lllustration of the theory -----Transverse confine (侧向约束) can greatly increase axial compressive strength >Spiral stirrups ,(螺旋箍筋) f=fc+40 Steel tube concrete (钢管混凝土)------Transverse confine （侧向约束）can greatly increase axial compressive strength ØSpiral stirrups（螺旋箍筋） f=fc+4σr ØSteel tube concrete （钢管混凝土）