Seismic Design of Eccentrically Braced Space Frame

Case studies of the design of an office building employing three-dimensional (3D) eccentrically braced frames (EBFs) as the primary seismic lateral force resisting system are discussed in detail. The floor framing system consists of composite beams supported by long span trusses, which are then supported by eight exposed composite columns. The lateral system is a dual system. The primary lateral system is made of four EBFs supported by the eight composite columns and folded around the four corners of the main building. The secondary lateral system is a moment resisting space frame consisting of the floor trusses and the composite columns. The development of an inelastic two-dimensional analytical model for the 3D EBFs are described. Nonlinear pushover and earthquake response history analyses indicate that the dual structural system possesses substantial reserve strength over the code prescribed minimum lateral loads. The member yielding sequence and the distribution, as well as the extent of the plastic hinge rotations observed from the analyses illustrate that the building is likely to perform satisfactorily under severe seismic events.