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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Infrared Thermal Integrity Testing Quality Assurance Test Method to Detect Drilled Shaft Defects
Author: Mullins, Gray | Size: 13.16 MB | Format:PDF | Quality:Original preprint | Publisher: University of South Florida, Tampa | Year: 2011 | pages: 176
Thermal integrity profiling uses the measured temperature generated in curing concrete to assess the quality of cast in place concrete foundations (i.e. drilled shafts or ACIP piles) which can include effective shaft size (diameter and length), anomaly detection inside and outside reinforcement cage, cage alignment, and proper hydration of the concrete. The ability to detect concrete volumes outside the reinforcing cage is perhaps its strongest feature. For this study, no anomalies within the reinforcing cage were encountered but various forms of external section changes were identified as well as several cases of off-center cages. Cage alignments generally varied with depth. Notably, only two cases of reduced concrete cover were detected; bulges were most common.
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Predicting Camber, Deflection, and Prestress Losses in Prestressed Concrete Members
Author: Abu-Farsakh, Murad Y | Size: 1.88 MB | Format:PDF | Quality:Original preprint | Publisher: Louisiana State University, Baton Rouge | Year: 2011 | pages: 81
Piezocone penetration tests (PCPT) have been widely used by geotechnical engineers for subsurface investigation and evaluation of different soil properties such as strength and deformation characteristics of the soil. This report focuses on the verification of the PCPT settlement prediction methods for estimating the magnitude and time-rate of consolidation settlement of embankments over fine-grained soils. The settlement prediction methods involve the interpretation of piezocone penetration soundings and dissipation tests to determine the consolidation parameters, which include constrained modulus (M), overconsolidation ratio (OCR), and the horizontal and vertical coefficients of consolidation (ch ,cv). This Louisiana Transportation Research Center (LTRC) research team selected two case study sites, Juban Road Interchange Bridge at I-12 and Bayou Courtableau Bridge, to verify the PCPT predicted magnitude and time-rate of settlement. The embankments at each site were instrumented with horizontal inclinometers and vertical extensometers to monitor/measure their settlement with time. Both conventional one-dimensional consolidation tests and PCPT tests were performed to determine the consolidation parameters needed to calculate the magnitude and time-rate of consolidation settlements. The predicted magnitude and time-rate of consolidation settlements estimated using the laboratory one-dimensional consolidation tests and the PCPT tests were compared with field measurements. The results of this study showed that the piezocone penetration and dissipation data can reasonably estimate the magnitude and rate of consolidation settlement within the same range of accuracy as of the laboratory calculation. Friendly, visual basic software (Louisiana Embankment Settlement Prediction Program from PCPT, LESPP-PCPT) was also developed to calculate the magnitude and time-rate of consolidation settlements for symmetrical and unsymmetrical embankments utilizing the PCPT and dissipation tests for use by geotechnical engineers.
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Predicting Camber, Deflection, and Prestress Losses in Prestressed Concrete Members
Author: Morales, Reinaldo Ettema, Robert | Size: 4.49 MB | Format:PDF | Quality:Original preprint | Publisher: University of Wyoming, Laramie | Year: 2011 | pages: 123
Two-dimensional, depth-averaged flow models are used to study the distribution of flow around spill-through abutments situated on floodplains in compound channels and rectangular channels (flow on very wide floodplains may be treated as rectangular channels). The study leads to useful insights regarding distributions of flow velocity, unit discharge, and boundary shear stress at spill-through abutments. It also presents insights from extensive assessment of uncertainty associated with the use of depth-averaged modeling of flow at abutments. Of substantial use for design determination of abutment scour at bridge waterways is estimation of the magnitude of peak values of flow velocity, boundary shear stress, and unit discharge in the region where scour develops. The study, by showing how abutment flow fields adjust in response to variations of abutment length, floodplain width, and main channel dimensions, yields important trends regarding the magnitude of amplification factors for depth-averaged velocity, unit discharge, bed shear stress, and distance to peak unit discharge. Early studies are shown to provide rather limited and inadequate amplification values associated only with a narrow range of abutment and channel geometries examined. The present study comprises a much broader range of abutment lengths, channel shapes, and floodplain dimensions than heretofore reported in the literature. The study’s insights, from its assessment of uncertainty associated with the use of depth-averaged modeling of flow at abutments, yield a relationship for estimating the optimum mesh size for use with depth-averaged models. The relationship is applicable to other subsequent studies using depth-averaged models of flow around abutments or similar hydraulic structures. Prior studies addressing the effect of mesh size on numerical error have not provided a recommendation for an average optimum mesh size. The study also gives focused recommendations for topics requiring further investigation.
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Posted by: mahyarov - 10-29-2012, 07:25 AM - Forum: Concrete
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Predicting Camber, Deflection, and Prestress Losses in Prestressed Concrete Members
Author: Rizkalla, Sami Zia, Paul Storm, Tyler | Size: 2.97 MB | Format:PDF | Quality:Original preprint | Publisher: North Carolina State University | Year: 2011 | pages: 174
Accurate predictions of camber and prestress losses for prestressed concrete bridge girders are essential to minimizing the frequency and cost of construction problems. The time-dependent nature of prestress losses, variable concrete properties, and problems related to production variables make it difficult to predict camber accurately. The recent problems experienced by NCDOT during construction are mainly related to inaccurate prediction of camber. In this report, several factors related to girder production are shown to have a significant impact on the prediction of camber. A detailed method and an approximate method for predicting camber that both utilize adjustments to account for the production factors are proposed. The detailed method uses time-dependent losses calculations and creep factors to predict camber, while the approximate method uses multipliers. The current NCDOT method and the proposed methods are analyzed and compared using an extensive database of field measurements. The proposed methods are shown to provide significant improvements to the camber predictions in comparison to the current NCDOT method. Recommendations for design and production practices are provided.
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