The 14 th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China DISPLACEMENT-BASED DESIGN OF TALL BUILDINGS STIFFENED WITH A SYSTEM OF BUCKLING RESTRAINED UNBONDED BRACES Amador Teran-Gilmore 1 and Guillermo Coeto 2 1 Professor, Departamento de Materiales, Universidad Autonoma Metropolitana, Mexico City 2 Project Manager, Alonso y Asociados, Mexico City Email: tga@correo.azc.uam.mx, gcoeto@alonsoasociados.com.mx ABSTRACT : A displacement-based methodology for the preliminary design of a system of buckling-restrained braces is introduced. The methodology applies to the case of tall buildings, whose dynamic response is significantly influenced by global flexural behavior. The methodology is applied to the preliminary design of a twenty four-story building located in the Lake Zone of Mexico City. From the evaluation of the global mechanical characteristics of the building and of its seismic performance when subjected to ground motions generated in that zone, it is concluded that the proposed methodology yields an adequate level of seismic design. KEYWORDS: buckling-restrained braces, displacement-based design, capacity curve 1. INTRODUCTION Innovation in earthquake-resistant design has been directed towards the conception of structural systems, either traditional or innovative, that are capable of adequately limiting their level of structural and non-structural damage through the explicit control of their lateral deformation. An attractive option for response control is the development of passive energy dissipating systems. Within this context, the use of buckling-restrained (BR) braces is an attractive and fairly inexpensive solution to earthquake resistance. The idea behind a buckling-restrained brace is to fabricate a structural element that is able to work in a stable manner when subjected to compressive deformations. Because braces are normally able to behave in a stable manner when subjected to tensile forces, a buckling-restrained brace is capable of dissipating large amounts of energy in the presence of multiple yield reversals (Uang and Nakashima 2004). This paper introduces, within the framework for the design of “damage-tolerant” structures (Wada et al. 2004), a displacement-based design methodology for the preliminary design of a system of BR braces for tall buildings. 2. DESIGN METHODOLOGY The methodology offered in this paper is based on the conception of a building whose gravity forces are carried by steel frames with standard detailing (as opposed to ductile), and whose earthquake-resistance is provided by a system of buckling-restrained braces that provides lateral stiffness and a large energy dissipation capacity. 2.1 Design Scope Under the effect of low intensity ground motion, the building exhibits adequate performance if it satisfies the immediate operation performance level. This implies that the gravitational and bracing systems should not exhibit significant structural damage, and that the non-structural system should remain undamaged. Regarding performance for severe ground motion, the gravitational system should satisfy the immediate operation performance level while the bracing system develops significant plastic behavior that allows it to dissipate a large percentage of the input energy; partial or total non-structural collapse should be avoided.