Behavior of Reinforced Concrete Under Repeated Load

An experimental investigation of strains, stresses, crack widths and end slips in axially reinforced concrete prisms subjected to repeated tension loads is presented. Cylindrical specimens were reinforced with deformed steel bars. To obtain the strain distribution along the length of the bars, these were sectioned longitudinally, grooved for installation of 30 strain gages along the length, and after wiring the gages, the sections were rewelded to form instrumented bars with effectively undisturbed exterior. The specimens were subjected to repeated loads at different stress levels. Residual effects after unloading and changes in strain distribution which results from prior loading history are analyzed. Results show that effectiveness of stress transfer between concrete and steel depends primarily on the magnitude of the previous maximum load. The greater the magnitude of this load, the lesser is the effectiveness of stress transfer at subsequent lower stress levels. Analytical evaluations of the effects of shrinkage and tension loading are also presented. The results of these evaluations give an insight into the phenomena of cracking and stress transfer between steel and concrete.