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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Evaluation of Continuity Detail for Precast Prestressed Girders
Author: Loehr, J Erik | Size: 598 KB | Format:PDF | Quality:Original preprint | Publisher: Missouri University of Science and Technology, Rolla | Year: 2011 | pages: 26
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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Evaluation of Continuity Detail for Precast Prestressed Girders
Author: Loehr, J Erik | Size: 7.26 MB | Format:PDF | Quality:Original preprint | Publisher: Missouri University of Science and Technology, Rolla | Year: 2011 | pages: 77
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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Engineering Policy Guidelines For Design Of Spread Footings
Author: Loehr, J Erik | Size: 7.08 MB | Format:PDF | Quality:Original preprint | Publisher: Missouri University of Science and Technology, Rolla | Year: 2011 | pages: 44
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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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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