Seismic Design of Reinforced Concrete Special Moment Frames

Reinforced concrete special moment frames are used as part of seismic force-resisting systems in buildings that are designed to resist earthquakes. Beams, columns, and beam-column joints in moment frames are proportioned and detailed to resist flexural, axial, and shearing actions that result as a building sways through multiple displacement cycles during strong earthquake ground shaking. Special proportioning and detailing requirements result in a frame capable of resisting
strong earthquake shaking without significant loss of stiffness or strength. These moment-resisting frames are called “Special Moment Frames” because of these additional requirements, which improve the seismic resistance in comparison with less stringently detailed Intermediate and Ordinary Moment Frames.

The design requirements for special moment frames are presented in the American Concrete Institute (ACI) Committee 318 Building Code Requirements for Structural Concrete (ACI 318). The special requirements relate to inspection, materials, framing members (beams, columns, and beam-column joints), and construction procedures. In addition, requirements pertain to diaphragms, foundations, and framing members not designated as part of the seismic force-resisting system. The numerous interrelated requirements are covered in several sections of ACI 318, not necessarily arranged in a logical sequence, making their application challenging for all but the most experienced designers.