Direct displacement-based seismic design of buckling-restrained braced RC frames

The experiences of past earthquakes show that the moment-resisting reinforced concrete structures suffered damage due to the inherent brittle behaviors of concrete and lack of structural stiffness. The configuration of buckling restrained brace (BRB) in RC frame is widely increased for the development of the reinforced concrete buckling‐restrained braced (RC-BRB) dual system since the implementation of BRBs can significantly improve the dissipative capacity and lateral stiffness of the main reinforced concrete frames. On the other hand, the structural damage amount is strongly related to the induced displacements and deformations during an earthquake. Therefore, the robust design method must take into account the displacement as the main designing parameter to control the damage of the structures. To this end, researchers have proposed the direct displacement-based design (DDBD) method, which employs displacement as a main designing criterion throughout the design process. In this study, a DDBD method for dual RC-BRB frames is developed by considering the ultimate capacity of BRB elements. New yield displacement and stiffness expressions are proposed to determine the characteristics of the equivalent single-degree-of-freedom (SDOF) system. The developed method is evaluated by designing twelve RC-BRB frames corresponding to different storey numbers and two types of BRB configurations. The Numerical model is developed and validated using available experimental data to be used in the nonlinear time-history analysis (NTHA). In order to gauge the performance of the developed DDBD method, the seismic behavior of designed frames subjected to 20 real ground motions is investigated through NTHA procedure. In addition, the expressions for the design displacement profile of the RC-BRB frames are provided as a function of relative height using the average maximum displacements calculated from NTHA outputs. The developed design displacement profile leads to significant improvements in the coefficient of determination, R2, which is increased from 0.69 for low-rise to 0.98 for high-rise frames. The results indicate that the RC-BRB frames designed by the developed DDBD method can successfully achieve the desired performance objectives. Furthermore, the comparison between the estimated results and the corresponding ones obtained from NTHA indicates that the proposed displacement profile expressions can be found to be efficient and effective for estimating the displacements of the RC-BRB dual frames.