HomeMy WebLinkAboutP_Sounder Proposed RTU 03_09_23_20230623
Project Record
DATE March 09, 2023
TO Gretchen Blain, AIA, NCARB,
LEEDAP BD+C
Senior Project Manager
Generator Studio
1615 Baltimore Ave
Kansas City, Missouri 64108
FROM Steve Savage
PROJECT Seattle Sounders
CPL PROJECT # S222017
CC
RE Rooftop Mechanical Units – Structural Loading
Coughlin Porter Lundeen has reviewed the proposed addition of a new rooftop mechanical unit. The unit,
including curb system, is assumed to be less than 8,000lbs. The existing roof framing system is composed of
mildly reinforced concrete slabs supported by mildly reinforced concrete joists. The joists are supported by
post-tensioned concrete beams. The new unit will be placed directly over the existing column at Grid E/2 (see
attached plan). Attached calculations indicate the increase in shear and bending in the beams will be less
than 5%.
Per the 2018 IEBC, Section 706.2, the load increase is less than the 5% threshold for new equipment. As
such, reinforcement of the existing roof framing is not required.
Feel free to contact us if you have further questions.
Sincerely,
Steve Savage, PE, SE
Structural Associate
Previously proposedRTU location(DIMS ~ 8' x 13')
NEW ROOFTOP UNIT ADDITION - LOADING STUDY
03/09/23
Roof Loading at
Existing Structure
159 psf
total SDL
Information from the Longacres facility original
General Structural Notes and drawings
location of
column D/2
proposed location for
addition of new rooftop unit
Load Case 1: Rooftop unit fully north of column D/2
Beam Loading
Post-tensioned beam tributary width = 32'-0"
Controlling load combination: 1.2DL + 1.6SL
SDL = 159psf * 32ft = 5088 lb/ft
1.2*SDL = 6105.6 lb/ft
Self-Weight for 36"wd, 29"dp beam =
150pcf*(36/12ft)*(29/12ft) = 1087.5 lb/ft
1.2*SW = 1305 lb/ft
Snow Load = 25psf * 32ft = 800 lb/ft
1.6*SL = 1280 lb/ft
New rooftop unit weight = 8000lb/(155.51/12ft) = 617.33
lb/ft
1.6*RTUDL = 740.8 lb/ft
SDL
Beam self-weight
Snow Load
SDL
Beam self-weight
Snow Load
New rooftop unit added weight
Vmax = 217.265 kip
Mmax
(+) = 977.69 kip-ft
Mmax(-) = -1738.12 kip-ft
Vmax = 226.428 kip
Mmax
(+) = 984.714 kip-ft
Mmax(-) = -1782.03 kip-ft
Change in loading demand
V: increase of 4.22%
M(+) : increase of 0.72%
M(-) : increase of 2.53%
full length of RTU = 13ft
Existing loading only Existing loading with added RTU weight
Load Case 2: Rooftop unit centered over column D/2
Beam Loading
Post-tensioned beam tributary width = 32'-0"
Controlling load combination: 1.2DL + 1.6SL
SDL = 159psf * 32ft = 5088 lb/ft
1.2*SDL = 6105.6 lb/ft
Self-Weight for 36"wd, 29"dp beam =
150pcf*(36/12ft)*(29/12ft) = 1087.5 lb/ft
1.2*SW = 1305 lb/ft
Snow Load = 25psf * 32ft = 800 lb/ft
1.6*SL = 1280 lb/ft
New rooftop unit weight = 8000lb/(155.51/12ft) = 617.33
lb/ft
1.6*RTUDL = 740.8 lb/ft
SDL
Beam self-weight
Snow Load
SDL
Beam self-weight
Snow Load
New rooftop unit added weight
Vmax = 217.265 kip
Mmax
(+) = 977.69 kip-ft
Mmax(-) = -1738.12 kip-ft
Vmax = 222.019 kip
Mmax
(+) = 978.61 kip-ft
Mmax(-) = -1751.33 kip-ft
Change in loading demand
V: increase of 2.19%
M(+) : increase of 0.1%
M(-) : increase of 0.76%
half length of RTU = 6.5ft
Existing loading only Existing loading with added RTU weight