Extension of Hybrid Force/Displacement Seismic Design (HFD) for Eccentric Braced Frames under Near-Fault Earthquakes

The computational complexity of performance based seismic design methods makes most engineers prioritize the use of simpler force-based methods. Having a practical relationship between force and performance methods can solve this challenge. The hybrid force/displacement method has the advantages of the design method based on the performance and computational ease of force design methods. In this research, frames with 3, 6, 9, 12, 15 and 20 story with 3 bays with a width of 5 meters have been considered. The length of the link beam is defined as another parameter affecting the response, 1, 1.75 and 2.50 meters. The studied models have been developed by designing the method of load and resistance factor design method, for 3 performance levels of immediate occupancy, life safety and collapse prevention, as well as the first occurrence of the plastic joint. The final models are analyzed under 20 pulse-type near-fault records using time history analysis. Finally, using the genetic algorithm, the corresponding experimental relationships are presented to determine the behavior factor, local and global ductility. The proposed relationships are influenced by geometric characteristics such as the number of stories, the stiffness ratio of the columns, the slenderness of the braces, the length of the beam and the ductility levels. The results of the hybrid force/displacement seismic design of structures outside the range of the defined database, in comparison with the force methods, show the accuracy of this method in estimating the seismic needs of divergent bracing frames.