An Analytical Investigation of Modular Concrete-filled Square Steel Tubes based on the Strain Compatibility

Abstract

Concrete-filled square steel tubes demonstrating good structural resistance against vertical and lateral loads can be used for modular constructions. To promote the applications of the composite tubes to modular construction, it is important to provide simple but accurate analytical methods that can elucidate the structural behaviour of the composite tubes. A number of international design codes are known to calculate the flexural load bearing capacity of the concrete-filled square steel tubes. Some, however, are not predicting the behaviour of the composite tubes accurately. An analytical investigation of concrete-filled square steel tubes was presented in this paper. A strain compatibility based design method considering confinement effect of concrete in tubes was proposed to estimate the flexural strength of composite steel tube filled with concrete. Nominal moment capacities estimated in accordance with the standards of AIJ(Japan), AISC(USA), Eurocode4(Europe) and KSSC(Korea) were compared with the analytical value obtained using the strain compatibility based design method. Since the design method with strain compatibility proposed in the study reflects the concrete confinement with accurate estimation of the neutral axis of composite tube section, the flexural moment capacity of composite tube section can be accurately obtained. The test results of other researchers including Lu and Kennedy were used to verify the reliability of the proposed design method. These experimental results were shown to be the best correlated with the analytical results provided by the proposed method in this paper than any other analytical methods proposed by the international codes that were used to calculate flexural load bearing capacity. The 6% of errors were demonstrated by the proposed approach while bigger errors were observed in the analytical calculations of other design codes as large as 17%.