Direct Answer
A braced frame is a structural system that resists lateral loads through diagonal steel braces that work in tension and/or compression. The primary types are: Concentrically Braced Frame (CBF — braces connect at member intersections), Eccentrically Braced Frame (EBF — braces connect with a deliberate offset creating a ductile 'link beam'), and Buckling-Restrained Braced Frame (BRBF — special braces designed to yield in both tension and compression without buckling).
Full Explanation
CBF types: X-brace (two diagonals), chevron or inverted-V brace (two diagonals meeting at the midpoint of a beam), single-diagonal, and K-brace (K-brace is generally not permitted in seismic design because it creates an unbalanced force on the beam). For seismic applications, Special Concentrically Braced Frame (SCBF) is governed by AISC 341 Chapter F with additional requirements for gusset plate clearance zones, brace slenderness limits, and connection design. EBF and BRBF are used where architectural flexibility requires fewer braces or where higher ductility demands exist.
What This Means for Your Shop
SCBF gusset plate connections require precise clearance zone geometry (2t ellipse). BRBF cores must be purchased from licensed manufacturers who provide the core and the brace casing. Your scope in a BRBF project is typically the gusset plates and connection hardware, not the brace itself.
Common Mistakes
Not accounting for the gusset plate clearance zone on SCBF braces. If the gusset edge impinges on the brace's plastic hinge zone, the system cannot develop the required ductility — a structural deficiency.
Recommended Process
For SCBF projects, have your detailer explicitly check and label the 2t ellipse clearance zone on every gusset plate shop drawing. Require the special inspector to verify clearance zones during installation.