Development of a Multiple Truck Presence Model

In bridge design and evaluation, the characteristics of truck traffic is particularly important. Truck weights and axle configurations are directly used in calculations of maximum load effects including positive bending moments and shear forces in simply-supported bridges as well as negative bending moments of continuous spans. The loading event that is likely to govern a bridge design is t he simultaneous occurrence of two or more heavily loaded trucks- called Multiple Presence. Consequently, the statistics of different loading patterns as well as the weight correlation among coincident trucks are equally important to live load analysis. However, studies of Multiple Presence events are either convolution models or models based on visual observation of the traffic, but very little research has been undertaken to analyze Weigh-in-Motion data. In t his study, Weigh-in-Motion data collected on highways is analyzed in order to determine the occurrence of Multiple Presence events incorporating two trucks and their weight correlation. Based on the analysis, a prediction model is developed to estimate the frequency of t he Multiple Presence events using known site parameters. Also, probabilities for full weight correlations are found for t he Multiple Presence loading cases. A special remark is given to the influence of the Gap distances between the t rucks involved into a Multiple Presence event . It is found that t he Gaps do not have a threshold distance for t he influence of the lighter truck that could be utilized to reduce t he Multiple Presence occurrence probabilities