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Home My WebLink AboutSTRUCTURAL LETTER 11/28/22 - 22-00794 - 80 K St - Solar PanelsDate: 28 November 2022 Big Dog Solar Energy 620 Pheasant Ridge Dr Chubbuck, ID 83202 Darian Bess Residence: 80 K St, Rexburg, ID 83440 Dear Sir/ Madam, Conclusion Page 1 of Darian Bess letter Structural Letter of Approval Terra Engineering Consulting (TEC) has performed a structural analysis for the existing framing and load conditions and determined that the structure requires a structural retrofit in order to meet code standards and hold the additional proposed load. The proposed structural retrofit requirement is designed to improve the structural capacity of the area for the proposed panels. TEC has reviewed the site survey, photographs of the existing framing, and the proposed PV array. The attached calculations are based off the assumptions that the existing structural components are in good condition, and that the site survey provided by the client is accurate. The design assumptions, and the calculations are located in the attached References page. The contractor shall notify TEC of any damage to the roof system encountered at the time of installation. The design of the solar panel’s mounting hardware is to be provided by the manufacturer or installer. The proposed structural retrofitting must be completed prior to installation of proposed PV panels. TEC, Engineer-of-Record (EOR) nor their representatives shall not be held liable, nor can guarantee that the proposed structural retrofit requirements have been properly installed without conducting a structural observation or construction inspections by authority having jurisdiction. Structural observation or construction inspections will not be performed by TEC, EOR or their representatives. The total load of the solar panels is assumed to not exceed 3 psf, and the typical 20 psf live load will not be present in the area of the panels, as defined per Section 1607.12.5 in 2015 IBC. The structural analysis concluded that the existing rafters needs to be reinforced by adding a knee- wall at approximately mid-span of the rafters and connects it to the existing interior bearing wall; contractor to verify the location of the interior bearing wall. Regarding lateral loads, the wind load controls, and due to the low profile of the panels (3” to 6”) as well as PV frame, wiring, conduit, and structural component below the module causing restriction in airflow which allow it to be considered as “partially enclosed structure”; thus the additional pressure on the structure is considered negligible. TEC concludes that upon the completion of the required structural retrofit, the structure will be adequate to support the design loads with addition to the proposed solar panels load. These conclusions are based on the attached calculations. 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 General Instructions Best Regards, Terra Engineering Consulting, PLLC Ahmad Alshakargi, PE Civil Engineer References Design Parameter Risk Category: II Ground Snow load: 50 psf Roof Snow load: 35 psf Design Wind Speed: 115 mph (3 sec gust) per ASCE 7-16 Seismic Design Category: D Wind Exposure Category: C Existing Roof Structure (Shop) Existing roof framing: 2x6 Rafters at 24” O.C. Roof material: Metal seam Roof slope: 24° Roof type: Gable Solar Panels Weight: 3 psf Page 2 of Darian Bess letter Code: 2018 International Building Code/ International Existing Building Code, ASCE 7-16, and National Design Specification for Wood Construction (NDS) 2015 Edition Connections: Series 100 UL The solar array mounting system shall be connected to every other truss/rafter (48" maximum penetration spacing) in order to distribute the load evenly. The installer shall stagger the connections into the roof framing to not overload any existing structural members. Installation and waterproofing shall be performed within accepted industry standards. Retrofit addition: Knee-wall 11/28/2022 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 Date:11/28/2022 Client:Darian Bess Subject:Gravity load Gravity load calculations Snow load (S)Existing w/ solar panels Roof slope (°):24 24 Ground snow load, pg (psf):50 50 ASCE 7-16, C7.2 Terrain category:C C ASCE 7-16, table 