HomeMy WebLinkAboutConnection Review-Roof i 107 Beach Street
Dennis,MA 02638 PHILBROOK
1-508-364-1301(cell) ENGINEERING
1-508-385-8682(offc)
Memo for Record R E C E I_V E D
To: Mr.Tim Sears—Building Inspector,Town of Yarmouth, MA MAY 2 9 201g
From: T.Vamum Philbrook, P.E. BUILDING DEPARTMENT
CC: Patrick Jacobs-Builder/Agent By --Date: May 7,2019
Re: Connection Review; Roof-top Mini-split Condensors
Surf&Sand Beach Motel,South Shore Drive,South Yarmouth,MA
1
Dear Mr. Sears:
I met Mr. Jacobs and together inspected the connections for the roof-top mini-split (suitcase style)
condensers located on the 2nd story flat roofs of the motel. As installed the units fasten to pairs of 4"x
4"PT pine sleepers using 4 ea 14"hex drive screws through the factory provided base brackets—1 pair
of screws on each side of the long face. In turn the 4"x 4"wood sleepers extend away from the units
approx. 12"+ in each direction perpendicular to the same long face. The sleepers are screwed into the
roof substrate framing using 4 ea 6"Timber-Lok®screws—2 screws on each side of the unit. There is
a new rubber membrane roof installed over the sleepers, covering the heads of the Timber-lok®
screws. There is asphalt tar spread over the heads of the Y" hex drive screws. The condition of the
substrate is unknown at this time due to the new roofing product so the terminal screw connection
below the roof deck is unknown. From builder records the driving was difficult so my only assumption
in this process is that the screw connection (not the screw itself) to the substrate is adequate. The
actual pull-out load is not excessive by calculation.
Summarizing; both the %" hex drive screw and the 6"Timber-lok®screw provide enough connection
strength to meet design loads plus 15%. No duration of load increases were considered and the dead
load of the units was neglected—additional conservative allowances. Short of an actual pull-out test of
the connection to the substrate the hardware and geometry of the installation exceed the high wind
requirements for this site.
Thank you and as always if you need anything further please do not hesitate to contact me directly.
Respectfully submitted, P
3,��tF P rl�s9\
T.VARNUM PHILBROOK, P.E. �° r VARNUM s�
PHILBROOK
Tvp/encl.—Design Development Sheet MECHANICAL
-o 0.34691
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1
PHILBROOK ENGINEERING
107 BEACH STREET Project: SURF&SAND
DENNIS,MA 02638 Project No: P18-54
1-508-385-8682 Date: 7 May 2019
GENERAL, DESCRIPTION Contact, Pat Jacobs 774-353-6852 9th ed.
---- = P18-54
Narrative: Open Spaced Mini-Split Rooftop Condensors on Wood Stringer: bz4645
Location: SURF & SAND Motel, South Shore Drive, South Yarmouth, MA i J5. 0y��\\j f
SSA
Construction: Suitcase Rooftop Condensors on Pair of PT Timber Stringers (//ca c-
T VARNUM f'
O PHILBROOK
SPECIAL CONSIDERATIONS MECHANICAL
--- -o o.�16.1 �Use Group(s) : U (Utility) L `1 y�V0
Construction Type: III (Non-combustible Walls) - Exterior S �O��NALj
Misc or Comments: o Site Check & Measure Existing Conditions
o Design Layout Checks - Combined Wind Directions
Lateral for Overturning/Sliding
o Construction Notes & SK Note Sheet
DESIGN CONSIDERATIONS
Soil Data: - Site Plan or Boring Log available: NO
Preparer of plan or log:
- Direct Observation: YES - P87-10 Foundation
Coarse-Medium Silty Sands, Some Cobbles
Description:
USCS = SP/SM SBC Class = _-8-_
Specifics: Br(allow) = 2,400 lb/sq ft
Fire Data: n/a - Exterior Open Roof - Metal Cabinetry
Loads SBC Location #/sq ft Dur Note
Mini-split Condensors 175 lb ea 1.0 Self-weight
Snow Loads from 9th ed (Tbl. 1604.11 MA Amend) & ASCE 7-10
Pg = 30 lb/sq ft & Pf = 25 lb/sq ft; P(flat) = .7CeCtiPg
Pf (flat), Ce = 1.0, Ct = 1.0, Is = 1.0 & Ps (slope) = CsPf
Pf OR = 0/12) 18 1.15 Flat Roof
Wind Loads from 9th ed (Para. 1609.6 & Tbl. 1604.11 M► Amend)
V(33) Speed (tbl) = 140 MPH(ult); MCP = C (Open) & Mrh = 18 ft (w/ parapet)
Converted to 108 MPH(asd) Tbl. 1609.3.1 - Use 110 MPH
Wind - qs (Ref Pres) 31 Tbl. 1609.6.2(1)
Pnet = q(s)KzCnet(IwKzt] Eqn. 16-35 & Tbl. 1609.6.2
Kz = 0.88, Cnet = -1.40, Iw = 1.0, Kzt = 1.0 Partial Open
Pnet On = 0/12) -38 1.33 Suction
Loadings 1 Mini-Split Snow Sliding lb Over-M ft-lb
LATERAL LOAD 1 -38 0 -380 -887
I 'Solid' Wide Face for Projection/Loads
DESIGN ANALYSIS (The unit self-weight righting effects were not considered) :
1. Overturning Restraint by the Mini-split Bracket Feet - 16" o/c - 2 sets of screws
Over-M =-887 ft-lb Right-M = -887 ft-lb/1.33 = 667 lb per side
667 per side x 1.15/2 = 385 lb/screw for 2 screws
1/4" Hex Drive - 2-1/2" effective threads = 418 lbs/scrE OK by Design
2. Overturning Restraint by the Mini-split Sleepers - 36" o/c - ave. center
Over-M =-887 ft-lb Right-M = -887 ft-lb/3.0 = 296 lb per side
296 per side x 1.15/2 = 170 lb/screw for 2 screws
6" Timber-Lok - 2" effective threads = 220 lbs/screw OK by Design
3. Sliding Restraint by the Mini-split Sleepers - 2 ea 6" Timber-lok Screws
Sliding = 380 lb x 1.15/2 = 219 lb/screw for 2 screws
6" Timber-Lok - 2" effective threads = 270 lbs/screw OK by Design