Derivation of complete stress-strain curve for SSTT-confined high-strength concrete in compression

For concrete structural behavior analysis, the complete axial stress-strain curves in compression can be determined by using a closed-loop servo-controlled hydraulic testing machine. The applied loading as well as the axial deformation reading of the loaded concrete specimen is recorded from the built-in displacement transducers or externally installed transducers placed between the machine platens. However, the recorded axial strain in the ascending branch is not purely concrete deformations but includes some additional deformation because of machine flexibility and specimen's end restraint. Strain gauges can be diametrically installed at the middle of specimen for a more precise deformation reading but additional costs are required for the gauges and data acquisition system. Moreover, the concrete stress-strain curve and ductility performance beyond its ultimate is difficult to be recorded without special strain measuring devices. Hence, a correction equation is needed to account for these effects to obtain the complete stress-strain curves for unconfined and confined concrete. In this paper, a total number of 84 unconfined and steel strapping tensioning techniques (SSTTs) confined high-strength concrete cylinders of compressive strength ranging from 62.48 MPa to 184.85 MPa were tested in compression in accordance with ASTM C39/C39M-11. The details for the testing setup, testing machine, strain measuring instruments, loading rate, loading patterns, etc. are described and at the same time a correction factor equation is proposed in this paper