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Author: Naresh C. Samtani
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 84
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Book Description
The FHWA believes that spread footings on soils are underutilized because designers encounter one or more of the following obstacles: (a) limited knowledge of AASHTO/FHWA technical references that pertain to spread footings on soils to support bridges; (b) limited knowledge of adequate performance data for spread footings; (c) unrealistic tolerable settlement criteria; (d) overestimation of loads used to calculate settlement; and (e) the use of conservative settlement prediction methods. These obstacles have resulted in institutional biases and overly conservative and excessively costly institutional processes that lead to the unnecessary use of costlier deep foundation systems. The primary goal of this report is to promote the use of spread footings bearing on competent natural soils, improved soils, and engineered fill materials as a routine alternative to deep foundations for support of bridges by addressing the factors identified above. Documented performance data is used to make this case. The report also presents powerful concepts such as construction-point analysis and angular distortions to demonstrate the efficacy of using spread footings. Implementation of these concepts requires only that conventional computations be taken one step further without any requirement for advanced computational skills. The report presents sources of information that agencies and designers can use as references in their project applications. The report contains comprehensive appendices that treat in detail many of the topics discussed in the report. For example, one such appendix provides an introduction to Load and Resistance Factor Design (LRFD) that permits a rational approach to the consideration of spread footings on soils as a feasible alternative to deep foundations.
Author: Naresh C. Samtani
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 84
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Book Description
The FHWA believes that spread footings on soils are underutilized because designers encounter one or more of the following obstacles: (a) limited knowledge of AASHTO/FHWA technical references that pertain to spread footings on soils to support bridges; (b) limited knowledge of adequate performance data for spread footings; (c) unrealistic tolerable settlement criteria; (d) overestimation of loads used to calculate settlement; and (e) the use of conservative settlement prediction methods. These obstacles have resulted in institutional biases and overly conservative and excessively costly institutional processes that lead to the unnecessary use of costlier deep foundation systems. The primary goal of this report is to promote the use of spread footings bearing on competent natural soils, improved soils, and engineered fill materials as a routine alternative to deep foundations for support of bridges by addressing the factors identified above. Documented performance data is used to make this case. The report also presents powerful concepts such as construction-point analysis and angular distortions to demonstrate the efficacy of using spread footings. Implementation of these concepts requires only that conventional computations be taken one step further without any requirement for advanced computational skills. The report presents sources of information that agencies and designers can use as references in their project applications. The report contains comprehensive appendices that treat in detail many of the topics discussed in the report. For example, one such appendix provides an introduction to Load and Resistance Factor Design (LRFD) that permits a rational approach to the consideration of spread footings on soils as a feasible alternative to deep foundations.
Author: Shad M. Sargand
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 338
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Book Description
Spread footing foundations have been used to support various types of civil engineering structures over the years. However, one type of structure to which they have not seen much widespread application is highway bridges. This is because bridge engineers generally take a rather conservative approach and specify deep foundations, such as H-piles and drilled pier shafts, to support the bridge superstructure weight and live loads. In the current research project, the ORITE team continued to investigate several technical aspects related to spread footing foundations. Four additional spread footings constructed at two interstate highway construction sites were instrumented with modern sensors and monitored through construction stages and beyond. The spread footing design methods presented in the AASHTO LRFD Bridge Design Specifications (2004) were validated on the basis of the field performance data accumulated during the ORITE research project(s). Twelve SPT-based settlement prediction methods (for footings resting on cohesionless or slightly cohesive soils) were evaluated in light of the field performance data. General performance analysis of spread footing foundations at bridge construction sites was made to draw some guidelines concerning the use of spread footings for supporting highway bridge structures. Finally, detailed cost comparisons were made between spread footing and pile foundation options. Overall, the results of the research project indicated that: 1) spread footing can be a viable option as the highway bridge foundation; and 2) the design methods presented in the AASHTO LRFD Bridge Design Specifications (2004) appear to be satisfactory.
Author:
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 242
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Book Description
"A long-term study of the settlement performance of 21 bridge foundations supported on cohesionless soil-sand or silt- was completed to provide a reliable data base for engineering evaluation"--Abstract
Author: Shad M. Sargand
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 234
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Book Description
The performance of five highway bridge structures, located in Ohio and supported by spread footings on cohesionless soils or cohesive soils, was monitored in the field throughout construction and under service conditions. The performance of these structures was also examined through centrifuge modeling in the laboratory. Factors used in evaluating these bridges were overall settlement, tilting of abutment walls/pier columns, and pressure distribution under the footings. Field and experimental measurements were then compared against estimates made by selected geotechnical methods.
