EXPERIMENTAL STUDY ON AXIAL COMPRESSION BEHAVIOR OF CONCRETE COLUMNS CONFINED BY GRID STIRRUPS

In order to study the axial compression behavior of the confined concrete with grid stirrups of different strength and plain concrete of different axial compressive strength, the axial compression tests of 39 concrete square columns confined by grid stirrups were completed. The stirrups are made of HRB335, HRB400, HRB500 and HRB600 reinforced bar. The volume stirrup ratio is between 1.0% and 2.2%. The design strength grades of concrete are C20, C30, C40 and C50. The test results show that stirrups yield under the peak stress of confined concrete. With the increase of the stirrup characteristic value, the increasing degree of peak stress and peak strain of the concrete confined by grid stirrups increases and the descending branch of stress-strain curve become flat. According to the test results, formulas for calculating peak stress and peak strain of concrete confined by grid stirrups are obtained. The corresponding axial compression stress-strain model is established. The comparison with several typical stress-strain models of concrete confined by stirrups shows that: the results calculated by the axial compressive stress-strain model are in a good agreement with the test results, thusly another method for calculating the ultimate compressive strain of confined concrete is proposed.