Analogue computer techniques in a seismic design

Aseismic design is handicapped by a lack of statistical knowledge of earthquakes and the difficulty of analyzing the response of a complex frame to these irregular forcing functions. Structures subject to earthquake motion present a complex picture of linear and non-linear vibration. An explicit solution in terms of the participation factors of the modes and spectrum of the earthquake is useful when considering linear vibrations of the structure but the introduction of non-linearities such as friction and plastic yielding make this approach untenable. The general complexity of both linear and non-linear cases has led to the simulation of structures by various mechanical and electrical models. These models are highlyidealized and, in general, simulate only the major motions of the structure such as shearing, bending, and rocking of the structure on its base. Mechanical modellhg produces satisfactory results but suffers from complexity and lack of versatility. Further, it is difficult to apply to a mechanical model, which is necessarily not small, a prescribed forcing function as complicated as that of an earthquake. On the other hand thismethod has the advantage that the structure may be more faithfully modelled than by other means. Electrical models of various types have been made and have the advantage that their parameters may be readilychanged over large ranges and measurements recorded by convenient instruments.La conception as\ue9ismique se trouve entrav\ue9e par une p\ue9nurie de connaissances statistiques li\ue9es aux s\ue9ismes et par la difficult\ue9 inh\ue9rente \ue0 l?analyse de la r\ue9ponse d?ossatures complexes \ue0 de telles fonctions de contrainte irr\ue9guli\ue8res. Les structures qui sont sujettes aux mouvements sismiques pr\ue9sentent un ensemble complexe de vibrations lin\ue9aires et non lin\ue9aires. Il est utile, pour prendre en compte les vibrations lin\ue9aires de la structure, de disposer d?une solution explicite en termes de facteurs participatifs des modes et du spectre du s\ue9isme. Or, l?introduction de non-lin\ue9arit\ue9s telles que la friction et l?\ue9coulement plastique invalide cette m\ue9thode. En raison de la complexit\ue9 g\ue9n\ue9rale des vibrations tant lin\ue9aires que non lin\ue9aires, on a simul\ue9 les structures au moyen de divers mod\ue8les m\ue9caniques et \ue9lectriques. Ces mod\ue8les sont hautement th\ue9oriques et, en g\ue9n\ue9ral, ne permettent que la simulation des mouvements majeurs de la structure, comme le cisaillement, la flexion et le balancement de la structure sur son socle. La mod\ue9lisation m\ue9canique produit des r\ue9sultats satisfaisants mais demeure trop complexe et d?un emploi peu souple. En outre, il est difficile d?appliquer \ue0 un mod\ue8le m\ue9canique, n\ue9cessairement d?une envergure importante, une fonction de contrainte prescrite aussi complexe que celle d?un s\ue9isme. Par contre, cette m\ue9thode pr\ue9sente l?avantage d?une mod\ue9lisation potentiellement plus fid\ue8le de la structure que ne l?autorisent les autres m\ue9thodes. Des mod\ue8les \ue9lectriques de divers types ont \ue9t\ue9 d\ue9velopp\ue9s, avantageux en ce sens que l?on peut en changer facilement les param\ue8tres sur des plages \ue9tendues et que les mesures peuvent \ueatre enregistr\ue9es au moyen d?instruments d?un emploi pratique et commode.Peer reviewed: NoNRC publication: Ye