Analytical model for deflection of the runway pavement at touchdown point caused by an aircraft during landing

An estimation of the runway pavement deflection during landing for design purposes has been a challenging problem for engineers. This paper presents a simple analytical model to predict dynamic deflection of a runway pavement at touchdown point caused by a landing gear load during aircraft landing. Three independent parameters, modulus of subgrade reaction (k_s), contact pressure (p), and vertical component of aircraft velocity (v_v), are required to estimate the deflection using this model. This model shows that the dynamic deflection increases with an increase in vertical velocity and contact pressure. These observations follow an expected trend and the field observations made during inspection of the runways. Likewise, the impact factor, which is defined as the ratio of the dynamic deflection to static deflection, also increases with an increase in vertical velocity for a given value of the contact pressure. Irrespective of contact pressure values, the impact factor for zero vertical velocity is 2 under elastic runway pavement conditions. An illustrative example is presented to explain the use of model expressions as well as the use of graphical presentations as design charts for calculating the dynamic deflection and associated impact factor.