Experimental Research on Influence of Loading Methods to Behavior of Concrete Filled Steel Tubular Stub Columns under Axial Loads

The concrete filled steel tubular(CFST) structure has wide application prospects in construction of railway arch bridges and piers.Four different loading methods of the CFST structure used in real engineering projects are presented,which are loading on the full section,on only core concrete and on only steel,and the steel tube having initial stresses.Experimental research on influence of different loading methods to behaviors of CFST stub columns subjected to axial loads is carried out.Analyses results indicate that for the specimens subjected to loading on the full section,on only core concrete,and on the steel first and then on the full section(with an initial stress),the ultimate load carrying capacities are similar but the hooping effect and stiffness are different to some extent.For the specimens under a load acted only on the steel tube throughout the whole process,the ultimate load carrying capacity and stiffness decreases obviously,the hooping effect of outer steel on core concrete can be neglected.Lastly,the estimating method of the ultimate load carrying capacity for CFST stub columns under four axial loading methods are analyzed and discussed.