Effects of Creep on the Strength of Eccentrically-Loaded Slender Reinforced Concrete Columns

Abstract

Creep and shrinkage effects in concrete structures increase deformations over time but do not normally affect the strength of the structure in any appreciable way. However, for a concrete structure which is subject to second order effects, the loads experienced by the structure are dependent on its deformed shape and therefore the capacity of the structure to withstand the applied loads is dependent on the way it deforms over time. A slender reinforced concrete column is such a structure. This paper presents a first-principles method of analysing the time-dependent behaviour of slender concrete columns subjected to sustained eccentric loads and compares theoretical estimates of critical loads (at which the strength of the critical cross-section is exceeded by creep-induced internal actions) to the allowances made for the design of slender concrete columns by the Australian Standard for Concrete Structures AS3600-2009. In particular, the effects of the concrete compressive strength and the reinforcement ratio are investigated in terms of their influence on the creep-induced reduction of strength of slender columns. The method is based on the principle of superposition and makes use of the age-adjusted effective modulus method to predict the time-dependent behaviour of columns.