Improvements in the application of infinite elements to the NIKE3D program for airport pavement response analysis

A 3D, nonlinear finite element program NIKE3D is used in the Federal Aviation Administration's pavement design and response analysis of the rigid pavement structures. In 2000, an infinite element method was added to the NIKE3D program to simulate the infinitely deep subgrade. Using infinite elements efficiently can reduce the total number of elements, thereby saving the computational time. However, some computational results from the current infinite element formulation are questionable. Errors have been identified in the current mapping and shape functions of infinite elements. A new finite element formulation based on the improved mapping functions and shape functions has been developed and added to the NIKE3D program. The improved program allows meshing pavement foundation with traditional compatible elements, while using incompatible elements to the other layers with flexure deformations for more accurate analysis. In order to reduce geometric effects from meshing infinite elements, and errors arising from coupling of finite and infinite elements, a decay function is proposed and calibrated to the airport pavement application. The analytical results and other finite element programs, such as ABAQUS, are used for the comparison and verification of improvements.