A consideration of P-delta effects in ductile reinforced concrete frames
DOI:
https://doi.org/10.5459/bnzsee.11.3.151-160Abstract
The likely effects of secondary moments due to the gravity load, which is being laterally displaced during inelastic seismic storey drift, upon ductile reinforced concrete frames is examined. Existing building code recommendations and design procedures relevant to the phenomenon are briefly reviewed. The probable effect of P-delta moments on inelastic dynamic frame response is discussed. With the aid of illustrations various design considerations are presented. It is suggested that if strength demand due to P-delta effects exceeds 15% of the ideal lateral load carrying capacity of a subframe, this strength demand should be met. From the comparison of the elastic and inelastic deformations of a frame due to earthquake loading, recommendations are made for the estimation of critical inelastic drifts in the lower half of the frame. This is subsequently used to quantify the problem with the aid of the "stability index". The quantitative evaluation of P-delta effects for an 18 storey frame is illustrated in the appendix.
References
"Recommended Lateral Force Requirements and Commentary", Seismology Committee Structural Engineers Association of California, 1973, 146 pp.
"Final Review Draft of Recommended Comprehensive Seismic Design Provisions for Buildings", ATC -3-05, Prepared by Applied Technology Council, Palo Alto, California, January 1977.
New Zealand Standard - Code for Design of Steel Structures (with Commentary) NZS 3404:1977 Standards Association of New Zealand 27 pp.
Andrews, A. L., "Slenderness Effects in Earthquake Resisting Frames", Bulletin of the New Zealand National Society for Earthquake Engineering, Vol. 10, No. 3, September 1977, pp. 154-158. DOI: https://doi.org/10.5459/bnzsee.10.3.154-158
New Zealand Standard - Code of Practice for General Structural Design and Design Loadings for Buildings, NZS 4203:1976, Standards Association of New Zealand, 80 pp.
Bertero, V. V. and Popov, E. P., "Seismic Behaviour of Ductile Moment- Resisting Reinforced Concrete Frames", Reinforced Concrete Structures in Seismic Zones, Publication SP-53, American Concrete Institute, Detroit, 1977, pp. 247-291.
Building Code Requirements for Reinforced Concrete (ACI318-77), American Concrete Institute, Detroit, 1977, 102 pp, Commentary 132 pp.
Paulay, T., "Seismic Design of Ductile Moment Resisting Reinforced Concrete Frames, Columns-Evaluation of Actions", Bulletin of the New Zealand National Society for Earthquake Engineering, Vol. 10, No. 2, June 1977, pp. 85-94. DOI: https://doi.org/10.5459/bnzsee.10.2.85-94
Jury, R. D., "Seismic Load Demands on Columns of Reinforced Concrete Multi-storey Frames", Research Report No. 78-12, February 1978, Department of Civil Engineering, University of Canterbury, 129 pp.
Powell, G. H. and Row, D. G., "Influence of Analysis and Design Assumptions on Computed Inelastic Response of Moderately Tall Frames", Earthquake Engineering Research Center, University of California, Berkeley, Report No. EERC 76-11, April 1976, 111 pp.
Kelly, T. E., "Some Comments on Rein forced Concrete Structures Forming Column Hinge Mechanisms", Bulletin of the New Zealand National Society for Earthquake Engineering", Vol. 10, No. 4, December 1977, pp. 186-195. DOI: https://doi.org/10.5459/bnzsee.10.4.186-195
MacGregor, J. G. and Hage, S. E., "Stability Analysis and Design of Concrete Frames", Journal of the Structural Division, ASCE, Vol. 103, No. ST10, October 1977, pp. 1953-1970. DOI: https://doi.org/10.1061/JSDEAG.0004745
