In order to account for uncertainties in the location of center of mass on the floor slab and in the spatial variation of the seismic motion, seismic codes introduce the so-called accidental eccentricity. Generally, the Eurocode 8 (EC8) considers the accidental eccentricity by requiring that the center of mass at each floor be displaced from its nominal location in each direction at a distance equal to 5% of the oor dimension. However, if the simplifled lateral force method can be applied, then, according to EC8, the effects of accidental eccentricity may be accounted for in a different manner, i.e. by amplifying the action effects in individual load resisting elements. Furthermore, if the modal response spectrum analysis is applied, then the effects of accidental eccentricity may be determined as the envelope of the effects resulting from the application of static loadings, consisting ofsets of torsional moments. In this paper, a practically symmetric 4-story RC building is designed according to the above different specifications for accidental eccentricity. A comparison is carried out regarding design member forces obtained from application of the three specifications. Furthermore, nonlinear dynamic analyses are conducted in order to assess the building response under severe earthquakes in the presence of accidental eccentricity due to mass uncertainty only, as design is conducted with the three different specifications. A suite of 20 accelerograms, generated within the SAC Steel Project for the Los Angeles area, having a probability of exceedance of 10% in 50 years, has been considered as seismic input. Local and global damage parameters are computed in order to define performance levels attained by the structure during seismic excitation. From response analysis it emerges that displacing the mass center at a distance equal to 5% of the floor dimension perpendicular to the direction of the seismic action is the most effective design specification.
Seismic performance of RC structures designed for accidental eccentricity / A. D'Ambrisi; M. De Stefano; M. Tanganelli. - ELETTRONICO. - (2006), pp. 1-8. (Intervento presentato al convegno First European Conference on Earthquake Engineering and Seismology tenutosi a Geneva, Switzerland nel 3-8 september 2006).
Seismic performance of RC structures designed for accidental eccentricity
D'AMBRISI, ANGELOMembro del Collaboration Group
;DE STEFANO, MARIOMembro del Collaboration Group
;TANGANELLI, MARCOWriting – Original Draft Preparation
2006
Abstract
In order to account for uncertainties in the location of center of mass on the floor slab and in the spatial variation of the seismic motion, seismic codes introduce the so-called accidental eccentricity. Generally, the Eurocode 8 (EC8) considers the accidental eccentricity by requiring that the center of mass at each floor be displaced from its nominal location in each direction at a distance equal to 5% of the oor dimension. However, if the simplifled lateral force method can be applied, then, according to EC8, the effects of accidental eccentricity may be accounted for in a different manner, i.e. by amplifying the action effects in individual load resisting elements. Furthermore, if the modal response spectrum analysis is applied, then the effects of accidental eccentricity may be determined as the envelope of the effects resulting from the application of static loadings, consisting ofsets of torsional moments. In this paper, a practically symmetric 4-story RC building is designed according to the above different specifications for accidental eccentricity. A comparison is carried out regarding design member forces obtained from application of the three specifications. Furthermore, nonlinear dynamic analyses are conducted in order to assess the building response under severe earthquakes in the presence of accidental eccentricity due to mass uncertainty only, as design is conducted with the three different specifications. A suite of 20 accelerograms, generated within the SAC Steel Project for the Los Angeles area, having a probability of exceedance of 10% in 50 years, has been considered as seismic input. Local and global damage parameters are computed in order to define performance levels attained by the structure during seismic excitation. From response analysis it emerges that displacing the mass center at a distance equal to 5% of the floor dimension perpendicular to the direction of the seismic action is the most effective design specification.
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