Prediction of the elastic and inelastic shortening of reinforced concrete columns

摘要

A computer program, COLSHO has been developed to estimate the time-dependent shortening due to creep and shrinkage of reinforced concrete columns. In essence, the variation of both creep and shrinkage of concrete is an extremely complicated issue. Based primarily on experimental work, for years researchers have been developing methodologies to determine shortening of reinforced concrete columns caused by creep and shrinkage. None of the available literature provides information on the effects of construction sequence and the resulting varied loading conditions. In particular, for composite columns (steel encased concrete), shortening of the columns due to additional loads superimposed on columns is greatly influenced by the sequence of construction. Therefore, a rigorous procedure is implemented into a computer program developed in this study (COLSHO) to include the construction sequence. In addition, a modified modulus of elasticity for high strength concrete is used in the computer program which is executable on a personal computer. The input data is prepared in Excel worksheets and the elastic and inelastic shortening due to creep and shrinkage is calculated using a Fortran executable file. By utilizing a cumulative scheme, the effect of creep and shrinkage can be considered at either the end of the construction stage of each floor or at a certain period after the completion of the whole building. Application to actual design cases reveals quite accurate predictions using the proposed method. With the growing necessity to take account of the shortening of columns due to creep and shrinkage of concrete, the computer program COLSHO facilitates such assessment in design practice.