the bridge was already scheduled for painting; however, the monitoring system was significantly damaged during the preparation, sandblasting and painting despite the considerable efforts of FDOT personnel to protect the system. This extension project therefore focuses on repairing the monitoring system, which was affected by the painting operation, collecting and analyzing more data and preparing the system for FDOT. First, details of the field work conducted to repair the damaged monitoring system are presented. Then, analysis of data that were collected after the monitoring system was repaired is presented for different components. The baseline response and the thresholds for acceptable behavior were established. During this phase of the project, unanticipated behaviors were observed for two components (one at the span locks and one at the gearbox) at two different times. These findings indicating the unanticipated behavior using the monitoring system are also corroborated with the independent maintenance reports. These changes in behavior required maintenance work at the span lock and gearbox as given in the maintenance logs. Finally, recommendations are provided based on the findings and experiences from this project.
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A new bridge design and construction trend to help improve durability and rideability is to remove expansion joints over piers and abutments. One approach to achieve this is to make the deck continuous over the piers by means of a link slab while the girders remain simply supported. The need to implement link slabs is indicated by American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) section 2.5.2.4 which requires using a minimum number of expansion joints to improve rideability. Further, due to durability concerns associated with bridge deck joints, it is preferred to have a least number of joints or develop jointless decks. The expansion joints over the abutments can be removed by one of three methods: deck sliding over back wall, semi-integral abutments, and integral abutments. This results in expansion joints at either or both ends of the approaches. The design concerns other than link slab include backwall and wing-wall design and bearing movement. The behavior of a jointless bridge brings about many challenges to bridge designers. The complexity is augmented when skew is involved. This report complements an earlier report based on previous research on Combining Link Slab, Deck Sliding Over Backwall and Revising Bearings (Aktan et al., 2008) where the behavior of straight and moderately skew (skew < 200) link slab bridges were investigated and design recommendations were developed. This report describes the behavior and performance of high skew (skew > 200) jointless bridges with link slabs and two abutment configurations. These abutment configurations are deck sliding over backwall and backwall sliding over abutments (i.e. semi-integral abutments). Four tasks were performed in this project. The first task was to review and synthesize information related to the behavior, performance, design, and analysis of skew bridges. The second task was field assessment of skew bridge behavior under static truck loads and thermal loads. The third task was analytical and numerical analysis of skew link slabs. The final task was analytical and numerical analysis of skew sliding deck over backwall systems and semi-integral abutments. Design recommendations are developed based on literature, field assessment data analysis, finite element modeling, and subsequent simulations of the numerous models developed in this project. One recommendation deals with the skew link slab design and the remaining recommendations are for bearing selection and selection and design of a transverse restraint system at abutments of skew link slab bridges.
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Combined Seismic Plus Live-Load Analysis of Highway Bridges
Author: Scott, Michael H | Size: 4.74 MB | Format:PDF | Quality:Original preprint | Publisher: Oregon State University, Corvallis | Year: 2011 | pages: 44
The combination of seismic and vehicle live loadings on bridges is an important design consideration. There are well-established design provisions for how the individual loadings affect bridge response; structural components that carry vertical live loads are designed to remain well within the linear-elastic range, while lateral load carrying components are designed to yield under large seismic excitations. The weight of the bridge superstructure is taken into account as dead load in structural analysis for seismic loads; however, the effects of additional mass and damping of live loads on the bridge deck are neglected. To improve the design of highway bridges for multi-hazard effects of seismic plus live load, many questions arise and are addressed in this project via numerical simulations of short span bridges. Further extensions of this research can be extended to long span bridges whose seismic response is more heavily influenced by vehicle mass on the bridge deck.
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Large-Scale Laboratory Observations of Wave Forces on a Highway Bridge Superstructure
Author: Bradner, Chris Schumacher, Thomas | Size: 2.84 MB | Format:PDF | Quality:Original preprint | Publisher: Oregon State University, Corvallis | Year: 2011 | pages: 170
The experimental setup and data are presented for a laboratory experiment conducted to examine realistic wave forcing on a highway bridge superstructure. The experiments measure wave conditions along with the resulting forces, pressures, and structural response of a 1:5 scale, reinforced concrete model of a typical section of the I-10 Bridge over Escambia Bay, Florida that failed during Hurricane Ivan in 2004. A unique feature of this model is its roller and rail system which allowed the specimen to move freely along the axis of wave propagation to simulate the dynamic response of the structure. The data are analyzed to study the relative importance of the impulse load versus the sustained wave load, the magnitudes of the horizontal to vertical forces, and their time histories to identify the modes of failure. The thesis examines the relationship between measured forces and wave momentum flux. The measured forces are also compared to recently published AASHTO guidelines. The author evaluates the distribution of forces under random wave conditions and proposes a method that calculates design loads based on exceedance probabilities.
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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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