Research on design and calculated methods of concrete filled steel tube columns with initial stress under axial loads

Applying finite element method,the elastic ultimate load and plastic or stability ultimate load corresponding to the allowable stress method and ultimate state method of concrete filled steel tube(CFST) columns with initial stress under axial loads are calculated and analyzed.Results indicate that it is impossible for the steel and concrete stresses reaching their allowable stress simultaneously in generally,but the stress of steel is more feasible for the checking stress than the concrete's for the suited match of CFST.It can be regarded as the elastic ultimate load when the moment of the steel tube is yielded.The allowable stress method for calculating elastic ultimate load of members and structures of CFST is irrational in practice engineering.The presence of initial stress drops the elastic ultimate load more distinct than the strength and the ultimate load-carrying capacity.The ratio of elastic ultimate load to plastic ultimate load is decreased with the increasing of initial stress degree(ISD) and allowable stress method is conservative.As to the CFST arch bridge with large ISD,the ultimate state method is suited to use in practical engineering.