Steel-Encased Expansive Cement Concrete Column

The use of high-strength thin steel tubes filled with expansive cement concrete results in the fabrication of very efficient composite columns. An optimization study shows that the condition for achieving maximum elastic range during loading of such columns is that the ratio between the longitudinal and the circumferential stresses in the steel tube developed prior to loading, due either to expansion or other means of prestressing, should be the same as that induced by the loading. Results obtained in previous investigations shows that the ratio of circumferential to longitudinal stresses in the steel tube due to expansion of the concrete prior to loading is considerably larger than that induced during loading. The writers investigated experimentally the use of circumferential prestressing of the empty steel tube for improving such a ratio. The evaluation of the results obtained in the experiments carried out on four short high-strength thin-wall steel tubes, proved the validity of the results obtained in the optimization studies and shows that the initial prestressing not only increases the available elastic range of the composite element for service load but also increases its inelastic range with consequent improvement of ultimate strength, ductility and energy absorption capacity.