Size Effect in Brittle Failure of Unreinforced Pipes

Unreinforced concrete pipes basically can fail in two modes: beam failure and ring failure. According to the existing test data, the nom· inal stress at beam failure is much less than that at ring failure. Fur· thermore, the nominal stress for either failure mode decreases as the pipe diameter or thickness increases. These size effects can be de· scribed in a unified manner by means of the recently established sizeeffect law for failures which are preceded by the formation of microcracking zones. A simple formula involving the size effect is proposed and is justified by comparisons with existing test data.