Keywords: finite element, infinite element, soil structure interaction, shear wall building, super element, condensation.

Shear walls are commonly employed as a principal element to resist lateral loads due to wind or earthquake forces. An accurate model for shear wall systems needs to consider the effects of all components in the system i.e. shear wall, foundation, and subsoil. More accurate modelling to simulate shear wall-foundation-soil interaction becomes necessary due to the significant role of shear walls in the design of tall buildings. At the same time, the model must be computationally efficient to reduce finite element data input and computation time.

This investigation focuses on more effective modelling of shear wall-foundation-soil system using super elements, finite and infinite elements to reduce the computational time and effort. Furthermore the paper describes the effect of different types of soil on the structural response of the system.

A finite element computer code has been written in the Fortran language for the analysis of shear wall-foundation-soil system. The following different type of elements was utilized to model the shear wall system:

(a)

Eight node isoparametric parabolic finite elements

(b)

Super elements generated using the conventional finite element formulation.

(c)

Six node infinite element to represent the far field of soil.

In order to explore the efficiency of using super element, an attempt has been made to model the shear wall structure using fully conventional finite element discretization. Furthermore the paper investigates the necessity of including soil structure interaction in the analysis of shear wall structures. The proposed physical model has been applied to the analysis of a shear wall structures combined with foundation - soil media. The structure is subjected to both vertical and lateral loads. The materials of the superstructure - foundation - soil system are assumed to obey Hooke's law.

The developed modelling using finite-infinite-super elements shows significant reduction in computational time and effort compare to conventional finite element model. The computational times for analysis with super element show considerable reduction in the computational time (400%), which clearly shows the efficiency of the super element.

The maximum drift of shear wall soil system was found to be 50 times and 6 times higher than fixed shear wall in case of clay and sand soil respectively. Furthermore results show that neglecting effect of soil flexibility by using fixed base assumption highly underestimates the displacement response of the shear wall system.

The variation of maximum lateral displacement at the top of the shear wall for different moduli of elasticity and different Poisson's ratios elaborates the sensitivity of the soil structure interaction analysis for both, their modulus of elasticity and the Poisson's ratio of the soil media.

The variation of normal stress in the width of shear wall highlights the stress distribution which is linear in the case of non-interactive and nonlinear for the interactive analysis.

This study clearly shows that neglecting the soil flexibility will lead to significant effect on the magnitude and redistribution of the stress in the shear wall. This investigation shows that the effect of interaction between the soil and the shear wall structure is significant and cannot be neglected if accurate results and proper safety are to be ensured. The interaction analysis shows remarkable different in stress distribution for shear wall.

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