Composite braced frames consisting of steel, composite, and/or reinforced concrete elements have been used in low- and high-rise buildings in regions of low and moderate seismicity. The composite ordinary braced frame (C-OBF) category is provided for systems without special seismic detailing that are used in seismic design categories A, B, and C. Thus, the C-OBF systems are considered comparable to structural steel systems that are designed according to the Specification using a seismic response modification coefficient, , of 3 . Because significant inelastic load redistribution is not relied upon in the design, there is no distinction between frames where braces frame concentrically or eccentrically into the beams and columns.
H1.1 Scope
The combination of steel, concrete, and/or composite member types that is permitted for C-OB F is intended to accommodate any reasonable combination of member types as permitted by the Specification and ACI 318 (ACI, 2019).
H1.6 Connections
Examples of connections used in C-OBF are shown in Figures C-H1.1 through C-H1.3. As with other systems designed in accordance with the Specification for a seismic response modification coefficient, , of 3 , the connections in C-OBF should have design strengths that exceed the required strengths for the earthquake loads in combination with gravity and other significant loads. The provisions of Section D2.7 should be followed insofar as they outline basic assumptions for calculating the strength of force transfer mechanisms between structural steel and concrete members and components.