BEHAVIOUR OF PRESTRESSED HIGH STRENGTH CONCRETE BEAMS IN FLEXURE

Abstract

In recent years, high strength concrete (HSC), has gained a wide acceptance and many new high-rise reinforced concrete structures have been designed with compressive strength ranging from 60-150 Mpa. High strength concrete concrete (HSC) is preferred in prestressed concrete, as the material offers high resistance in compression. In the zone of anchorages, the bearing stresses being higher, HSC is invariably preferred to minimize the costs. However, HSC has been found to be more brittle and has a lower shear resistance than normal strength concrete (NSC). The deficiencies of low tensile strength and insufficient ductility are minimized by providing conventional steel in the tensile regions of the concrete cross-section. Further, short discrete fibres are often introduced in to the cement concrete matrix to enhance the concrete resistance to crack propagation, reduce the crack width and increase the ductility of the member. Partially prestressed structures are those in which certain tensile stresses are permitted in concrete at full service loads and this can be achieved by using less prestressed steel and adding some mild or deformed steel for reinforcing. TheSleads to economy i.e., significant reduction in overall cost of the structure. There are certain disadvantages that restrict their usefulness. These are i) early appearance of cracks, ii) greater deflection under overloads and, iii) higher principal tensile stresses under working load. In order to make it more useful its design must satisfy the limit state of serviceability criteria. With this reference this study has been done to investigate the behaviour of steel fibre reinforced partially prestressed concrete structure with regard to cracking and deflection. For this purpose 5 partially prestressed concrete beams and 2 reinforced concrete beams were casted. Prestressed concrete beams each having same prestressing steel (2 No.-7mm0) and untensioned reinforcement (2 No.-10mmO) and reinforced concrete beams having (4 No.- 1 Omm0) but with different fibre content. In order to study the effect of increase in fibre content, in these beams percentage of steel fibre is increased keeping the untensioned reinforcement same and the experimental results have been compared with existing literature and codal provisions.