TRAFFIC LOADS ON LARGE BRIDGES MODELED AS WHITE-NOISE FIELDS

A load effect from the traffic load on a large bridge with a large interval of slowly varying nonzero influence on the load effect can be modeled as a Gaussian random process. The mean value function and the covariance function that completely determines the process can be obtained by modeling the traffic load along each lane as a translating white-noise field. On the basis of a realistic traffic theoretical modeling of instantaneous random positions of single vehicles as represented by their random weights, the paper derives formulas for the mean and intensity of the white-noise traffic-load field in terms of traffic parameters and vehicle weight mean and variance. The formulas cover the entire range of traffic from free Poissonian traffic to congested traffic with the full stop queue as a limit case. The standard level crossing rate approximation method, used for the distribution of the maximal load effect over a given period of time due to moving traffic of any type, is taken as an example of an application of the white-noise traffic-load model. In a companion paper, Ditlevsen and Madsen (in press, 1994) used the model to obtain the distribution of the maximal load effect during a given period of time due to the formation of standing queues on the bridge.