Torsional Vibration of Eccentric Building Systems（古怪的建筑系统的扭转振动）.pdf

9 Torsional Vibration of Eccentric Building Systems Ramin Tabatabaei Civil Engineering Department, Islamic Azad University, Kerman Branch, Islamic Republic of Iran 1. Introduction The comprehensive studies conducted by a number of researchers in the past few decades and investigations of the effects of past earthquakes have shown that in buildings with non- coincident the center of mass (CM) and the center of rigidity (CR), significant coupling may occur between the translational and the torsional displacements of the floor diaphragms even when the earthquake induces uniform rigid base translations (Kuo, 1974; Chandler Hutchinson, 1986; Cruz Chopra, 1986; Hejal Chopra, 1989). In investigating the seismic torsional response of structures to earthquakes, it is customary to assume that each point of the foundation of the structure is excited simultaneously. Under this assumption, if centers of mass and rigidity of the floor diaphragms lie along the same vertical axis, a horizontal component of ground shaking will induce only lateral or translational components of motion. On the other hand, if the centers of mass and rigidity do not coincide, a horizontal component of excitation will generally induce both lateral components of motion and a rotational component about a vertical axis. Structures for which the centers of mass and rigidity do not coincide will be referred to herein as eccentric structures. Torsional a