The bearing capacities of concrete-filled steel tubes are normally derived through experiments with small-scale specimens, but it\nis uncertain whether such derivations are appropriate for the much larger components used in practical engineering. This study\ntherefore investigates the effect of different diameters (219, 426, 630, and 820 mm) on the axial compression of short concrete\ncolumns in steel (Q235) tubes. It is found that the peak nominal stress decreases with increasing specimen size and that the axial\nbearing capacity is determined by three separate components: the cylinder compressive strength of the concrete, the improvement\nin strength due to the confining effect of the steel tube, and the longitudinal strength of the steel tube. At peak load, increases in the\nspecimen diameter reduce the hoop stresses in the steel tube, thereby reducing the strengthening effect of confinement. Vertical\nstress in the steel tube is increased with diameter; therefore, the axial bearing capacity of the steel tube is directly related to the\nspecimen size. Size effect coefficients for these three aspects of bearing capacity are defined and used to develop a size-dependent\nmodel for predicting the axial bearing capacity of large, concrete-filled steel tubes.The model is then validated against experimental\ndata.
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