Abstract:The performance of concentrically braced steel frames and moment resisting steel frames during the January 17, 1994, Northridge, California, earthquake is examined. Most of the observations made during the reconnaissance visits confirmed the current knowledge on the inelastic response of these structural systems. This permits the anticipation of proper seismic behavior for buildings designed according to the seismic provisions that have been recently introduced in the Canadian building code and standard for steel structures. In some cases, however, the observed damage raised concerns that should be addressed in future investigations or next editions of these codes. Preventing potentially hazardous nonstructural damage, avoiding premature nonductile failures anywhere along the lateral load paths, limiting structural and nonstructural damage due to brace buckling, and accounting for the vertical ground motion are among those issues.Key words: earthquake, seismic, steel, concentrically braced frames, moment resisting frames, weld.R&um& : Dans cet article, on examine et commente le comportement de charpentes mCtalliques avec contreventement en treillis ou cadres rigides lors du stisme qui a eu lieu le 17 janvier 1994 5Northridge, en Californie. La majorit6 des observations faites lors des visites effectuCes sur le site confirment les connaissances dCji acquises sur le comportement non lintaire de ces systbmes structuraux lorsque soumis aux stismes. Ceci permet de croire que les bitiments conGus selon les dispositions sCismiques nouvellement introduites dans le code du bitiment canadien et la norme canadienne pour la calcul des structures d'acier seront adCquats dans 1'CventualitC de tremblements de terre importants. Dans certains cas, cependant, les dommages subis soulbvent des interrogations qui devraient faire l'objet d'Ctudes futures en vue dlamCliorer ces normes. Parmi les points qui devraient Ctre examinks, on retrouve la prCvention des dommages non-structuraux 5 risque, la prevention de ruptures subites et non-ductiles le long du cheminement des efforts induits par les charges latCrales, la rkduction des dommages imposCes aux ClCments structuraux ou non-structuraux lors du flambement des membrures diagonales des contreventements ainsi que la prise en compte des effets des mouvements verticaux du sol.Mots c l b : tremblement de terre, sCisme, charpentes mttalliques, contreventement en treillis, cadre rigide, soudure.

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It is demonstrated that the temperature oscillations near the edge of the thermoacoustic stack are highly anharmonic even in the case of harmonic acoustic oscillations in the thermoacoustic engines. In the optimum regime for the acoustically induced heat transfer, the amplitude of the second harmonic of the temperature oscillations is comparable to that of the fundamental frequency.