Title

Design and Implementation of a New Retrofit for Prestressed Concrete Bridge Elements Using Mechanically-Fastened Fiber-Reinforced Polymer

USMA Research Unit Affiliation

Center for Innovation and Engineering, Civil and Mechanical Engineering

Date of Award

3-7-2019

Degree Type

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

Department

Department of Civil, Construction, and Environmental Engineering

Abstract

Currently, departments of transportation (DOTs) must post load restrictions or closures on bridges with deteriorated prestressed concrete superstructures that can no longer carry original design loads. These posted restrictions and closures result in detours that increase travel time and vehicle operating costs for detoured vehicles, impacting commerce, public transportation, and emergency services. Often, load restrictions and closures must remain in place for several years to allow for budgeting, design, and contracting cycles prior to scheduling and completion of permanent repairs or superstructure replacement which must occur to remove posted restrictions. A retrofit solution, which is capable of restoring prestress losses and strength reduction in mild to moderately deteriorated prestressed concrete bridge superstructures such that the useful service life of the bridge can be extended for 3 to 5 years allowing a more permanent solution to be planned and budgeted, would be useful. A practical retrofit alternative is one that that can be installed relatively rapidly by DOT maintenance personnel, can immediately restore traffic upon installation, can be easily inspected and maintained as necessary, and should not be more costly than user costs associated with load restrictions or closures. The thesis describes the results of an experimental program to examine the practical and technical feasibility of restoring prestress losses in deteriorated prestressed concrete C-channel beams using a mechanically-fastened fiber-reinforced polymer (MF-FRP) retrofit methodology. This study found that the developed MF-FRP retrofit methodology is capable of restoring the original bridge load rating and can be installed by a single DOT maintenance crew within 1 to 2 days, depending upon the length and level of deterioration of the candidate bridge. Small-scale testing to optimize the mechanical anchor pattern with respect to the capacity of the FRP material was examined and the number of fasteners required for a typical application was determined. A prestressing mechanism for the retrofit and connection design to attach the MF-FRP retrofit system was developed, including effects of the significant spatial restrictions found in the field. The methodology was optimized with respect to FRP efficiency and retrofit installation time. The MFFRP retrofit solution was tested on 6 full-scale prestressed concrete C-channel beams recently removed from service. The full-scale tests examined the behavior of the undamaged (control) and deteriorated beams with and without the MF-FRP retrofit. The results of the full-scale tests indicated that the MF-FRP retrofit solution presented in this study is capable of restoring the original load rating of prestressed concrete C-channel beams with mild to moderate prestress loss due to deterioration, and it is feasible for the MF-FRP retrofit to be rapidly installed on-site on a bridge and immediately restore traffic upon installation. Technical limitations and difficulties with field installation techniques used in the initial design resulted in significant changes in both the design and field-fabrication methods. Basic production rates for the initial and improved designs were determined, confirming that the field installation can be completed in as little as a single work day by a typical 4-worker DOT maintenance crew. Additionally, a limited qualitative cost comparison indicates that the proposed MF-FRP methodology is economically feasible with the break-even point between the initial installation and material cost to the DOT and the vehicle operating cost savings occurring between a few days and a few months, depending upon the traffic volume, detour length, and posted restriction level for a deteriorated bridge.

USMA Research Goals Supported

Develop the Faculty Professionally, Address Important Issues Facing the Army and Nation

Partnered Organization(s)

North Carolina Department of Transportation

First Advisor

Dr. Rudolf Seracino

Second Advisor

Dr. Min Liu

Funder

North Carolina Department of Transporation

Publisher

North Carolina State University

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