Author: Adams, Michael Nicks, Jennifer Stabile, Tom Wu, Jonathan Schlatter, Warren Hartmann, Joseph | Size: 8.67 MB | Format:PDF | Quality:Original preprint | Publisher: Federal Highway Administration | Year: 2011 | pages: 174
This manual outlines the state-of-the-art and recommended practice for designing and constructing Geosynthetic Reinforced Soil (GRS) technology for the application of the Integrated Bridge System (IBS). The procedures presented in this manual are based on 40 years of State and Federal research focused on GRS technology as applied to abutments and walls. This manual was developed to serve as the first in a two-part series aimed at providing engineers with the necessary background knowledge of GRS technology and its fundamental characteristics as an alternative to other construction methods. The manual presents step-by-step guidance on the design of GRS-IBS. Analytical and empirical design methodologies in both the Allowable Stress Design (ASD) and Load and Resistance Factor Design (LRFD) formats are provided. Material specifications for standard GRS-IBS are also provided. Detailed construction guidance is presented along with methods for the inspection, performance monitoring, maintenance, and repair of GRS-IBS. Quality assurance and quality control procedures are also covered in this manual.
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Calibration of Load and Resistance Factors in LRFD Foundation Design Specifications
Author: Wang, Zuocai | Size: 5.27 MB | Format:PDF | Quality:Original preprint | Publisher: Missouri University of Science and Technology, Rolla | Year: 2011 | pages: 146
This report summarizes the findings and recommendations on the impact of foundation settlements on the reliability of bridge superstructures. As a collaborative effort of an overall initiative for the development of load and resistance factor design (LRFD) foundation design specifications, this study is focused on the investigation of pros and cons for including foundation settlements in bridge designs under gravity loads. Settlement was modeled both probabilistically and deterministically. In the case of a random settlement variable, a lognormal distribution was used in reliability analysis with a fixed coefficient of variation of 0.25. Dead and live loads were modeled as random variables with normal and Gumbel Type I distributions, respectively. Considering the regional traffic condition on Missouri roadways, the effect of a live load reduction factor on bridge reliability was also investigated. Therefore, a total of eight cases were discussed with a complete combination of settlement modeling (mean and extreme values), design consideration (settlements included and excluded), and live load reduction (unreduced and reduced live loads). Based on extensive simulations on multi-span bridges, bridges designed without due consideration on settlements can tolerate an extreme settlement of L/3500 - L/450 under unreduced live loads and up to L/3500 under reduced live loads without resulting in a reliability index below 3.5 (L=span length). Depending upon span lengths and their ratio, the reliability of existing steel-girder bridges is consistently higher than prestressed concrete and solid slab bridges. The shorter and stiffer the spans, the more significant the settlement’s effect on the reliability of bridge superstructures. As the span length ratio becomes less than 0.75, the girder and solid slab bridges’ reliability drops significantly at small settlements. A concrete diaphragm is very susceptible to the differential settlement of bridges, particularly for moment effects. Two recommendations were made to address settlement effects in bridge design: (1) settlement is considered in structural design and no special requirement is needed for foundation designs unless settlement exceeds the AASHTO recommended settlement limit of L/250, and (2) settlement is not considered in structural design as in the current Missouri Department of Transportation (MoDOT) practice but ensured below the tolerable settlement (e.g., L/450 for steel girders, L/2500 for slabs, and L/3500 for prestressed concrete girders). The first method provides a direct approach to deal with settlements and has potential to reduce overall costs in bridge design. The second method may result in oversized foundations.
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Author: Pantelides, Chris P University of Utah, Salt Lake City Liu, Ruifen University of Utah, Salt Lake City | Size: 2.65 MB | Format:PDF | Quality:Original preprint | Publisher: University of Utah, Salt Lake City | Year: 2011 | pages: 69
The present research project investigates lightweight and normal weight concrete precast panels for highway bridge decks. The deck panels are reinforced with Glass Fiber Reinforced Polymer (GFRP) bars. Due to the lack of research on lightweight concrete members reinforced with GFRP bars, the AASHTO LRFD Bridge Design Guide Specifications for GFRP Reinforced Concrete Decks do not permit the use of lightweight concrete when GFRP bars are used as flexural reinforcement. The ACI 440.1R-06 design guidelines do not provide any design information regarding the use of lightweight concrete reinforced with GFRP bars. In this research, the experimental performance of lightweight concrete versus normal weight concrete precast GFRP reinforced deck panels is investigated in terms of flexural capacity, panel deflections, and shear capacity.
