Time‐Dependent Cyclic Deflections in R/C Beams

Abstract

A numerical integration method to predict the time‐related deflections of reinforced concrete beams, which includes cyclic loading and unloading, is presented. It requires little computer storage capacity. The major aspects of this method include the time‐dependent strains in the stress‐strain relationships for concrete compression and tension in terms of the creep coefficient, the creep‐moment‐curvature relationships, the deflection‐creep coefficient diagrams, and shrinkage deflections. Variations in the flexural stiffness caused by cracking are accounted for in the tension stress‐strain relationship in terms of maximum tensile stress. By applying the principle of strain superposition, the effect of loading history on the beam is incorporated into the creep coefficient for the specific concrete age at which deflection is desired. Deflections are determined from the deflection‐creep coefficient diagrams. The procedure eliminates the inconsistency in the zero strain surface location caused by superimposing deflection components from loading and unloading. Comparisons between the calculated deflections and test data from beams under cyclic loading and unloading are very good.