Ermüdung von Spannbetonträgern mit Bügelbewehrung unter Querkraftbeanspruchung

Fatigue of prestressed beams with web reinforcement under cyclic shear

Many existing bridge structures built in the 1960s and 1970s typically feature a high degree of prestressing and low shear reinforcement ratios. Therefore, their shear bearing capacity, originally determined based on the principal tensile strength criterion, can often not be verified with the strut and tie models of DIN-Fachbericht 102. To investigate the shear strength of prestressed concrete beams with web reinforcement under cyclic loading, fatigue tests on 14 beams with a low amount of shear reinforcement (&rgr;w = 0,15%, &rgr;w = 0,22% and &rgr;w = 0,33%) were performed.
The present paper describes the fatigue tests and the occurring gradually stirrup fractures with increasing number of load cycles. Based on comparative calculations and the experimentally determined strut inclinations, a modified approach to calculate the stirrup stress amplitude under cyclic loading has been developed. It is based on a truss model with variable strut inclination.