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Evaluation of Long-Term Prestress Losses in Post-Tensioned Box-Girder Bridges
Author: Shing, P Benson Kottari, Alexandra | Size: 1.37 MB | Format:PDF | Quality:Original preprint | Publisher: University of California, San Diego | Year: 2011 | pages: 90
This study assessed the accuracy of the long-term prestress-loss estimation methods given in the current AASHTO LRFD Specifications for post-tensioned bridge girders, and developed more suitable analysis methods for these members. A refined analysis method and a simplified method were proven to be accurate using field data collected from two bridge structures that were monitored for prestress losses over a period of more than four years. Formulas for calculating the creep and shrinkage of concrete have been evaluated with the material data obtained from concrete cylinders cast with the same batches of concrete used for the monitored bridge girders, and have been used for the loss calculations. The formulas in AASHTO 2004 provide a much better correlation with the creep and shrinkage data obtained from the concrete cylinders than AASHTO 2007. In general, the AASHTO 2007 formulas significantly under-estimate the creep and shrinkage of the concrete cylinders, and result in calculated long-term losses that are much lower than the measured values. The creep and shrinkage formulas provided in AASHTO 2004 therefore are recommended for the prestress-loss calculations using the proposed refined analysis method. Suggestions are provided for possible implementation of the proposed analysis methods in the AASHTO LRFD Specifications for calculating long-term prestress losses in post-tensioned bridge girders. Both methods are expressed in forms that can be readily implemented in the AASHTO LRFD Specifications.
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Evaluation of a Highway Bridge Constructed Using High Strength Lightweight Concrete Bridge Girders
Author: Holland, R Brett | Size: 2.46 MB | Format:PDF | Quality:Original preprint | Publisher: Georgia Institute of Technology, Atlanta | Year: 2011 | pages: 112
The use of high performance concretes to provide longer bridge spans has been limited due to the capacity of existing infrastructure to handle the load of the girders during transportation. The use of High Strength Lightweight Concrete (HSLW) can provide the same spans at a 20% reduction in weight. This paper presents the findings from an ongoing performance evaluation of HSLW concrete bridge girders used for the I-85 Ramp “B” Bridge crossing SR-34 in Coweta County, Georgia,. The girders are AASHTO BT-54 cross-sections with a 107 ft 11½ in. (32.9 m) length cast with a 10,000 psi (68.9 MPa) design strength HSLW mix and an actual average unit weight of 120 lb/ft³ (1922 kg/m³). The prestressing losses measured experimentally by embedded vibrating wire strain gauges have been compared to the AASHTO LRFD loss equations, as well as the proposed methods by Tadros (2003) and Shams (2000). The investigation also included camber measurements and the effect of temperature changes. A load test was performed on the girders at 56-days of age and on the bridge after completion of construction to determine a stiffness estimator for use with the girders and to determine their performance as a completed system. The girders are the first use of HSLW girders in the state of Georgia, and they have proven to perform well for use in highway bridges.
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Engineering Policy Guidelines for Design of Earth Slopes
Author: Loehr, J Erik | Size: 616 KB | Format:PDF | Quality:Original preprint | Publisher: Missouri University of Science and Technology, Rolla | Year: 2011 | pages: 21
These guidelines were developed as part of a comprehensive research program undertaken by the Missouri Department of Transportation (MoDOT) to reduce costs associated with design and construction of bridge foundations while maintaining appropriate levels of safety for the traveling public. The guidelines were established from a combination of existing MoDOT Engineering Policy Guide (EPG) documents, from the 4th Edition of the AASHTO LRFD Bridge Design Specifications with 2009 Interim Revisions, and from results of the research program. Some provisions of the guidelines represent substantial changes to current practice to reflect advancements made possible from results of the research program. Other provisions were left essentially unchanged, or were revised to reflect incremental changes in practice, because research was not performed to address those provisions. Some provisions reflect rational starting points based on judgment and past experience from which further improvements can be based. All of the provisions should be considered as “living documents” subject to further revision and refinement as additional knowledge and experience is gained with the respective provisions. A number of specific opportunities for improvement are provided in the commentary that accompanies the guidelines.
