Creep Buckling of Reinforced Concrete Columns

The effect of creep on the buckling strength of pinned, axially-loaded, initially-bent reinforced concrete columns under static sustained loading is investigated. An unstable column is defined as one which collapses before a finite desired life time has elapsed. The analysis is geometrically linear, physically nonlinear and quasistatic. The governing equations, which are of the quasilinear parabolic type, are solved by approximate mathematical and numerical methods. A digital computer program, which solves for the life time of a given column, is developed, Elasto-plastic buckling induced by creep is found to be the only important creep buckling mode. This mode is called indirect creep buckling. Results are given by graphs for the critical loads for short-time and sustained loading as functions of the slenderness and the initial imperfectness. They show that creep can significantly reduce the capacity of the type of columns investigated. The most important parameters affecting the reduction factor are the slenderness and the initial imperfectness of the column, the creep coefficient, the relative amount and yield stress of the reinforcing steel.