Energy Method for Structures Interacting with Dissipative Soils

Itai Einav, APD Fellow, Centre for Offshore Foundation Systems, University of Western Australia

The combination of energy methods and variational principles has provided a valuable tool to analyze the behaviour of elastic structures for quite a long time. It has also been used infrequently to study soil-pile interaction problems, considering the soil as elastic material by following the traditional method that was developed for the elastic structures. However, soil is not a non-dissipative elastic medium. In this seminar an alternative energy-based variational approach will be presented, showing how to account for the dissipative nature of soils. The applicability of the new method will be discussed for the modelling of (a) rigid shallow foundations and (b) deformable piles. (a)Rigid shallow foundations: The general formulation allows idealization of the problem using uni- or bi-continuous (Winkler) model systems, all encapsulated in two thermodynamics potential functionals. In the uni-continuous system, the global foundation behaviour can be described by defining a continuous field of reaction stress-displacement models along the interface of the problem. By also ormulating each of these reaction stress-displacement interface models to be continuous along an internal coordinate, a bi-continuous system can be modelled. The seminar presents an outline of the approach with examples for strip and circular footing under both monotonic and cyclic loading conditions.(b)Deformable piles: An interesting feature of the approach is that the possibility of internal elastic deformations within the structures may be incorporated within the two potential functionals. For that purpose, the seminar demonstrates the applications for the classical problem of lateral and axial loading of piles. The new method enhances previous energy based variational methods that were applied for this problem. Compared to those methods the current method allows accounting for the dissipative nature of the soil and thus enables to model the response of the pile when it is subjected to cyclic loading conditions.

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