Analysis of Prestressed Concrete Beams for Fatigue Loading

F atigue is a process of progressive permanent internal structural damage in a material subjected to repetitive stresses. Progressive growth of cracks and complete fracture of steel or concrete may result if the stress amplitudes are sufficiently large. There are several reasons given by ACE Committee 2151 to point out that the fatigue strength of concrete members may be an important design consideration. Several researchers have investigated the fatigue properties of prestressed concrete beams using experimental techniques. ze These investigations were undertaken mainly to evaluate the fatigue strength of prestressed concrete beams. A few publications also deal with increase in deflection and crack widths. An excellent review of these publications can be found in Reference 10. Using the experimental results available, AC! Committee 2151 has developed comprehensive recommendations to design reinforced and prestressed concrete beams for fatigue life. To the best of the author's knowledge, very little information on how to predict the increase in deflection and crack widths using the properties of the constituent materials is available for prestressed concrete beams. With the increasing use of prestressed concrete for offshore structures, bridges, containments, and other structures, such information is becoming vital. In this paper, a theoretical model is presented to predict the fatigue life, increase in deflection and crack widths of prestressed concrete beams using the fatigue properties of the constituent materials, namely concrete, prestressed and non-prestressed steel. The analytical expressions are compared with the limited experimental data available. It is hoped that with the availability of more experimental data and better understanding of some of the complex be-