Uncertainty of Code-Torsional Provisions to Mitigate Seismic Hazards of Buildings with Setback

Static torsional provisions in most of the seismic codes require that the earthquake-induced lateral force at each story be applied at a distance equal to design eccentricity (e d) from the center of resistance of the corresponding story. Such code-torsional provisions, albeit not explicitly stated, are generally believed to be applicable to the regularly asymmetric buildings. Examined herein is the applicability of such code-torsional provisions to buildings with setback. A set of low-rise setback systems are analyzed using static torsional provisions and by response-spectrum-based procedure. A comparison of the response in terms of frame shear located at the perimeter and diaphragm displacements suggests the degree of reliability of code-torsional provisions for low-rise setback building.

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