Engineering Structures 26 (2004) 543–551 www.elsevier.com/locate/engstruct Seismic design of low-rise steel frames with buckling-restrained braces Jinkoo Kim  , Youngil Seo Department of Architectural Engineering, Sungkyunkwan University, Suwon 440 746, South Korea Received 26 January 2003; received in revised form 27 October 2003; accepted 11 November 2003 Abstract In this study, a direct displacement design procedure for steel frames with buckling-restrained braces (BRBs) is presented. The proposed structure system is composed of a hinge-connected main structure, which is designed to remain elastic under seismic load, and BRBs resisting all lateral loads. At seismic event, the BRBs dissipate dynamic energy through stable hysteretic beha- vior. A displacement-based seismic design procedure is applied to model structures to check the applicability of the design pro- cedure. Two artificial earthquake records are generated from a design spectrum, and the response spectra constructed based on the earthquake records are utilized in the design process. Time-history analyses are carried out to confirm that the maximum dis- placements coincide with the target displacements. The results show that the seismic performance of the 3- and 5-story model structures designed in accordance with the proposed method coincide well with the given design objectives. # 2003 Published by Elsevier Ltd. Keywords: Seismic design; Buckling-restrained braces; Direct displacement-based design; Steel frames 1. Introduction The conventional philosophy of seismic design depends on inelastic deformation of structural mem- bers for dissipation of input earthquake energy. This design concept may provide safety and economy in seismic design, but may not prevent damages in struc- tures after being shaken by an earthquake. The damage in main structural members can be prevented or mini- mized by connecting beams and columns with hinges, and employing lateral-load resisting members to with- stand lateral seismic load [1]. In this so-called a dam- age-tolerant braced frame (DTBF), most of the energy dissipation and structural damages caused by an earth- quake will be concentrated on the lateral-load resisting members, and the main members will remain elastic. After earthquake, the damaged lateral-load resisting members can be replaced easily at reasonable cost. Generally, steel braces are used as an economic means of providing lateral stiffness to a steel structure. However, the energy dissipation capacity of a steel braced structure subjected to earthquake loads is lim- ited due to the buckling of the braces. This is the main reason for most seismic design provisions to regulate lower value for the response modification factor to a braced frame than to a moment frame. The energy dis- sipation or damage prevention capacity of a steel framed structure can be greatly enhanced by employing buckling-restrained braces (BRBs). They usually con- sist of a steel core capable of undergoing significant inelastic deformation and a casing for restraining glo- bal and local buckling of the core element. According to previous research [2–5], an BRB exhibits stable hys- teretic behavior with high-energy dissipation capacity. The use of BRBs greatly enhances the energy dissi- pation capacity of the structure and decreases the demand for inelastic deformation in main structural members. In this study, the applicability of the direct displace- ment design method [6] on an DTBF structure is investigated. The design procedure is applied to a single-degree-of-freedom (SDOF) system first, and is further extended to 3- and 5-story structures to verify the applicability of the method. The BRBs are  Corresponding author. Tel.: +82-31-290-7563; fax: +82-31-290- 7570. E-mail address: jinkoo@yurim.skku.ac (J. Kim). 0141-0296/$ - see front matter # 2003 Published by Elsevier Ltd. doi:10.1016/j.engstruct.2003.11.005