Lower bound shakedown analysis of layered pavements using discontinuous stress fields

Pavements and railways are subjected to repeated wheel loads of different m agnitudes. Both load magnitudes and number of repetitions of load need to b e considered in order to avoid significant damages to a pavement. A convent ional finite element technique is convenient for calculating static pavemen t responses, but the prediction of pavement performance under repeated load ing is much more difficult as it needs a large number of time steps or load ing cycles. Shakedown analysis with a statically admissible residual stress field offers a simple approach for predicting the maximum magnitude of rep etitive load which can be allowed to act on the pavement in order to preven t excessive permanent deformation. This paper presents a lower bound shaked own formulation using a linear approximation of the Mohr-Coulomb yield crit erion. The residual stress field is modelled using 3-noded triangles where stress discontinuities are allowed to occur at the edges of each triangle. Lower bound shakedown limits are obtained by insisting that both the total and the residual stress fields don't violate the yield condition everywhere in the pavement. The proposed formulation is first verified using a homoge neous isotropic half space and then applied to a two-layer pavement. The va riation of shakedown limits with material properties and layer thickness ar e investigated. The results presented can be used to form a sound theoretic al basis for pavement design. (C) 1998 Elsevier Science S.A. All rights res erved.