Date of Award

1-2010

Document Type

Thesis

Degree Name

Master of Civil Engineering (MCE)

Department

Civil Engineering

First Advisor

Tamer Mohamed El Sayed

Second Advisor

Khaldoun N. Rahal

Third Advisor

Amr EI-Dieb

Abstract

Strengthening of reinforced concrete (RC) structures with Carbon Fiber Reinforced Polymer (CFRP) composites has been a popular subject that attracted considerable attention from researchers for the last two decades. The high specific strength, stiffness, environmental resistance, and ease of application make CFRP composites highly desirable for strengthening and rehabilitation of RC structural components.

For concentrically loaded RC members with a circular cross-section, the lateral CFRP-confinement of concrete results in a substantial increase in load capacity and ductility. CFRP-confinement is less effective for RC compression members with square and rectangular cross-sections due to stress concentration at the corners and lack of confinement on the flat sides. In contrast to the large available data-base on concentrically loaded RC members confined with CFRP, research on eccentrically loaded CFRP-confined RC members is relatively limited. Findings of these studies indicate that the CFRP-confinement is less effective under eccentric loading relative to concentric loading. Very little information is available on the performance of CFRP-confined RC members under pure bending and biaxial eccentric loading conditions. The combined effects of the cross-sectional shape and loading condition on the effectiveness of the CFRP-confinement have received little attention in the literature.

The present work is initiated to investigate the performance of CFRP-confined RC members with various cross-sectional shapes under different loading conditions. A total of thirty-six specimens have been tested. The cross-sectional shape includes circular, square and rectangular with different aspect ratios. The loading conditions include concentric loading, uniaxial eccentric loading with eccentricity ratios of 0.46 and 0.6, pure bending, and biaxial eccentric loading with an eccentricity ratio of 0.3 about each principle axis. The test set-up, instrumentation, control and specimens' manufacturing are presented along with a full description of the experimental results.

Test results indicate that the CFRP-confinement effectively improves the load capacity and ductility under concentric loading. The gain in load capacity and ductility of concentrically loaded members is strongly affected by the cross-sectional shape. The CFRP-confinement also improve the performance of eccentrically loaded members but to a lower extent. For the level of confinement and uniaxial eccentricity ratios used in this study, the cross-sectional shape had a slight effect on the ductility of eccentrically loaded members where rectangular cross-sections exhibited lower gain in ductility relative to the square and circular cross-sections, but it had no noticeable effect on the gain in load capacity. For the members of pure bending, the CFRP-confinement had no significant effect on the flexural capacity but resulted in a remarkable improvement in the member ductility. The results show that the performance enhancement under biaxial eccentric loading is affected by the cross sectional-shape. The square cross-section exhibited higher gain in load capacity and ductility relative to those exhibited by the rectangular cross-section.

An analytical model that can predict the load capacity of CFRP-confined RC members under different loading conditions is presented. The proposed analytical model is based on realistic materials constitutive laws, and accounts for the non-linear stress-strain behavior of both unconfined and CFRP-confined concrete. It also accounts for the effect of the cross-sectional shape on the CFRP-confinement and the change in geometry caused by the lateral deformation under eccentric loading condition. The member cross-section is discretized into finite layers. For a given strain distribution, the sectional forces are integrated numerically and the load capacity is predicted using an iterative process. A comparison between the model's predictions and the experimental results demonstrated the accuracy and validity of the proposed model.

General conclusions of the work along with recommendations for future studies and developments on the structural performance of CFRP-confined RC members are documented.

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