Stiffness and energy degradation of wood frame shear walls Harry W. Shenton III, David W. Dinehart, and Timothy E. Elliott Abstract: Tests have been conducted on wood frame shear walls to characterize the degradation of stiffness and energy dissipation that occurs under cyclic loading. A total of eight walls were tested, four sheathed in plywood and four sheathed in oriented-strand board. The tests were conducted in accordance with a draft test procedure recently proposed by the Structural Engineers Association of Southern California, which is based on a sequential phased displacement command input. The results indicate that effective stiffness decreases linearly with continued cycling at the same displacement and decreases with increasing amplitudes of displacement. Furthermore, the energy dissipation capacity of the wall decreases by 15–20% with the first cycle at a given amplitude, then decreases slightly with continued cycling at the same amplitude. The changes in effective stiffness and energy dissipation are generally independent of the type of sheathing for loads less than the wall ultimate, suggesting that the wall performance under cyclic loading is influenced more by the fastener and frame behavior. The results presented should be useful for design and for verifying hysteretic models of the shear wall behavior. Key words: cyclic, dynamic, energy dissipation, experimental, seismic, shear wall, stiffness, testing, timber, wood frame. Résumé : Des essais ont été réalisés sur de murs de cisaillement en charpente de bois afin de caractériser la dégradation de la rigidité et de la dissipation d’énergie qui se produit sous un chargement cyclique. Un total de huit murs a été soumit aux essais, dont quatre lamellés en contre-plaqué et quatre lamellés en planches de fibres orientées. Les essais ont été réalisés conformément à un premier jet d’une procédure récemment proposée par l’association des ingénieurs en structure de la Californie du Sud, une procédure basé sur une introduction de commande de déplacement séquentielle phasée (sequential phased displacement command input). Les résultats indiquent que la rigidité effective diminue linéairement avec un cycle continu au même déplacement et diminue avec l’accroissement de l’amplitude des déplacements. De plus, la capacité de dissipation d’énergie du mur diminue de 15% à 20% avec le premier cycle à une amplitude donnée, puis elle demeure à peu près constante ou diminue légèrement avec un chargement cyclique continu à la même amplitude. Les changements dans la rigidité effective et dans la dissipation d’énergie sont généralement indépendants du type de lamellé pour des chargements inférieurs au chargement ultime du mur. Ceci suggère que la performance du mur sous chargement cyclique est plus influencée par le comportement du cadre et de la fermeture. Les résultats présentés devraient être utiles pour la conception et la vérification de modèles sur le comportement des murs de cisaillement. Mots clés : cyclique, dynamique, énergie de dissipation, expérimental, sismique, mur de cisaillement, rigidité, essai, bois de charpente, cadre de bois. [Traduit par la Rédaction] Introduction Until 20 or 30 years ago, wood frame structures were usu- ally designed with let-in braces to resist wind and seismic loads. This changed, however, with the introduction of ply- wood, oriented-strand board (OSB), and other types of engi- neered sheathing. Today, most low-rise timber structures use wood frame shear walls to resist lateral loads. Used throughout the world, wood frame shear walls have demonstrated reason- ably good performance in regions of high seismicity and high wind. Problems still exist, however, in timber structures with nonstructural damage and inadequate connections, as illus- trated by recent U.S. natural disasters (e.g., the 1994 Northridge earthquake (Hall 1994) and hurricane Andrew in 1992 (U.S. Department of Housing and Urban Development 1993)). The design of wood frame shear walls is usually based on a design allowable shear force per unit length of wall. The allowable shear depends on the construction of the wall and usually takes into consideration the type and thickness of sheathing, the number of panels, the type of fastener, fastener penetration, and the fastener spacing. Historically, the allow- Received May 21, 1997. Revised manuscript accepted October 6, 1997. H.W. Shenton III and T.E. Elliott. Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, U.S.A. D.W. Dinehart. Department of Civil and Environmental Engineering, Villanova University, Villanova, PA 19085, U.S.A.; formerly, Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, U.S.A. Written discussion of this article is welcomed and will be received by the Editor until October 31, 1998 (address inside front cover). Can. J. Civ. Eng. 25: 412–423 (1998) 412 © 1998 NRC Canada