Abstract—Buildings vulnerability due to seismic activity has been highly studied since the middle of last century. As a solution to the structural and non-structural damage caused by intense ground motions, several seismic energy dissipating devices, such as buckling-restrained braces (BRB), have been proposed. BRB have shown to be effective in concentrating a large portion of the energy transmitted to the structure by the seismic ground motion. A design approach for buildings with BRB elements, which is based on a seismic Displacement-Based formulation, has recently been proposed by the coauthors in this paper. It is a practical and easy design method which simplifies the work of structural engineers. The method is used here for the design of the structure-BRB damper system. The objective of the present study is to extend and apply a methodology to find the best combination of design parameters on multiple-degree-of-freedom (MDOF) structural frame – BRB systems, taking into account simultaneously: 1) initial costs and 2) an adequate engineering demand parameter. The design parameters considered here are: the stiffness ratio (α = K frame /K total ), and the strength ratio (γ = V damper /V total ); where K represents structural stiffness and V structural strength; and the subscripts "frame", "damper" and "total" represent: the structure without dampers, the BRB dampers and the total frame-damper system, respectively. The selection of the best combination of design parameters α and γ is based on an initial costs analysis and on the structural dynamic response of the structural frame-damper system. The methodology is applied to a 12-story 5-bay steel building with BRB, which is located on the intermediate soil of Mexico City. It is found the best combination of design parameters α and γ for the building with BRB under study. Keywords—Best combination of design parameters, BRB, buildings with energy dissipating devices, buckling-restrained braces, initial costs. I. INTRODUCTION HE use of seismic energy dissipating devices such as BRB is increasing in several parts of the world. These have proved to be effective in controlling displacement and absorbing a large portion of seismic energy, thus avoiding damage to the main structure [1]. For this reason, Segovia and Ruiz [2], which are the second and third coauthors of the present paper, have proposed a direct displacement-based Ángel de J. López-Pérez (M. Eng Graduate Student) is with the Universidad Nacional Autónoma de México, currently at the Structural Engineering Department of the Institute of Engineering, UNAM, CO 04510, Mexico City (e-mail: ALopezP@iingen.unam.mx). Sonia E. Ruiz (Professor) is with the Universidad Nacional Autónoma de México, at the Structural Engineering Department of the Institute of Engineering, UNAM, CO 04510, Mexico City (e-mail: SRuizG@iingen.unam.mx). Vanessa A. Segovia (M. Eng. Exgraduate Student) is with the Universidad Nacional Autónoma de México, UNAM, CO 04510 Mexico City (e-mail: VSegoviaO@iingen.unam.mx). design (DDBD) method for buildings with hysteretic energy dissipating devices (including BRBs), which takes into account both service and collapse limit states. The design parameters are defined by the stiffness- and strength-ratio of the main frame structure and the BRBs. In the present study, an extension of reference [2] is presented. Here the design parameters are selected based on the analysis of a set of three MDOF structural systems. II. METHODOLOGY The methodology used in this study outlines a scheme for finding the best combination of the design parameters α = K frame /K total , and γ = V damper /V total ; where K represents structural stiffness and V structural strength; and the subscripts "frame", "damper" and "total" represent: the structure without dampers, the BRB dampers, and the total frame-damper system, respectively. The methodology considers the initial cost of the combined frame–BRB system and the average of a suitable performance value to establish the BRB efficiency, obtained from several non-linear time-history analyses of the MDOF structure. The steps of the methodology are as follows: 1) Set different combinations of design parameters α = K frame /K total and γ = V damper /V total . 2) Apply the DDBD method [2], specifying the service and collapse tolerable drifts. 3) Select the commercial steel shapes corresponding to beams and columns [3]. The BRBs are chosen from a commercial catalog [4] with the areas that best approximate the design result. 4) The design obtained for the main frame and BRBs is modeled in a structural analysis program [5]. 5) Several ground motion records corresponding to the same family of stochastic processes are selected and scaled. 6) For each one of the selected and scaled records, a non- linear time-history analysis (NLTHA) is done. 7) From the results obtained from each NLTHA, a structural performance parameter (SPP) is calculated. In this study the SPP is the average value for maximum global ductility of the frame-BRB system. 8) The initial costs of the main frame and BRB system are estimated. 9) Then, with the data obtained from step 7 and step 8, a cost-efficiency criterion is applied, and the design parameters are obtained based on the minimum initial cost and the maximum efficiency of the building-damper system. Best Combination of Design Parameters for Buildings with Buckling-Restrained Braces Ángel de J. López-Pérez, Sonia E. Ruiz, Vanessa A. Segovia T World Academy of Science, Engineering and Technology International Journal of Civil and Environmental Engineering Vol:11, No:6, 2017 761 International Scholarly and Scientific Research & Innovation 11(6) 2017 scholar.waset.org/1307-6892/10007285 International Science Index, Civil and Environmental Engineering Vol:11, No:6, 2017 waset.org/Publication/10007285