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Home My WebLink AboutENGINEERING LETTER - 19-00420 - 59 Professional Plz St - Strobel Dentist Office Solar ProjectVSE Project Number: U1869-203-191 July 19, 2019 Blue Max Energy & Consulting LLC 26 N 2nd W Rexburg, ID 83440 REFERENCE: Dirk Strobel Dentist Office - Phase 2 Building: 59 Professional Plaza, Rexburg, ID 83440 Solar Array Installation To Whom It May Concern: Per your request,we have reviewed the existing structure at the above referenced site.The purpose of our review was to determine the adequacy of the existing structure to support the proposed installation of solar panels on the roof as shown on the panel layout plan.Based upon our review,we conclude that the existing structure is adequate to support the proposed solar panel installation. Design Parameters Code: International Building Code, 2015 Edition Risk Category: II Design wind speed: 115 mph (3-sec gust) per ASCE 7-10 Wind exposure category: C Ground snow load: 50 psf Existing Roof Structure Roof structure: 2x4 manufactured trusses @ 24" O.C. Roofing material: asphalt shingles Roof slope: 20° Connection to Roof Mounting connection: (1) 5/16" lag screw w/ min. 2.5" embedment into framing at max. 72" O.C. along rails Conclusions Based upon our review,we conclude that the existing structure is adequate to support the proposed solar panel installation. In the area of the solar array,other live loads will not be present or will be greatly reduced (2015 IBC,Section 1607.12.5). The glass surface of the solar panels allows for a lower slope factor per ASCE 7,resulting in reduced design snow load on the panels.The member forces in the area of the solar panels are decreased;thus,the stresses of the structural elements are decreased.Therefore,the requirements of Section 807.4 of the 2015 IEBC are met and the structure is permitted to remain unaltered. 651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com VSE Project Number: U1869-203-191 Dirk Strobel Dentist Office - Phase 2 Building 7/19/2019 The solar array will be flush-mounted (no more than 6"above the roof surface)and parallel to the roof surface.Thus,we conclude that any additional wind loading on the structure related to the addition of the proposed solar array is negligible. The attached calculations verify the capacity of the connections of the solar array to the existing roof against wind (uplift), the governing load case.Regarding seismic loads,we conclude that any additional forces will be small.With an assumed roof dead load of 10 psf,solar array dead load of 3 psf,and affected roof area of 33%(maximum),the additional dead load (and consequential seismic load)will be 9.7%.This calculation conservatively neglects wall weight.Because the increase in lateral forces is less than 10%,this addition meets the requirements of the exception in Section 807.5 of the 2015 IEBC. Thus the existing lateral force resisting system is permitted to remain unaltered. Limitations Installation of the solar panels must be performed in accordance with manufacturer recommendations.All work performed must be in accordance with accepted industry-wide methods and applicable safety standards.The contractor shall notify Vector Structural Engineering,LLC should any damage,deterioration or discrepancies between the as-built condition of the structure and the condition described in this letter be found.Connections to existing roof framing must be staggered,except at array ends,so as not to overload any existing structural member.The use of solar panel support span tables provided by others is allowed only where the building type,site conditions,site-specific design parameters,and solar panel configuration match the description of the span tables.The design of the solar panel racking (mounts,rails,etc.),and electrical engineering is the responsibility of others.Waterproofing around the roof penetrations is the responsibility of others.Vector Structural Engineering assumes no responsibility for improper installation of the solar array. VECTOR STRUCTURAL ENGINEERING, LLC ID Firm License: C2269 07/19/2019 _______________________________________________________ Wells Holmes, P.E. Project Engineer Enclosures WLH/ash 07/19/2019 651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com JOB NO.:U1869-203-191 SUBJECT:WIND PRESSURE PROJECT:Dirk Strobel Dentist Office - Phase 2 Building Label:Note: Calculations per ASCE 7-10 SITE-SPECIFIC WIND PARAMETERS: Basic Wind Speed [mph]:115 Notes: Exposure Category:C Risk Category:II Importance Factor, I: ADDITIONAL INPUT & CALCULATIONS: Height of Roof, h [ft]:15 (Approximate) Comp/Cladding Location:Hip?Yes Enclosure Classification: Zone 1 GCp:0.9 Figure 30.4-2B (enter largest abs. value) Zone 2 GCp:1.7 (enter largest abs. value) Zone 3 GCp:1.7 (enter largest abs. value) α:9.5 