Monitoring and Load Distribution Study for the Land Bridge
Author: Ghorbanpoor, Al | Size: 8.73 MB | Format:PDF | Quality:Original preprint | Publisher: University of Wisconsin, Milwaukee | Year: 2010 | pages: 179
A monitoring program and a live load distribution study were conducted for the Land Bridge, located on State Highway 131 between Ontario and LaFarge in southwest Wisconsin. The bridge is a 275-ft long curved double trapezoidal steel box girder construction. Hybrid HPS70W and A588 weathering steels were used for the construction of the bridge. The monitoring program included measurements of live load and thermal strains as well as displacements for the girders over a four-year period. The effects of the in-service live load, in terms of both the applied stresses and the number of load cycles, were found to be insignificant. The thermal stress levels were found to be more significant but with only a limited number of load cycles. It was also found that there was no significant change in the load pattern, for both the stress level and number of load cycles, over the four years of the monitoring program for the bridge. The observed stress levels in the bridge were found to be below the fatigue stress threshold prescribed by AASHTO. This indicated that an infinite life could be expected for the bridge when fatigue is a consideration for the steel box girders. The live load distribution study for the Land Bridge included a field testing, a 3-D numerical simulation, and a comparative study of the results with those determined by the provisions of the AASHTO standard and LRFD specifications. Good agreement was achieved between the load distribution factor values that were obtained from the field testing and the numerical simulation. The comparison of the results with the values obtained from the AASHTO specifications indicated that over-conservative results yielded from the standard specifications while the results from the LRFD specifications were under-conservative. It is recommended that an additional study be performed to overcome this shortcoming of the current design specifications.
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Calibration of Resistance Factors Needed in the LRFD Design of Drilled Shafts
Author: Abu-Farsakh, Murad Y | Size: 911 KB | Format:PDF | Quality:Original preprint | Publisher: Louisiana Transportation Research Center | Year: 2010 | pages: 110
The first report on Load and Resistance Factor Design (LRFD) calibration of driven piles in Louisiana (LTRC Final Report 449) was completed in May 2009. As a continuing effort to implement the LRFD design methodology for deep foundations in Louisiana, this report will present the reliability based analyses for the calibration of the resistance factor for LRFD design of axially loaded drilled shafts. A total of 16 cases of drilled shaft load tests were available to authors from Louisiana Department of Transportation and Development (LADOTD) archives. Out of those, only 11 met the Federal Highway Administration (FHWA) "5%B" settlement criterion. Due to the limited number of available drilled shaft cases in Louisiana, additional drilled shaft cases were collected from state of Mississippi that has subsurface soil conditions similar to Louisiana soils. A total of 15 drilled shafts from Mississippi were finally selected from 50 available cases, based on selection criteria of subsurface soil conditions and final settlement. As a result, a database of 26 drilled shaft tests representing the typical design practice in Louisiana was created for statistical reliability analyses. The predictions of total, side, and tip resistance versus settlement behavior of drilled shafts were established from soil borings using the FHWA O’Neill and Reese design method via the SHAFT computer program. The measured drilled shaft axial nominal resistance was determined from either the Osterberg cell (O-cell) test or the conventional top-down static load test. For the 22 drilled shafts that were tested using O-cells, the tip and side resistances were deduced separately from test results. Statistical analyses were performed to compare the predicted total, tip, and side drilled shaft nominal axial resistance with the corresponding measured nominal resistance. Results of this showed that the selected FHWA design method significantly underestimates measured drilled shaft resistance. The Monte Carlo simulation method was selected to perform the LRFD calibration of resistance factors of drilled shaft under strength I limit state. The total resistance factors obtained at different reliability index were determined and compared with those available in literature. Results of reliability analysis, corresponding to a target reliability index of 3.0, reveals resistance factors for side, tip, and total resistance factor are 0.20, 0.75, and 0.5, respectively.
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Development of Load and Resistance Factor Design for Ultimate and Serviceability Limit States of Transportation Structure Foundations
Author: Salgado, Rodrigo Purdue University Woo, San Inn Kim, Dongwook | Size: 3.57 MB | Format:PDF | Quality:Original preprint | Publisher: Joint Transportation Research Program | Year: 2011 | pages: 76
Most foundation solutions for transportation structures rely on deep foundations, often on pile foundations configured in a way most suitable to the problem at hand. Design of pile foundation solutions can best be pursued by clearly defining limit states and then configuring the piles in such a way as to prevent the attainment of these limit states. The present report develops methods for load and resistance factor design (LRFD) of piles, both nondisplacement and displacement piles, in sand and clay. With the exception of the method for design of displacement piles in sand, all the methods are based on rigorous theoretical mechanics solutions of the pile loading problem. In all cases, the uncertainty of the variables appearing in the problem and of the relationships linking these variables to the resistance calculated using these relationships are carefully assessed. Monte Carlo simulations using these relationships and the associated variabilities allow simulation of resistance minus load distributions and therefore probability of failure. The mean (or nominal) values of the variables can be adjusted so that the probability of failure can be made to match a target probability of failure. Since an infinite number of combinations of these means can be made to lead to the same target probability of failure, the authors have developed a way to determine the most likely ultimate limit state for a given probability of failure. Once the most likely ultimate limit state is determined, the values of loads and resistances for this limit state can be used, together with the values of the mean (or nominal) loads and resistances to calculate load and resistance factors. The last step in the process involves adjusting the resistance factors so that they are consistent with the load factors specified by American Association of State Highway and Transportation Officials (AASHTO). Recommended resistance factors are then given together with the design methods for which they were developed.
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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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