This report reviews theoretical investigations which have been conducted to determine the behaviour of reinforced concrete, prestressed concrete and structural steel elements subjected to well defined repeated and reversed loading of high intensity. It commences with a brief summary of the stress-strain characteristics of the materials under such loading in the plastic range and then reports on theoretical methods for determining the moment-curvature and load-displacement characteristics of the members. Some consideration is also given to complete structures. Areas where future research is necessary are indicated.