Author: Naser M. Abu-Hejleh
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages :
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Book Description
Recent FHWA national surveys revealed that State Departments of Transportation (DOTs) have safely and economically constructed highway bridges supported on spread footings bearing on competent and improved natural soils as well as engineered granular and MSE fills, and that many State DOTs may be missing an opportunity to save time and costs by not doing so more often. The goal of this report is to promote the consideration and use of spread footings on soils when appropriate to support highway bridges. Initially, perceived obstacles in using spread footings are identified. Then, the report presents recommendations to address these obstacles and a guidance to help State DOTs implementing these recommendations that are centered around: 1) deployment of AASHTO and FHWA technical resources; 2) highlighting practices of State DOTs that actively use spread footings, especially for selection of spread footings; 3) a performance review of bridges constructed with spread footings bearing on soils; and 4) LRFD implementation for spread footings. State DOTs' concerns with spread footings on engineered and MSE fills and with integral abutments are addressed. Consideration of load tests on spread footings, instrumentation programs for bridges with spread footings, and deployment of adequate subsurface investigation and construction programs are recommended. The main concern of State DOTs that do not consider spread footings is excessive settlement of bridges. This report advances a rational procedure for settlement analysis of bridges supported on spread footings bearing on soils. This procedure and the results of the national surveys demonstrate that bridges with spread footings on soil can perform very well with respect to settlement. Development of LRFD design bearing resistances for footings on various types of soils is discussed. Based on the previous recommendations, the report finally provides a technical resource for State DOTs to develop LRFD guidance that would allow selection of spread footings in design when appropriate, and development of accurate and economical design methods for spread footings.
Author: Chong Tang
Publisher: CRC Press
ISBN: 0429655959
Category : Technology & Engineering
Languages : en
Pages : 497
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Book Description
Model Uncertainties in Foundation Design is unique in the compilation of the largest and the most diverse load test databases to date, covering many foundation types (shallow foundations, spudcans, driven piles, drilled shafts, rock sockets and helical piles) and a wide range of ground conditions (soil to soft rock). All databases with names prefixed by NUS are available upon request. This book presents a comprehensive evaluation of the model factor mean (bias) and coefficient of variation (COV) for ultimate and serviceability limit state based on these databases. These statistics can be used directly for AASHTO LRFD calibration. Besides load test databases, performance databases for other geo-structures and their model factor statistics are provided. Based on this extensive literature survey, a practical three-tier scheme for classifying the model uncertainty of geo-structures according to the model factor mean and COV is proposed. This empirically grounded scheme can underpin the calibration of resistance factors as a function of the degree of understanding – a concept already adopted in the Canadian Highway Bridge Design Code and being considered for the new draft for Eurocode 7 Part 1 (EN 1997-1:202x). The helical pile research in Chapter 7 was recognised by the 2020 ASCE Norman Medal.
Author: Jamal Nusairat
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 39
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Book Description
The Ohio Department of Transportation (ODOT) needs to evaluate highway structures' performance supported on spread footings bearing on soils. This evaluation's outcomes are recommendations for future use of spread footings and potential limitations on their use. The project team completed the following tasks: 1. Reviewed the documented performance data. 2. Evaluated the performance of existing footings and compare to the bridge performance criteria. 3. Reviewed the calculated settlement. 4. Provided an estimate of the structure tolerable settlement at the foundation location. 5. Compared the measured settlement to the predicted long-term settlement. 6. Compared performance to soil conditions and calculated bearing pressures. 7. Reviewed IRI (International Roughness Index) and differential settlement between substructures. The data collected and the field review of all four sites included in this research showed that spread footing supporting structures perform as intended, and there were no signs of settlements and rideability issues. Spread footings constructed following the manuals and procedures by ODOT will perform satisfactorily. The requirements for monitoring of the settlement using rods specified in the plans need to be augmented with survey targets at the substructure units above finished ground for comparison and verification of plumbness of the substructure unit.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 838
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Book Description
Author: Fouad H. Fouad
Publisher: Transportation Research Board
ISBN: 0309087538
Category : Lampposts
Languages : en
Pages : 59
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Book Description
Author:
Publisher:
ISBN:
Category : Highway research
Languages : en
Pages : 44
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Book Description
