Beam Rotation Capacity in Steel Dual Systems: Moment Frames and Eccentrically Braced Frames

Dual Systems are defined in ASCE 7-22 in section 12.2.5.1. They consist of a moment frame combined with a more rigid system, such as a shear wall or a braced frame, and are capable of supporting 25% of the design seismic load. When Dual Systems are combined with Excentric Braced Frames (EBF), they can allow a building to exceed the height limit of 160 ft, as specified in Table 12.2-1 of ASCE 7-22. In Costa Rica and other countries in Latin America, Dual Systems are commonly used to enhance the redundancy of the building. However, there is limited information available on the interaction between the two systems, particularly concerning connections. This research compares dual systems in fiveand nine-story buildings. A Push Over analysis was performed for both buildings, comparing their behavior with and without the moment frame. Inelastic beam rotations in the moment frame were evaluated at the life safety performance level. The results indicated that rotations were close to 0.02 radians at the lower stories. Overall, building strength improved with the use of dual systems in the taller structure.