Publication Date

2012-07-18

Availability

Open access

Embargo Period

2012-07-18

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Civil, Architectural and Environmental Engineering (Engineering)

Date of Defense

2012-04-13

First Committee Member

Antonio Nanni

Second Committee Member

James Giancaspro

Third Committee Member

Wimal Suaris

Fourth Committee Member

Mohamed Fahmy

Abstract

In four studies, the live load factors for the design of reinforced concrete (RC) structures, and the strength reduction factors assigned to the elements that use FRP material as internal or external reinforcement, are reevaluated against the values in current practice. Taking advantage of the theory of the reliability of structures, Studies I and II incorporate the life-time into the live load factor of an RC element. To this end, a statistical model is established upon the recognized axioms about the probabilistic distributions of load and resistance and that the live load factor of 1.60, stated by the current building code for RC structures, may account for the variations of the live load in a period of 50 years. The outcome of these studies describes the live load factor as ascending functions of life-time, which meet the predetermined value of 1.60 for a life-time of 50 years. The same formulation also provides a solution to the problem of the effect of the under or over-design on the expected life-time of a member. Studies III and IV also employ the theory of reliability, but this time to calibrate the strength reduction factors of the elements that use FRP reinforcement. Study III concentrates on flexural members with internal FRP reinforcement, while the subject of Study IV is externally strengthened flexural members with the focus on near-surface-mounted (NSM) FRP bars. The novelty of Study III is the introduction of a new approach to the calibration of reduction factors which is referred to as the “comparative reliability”. The current North American guidelines that regulate the design of the RC members internally reinforced with FRP bars, derive their factors by targeting preset levels of reliability that are, sometimes, not even achievable by the ordinary steel reinforced concrete members. Conceding that the latter elements are of sufficient safety, the comparative reliability is a method to calculate the strength reduction factors of the newly introduced elements in harmony with the old ones. This approach to strength reduction factors minimizes the penalizing of one material in favor of the other, while maintaining a uniform level of safety for all. Unlike Study III, that uses a database of experimental results to obtain its essential statistical input, Study IV generates its own database of externally strengthened RC beams and slabs with NSM FRP bars, by benefiting from simulation techniques. The combination of the computerized simulation and comparative reliability creates an original approach to the calibration of the strength reduction factors of NSM systems, while in the current guidelines, the reduction factors are selected by judgment and consensus and lack a theoretical and experimental foundation. Furthermore, this study eliminates the current partial strength reduction factor, assigned by the current design guideline to FRP contribution, and achieves an inclusive factor for NSM FRP systems.

Keywords

life-time; limit state; reliability; FRP; reinforced concrete; NSM

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