The service life estimate of a steel bridge depends on the fatigue category and applied load for various levels of risk (probabilities of fatigue crack initiation). During the service life of a bridge, accumulated fatigue damage increases in time at different rates, depending on tonnage per year and train type. All these factors must be specified in order to obtain accurate results from any reliability analysis: 1. Use of fatigue life data specifically from full-scale girders, in conjunction with probability of failure, can provide the most versatile estimate of the remaining service life of a span; 2. Using a probabilistic method, the number of cycles or accumulated traffic is estimated in terms of probability of crack initiation. As a bridge management practice, inspections could be scheduled more often as a bridge member approaches a higher probability of crack initiation; 3. The reliability analysis also can be used for estimating years of service life (or MGT) of a bridge with different levels of safety. To date, the 32-foot span at FAST has performed well with no maintenance required. Since its commissioning, the span has accumulated total estimated traffic in the amount of 2,280 MGT, with over 580 MGT of HAL traffic since its installation at FAST. This level of traffic corresponds to about 50 percent probability of crack initiation.
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