عنوان مقاله [English]
Prestressed concrete structures have become popular among the researchers and designers because of their ability to withstand loadings imposed to buildings mainly due to earthquakes. One of the major problems associated with concrete structures is their low resistance to tensile stresses. Cracks in concrete initiate from the very lower edge of its cross section where tensile stresses reach their peak value. To prevent concrete from premature cracking due to tensional forces, high-performance steel bars under tension could be utilized as a reinforcement method. Pre-stressed concrete beams are an example of where this design method is applicable. Structural performance characteristics such as failure loads, maximum loads, and ductility along with occurrence and extension of cracks in prestressed concrete beams have been studied by many researchers.
In this study, an attempt has been made to investigate the effects of increasing non prestressed bars having different arrangements in six concrete specimens. The present study further investigates how the amount and arrangement of non prestressed longitudinal and transverse bars can improve the performance efficiency of six prestressed concrete beam specimens fabricated with the same geometry and quality concrete under static loading. Seven strands cables with 0.5 inch diameter and grade 270, which were embedded in straight position inside concrete beams, were prestressed by post tensioning technique. As a result of the experimental plan carried out for this study, ductility appeared to increase significantly due to the addition of longitudinal and transverse bars, but brittle behavior of specimens decreases in final load. In addition to the failure load, the maximum load that is carried by each specimen were observed to follow a close relationship with the quantity of bars that were used to fabricate beam samples.
Steel bar arrangements turned out to play a major role in the occurrence and extension of cracks. In that, a well-designed steel bar arrangement can mitigate cracking potential and improve durability by high extents. One of the other conclusions drawn from the present paper is the advantage of using the whole capacity of beams against applied loads. Considerations regarding cost effectiveness and construction effort associated with each project may dictate the type of reinforced concrete needs to be implemented in designing structural beams.