Fatigue reliability of AASHTO girders

The dissertation deals with the problem of fatigue changes in AASHTO concrete girders and their effect on girders reliability. Assessing the reliability of girders as bridges' main structural component is carried out in this study. The girders are designed based on the current AASHTO LRFD Bridge Design Specifications 2010.;The four types with the greatest maximum spans of the six Types of AASHTO Girders are considered. The girders are analyzed and designed according to latest code, Strength Limit State and Serviceability Limit States. Traffic load is the only dominate source of fatigue on small and medium span bridges. Since this study is concerned with the fatigue reliability, the live load applied in design is the fatigue live load defined by the code. Reliability analysis of the Girders is developed twice. First one developed reliability index at design using Monte Carlo simulation based on strength analysis of the composite section of AASHTO Girder with deck. Second analysis covers fatigue reliability analysis of the same designed girders considering measured fatigue live load effect that causes fatigue after 75 years. The fatigue analysis considered the cyclic nature of traffic loads, traffic growth, time-dependent losses due to creep, shrinkage, and relaxation, fatigue damage of materials, transformation of section and composite action between girder and deck. The statistical parameters of fatigue strength for bridge concrete components after 75 years are developed considering cumulative damage models using a complex model software program. Statistical parameters for resistance and load effects are developed based on strain compatibility theory and stress levels after all losses due to applied loads. Fatigue reliability Indices are obtained using Monte Carlo simulation.;Combinations of different spans, concrete grades (girder and deck), and different prestressed steel ratios, reinforcing steel in deck, different dimensions, and section properties are considered. Resistance parameters are calculated based on three categories: statistical parameters of material, fabrications, and professional factor.