Fatigue effect in concrete

Fatigue effect is the loss of strength and eventual failure of concrete under repeated or fluctuating loads, even though the maximum stress is lower than the static strength. Microcracks at the aggregate-paste interface grow with each cycle until they join and cause rupture.

The fatigue strength of concrete for 10 million cycles is about 50 to 55% of its static strength (compressive or flexural). It is shown by an S-N curve and is important in bridges, pavements, crane girders and machine foundations.