Inelastic design of low-axially loaded high-strength reinforced concrete columns

The post-elastic behaviour of low-axially loaded high-strength reinforced concrete (HSRC) columns containing transverse reinforcement designed complying with the shear resistance requirement of BS 8110 and the authors’ proposed equation have been studied experimentally. Four HSRC columns, three for the former case and one for the latter, having concrete compressive cube strengths of about 85 MPa (cylinder strength of about 75 MPa) with cross-section dimensions of 325×325 mm were fabricated and tested under low compressive axial load as well as reversed cyclic inelastic displacement excursions. From the test results, it was observed that: (1) low-axially loaded HSRC columns designed according to BS 8110 behaved slightly ductile with the ultimate curvature ductility factor reached at least 7, (2) for a given range of volumetric ratio of transverse steel, the flexural ductility of low-axially loaded HSRC columns was not influenced by the transverse steel spacing that is less than three-quarters of the effective depth, (3) a series of single rectilinear closed-hoops of transverse steel was adequate for HSRC columns requiring to behave moderately ductile, and (4) the HSRC column containing transverse reinforcement calculated using the authors’ proposed equation behaved in a more ductile manner by achieving an ultimate curvature ductility factor of 12, which is higher than the normally assumed limited ductility measure of 10. Based on these results, some guidelines for the design of low-axially loaded HSRC columns are proposed.