Table 26.9-1 zg [ft]:900 Table 26.9-1 Kh:0.85 Table 30.3-1 Kzt:1 Equation 26.8-1 Kd:0.85 Table 26.6-1 Velocity Pressure, qh [psf]:24.4 Equation 30.3-1 GCpi:0 Table 26.11-1 (largest abs. value) OUTPUT:Equation 30.9-1 Zone 1 Pressure, p [psf]:22.0 psf (1.0 W, Interior Zones*) Zone 2 Pressure, p [psf]:41.5 psf (1.0 W, End Zones*) Zone 3 Pressure, p [psf]:41.5 psf (1.0 W, Corner Zones* within a) (a= 3 ft) Solar Panel Array Gable/Hip Roofs 7° < θ ≤ 27° Enclosed Buildings Components and Cladding Wind Calculations ()()piphGCGCqp−= JOB NO.:U1869-203-191 SUBJECT:SEISMIC LOADS PROJECT:Dirk Strobel Dentist Office - Phase 2 Building COMPARE WIND & SEISMIC LOADS FOR CONNECTION (1 Sq. Ft. Section) 13.2 psf (Zone 1: 0.6 W from wind pressure calculation) 1.0 ft 1.0 ft Fperp:13.2 lb (Uplift)Wind Controls Connection Design Seismic Load, E: II Fa:1.4 D Fv:2.2 1.00 SMS:0.646 D SM1:0.341 1.5 SDS:0.431 0.448 SD1:0.227 0.157 1 0.7 * Fp,min: 0.271 lb 1.0 ft 0.7 * Fp,max: 1.447 lb 1.0 ft 0.7 * Fp,vert: 0.181 lb 1.0 0.7 * Fp,long: 0.723 lb 0.7*Fp,perp:0.4173 lb (uplift) CHECK INCREASE IN OVERALL SEISMIC LOADS SEISMIC:10 psf 33 % 3 psf 11.2 psf (DL+% of roof w/ Panels*Panel DL) 9.7% Wind Load, W: Wind pressure, p: Height, h: Width, w: Risk category: Seismic Design Category: Ip: Site Class: Rp: Ss: S1: ap: z: h: z/h: Conservatively neglecting the weight of existing wall materials, the installation of the solar panels represents an increase in the total weight (and resulting seismic load) of 9.7%. Because the increase is less than 10%, this addition meets the requirements of the exception in Section 807.5 of the 2015 IEBC. Thus the existing structure is permitted to remain unaltered. Estimated Roof Dead Load Max. % of Roof w/ Panels Dead Load from Panels Total Dead Load Increase in Dead Load VECTOR STRUCTURAL ENGINEERS JOB NO.:U1869-203-191 SUBJECT:CONNECTION PROJECT:Dirk Strobel Dentist Office - Phase 2 Building Lag Screw Connection Capacity:Demand: Lag Screw Size [in]:5/16 Cd:1.6 NDS Table 2.3.2 Embedment1 [in]:2.5 Grade: Capacity [lbs/in]:205 NDS Table 12.2A 1 13.2 6.0 33.0 435 Number of Screws:1 2 24.9 6.0 16.5 411 Prying Coefficient:1.4 3 24.9 6.0 16.5 411 Total Capacity [lbs]:586 Demand< Capacity:CONNECTION OKAY SPF (G = 0.42) Pressure (0.6 Wind) (psf) Max Tributary Width (ft) Max. Trib. Area2 (ft2) Max. Uplift Force (lbs) Zone 1. Embedment is measured from the top of the framing member to the beginning of the tapered tip of the lag screw. Embedment in sheathing or other material is not effective. The length of the tapered tip is not part of the embedment length. 2. 'Max. Trib Area' is the product of the 'Max. Tributary Width' (along the rails) and 1/2 the panel width/height (perpendicular to the rails). VECTOR STRUCTURAL ENGINEERS JOB NO.:U1869-203-191 SUBJECT:GRAVITY LOADS PROJECT:Dirk Strobel Dentist Office - Phase 2 Building CALCULATE ESTIMATED GRAVITY LOADS ROOF DEAD LOAD (D) Increase due to pitch Original loading Roof Pitch/12 4.4 Asphalt Shingles 2.1 1.06 2.0 psf 1/2" Plywood 1.1 1.06 1.0 psf Framing 3.0 psf Insulation 0.5 psf 1/2" Gypsum Clg.2.0 psf M, E & Misc 1.5 psf DL 10 psf PV Array DL 3 psf ROOF LIVE LOAD (Lr) Existing Design Roof Live Load [psf]20 ASCE 7-10, Table 4-1 Roof Live Load With PV Array [psf]0 2015 IBC, Section 1607.12.5 SNOW LOAD (S):Existing w/ Solar Panel Array Roof Slope [x:12]:4.4 Roof Slope [°]:20 Snow Ground Load, pg [psf]:50 ASCE 7-10, Section 7.2 Terrain Category:C ASCE 7-10, Table 7-2 Exposure of Roof:Fully Exposed ASCE 7-10, Table 7-2 Exposure Factor, Ce:0.9 ASCE 7-10, Table 7-2 Thermal Factor, Ct:1.1 ASCE 7-10, Table 7-3 Risk Category:II ASCE 7-10, Table 1.5-1 Importance Factor, Is:1.0 ASCE 7-10, Table 1.5-2 Flat Roof Snow Load, pf [psf]:35 ASCE 7-10, Equation 7.3-1 Minimum Roof Snow Load, pm [psf]:0 ASCE 7-10, Section 7.3.4 Unobstructed Slippery Surface?Yes ASCE 7-10, Section 7.4 Slope Factor Figure:Figure 7-2b ASCE 7-10, Section 7.4 Roof Slope Factor, Cs:0.83 ASCE 7-10, Figure 7-2 Sloped Roof Snow Load, ps [psf]:29 ASCE 7-10, Equation 7.4-1 Design Snow Load, S [psf]:29 1.00 35 35 4.4 20 50 C Fully Exposed 0.9 1.1 II 1.0 35 0 No Figure 7-2b JOB NO.:U1869-203-191 SUBJECT:LOAD COMPARISON PROJECT:Dirk Strobel Dentist Office - Phase 2 Building Summary of Loads Existing With PV Array D [psf]10 13 Lr [psf]20 0 S [psf]35 29 Maximum Gravity Loads: Existing With PV Array (D + Lr) / Cd [psf]24 15 ASCE 7-10, Section 2.4.1 (D + S) / Cd [psf]39 37 ASCE 7-10, Section 2.4.1 Maximum Gravity Load [psf]:39 37 Ratio Proposed Loading to Current Loading:94%OK (Cd = Load Duration Factor = 0.9 for D, 1.15 for S, and 1.25 for Lr) The gravity loads in the area of the solar array are decreased; thus, the stresses of the structural elements are decreased. Therefore, the requirements of Section 807.4 of the 2015 IEBC are met and the structure is permitted to remain unaltered.