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Author: Hanna, Kromel E University of Nebraska, Lincoln Morcous, George Tadros, Maher K University of Nebraska, Lincoln | Size: 2.34 MB | Format:PDF | Quality:Original preprint | Publisher: University of Nebraska, Lincoln | Year: 2012 | pages: 41
Precast prestressed concrete I-Girder bridges have become the most dominant bridge system in the United States. In the early design stages, preliminary design becomes a vital first step in designing an economical bridge. Within the state of Nebraska, the two standard precast prestressed products used are Inverted Tee (IT) girders and University of Nebraska (NU) I girders. In the early 1990s, Nebraska Department of Roads (NDOR) developed design charts for NU-I girders in order to assist in member selection and preliminary design. In 2004, design charts were developed for IT girders. However, the NU-I girder charts have since become obsolete because they were developed for low strength concrete (6 ksi) and 0.5 inch prestressing strands. In addition, the charts were based off of American Association of State Highway and Transportation Officials (AASHTO) standard specifications. Since then, NDOR has adopted AASHTO Load and Resistance Factor Design (LRFD) specifications for superstructure design and the Threaded Rod (TR) continuity systems in their standard practice. Therefore, the new design charts are based on the latest AASHTO LRFD Specifications for superstructure design and NDOR Bridge Operations, Policies, and Procedures (BOPP manual). With the increasing use of 0.6 and 0.7 inch diameter strands as well as increasing concrete strengths, there is a need for new preliminary design charts for NU-I girders. The new design aids provide bridge designers with different alternatives of girder section size (from NU900 to NU2000), girder spacing (from 6-12 ft), prestressing strands (up to 60), prestressing strand diameter (from 0.6 to 0.7 inch), and compressive strength of concrete (from 8 ksi to 15 ksi). Two sets of design charts are developed to cover simple span and two-span continuous bridges. Each set contains two different types of charts: summary charts and detailed charts. Summary charts give designers the largest possible span length allowed given girder spacing, concrete strength, and NU-I girder sections. Detailed charts give designers the minimum number of prestressing strands required given girder spacing, span length, and concrete strength. Both sets of charts provide designers with the limit state that controls the design. If needed, this allows the design to be optimized in an efficient manner.
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Posted by: mahyarov - 10-30-2012, 07:57 AM - Forum: Concrete
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Continuous Prestressed Concrete Girder Bridges. Volume 1: Literature Review and Preliminary Designs
Author: Hueste, Mary Beth D Texas Transportation Institute Mander, John B Parkar, Anagha S | Size: 3.60 MB | Format:PDF | Quality:Original preprint | Publisher: Texas Transportation Institute | Year: 2012 | pages: 176
The Texas Department of Transportation (TxDOT) is currently designing typical highway bridge structures as simply supported using standard precast, pretensioned girders. TxDOT is interested in developing additional economical design alternatives for longer span bridges, through the use of the continuous precast, pretensioned concrete bridge structures that use spliced girder technology. The objectives of this portion of the study are to evaluate the current state-of-the-art and practice relevant to continuous precast concrete girder bridges and recommend suitable continuity connections for use with typical Texas bridge girders. A wide variety of design and construction approaches are possible when making these precast concrete bridges continuous with longer spans. Continuity connection details used for precast, prestressed concrete girder bridges across the United States were investigated. Several methods were reviewed that have been used in the past to provide continuity and increase the span length of slab-on-girder prestressed concrete bridges. Construction issues that should be considered during the concept development and design stage are highlighted. Splice connections are categorized into distinct types. Advantages and disadvantages of each approach are discussed with a focus on construction and long-term serviceability. A preliminary design study was conducted to explore potential span lengths for continuous bridges using the current TxDOT precast girder sections, standard girder spacings and material properties. The revised provisions for spliced precast girders in the "AASHTO LRFD Bridge Design Specifications" (2010) were used in the study. The results obtained from the literature review and preliminary designs, along with precaster and contractor input, are summarized in this report.
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Seismic Performance of Pile-Supported Wharf Structures Considering Soil-Structure Interaction in Liquefied Soil
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