Effect of alternative truck configurations and weights on the fatigue life of bridges

The life of a bridge is principally influenced by repetitive loading resulting from vehicular traffic. The service data on the fatigue life of concrete, reinforcing bars, and prestressing steel show considerable scatter in their service life. This is due to both the stochastic nature of the imposed loading and the variability in their strengths as determined by the quality control in their manufacture. The fatigue life of partially prestressed concrete girder bridges, subjected to a spectrum of traffic imposed by the Poisson arrival of various categories is investigated. Each category examined has a different expected frequency of arrivals per unit time and a different distribution of gross weight. The allocation of the live load to the girders in skew and normal bridges is determined using the finite element method. The girders of the bridge are each assumed to be part of a series system consisting of four components; prestressing strands, reinforced bars, cast-in-place concrete slab, and precast girder. The nine-axle B-train double trucks were found to be most damaging, whereas two-axle single trucks were least damaging. The incremental damage caused by each truck depends on the truck configuration, gross weight, axle-load distribution, and lateral load distribution. The median life of ordinary reinforcing bars is the lowest among the girder components.