ESTIMATION OF THE TORSION EFFECT ON BUILDINGS SUBJECTED TO SEISMIC LOAD

M. Draidi BENSALAH, M. BENSAIBI

Résumé


Abstract:
Nowadays, buildings with irregular forms are often constructed, in which torsion
phenomenon is induced during seismic loading. This phenomenon is not simple to define due
to the fact that its causes and effects are multiple. In the building codes, the torsion effects are
considered as equivalent static forces applied at distances ed from the centre of stiffness. The
effect is then added to shear forces and moments. This eccentricity could vary between 5 to
10% in the direction perpendicular to that of ground motion. In this work, we propose to
study the effects of induced torsion on the behaviour of an asymmetrical structure. Two types
of structures are considered, one symmetrical and other asymmetrical in terms of rigidity.
They are one floor reinforced concrete buildings with rigid slab and frame columns. In order
to estimate the influence of the torsion effect we use a finite element code which takes into
account the nonlinear behaviour of the structural elements. A data base of 106 seismic hazards
is used. These signals represent earthquakes with a variable magnitude between 6.2 and 7.3.
The responses of the buildings subjected to the seismic hazard are compared in terms of: top
displacement (Drift), the ductility and the reduction factor. According to our results, the
torsion phenomenon reduces the strength in terms of capacity and increases the vulnerability
of the structure under different seismic hazards. This demonstrates that it is very important to
take into account the torsion in the design of buildings subjected to seismic load.

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