CONFINEMENT OF PRESTRESSED CONCRETE COLUMNS
ELIAS, HANI ELBAYADI
Doctor of Philosophy
Prestressed concrete columns generally have a much smaller amount of longitudinal reinforcement compared to reinforced concrete columns and the confinement of the core is thus provided mainly by the lateral reinforcement. The main objective of this study was to evaluate the need for lateral reinforcement and its influence on the confinement in short prestressed concrete columns. In the experimental part of this investigation, twenty-three specimens were tested under axial loading. Primary variables were the type and amount of lateral reinforcement. Three types of lateral reinforcement were investigated: conventional ties, continuous square spiral and the welded wire mesh. The volumetric ratio of lateral reinforcement to concrete core was varied between 1.09% and 2.18%. Experimental results showed that lateral reinforcement was much more effective in increasing the ductility than the strength. It was also found that the currently available analytical confinement models did not accurately represent the behavior of prestressed concrete columns and considerably overestimated the strength in the post-peak loading region. Therefore, based on the observed behavior, an analytical model for predicting the stress-strain relation of confined concrete in axially loaded precast prestressed concrete columns with rectilinear lateral reinforcement is proposed. The ascending part of the model consists of a second degree parabola followed by a linear segment and an exponentially decreasing curve. This model takes into account any increase in strength and ductility resulting from lateral reinforcement, and more realistically represents the post-peak behavior. Finally, some design implications are suggested and the concept of strain ductility factor as a measure of ductility is proposed.