MODELLING OF NORMAL AND SHEAR BEHAVIOR OF INTERFACE IN DYNAMIC SOIL-STRUCTURE INTERACTION.

The interface normal behavior between Ottawa sand and concrete for static and cyclic loading has been studied using Cyclic Multi Degree-of-Freedom test device. The static force controlled test for the interface showed exponential relation between normal stress and strain during initial loading, hyperbolic relation during unloading and linear relation during reloading. A series of cyclic force controlled interface tests are described for normal behavior and the interface behavior is found to be a function of the applied initial normal stress, the amplitude of the stress and the number of loading cycles. The reloading modulus is shown to increase with number of loading cycle. Also, a series of combined normal (force controlled) and shear (displacement controlled) tests are described in which the shear stress for given amplitude of shear displacement is found to increase as normal stress and number of loading cycles increases. The results of the laboratory tests for normal behavior are used to determine the parameters to describe the interface stress-strain response. The model is shown to describe the hysteresis behavior of the interface as a function of amplitude of normal stress and number of loading cycles. The model is used to predict the results of cyclic normal tests and combined normal and shear tests, and was found to yield satisfactory results. The interface model is implemented in a 2D nonlinear soil-structure interaction finite element procedure. The finite element procedure is verified with respect to simple problems for which close form solution or laboratory results are available. The response of the force controlled cyclic test and combined normal and shear test is then predicted using the FE procedure and reasonable results are obtained. A pier foundation subjected to base displacement is then analysed for different combinations of soil and interface behavior. Computer results are qualitatively compared with displacement and contact stresses and the effect of including the interface behavior is identified with respect to debonding and rebonding of the interface. The results of this research have provided understanding of the cyclic behavior of sand-concrete interface subjected to normal and combined normal and shear loading. The interface behavior has been represented by simple mathematical model for which parameters can be easily determined from static and cyclic tests. The model is also defined for general loading to incorporate debonding and rebonding and it is easy to implement into a FE procedure