Fatigue reliability analysis of prestressed concrete bridges

A model for the fatigue analysis of prestressed concrete bridges is developed. The uncertainties in the geometrical and mechanical variables involved in the problem are included. Traffic actions, thermal effects, and differential settlement are considered. The model also includes the nonlinear behavior under the action of external loads causing cracking. The S-N curves and the Palgrem-Miner hypothesis were chosen for the definition of the fatigue strength of the studied materials (reinforcing and prestressing steels). The fretting fatigue effect is considered in the definition of the resistance of posttensioning steel strands. This effect causes a very significant drop in the fatigue resistance of these elements predicted after tests in air. Weibull distributions are adopted for describing the uncertainty in the definition of the fatigue strength of the steel elements. The limit state functions for the fatigue assessment of reinforcing and prestressing steel-are derived. Finally, the statistical definition of the variables affecting the fatigue resistance of posttensioning steel strands under fretting conditions is given. The variability of the random variable damage of Miner at failure is derived from the variability in the S-N curves and a model for the calculation of the parameters of the cumulative distribution function is also proposed. The paper shows that the calculation of the reliability index of posttensioned concrete bridges under fatigue is a straightforward process.