Relevant risk factors are reviewed and a methodology is presented for determination of vessel impact energies and return periods forbridges located over navigable waters. The approach integrates vessel traffic and operating characteristics, bridge geometry, marine environment conditions, and aberrance frequencies of vessels. The method is generic and can be applied to multispan as well as to short bridges located either in a marine environment or over inland waterways. Main and side piers and spans are considered the objects of vessel impact threats. The analysis can be useful in bridge planning and in selection of design criteria for impact loads on bridge elements.The methodology recommends calculation of impact velocities of vessels by the application of mechanistic equations describing the behavior of errant vessels in wind, currents, and waves as a function of the vessels' operating speed and location at the instance of aberrance. The method can also be used if the impact velocity distributionsare assumed by judgment. Examples from two canadian bridge projectsare given. This paper appears in transportation research record no.1275, Bridge research 1990.
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