A simplified formula for the determination of the fundamental period of mixed structures with vertical combination of different seismic resisting systems

Vertical combination of different seismic resisting systems, permitted in the design codes such as ASCE/SEI7-16, is an effective choice for structural mid- and high-rise buildings. In analysis structures, according to codes, estimate fundamental period vibration needed. On other hand, there no simplified equation compute mixed buildings with vertical systems. this study, by using Rayleigh’s method, a formula proposed determining type structures. The verified eigenvalue mathematical model 11 building frames characteristics along their height. Also, two structures composed steel reinforced concrete moment-resisting frame (MRF) well concentrically braced (CBF) MRF are examined. 3-dimensional (3D) vertically irregular 6-story setbacks also determined show efficiency method Furthermore, obtained from experimental full-scale test structure. results indicate that satisfactory accuracy. largest average errors under consideration, formula, less than 10% 6%, respectively, compared analysis. Therefore, can be used evaluation process existing new ones.