LONG-TERM SHORTENING OF CONCRETE COLUMNS IN TALL BUILDINGS

The accurate estimation of the long-term shortening of the vertical members of tall concrete buildings is often an important issue in their design. Differences in the shortening of adjacent columns or between columns and the shear core can induce significant moments and shears in connecting floor slabs or beams. The effects of such differential vertical movements have to be carefully considered where adjacent vertical members are closely spaced, carry different loads, or have different cross sections. The total shortening of concrete columns consists of the sum of the instantaneous axial deformations and the deformations induced by creep and shrinkage. The paper describes a method for the prediction of the long-term axial deformations of reinforced concrete columns of tall buildings. The method is based on the incremental superposition procedure in which the stresses due to loads and creep and shrinkage are assumed to vary discretely at selected instants of time. Predicted values are shown to be in good agreement with column shortening measured in a tall building.