Pavement Responses Due to Hard Landings of Heavy Aircraft

Abstract

The effects on airport runways of impact loads induced by hard landings of heavy aircraft have been investigated. A hard landing is defined as a landing in which the angle of landing by a single-wheel impact load is greater than the static load for the same aircraft, with inclusion of the effects of the shock-absorption system. A numerical model, based on some earlier work by others, was developed to define the impact load for any given landing angle. With the impact-load values calculated from the model, theoretical stresses and strains were computed by existing elastic-layer and finite-element computer programs. The results indicated that tensile strains at the base of the asphalt layer and compression strains at the top of the subgrade could be up to 10 times as high under impact loading than under static loading. The study concluded that impact loads caused by angles of landing between 0.2° and 0.8° above horizontal were not greater than the static load of the aircraft (upon which current design standards are based). However, at angles of landing greater than about 0.8°, the fatigue cracking and permanent deformation of airport runway pavements increased exponentially with an increase in landing angle. As a result of this study, the effects of impact loads due to hard landings were demonstrated to be sufficiently significant to be considered in the design of airport runway pavements.