Analytical model of concrete-filled fiber-reinforced polymer tubes based on multiaxial constitutive laws

A model is proposed for predicting the compression behavior of axially loaded concrete cylinders confined by fiber reinforced polymer (FRP) shells. To capture the active confinement applied by the FRP, an orthotropic hypoelasticity-based constitutive law is used for the concrete. This law is defined the triaxial stress space. The confinement-induced concrete strength enhancements are computed from a four-parameter failure surface. The corresponding peak strain increase is computed using a newly proposed strain enhancement factor. The FRP shell behavior is modeled using a stress-strain relation for plane stress orthotropic laminated composites. The proposed model is implemented into an incremental approach for the analysis of compression tests. No iterations are needed to find the stresses corresponding to prescribed axial strains. The model is verified with correlation studies with different experimental tests on concrete-filled FRP cylinders.