Mechanical response of CFRP-reinforced hollow ultra-high strength steel circular tubes under static axial compression and bending loads: Experimental and numerical investigations

• CFRP-reinforced ultra-high strength steel columns are tested under compression load. • Combined effect of CFRP and steel grade on column performance are investigated. • Finite element models were developed and validated against experimental result. • The effect of column length on the effectiveness of CFRP reinforcement was studied. • CFRP provided more strength enhancement to columns with lower steel grade. This paper aims to investigate the mechanical performance of CFRP-reinforced hollow ultra-high strength steel (UHSS) circular tubular columns under static axial compression and three-point bending tests. Using CFRP sheets to strengthen steel members with the aid of epoxy as the bonding agent can increase the stiffness, strength-to-weight ratio, and corrosion resistance, which can extend the service life of structures while reducing maintenance requirements. Bare and CFRP-reinforced circular hollow section steel columns made of four different grades of steel, including mild steel (MS) grade 350 and UHSS grades 700, 800, and 1200, are examined. To explore the effect of shape, the results of circular hollow tubular sections are compared with square hollow sections. The load-displacement curves, strength and failure modes obtained from the large-scale experimental tests and nonlinear finite element (FE) models are discussed. Analytical predictions are also compared with experimental results. The outcome of this study will provide insights into the coupled effects of CFRP reinforcement and steel grade, in improving the static axial and lateral responses of the steel columns.