Evaluation of the Dynamic Seismic Analysis Recommended for the 1975 National Building Code

As an alternative to the static seismic load analysis of buildings, a recommended dynamic seismac procedure is presented in Commentary K of Supplement No. 4 t0 the 1975 Edition of the National Building Code of Canada (NBC). In this paper comparisons are presented between the recommended response spectrum and the following: a) the average response spectrum by Housner; b) the response spectra by Newark, Blume and Kapur, and by Newark and Hall; c) the seismic coefficient S of the 1975 NBC; and d) the product of the coefficients SKI applicable to cross-braced water towers. Detailed comparisons of storey shears and overturning moments are presented for three buildings, as calculated from the 1975 NBC and the recommended dynamic analysis. Although there is over-all agreement in the forces obtained from the two methods, for regular buildings the recommended dynamic analysis is more conservative in the short period range (approximately 0.5 s), and less conservative in the long period range (approximately 2 s and greater) than the 1975 NBC seismic requirements.Devant l'analyse statique existante des surcharges dues aux s\ue9ismes, le commentaire K du suppl\ue9ment no. 4 de l'\ue9dition de 1975 du Code national du b\ue2timent du Canada (CNB) recommande une m\ue9thode s\ue9ismique dynamique. Le pr\ue9sent article d\ue9crit bri\ue8vement cette m\ue9thode, fond\ue9e sur la superposition des r\ue9ponses modales de la construction. L' auteur compare le spectre de r\ue9ponses recommand\ue9 a) au spectre de r\ue9ponses moyennes de Housner; b) aux spectres de r\ue9ponses de Newmark, Blume et Kapur, et de Newmark et Hall; c) au coefficient s\ue9ismique S du CNB de 1975; et d) au produit des coefficients SKI applicable aux r\ue9servoirs d'eau sur poteaux avec traverses de contreventement. L'auteur pr\ue9sente des comparaisons d\ue9taill\ue9es, pour trois \ue9difices, des cisaillements des \ue9tages et des moments de renversement, conform\ue9ment au CNB de 1975 et \ue0 l'analyze dynamique recommand\ue9e. Bien que les forces calcul\ue9es \ue0 l'aide des deux m\ue9thodes s'accordent dans l'ensemble, l'analyse dynamique recommand\ue9e est plus prudente, en ce qui concerne les \ue9difices ordinaires, pour de br\ue8ves p\ue9riodes (environ 0, 5 s), et moins prudente pour les p\ue9riodes d'environ 2 s et plus, que ne le sont les exigences s\ue9ismiques du CNB de 1975.Peer reviewed: NoNRC publication: Ye