Torsional Irregularity of Buildings

Abstract eng:
In the present work; the recently introduced parameter Q which is a ratio of the effective modal masses is modified and used to define the torsional irregularity of buildings. The code (ASCE 7-05) proposed ratio for the definition of the torsional irregularities is compared with the modified Q ratio. Parametric analyses are utilised for this investigation. 300 one storey and 300 five storey buildings having eccentricities in two orthogonal directions at the same time are analyzed by “time history method” under 8 historical earthquakes, 4800 analyses are carried out in total. To eliminate human errors from the calculations, a computer program capable of making above-mentioned analyses in one-run is coded. The code proposed parameter of the torsional irregularity is the ratio of the maximum drift of a floor corner to the average drift of the considered edge of the floor. Since this ratio is calculated under the static loading, it does not consider the eccentricity in the direction parallel to the earthquake excitation direction. It is found that, the use of this code parameter resulted in maximum of 101% difference in the drifts of the corner columns with regard to the ratio of the eccentricity in the direction of the excitation to the radius of gyration. For that case, the use of modified Q ratio resulted in maximum difference of 59%. Moreover, the calculation of the modified Q ratio depends on but does not require the determination of the eccentricities instead; it is calculated by means of the effective modal mass values of the building. The torsional coupling of 3D buildings in the inelastic range is currently being investigated by authors.

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