Inelastic seismic response of concrete shear walls considering P-delta effects

The inelastic response of a typical 12-storey ductile reinforced concrete f lexural wall is examined under strong earthquake ground motions to determin e the importance of P-delta effects and assess the seismic demand in shear and flexure. According to the stability factor approach of the National Bui lding Code of Canada (NBCC) to account for P-delta effects, the flexural st rength of the wall has to be increased by as much as 29%. However, the inel astic dynamic analyses indicate that P-delta effects on lateral deformation s and curvature ductility demand are negligible for walls that meet the 2% NBCC interstorey drift requirement. The current NBCC stability factor appro ach 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 ob tained using the NBCC static design procedure. Plastic hinges can occur abo ve the base of the wall, although the probable moment resistance diagram ex ceeds 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 amplificati on factors proposed for wall structures in the commentary to the current st andard for design of concrete structures in Canada compared well with the r esults of this study. The inelastic response of a typical 12-storey ductile reinforced concrete f lexural wall is examined under strong earthquake ground motions to determin e the importance of P-delta effects and assess the seismic demand in shear and flexure. According to the stability factor approach of the National Bui lding Code of Canada (NBCC) to account for P-delta effects, the flexural st rength of the wall has to be increased by as much as 29%. However, the inel astic dynamic analyses indicate that P-delta effects on lateral deformation s and curvature ductility demand are negligible for walls that meet the 2% NBCC interstorey drift requirement. The current NBCC stability factor appro ach 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 ob tained using the NBCC static design procedure. Plastic hinges can occur abo ve the base of the wall, although the probable moment resistance diagram ex ceeds 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 amplificati on factors proposed for wall structures in the commentary to the current st andard for design of concrete structures in Canada compared well with the r esults of this study.