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  • Sample of Floor Beam Investigation


    Floor beam bracing

    The braces located in the center portion of each beam (tension flange brace), and those
    located at and near columns (compression flange brace), are treated differently in design.

    1) Braces in center portion: The only requirement I am aware of is the Sidesway web
    buckling provisions of AISC 9th, K1.5. The Mfg. drawings (partial set) we have,
    do not indicate beam section geometry, or WF size, so the following shows K1-5 calculations
    for beams roughly similar in size.

    K1-5 is for point loaded beams, and it excludes uniformly loaded beams from the
    check altogether. Since our case is somewhat in-between, (joist point loads at 2' o.c.)
    I used the load from 2 joists arbitrarily.

    The midspan braces can be removed, but it is necessary to install stiffeners per K1-5,
    unless more detailed review is undertaken. (K1-5 is based on research by Yura (1982),
    which could be studied further.

    2) Braces at and near columns: These braces are critical, as they determine the unbraced
    length utilized in the original design for allowable bending stress. At 2' o.c. the beam
    Fb was likely 0.6Fy. If unbraced length increases to the length between inflection points,
    due to brace removal, the allowable bending stress likely goes down significantly.

    A suggested work around is to install stiffeners, and run brace from joist top choDr to a
    point in the lower thiDr of the stiffener.

     



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