Behavior of Rectangular Partially Prestressed High Strength Concrete Beams

Abstract

In the last few decades, prestressed concrete has been rapidly used in bridge engineering due to the enormous development in the construction techniques and the increasing need for long span bridges. High strength concrete has been also more widely spread than the past. It currently becomes more desirable as it has better mechanical properties and durability performance. Major defect of fully prestressed concrete is its low ductility; it may produce less alarming signs than ordinary reinforced concrete via smaller deflection and limited cracking. Therefore, partially prestressing is considered an intermediate design between the two extremes. So, combining high strength concrete with partial prestressing will result in a considerable development in the use of prestressed concrete structures regarding the economical and durability view points. This study presents the results of seven partially prestressed high strength concrete beams in flexure. The tested beams used to investigate the influence of concrete compressive strength, prestressing steel ratio and flange width on the behavior of partially prestressed beams. The experimental program was conducted on seven partially prestressed concrete beams with total length of 4800mm.The beams were simply supported with 4500mm clear span and 150mm projection at each end. All the beams were 150mm wide and 250mm deep for all the five rectangular sections. The web of the T-section specimens was similar to the rectangular ones while flange widths were 350 and 550mm. The experimentally observed behaviors of all beams were presented in terms of the cracking load, ultimate load, deflection, cracking behavior and failure modes. Strains at the bottom longitudinal reinforcement steel and concrete (top and reinforcement levels) were also measured so as to monitor the strain propagation across the concrete cross section The research program developed an analytical approach to predict the behavior of the partially prestressed high strength beams under the studied parameters. The program based on rational and empirical methods available in the literature to model both deflection and crack width of partially prestressed high strength concrete. Failure modes and ultimate carrying capacity of the beams were predicted and then compared to the experimental values.