Publication Date

2019-10-31

Availability

Open access

Embargo Period

2019-10-31

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Civil, Architectural and Environmental Engineering (Engineering)

Date of Defense

2019-10-04

First Committee Member

Antonio Nanni

Second Committee Member

Landolf Rodhe-Barbarigos

Third Committee Member

Wimal Suaris

Fourth Committee Member

Fabio Matta

Fifth Committee Member

Carlo Poggi

Sixth Committee Member

Saverio Spadea

Abstract

Corrosion of steel reinforcement is the primary cause of durability problems in aged Prestressed and Reinforced Concrete (PC and RC) structures. Fiber-Reinforced Polymer (FRP) reinforcement is a reliable non-metallic solution, able to ensure the required mechanical performance and ensure long-term durability. This dissertation includes three self-contained but closely related studies that tackle three fundamental components of applied research: field deployment and critical assessment of existing technologies; development and investigation of innovative solutions; and, generation of new knowledge. The first study addresses the opportunities and challenges related to Carbon FRP (CFRP) prestressing while developing the design, construction, and load testing of a short-span bridge entirely reinforced and prestressed with FRPs. The lack of design guidance was identified as a limiting factor for wider applicability of FRP prestressing. To address this knowledge gap, a unified framework was developed for the design of FRP reinforced and prestressed structures that was later formalized in the second edition of the AASHTO LRFD Bridge Design Guide Specifications for GFRP-Reinforced Concrete and is consistent with the first edition of the AASHTO Guide Specifications for the Design of Concrete Bridge Beams Prestressed with CFRP Systems. The experience gathered highlighted some limitations of CFRP prestressing including the inherent complexity of the tensioning operations, the brittleness at pull, the tendency to cause concrete splitting, and the relevant material cost. Therefore, in the second study, mild pre-tensioning using GFRP reinforcement was proposed as a novel approach to the design and construction of those elements that require a relatively low level of prestress and are most exposed to environmental weathering and chloride penetration in coastal areas. To limit the level of prestress greatly eases tensioning operations and allows to use traditional steel anchors available at any precast yard. It also prevents failures at pull and concrete splitting. The use of a cost-efficient material system that is also less prone to prestress losses offsets the need for a larger number of strands. Experimental evidences to support this innovative approach are gathered for the first time on a prototype GFRP strand specifically developed through a federally-funded partnership with industries. To be effectively used in prestressing, a material system must maintain its initial pull without delayed failures. Historically, the main limitation to GFRP prestressing laid in the relatively low creep-rupture strength reported in codes and standards because of the lack of experimental evidence and reliable predictive models in archival literature. To address this gap, the third study collects and analyzes a large number of creep-rupture and tensile test results to develop a rational predictive model based on statistical considerations. This novel approach allows for a reliable assessment of the long term properties of GFRP reinforcement and shows how previous limitations may be overly conservative and GFRP can be effectively used in prestressing applications.

Keywords

Bridges; Creep rupture; CFRP; GFRP; Prestressed concrete; Prestressing strands

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