BEHAVIOR OF RC CONTINUOUS SLABS STRENGTHENED BY EXTERNAL PRESTRESSING SYSTEMS

Abstract

External prestressing is a post tensioning technique where the prestressing reinforcement strands are placed outside the concrete elements. The prestressing force is transmitted to the structural element through mechanical anchorages and deviators. It is one of the widely used methods of enhancing the flexural strength of the Reinforced Concrete (RC) slabs because it is fast, effective, and economic compared to other strengthening techniques. In addition, external prestressing is an active method of strengthening since it results in closure of the concrete cracks and partial retaining of the member’s deflection. On the other hand, application of external prestressing systems to strengthen RC continuous slabs needs more research to have a full understanding of its behavior due to its complexity arising from the moment redistribution in the statically indeterminate members and large slab deformations affecting the stress level of the prestressing steel. On the other hand, external prestressing is a fast applied technique in case of strengthening distressed concrete structures. It is also a useful tool to construct new bridges with advantages such as better ductility and ease of maintenance, compared to traditional prestressed concrete bridges. The “Truc de la fare” bridge, which was built in France in 1993 can be considered a good example for using external unbonded prestressing steel system. Clearly, Analysis of externally prestressed members is different from that with bonded prestressed steel and members with internally unbonded prestressed steel. This is due to lack of bond between steel strand and concrete in addition to the large deformations, which requires taking into consideration the second order effect. The reduction in the effective depth of the steel strands during loading should be also accounted for. A large number of experimental investigations has been directed to study the flexural behavior of simple (single-span) prestressed elements. However, less researches and studies addressed the behavior of multi-span concrete members externally strengthened with steel strands. In this research, an experimental study is conducted to investigate the flexural behavior of two-span continuous slabs strengthened with external prestressing steel strands and CFRP laminates using different profiles. Deflections, cracking patterns, support reactions, stiffness, moment redistribution and ductility of the tested specimens are discussed in this study. Comparison between the behavior of specimens is also introduced to evaluate the different profiles, which are used in this study, in terms of easy installation of profiles and the overall gain in strength for specimens.

An experimental study is conducted to investigate the flexural behavior of two-span continuous slabs strengthened with external prestressing steel strands and CFRP laminates using different profiles. Comparison between the specimens' behavior is introduced to evaluate the best profile in terms of strength and easy installation.

Keywords: external prestressing; prestressed concrete; continuous slabs; flexural strength; deflection; strengthening.