Fatigue of concrete and its effect upon prestressed concrete beams

The paper reviews the extensive literature on fatigue of concrete and summarizes the most important conclusions. Fatigue hardening of the compressive zone and fatigue softening of the tension zone are examined in detail, and the authors' tests to verify these effects are described. The effects are illustrated by suggested transformations in equivalent section properties in members subjected to fatigue. The increase or decrease of fatigued strength is plotted against maximum stress in the fatigue stress range. It is finally concluded that, with a load factor of 2 specified in the Code of Practice for prestressed concrete, fatigue is never likely to be a design criterion for strength.