Confinement of Prestressed Concrete Columns

Abstract

P restressed concrete columns have several advantages over columns reinforced with deformed reinforcing bars as the main vertical reinforcement. Besides being economical to construct and transport, prestressed columns make use of both concrete and steel more efficiently and require a smaller amount of longitudinal reinforcement. The precompression of concrete provides additional resistance to tensile stresses encountered during transportation and erection stages, and protects against accidental loads resulting from small eccentricities, Prestressed columns also have the added structural advantage of maintaining a higher uncracked stiffness longer to resist axial and transverse loads. Numerous investigations 14 have been carried out in the past to evaluate the effects of eccentricity, level of prestress, slenderness, and material properties on the strength of prestressed columns. In most of these and other similar studies, the effect of different types of lateral reinforcement on strength and ductility of prestressed columns was seldom a variable in the investigation. Considerable test data are available on the effect of lateral reinforcement on the ductility of nonprestressed columns, but similar information on prestressed columns is severely lacking. As indicated by the test results reported herein, the conclusions derived concerning lateral reinforcement from tests on nonprestressed columns may not be directly applicable to prestressed columns. Lateral reinforcement in prestressed columns is typically provided in the form of individual closed ties, the fabrication and placement of which can be quite labor intensive. The use of a continuous square spiral as lateral reinforcement has proven economical in precast piles and holds a similar promise in prestressed columns. Welded wire fabric is another type of reinforcement which, because of its economy in fabrication and placement, could possibly be used as lateral reinforcement in pre-