Abstract: In order to study deformation behaviors of concrete under cyclic loading, we performed axial cyclic loading and unloading tests of concrete were performed at two strain rates (10^-5/s and 10^-4/s).Relationship between the residual plastic strain of concrete and unloading point strain were analyzed,as well as the relationship between common point strain and the unloading point strain. Envelope curves of stress-strain under cyclic loading and unloading were fitted by using improved Weibull statistical model. The results show that,envelope curves of stress-strain under cyclic loading and unloading are basically in correspondence with stress-strain curves under monotonic loading; moreover ,envelope curves can be well fitted with the improved Weibull statistical model.

Key words: concrete, cyclic loading and unloading, deformation properties, envelope curve, strain rate