United States Department of Transportation
i
Implementation Guide for Using Spread Footings on Soils to Support Highway Bridges
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2014-05-01
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[PDF-1.17 MB]
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Abstract: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 using 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.
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Content Notes:This report is issued by the FHWA Resource Center as a deployment aid to help highway engineers and agencies recognize the value of spread footings and overcome obstacles to their effective use. This report reinforces and supports the guidance for selection, design, and construction of spread footings provided by the AASHTO and FHWA technical references cited herein.
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