wu = 1.2 DL + 1.6 LL = 1.2(400) + 1.6(400) = 1120 plf (16.34 KN / m)
Mu = wL2/8 = (1120plf)(20ft.)2/8 = 56 kipft. (75.9 KN-m)
Try W12 x 26, BF=2.99 Lp = 6.3'φMp = 100 kipft. A36 steel. Assume the beam is laterally supported at 6' 8" by
the joists. Therefore, Lb > Lp, use the following check for the beam design;
φb M n = C b φb M p - BF( L b - Lp )
From AISC LRFD 93 Part 4 (Beam Design)
φb M n = 1.0 100 - 2.99(6.67 - 6.3) = 98.9kipft (134KN-m)> 56 kipft. (75.9 KN-m) OK.
The beam is slightly overdesigned in anticipation of the combined action due to collector and chord action.
Tributary Area = 20'x 20'= 400 ft.2 (37.21 m2)
Roll-Up Doors: 1.2 kips (Each column must support the door wt. on either side)
Pu = 1.2[(18psf)(400 ft.2) + 1.2 k] + 1.6(20psf)(400 ft.2) = 23 kips (102.3 KN)
This is a very low axial load. The columns at the end bays where the mezzanines occur must support the
axial forces generated by the braced frames in addition the extra weight from the mezzanine beams. The
columns are slightly overdesigned in anticipation of these forces.
Try W10x33, ry = 1.94, A = 9.71 in.2
KL/r = (1.0)(20'(12"/' /1.94" = 124 look up design strength from AISC design manual:
φFcr = 13.62 ksi
AISC LRFD ' 3 Table 3-36
Pn = AgFcr
AISC LRFD ' 3 Eq. E2-1
φ n = (13.62 ksi)(9.71in. ) = 132 kips (589.1 KN) > 23 kips (102.3 KN), OK
Mezzanine Roof / Deck Slab
The mezzanine deck will be selected from a manufacturer' catalog. The mezzanine must support high live
loads (125 psf or 5.99 KN/m ) which suggest the use of metal decking with a topping slab. The catalog
lists allowable superimposed service loads.
Dead Loads to Deck:
(Only superimposed loads are considered)
Live Loads to Deck:
129 psf (6.18 KN/m2)
Enter the catalog with 8'(2.44m) span between supporting beams and select 20 gage (1mm) decking with
3-1/2" (89mm) total depth including concrete topping.
The beams span 20'(6.10m) and are spaced at 8'(2.44m) on centers. The interior beams are simply supported on
base plates anchor bolted to CMU pilasters at the exterior and interior walls, while the exterior beams frame into the
steel columns. It is assumed that the beams are supported laterally along the full length by the decking and concrete