Date of Award

6-2019

Degree Name

Doctor of Philosophy

Department

Civil and Construction Engineering

First Advisor

Dr. Houssam Toutanji

Second Advisor

Dr. Upul Attanayake

Third Advisor

Dr. Xiaoyun Shao

Fourth Advisor

Dr. Daniel Kujawski

Keywords

RC Bridger, CFRP compositer, RC beams, fatigue, NSM, strengthening

Abstract

Bridges have a fundamental role in improving the effectiveness of highways and providing an expedient and express traffic system. Over time, Reinforced Concrete (RC) bridges degrade due to gradually increased traffic loads and environmental deteriorations. Subsequently, service loads might cause higher stresses in concrete and steel reinforcement than stresses considered in the design stage. This affects the structural performance of RC beams and leads to sudden fatigue failure. As such, there is an essential need for rehabilitation to avoid hazards and tragedies.

Carbon Fiber Reinforced Polymer (CFRP) composites are becoming widely used to strengthen RC bridges. Near Surface Mounted (NSM) technique has proven its advantages over other applied strengthening techniques. This study investigates several factors associated with the fatigue performance of RC beams strengthened with NSM CFRP reinforcement, such as: the effect of strengthening techniques on the fatigue limit of RC beams; the influence of loading history on the fatigue behavior of rehabilitated RC beams; the development of deflections, stiffness degradation, and energy dissipation of strengthened RC beams under different loading patterns; and the viability of an accelerated fatigue approach for developing a fatigue stress-life predication model of RC beams.

Analytical, experimental, and numerical analyses were performed to achieve the study’s objectives. Empirical fatigue stress-life prediction models for non-strengthened and strengthened RC beams were developed based on least-squares regressions of eighty experimental data points obtained from the literature. The proposed models have a satisfactory precision for design purposes.

The experimental program in this study includes eleven cast-in-place RC beams with dimensions of 152.4 × 152.4 × 1,521 mm. Specimens were tested under four-point bending configuration to simulate long-span RC beams. Monotonic tests were performed to determine the flexural static capacity, ductility index, and cracking patterns of non-strengthened and strengthened RC beams. The effect of CFRP strengthening techniques on the fatigue limit of RC beams was examined using Locati method. A non-strengthened RC beam, a RC beam strengthened with NSM CFRP reinforcement, and a RC beam strengthened with Externally Bonded (EB) CFRP sheet were tested under a step-like constant amplitude cyclic loading to failure. Accordingly, CFRP strengthening techniques increase the fatigue limit of RC beams and improve their fatigue responses. Strengthened RC beams showed less stiffness degradation and energy dissipation when compared to non-strengthened RC beams. NSM CFRP technique demonstrated a better flexural static strength and fatigue life than EB CFRP technique.

Six RC beams were tested to investigate the influence of loading history on the fatigue behavior of rehabilitated RC beams. Two of the six RC beams were strengthened with NSM CFRP reinforcement and tested as a reference under constant amplitude cyclic load. To simulate the condition of service traffic loading, the other four RC beams were cyclically pre-loaded then rehabilitated with NSM CFRP reinforcement. These specimens were tested under the same loading conditions of the reference specimens. The rehabilitated pre-fatigued RC beams had stiffness degradation and failure modes similar to the reference specimens. The pre-fatigue induced an under-stressing effect that extends the fatigue life of the rehabilitated RC beams. Moreover, the post-fatigue monotonic behavior of the rehabilitated RC beams showed an increase in the elastic modulus and a decrease in ductility within the flexural static capacity.

Finally, numerical analyses were performed to predict the fatigue responses of RC beams strengthened with NSM CFRP reinforcement, and to check the viability of an accelerated fatigue approach for developing a fatigue stress-life predication model. The accelerated fatigue loading has a higher rate of damage accumulation than the standard testing approach. The developed model fits the upper 95% prediction band of RC beams tested under constant amplitude cyclic loading.

Access Setting

Dissertation-Open Access

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