30 November 1998
Built-up columns are fabricated by welding individual studs together to form a closed cross-section, using
flare V-groove welds. The same weld size and spacing shall be used between all studs in the built-up
column. These welds are design according to AISI (Section E2.5 Flare Groove Welds), assuming double
shear. The maximum spacing between centers of intermittent welds, smax is determined as follows:
s max = 1.5φ G t cFcu
φG = the resistance factor for flare grove welds, equal to 0.55.
tc = the stud thickness of the built-up columns.
Fcu = the ultimate strength of the column steel.
L = the length of intermittent grove welds.
q = the maximum shear determined in Equation 3-6.
Intermittent welds shall be made at both the top and bottom ends of the columns, regardless of the
maximum center-to-center spacing, smax.
d. Column Combined Axial and Moment Capacity. The combination of axial load and bending
shall be evaluated using a modification to AISI guidance (C5.2.2 Combined Compressive Axial Load and
Bending LRFD Method). The combination of axial and moment on the column shall be evaluated
based on the following interaction equation (modification of AISI Equation C5.2.2-2):
Pvu max Ma
Fcy A c Mnx
Pvumax = the applied axial load, defined in Equation 3-5.
Ac = the nominal column cross-sectional area.
Ma = the applied moment at maximum estimated strap yield strength, defined in Equation 3-11.
This equation conservatively assumes the column is fully fixed at its top and bottom by the
panel anchors. This moment is also conservatively based on the maximum panel lateral
deflection at which the diagonal strap will yield. This moment includes the column bending
and P-delta effect of axial load. Still, this moment will be less than the column moment with
no axial load (paragraph 3-8c). The applied moment, Ma is defined as follows:
6EIc δ sy max
+ Pvu max δ sy max
δsymax = the maximum estimated lateral panel deflection at the maximum estimated yield strength
of the diagonal straps, Fsymax and is defined as follows:
Fsy max H2 + W 2
δ sy max
Fsymax = maximum estimated yield stress of the diagonal straps, equal to 2Fsy for Grade 33 and
1.5Fsy for Grade 50 steel.