Experimental Study on Axial Compression Behavior of Concrete Doubly Confined in Square Steel Tube and Pectangular Hoops with Cross Ties

In order to study the axial compression behavior of concrete doubly confined in square steel tube and rectangular hoops with cross ties, a total of 20 specimens were tested. A main purpose of the experimental study is to discuss the application of the method of superposed strength on the compressive strength for confined concrete. Test specimens are plain concrete columns, concrete columns confined in rectangular hoops with cross ties, concrete columns doubly confined in square steel tube and rectangular hoops with cross ties. The size of these test specimens is 25cm x 25cm x 75cm. The axial maximum compressive strength and stress-strain curves on the basis of calculations using the known equations proposed by Mander or Sakino et al. are discussed and compared with experimental results on the axial compression behavior of concrete doubly confined in square steel tube and rectangular hoops with cross ties. As a result, the axial maximum compressive strength for the confined concrete can be roughly estimated by the known equations using the method of superposed strength