THE CONCRETE BRIDGE MAGAZINE

SUMMER 2018

ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

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F H WA 36 | ASPIRE Summer 2018 A c c o r d i n g t o F e d e r a l H i g h w a y Administration (FHWA) National Bridge Inventor y 2017 data, 9% of bridges are structurally deficient and 15% are older than the average design life of 70 years for bridges. 1 Widening, replacement, or significant rehabilitation of these bridges, particularly those in urban areas, is challenging because of mobility and traffic demands. In many cases, bridges will require superstructure replacement, while the foundation still has significant functional value. Therefore, reuse of these foundations can result in significant time and cost savings. Reconstruction Options Foundation reuse is herein defined as using existing foundation or substructure of a bridge, as whole or in part, when the existing foundation has been evaluated for ne w loads. Foundation reuse includes reuse of substructure components both above and below ground, including rehabilitation of existing substructure and foundation elements when the superstructure has been replaced. Figure 1 illustrates different foundation construction options with the following descriptions: 2 • In option 1, a new foundation is constructed that avoids the existing foundation. In this case, reconstruction is carried out at a new location without affecting the mobility on the bridge during construction, although switching to the new alignment may involve mobility impacts. • In option 2, the existing bridge foundation is demolished prior to construction of a new foundation. • In option 3, the existing foundation is reused as is, with or without minor repairs such as patching or chloride removal. • In option 4, the existing foundation is reused but with some form of retrofitting or strengthening. Options 3 and 4 illustrate foundation reuse. The remaining substructure elements of bridges in these two options may also be suitable for reuse, with or without rehabilitation. The for thcoming FHWA Best Practice Manual for Bridge Foundation Reuse (available summer 2018 at www.fhwa.dot.gov/research/ publications/technical) addresses critical issues encountered during decision-making on foundation reuse, such as assessment for structural integrity, durability, load-carrying capacity, repair, and strengthening. To highlight significant benefits of foundation reuse, the manual includes numerous case examples. Integrity Assessment Ex i s t i n g s u b s t r u c t u re e l e m e n t s b e i n g considered for reuse have been exposed to the environmental elements, and they were not necessarily constructed with quality assurance/control practices consistent with modern code requirements. To redesign existing foundations that are compliant with the American Association of State Highway and Transportation Officials' AASHTO LRFD Bridge Design Specifications, 3 there must be confidence in the material properties and the current condition of the substructure. Durability and Remaining Service Life At the forefront of foundation reuse are the following two questions: First, "How much remaining service life does the foundation have?" Second, "Will the advanced age of the reused components increase life cycle costs?" Some issues, such as chloride ingress or carbonation in concrete, may have reduced the service life remaining without yet creating noticeable damage. Repairs performed on issues identified during the integrity evaluation, such as spalling or delamination, can have service lives, or expected service life costs, unlike those of an intact structure. In many cases, strengthening is employed to simultaneously aid with both durability and capacity issues by repairing existing damage or planning for future deterioration that lowers the capacity of the damaged element. Capacity Assessment The overall goal of capacity assessment is to prove that a desired level of capacity exists Foundation Reuse: An Option for Bridge Reconstruction Projects by Frank Jalinoos, Federal Highway Administration Office of Infrastructure R&D Figure 1. Foundation reconstruction options. Figure: Federal Highway Administration. Option 1 Option 2

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