Strength and ductility of concrete filled steel tube with ultra-high strength materials

Abstract

In this study, UHSC about 150 MPa and UHSS about 960 MPa were combined to develop CFST beams and columns and leverage the properties of these two materials to evaluate the applicability of the existing design guidelines and design new models. Moreover, the influence of the spiral confinement of UHSC was investigated by using 24 test specimens of 150 mm diameter and 300 mm height concrete stub columns. CFST (fabricated with UHSC and UHSS) beams, beam-columns, and slender columns were experimentally tested. These experimental test specimens included 2 beams, 14 beam-columns, with eccentric loading up to 1.6 times the diameter of the column, and 8 slender columns including a slenderness ratio up to 108. The load-moment curve prediction for such CFST beam-column was also investigated. Similarly, the stability-slenderness curve prediction for such type of CFST slender column was also examined. These experimental test data were analysed against the prediction obtained from finite element simulations using ‘Abaqus’ software. After verifying the finite element model, parametric analysis was carried out for CFST with ultrahigh strength materials. Moreover, these experimental data were utilised to evaluate some major design code standards. A combination of the Eurocode 0 method and Kriging was also proposed to determine the safety factor for the CFST column with ultra-high strength materials. In this study, 150 MPa UHSC was produced in mass quantity using commercially available materials in Australia. The implementation of this UHSC for a spiral confined concrete column, with no longitudinal reinforcement, noticeably enhanced strength, and ductility when the spiral pitch was 25 mm, while a higher spiral pitch caused loss of the compressive strength of the concrete column due to spalling of the cover concrete. Further enhancement of the strength and ductility was also observed with CFST with UHSC and UHSS. Furthermore, CFST with additional spiral confinement provided significant ductility enhancement and strength gain compared to the corresponding CFST only. Although, the Australian Standards design code predicted load and moment capacities reasonably well for such CFST columns and beams, Eurocode 4 consistently predicted these capacities better. The reliability of CFST with UHSC and UHSS was found to be slightly more than CFST with normal strength concrete and mild steel. Furthermore, the initial cost of UHSC was found to be significantly higher than normal strength concrete due to expensive very fine silica sand rather than cement.

Date of Thesis submission	2023
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Kamyar Kildashti Komsari (Supervisor), Zhong Tao (Supervisor), Zhu Pan (Supervisor) & Won Hee Kang (Supervisor)