Optimum concrete filling ratio for partially filled noncompact steel tubes

Abstract

In this study, both experimental and analytical investigations have been carried out on noncompact Circular Hole Section (CHS) steel tubes with partial concrete filling. A total of nine specimens are tested as cantilever under flexural loading. The main parameters of the tests are the diameter-to-thickness ratio [D/t = 57, 80 and 101] and the ratio of concrete filling length measured from the fixed base [11–100% of the total length]. The test results showed that careful design of the filling ratio can prevent the occurrence of local buckling and hence increase the flexural capacity. An analytical model based on the moment-curvature analysis was also conducted to examine the behaviour of the partially filled steel tubes and estimate their ultimate capacities. The results of the model showed good agreement with the experimental results. The analytical model was then used in a wider parametric study to determine the optimum filling ratio for various (D/t) ratios and different steel grades. The study revealed that a maximum of 62% of concrete filling is enough to alleviate the expected local buckling and achieve the maximum capacity of the CHS tubes. This reduction in concrete portion saves at least 38% of the commonly used concrete volume required for the equivalent strength of the counterpart fully filled tubes.