A Comparative Study of Beams on Elastic Foundations Using Available Subgrade Models
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Date
2018
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Addis Ababa University
Abstract
Soil-structure interaction (SSI) is present in every problem, wherein a structural element is in
contact with soil. A concrete beam supported directly by the soil continuum is a very common
construction form. The response of the beam when it carries external load is influenced by
the soil, and the response of the soil is also influenced by the action of the beam under the
load. Thus, developing a subgrade model for soil-structure interaction problem is essential in
order to predict the response of both components of the system and arrive at an optimum
design. The simplest subgrade model is the single parameter Winkler mechanical model which
represents the foundation soil by a series of independent springs. Winkler model is widely
used and practiced in spite of its deficiency in depicting the continuous behavior of real soils.
Later, many advanced mechanical subgrade models have been proposed in order to improve on
the inherent lack of shear interaction among the individual springs. Moreover, these models
still have shortcomings with the nature of simplifying assumptions they make to ease the
mathematical relationships and not suggesting ways of estimating the model parameters. With
the objective to improve on such drawbacks, a generalized continuum-based model has been
recently proposed by Worku. This generalized subgrade model satisfies the fundamental elastic
laws and all the boundary conditions because it is derived by considering all stress, strain and
displacement components. The main objective of this work is to make a comparative study
between existing single and two parameter selected subgrade models. Microsoft Excel programs
are written for the computation of deflection, moment and shear force. Finite Element based
Plaxis 2D is used as a tool to determine the calibration factor for generalized models. Lastly,
numerical illustration is provided using these models in comparison with the Plaxis 2D model
and other simplified models for finite and infinite beam subjected to selected symmetrical
loading conditions. The results of the comparison show that the generalized models especially
the two-parameter model, are in very good agreement with the FE Plaxis 2D outputs.
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Keywords
Subgrade Models, Beams, Elastic Foundations