Inelastic seismic response of concrete shear walls consideringP–delta effects

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The inelastic response of a typical 12-storey ductile reinforced concrete flexural wall is examined under strong earthquake ground motions to determine the importance of P–delta effects and assess the seismic demand in shear and flexure. According to the stability factor approach of the National Building Code of Canada (NBCC) to account for P–delta effects, the flexural strength of the wall has to be increased by as much as 29%. However, the inelastic dynamic analyses indicate that P–delta effects on lateral deformations and curvature ductility demand are negligible for walls that meet the 2% NBCC interstorey drift requirement. The current NBCC stability factor approach to consider P–delta effects is thus overly conservative for shear wall structures, which respond significantly in their second and higher modes of vibration. The analyses also indicate that the magnitude and distribution of shear forces and bending moments in the wall are different from those obtained using the NBCC static design procedure. Plastic hinges can occur above the base of the wall, although the probable moment resistance diagram exceeds the assumed moment envelope after plastic hinge formation at the base. Dynamic amplification of shear forces due to higher mode effects was also observed, which must be accounted for in design. Dynamic shear amplification factors proposed for wall structures in the commentary to the current standard for design of concrete structures in Canada compared well with the results of this study.Key words: seismic, flexural wall, P–delta effects, stability coefficient, inelastic response, National Building Code of Canada, dynamic shear force amplification, higher mode effects.