Seismic behavior of 200 MPa ultra-high-strength steel-fiber reinforced concrete columns under varying axial load

Cyclic loading tests were carried out on ultra-high strength RC columns under high axial load conditions. Effective concrete strength of 200 MPa with high-strength steel fibers (SF) was used. The investigated parameters were: 1) volumetric ratio of steel fiber, 2) lateral reinforcement ratio, and 3) axial loading type. The main characteristics of the tested columns (maximum strength, deformation capacity and equivalent viscous damping factor) are presented and the influence of various parameters is discussed. The test results revealed the advantage of using SF in terms of strength and damage control. The maximum strength of the tested columns using SF, assessed using a number of different formulas, proved to be on the safe side. On the other hand, in the case of columns in which SF was not used, the estimated maximum strength was found to be larger than the tested value, except when using NZS3101 equation. This difference is probably due to early spalling off of the cover concrete.