Three -dimensional finite element analyses of flexible airport pavements for the next generation of aircrafts

With the advent of larger and heavier aircrafts with more complex wheel configurations, current design methods of airfield pavements are becoming inadequate. Current design procedures are typically conducted using a layered elastic approach, which assumes a two-dimensional environment with linear elastic material responses with theory of superposition to achieve the effect of multiple wheel loads. With the release of heavier aircraft with more complicated landing gears, the analysis situation has become more complex. The stress interactions between separate tires is not as simple to model; a two-dimensional model is incapable of modeling the three-dimensional problem of a triple-dual-tandem (TDT) axle used on B-777 and A380 aircraft. This paper documents the use of finite element analyses techniques to determine the failure mechanism in a pavement system under moving aircraft loads. The three-dimensionality of the failure surface under actual wheel loads with wander requires that computationally intensive three-dimensional models be used. The flexible pavement system that is modeled is comprised of a medium and low strength subgrade. The stress-strain response of the material is simulated using an elasto-plastic model. The finite element techniques employed are verified against available failure data from the National Airport Pavement Test Facility (NAPTF) of the Federal Aviation Administration based in Atlantic City. Several conclusions can be drawn from the analysis. The response of pavement structure using elastic properties does not accurately pzedict the pavement response. On the other hand, the elasto-plastic material model is able to emulate the response of pavement material. It is also seen that wander causes greater stresses and strains within the subgrade layer as well as greater upheaval when compared to models that neglect wander. The field of influence is also increased. The analysis which modeled the aircraft landing gear trafficking across the pavement section also indicates that pavements with less than 30 inches of pavement structure over the subgrade results in high levels of stress on the subgrade and adding additional subbase has diminishing returns in improving the pavement performance.