Time-dependent analysis of frames taking into account creep, shrinkage and cable relaxation

Abstract

This paper describes a new relaxation model for steel tendons based on the equivalent creep coefficient to enable the accurate estimation of the losses of cable forces. The equivalent creep coefficients of steel tendons work not only in the case of intrinsic relaxation but also in cases of relaxation under various boundary conditions. Based on the proposed relaxation model, an accurate finite element analysis of timedependent behaviour of concrete structures considering concrete creep, concrete shrinkage and cable relaxation is devised based on the time integration method. Concrete members are modelled by beamcolumn elements while tendons are modelled by truss elements with nodes connected to the beam axis by perpendicular rigid arms. Finally, the individual and combined effects of concrete creep, concrete shrinkage and cable relaxation on the long-term behaviour of a prestressed concrete frame are studied. It is found that the proposed relaxation model and the time marching method can provide a reliable method for time-dependent analysis. The results obtained indicate that the interactions among these factors should be considered carefully in analyzing long-term behaviour of concrete structures.