Axial compressive behavior of square concrete-filled steel tube columns with high-strength steel fiber-reinforced concrete

Adding fibers in the concrete is a practical approach to improving the deformation capacity of square concrete-filled steel tube (CFST) columns with high-strength concrete (HSC). To investigate the axial compressive behavior of square CFST columns with high-strength steel fiber-reinforced concrete (HSSFRC), 23 specimens were tested under monotonic axial compression, among which five specimens used an innovative testing method to directly obtain the load components of the steel tube and concrete infill. The test variables included the concrete compressive strength, the fiber volume fraction, and the yield strength and width-to-thickness ratio of the steel tube. The test results demonstrated that adding steel fiber basically did not change the failure modes of the specimens. In general, better postpeak behavior was observed as the fiber volume fraction increased; how-ever, for the specimens with 130 MPa matrix concrete, adding steel fibers of a volume fraction of 0.75% basically did not bring any improvement. When the confinement index was between 0.29 and 1.43, the compressive strengths of the HSC or HSSFRC in square CFST columns were close to the corresponding unconfined concrete strengths. Based on the test results, an average stress-strain model was developed for the HSC or HSSFRC in square CFST columns.