PREDICTION OF EQUIVALENT DAMAGE REPETITIONS FROM AIRCRAFT TRAFFIC MIXTURES FOR FULL-DEPTH ASPHALT AIRFIELD PAVEMENTS

A procedure is presented (applicable to Full-Depth asphalt pavement) which can be used to evaluate the effect of both differing aircraft type and variable traffic levels associated with each aircraft type for any anticipated air carrier traffic mixture. The Full-Depth design procedure is comprised of 2 separate design analyses to consider 2 types of distress modes: permanent deformation (repetitive subgrade shear) and asphalt concrete fatigue. The determination of equivalent damage repetitions evaluated for aircraft mixtures presented here considers 3 elements: the aircraft types comprising the mix; the transverse distance from the aircraft center line to the geometric center of the main gear(s); and the transverse wanger effect of slow moving aircraft operating in taxiway areas. A general equivalent damage equation is derived, and the factors considered in relation to the transverse distribution factor are detailed. The equivalent damage factor analysis is described, and the shell BISTRO multilayered computer program utilized to calculate the maximum principal tensile strain at the bottom of the asphalt concrete layer is outlined. A computer program was developed for the solution of any aircraft mixture forecasted within the service life of the Full-Depth pavement; the only input required by the design engineer is a traffic forecast of the aircraft types and estimated number of taxiway passes of each aircraft anticipated during given time intervals up to the service life. The adequacy of the predictive techniques (presented in this report) is illustrated by two example (Washington National Airport and Baltimore Friendship Airport) comparisons between observed transverse distress patterns on airfield pavements and the predicted lateral distribution of equivalent strain repetitions.