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1、ELSEVIEREngineering Structures, Vol. 18, No. 2, pp. 133-141, 1996 Copyright 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved0141-0296(95)00073-90141-0296/96 $15.00 + 0.00Behaviour of asymmetric building systems under a monotonic loadIA. Ferhi and K. Z. TrumanDepartment of Civi
2、l Engineering, Washington University, St Louis, MO 63130, USA (Received May 1994; revised version accepted October 1994)Buildings subjected to a large intensity ground motion deform well into the inelastic range. In particular asymmetric buildings undergo coupled inelastic lateral and torsional defo
3、rmations that could be the governing factors in their design. The relationship between the systems asymmetry and its inelastic deformations is yet to be determined. This study defines the asymmetric building system and its key components namely the stiffness and strength eccentricities. The solution
4、 is mathematically formulated and its accuracy is discussed. Selected examples are presented in order to show the characteristics of the inelastic behaviour of an asymmetric building system and how it is affected by the stiffness and strength eccentricities. rwo asymmetric building models are used.
5、One model is laterally supported on wall-column elements which provide resistance in one principal direction. The second model is laterally supported on columns which provide resistance in both principal directions making biaxial bending effects significant. For simplicity, the analytical models are
6、 a monosymmetric one-bay, one-storey frame; the lateral load resisting elements are replaced by nonlinear springs; and the loading is a monotonic static load applied at the centre of mass.Keywords: asymmetric buildings, inelastic behaviour, lateral- torsional coupling, stiffness eccentricity, streng
7、th eccentricity, biaxial bending#1. IntroductionIt would be ideal if all buildings had tneir lateral-load resisting elements symmetrically arranged and earthquake ground motions would strike in known directions. But most buildings have some degree or irregularity in the geometric configuration or th
8、e distribution of mass, stiffness, and/or strength and earthquakes; do not strike in a predetermined direction. Due to one or more of these irregularities, the structures lateral resistance to the ground motion is usually torsionally unbalanced creating large displacement amplifications and high for
9、ce concentrations within the resisting elements. This phenomenon, known as lateral-torsional coupling, is well understood within the limits of elastic deformations but is still far from being fully understood when significant inelastic deformations take place. Buildings subjected to high intensity e
10、arthquakes can deform well into the inelastic range making the success of their design and safety a trade-off with economic considerations. It is not economically feasible to elastically design these structures. An optimal solution would be to equip the designer with the same level of understanding
11、of the inelastic behaviour of asymmetric building systems as of the elastic behaviour.A survey of previous studies of asymmetric building systems reveals a wide range of differences and contradictions in their conclusions. Typical differences are in the assessment of the peak ductility demands1*3 an
12、d edge displacements1 -3 b9. Most researchers agree that inelastic torsional coupling induces torsion and reduces lateral response but they differ in their assessments of the amount of reduction14 7-810. These differences point to the difficulties in studying the inelastic response of asymmetric bui
13、lding systems. The main causes of most differences are linked to the wide range of modelling techniques used. Namely, models vary in the number, type and location of the lateralload resisting elements. The mathematical formulation uses either the centre of mass (CM) or the initial elastically define
14、d centre or rigidity (CR) as a point of reference. As yielding of the elements occurs the elastic CR changes location, therefore, the solution formulation should take this into consideration. A stiffness eccentric system is not identical to a mass eccentric one because in the inelastic range, the st
15、iffness distribution is a variable whereas the mass disInelastic behaviour of asymmetric buildingsI: A. Ferhi and K. Z Truman#tribution is always constant. It was not until the late 1980s that the strength eccentricity was formulated as a parameter that affects the behaviour of an inelastic system.
16、Much of the research done before that did not consider the strength eccentricity as a parameter. Comparisons oi inelastic systems without a common strength eccentricity are meaningless. In a dynamic study, the conclusions often reflect the choice of the loading function making it difficult to conduct direct comparisons. Often the analytical models are oversimplified to a point where they lack compatibility with realistic building
