Stress-Strain State of Centrally Compressed Concrete Filled Steel Tube Elements. Theoretical and Numerical Studies

Abstract

Compressed concrete filled steel tube elements exhibit a complex force resistance, primarily due to the presence of radial stress at the interface between the pipe and the concrete. For this reason, according to current regulations, even the strength of short, centrally compressed elements is calculated using methods based on empirical formulas. This paper proposes a methodology based on well-known relationships in solid mechanics and taking into account the key features of the force resistance of elements. The validity of this methodology, as well as the methods of EN 1994-1-1 and SP 266.1325800.2018, is assessed by comparing the calculation results with experimental data on specimens with large cross-sectional diameter from 530 to 720 mm. Additionally, numerical experiments were conducted to evaluate the stress-strain state of similar concrete filled steel tube specimens using computer modeling in ANSYS. The strength of volumetrically compressed concrete, radial stress in concrete, axial and circumferential stresses in a steel pipe, and the strength and axial strain of the specimens were compared. The results of the proposed methodology and numerical modeling virtually coincided with the data of physical experiments. Regulatory methods quite accurately estimate the strength of specimens, but they underestimate the ultimate stress in concrete by approximately 15% and significantly overestimate the compressive stress in tube. The data obtained should be taken into account when preparing a new version of the set of rules.