7.3-1 Exposure of roof:Fully exposed Fully exposed ASCE 7-16, table 7.3-1 Exposure factor, Ce:0.9 0.9 ASCE 7-16, table 7.3-1 Thermal factor, Ct:1.1 1.1 ASCE 7-16, table 7.3-2 Risk Category:II II ASCE 7-16, table 1.5-1 Importance Factor, Is:1 1 ASCE 7-16, table 1.5-2 Flat roof snow load, pf (psf):35.0 35.0 ASCE 7-16, equation 7.3-1 Minimum roof snow load, pm (psf):0 0 ASCE 7-16, equation 7.3-4 Roof Surface type: Unobstructed Slippery surface Unobstructed slippery surface ASCE 7-16, C7.4 Roof slope factor, Cs:0.77 0.77 ASCE 7-16, C7.4 Sloped roof snow load, ps [psf]:27.0 27.0 Roof dead load (D) Roof pitch/12 5.3 Metal seam 1 psf 1/2" Gypsum clg.1 psf 1/2" plywood 1 psf Insulation 1 psf Framing 3 psf M, E & Misc 0.5 psf Roof DL without PV arrays 8.2 psf PV Array DL 3 psf Roof live load (Lr)Existing w/ solar panels Roof Live Load 20 0 2015 IBC, Section 1607.12.5 ASD Load combination: Existing With PV array D [psf]8.2 11.2 ASCE 7-16, Section 2.4.1 D+L [psf]8.2 11.2 ASCE 7-16, Section 2.4.1 D+[Lr or S or R] [psf]35.2 38.2 ASCE 7-16, Section 2.4.1 28.4 31.4 ASCE 7-16, Section 2.4.1 Maximum gravity load [psf]:35.2 38.2 ASCE 7-16, equation 7.4-1, Design Snow Load (S) D+0.75L+0.75[Lr or S or R] [psf] Date:11/28/2022 Client:Darian Bess Subject: Wind pressure calculations Basic wind speed (mph)115 Risk category II Exposure category C Roof type Gable Figure for GCp values ASCE 7-16 Figure 30.3-2A-I Zone 1 Zone 2 Zone 3 GCp (neg)-0.9 -1.7 -2.6 GCp (pos)0.5 0.5 0.5 zg (ft)900 (ASCE 7-16 Table 26.11-1) α 9.5 (ASCE 7-16 Table 26.11-1) Kzt 1 (ASCE 7-16 Equation 26.8-1) Kh 0.9 (ASCE 7-6 Table 26.10-1) Kd 0.85 (ASCE 7-16 Table 26.6-1) Velocity Pressure,qh (psf)25.90 (ASCE 7-16 Equation 26.10-1) Gcpi 0 (ASCE 7-16 Table 26.13-1)(0 for enclosed buildings) Zone 1 Zone 2 Zone 3 W Pressure, (neg) [psf]-23.31 -44.03 -67.34 W Pressure, (pos) [psf]12.95 12.95 12.95 W Pressure, (Abs. max) [psf]23.31 44.03 67.34 Connection calculations Capacity Connection type:Lag screw Lag screw diameter:5/16 Embedment (in):2.5 Framing grade:SPF#2 G:0.42 Capacity [lbs/in]:205 (2015 NDS table 12.2A) Number of screws:1 Total capacity [lbs]:512.50 Demand Anchor spacing:48 in Anchor spacing in roof corners:48 in Zone ( 0.6 W Pressure, psf), see Note 1 Max. tributary area (ft^2)Max Uplift force (lbs) 1 14.0 11 153.8 2 26.4 11 290.6 3 40.4 11 444.4 (only changes if structure located on a hill or ridge) Connection Meets Demand Wind load and Connection Note 1: 0.6W results from dominant ASD combo [0.6D+ 0.6W] (ASCE 7-10 2.4.1). Date:11/28/2022 Client:Darian Bess Subject:Beam calculator Beam Design (Roof)2x6 Rafters at 24 in O.C., span with the knee-wall added, the span is shortened Load Combination Combo DL LL W SL LLR E Sum 1 1.4 11.2 0 0 0 0 0 27 0 0 0 15.68 2 1.2 11.2 1.6 0 0 0 0.5 27 0 0 0 26.94 3 1.2 11.2 1 0 1 0 1.6 27 0 0 0 56.64 4 1.2 11.2 1 0 1 0 0.5 27 0 0 0 26.94 5 1.2 11.2 0 0 0 0 0.2 27 0 1 0 18.84 6 0.9 11.2 0 0 1 0 0 27 0 0 0 10.08 7 0.9 11.2 0 0 0 0 0 27 0 1 0 10.08 Roof DL 11.2 psf (see Gravity load roof DL) S 27 psf W E LL 0 psf RLL 0 psf (see Gravity load LL with PV arrays) U 56.64 psf beam spacing 2 ft o.c. uniform load 113.28 plf span 9 ft Mu = w(l^2)/8 1146.96 lb-ft Number of joists 1 Flexure design Cr 1.15 (2015 NDS Supp, p32) Timber grade DFL#2 (2015 NDS Supp, table 4A) Fb 900 psi (set SPF#2 as default) Kf 2.54 (2015 NDS, table 2.3.5) bending fact.0.85 (2015 NDS, table 2.3.6) dimension Cf (table 4A, NDS supp 2015, p32) S in^3 (table1B, NDS supp 2015) Fbu = Mu/S (psf)Fbu (psi) moment of inertia in^4 (table 1B, NDS supp) 2x6 1.3 7.56 262162.3 1820.571 20.8 purlin size λ (Table N3, NDS 2015 p184)F'bn (psi)Fbu Fbu < F'bn 2x6 0.8 2323.9476 1820.571 Works Design for deflection we going to assume these calculations for U1 only since its clearly higher we use the following equation to calculation max deflection, minimum interia, and deflection service load combination:D+S U 38.2 lb Uniform load 76.4 plf *convert all the units in the equaion to inch max def. (ft) E psi(Table 4A)w (plf)l (ft) I (min) (in^4) Imin< Ipurlin 0.045 1600000 76.4 9 13.05366 Works Design for Shear fvu = 1.5V/A V is shear Vu, and A cross sectional area of purlin found in table 1B uniform load 113.28 plf Vu 509.76 lb Vu = wl/2 Framing cross section 8.25 in^2 fvu 92.68 psi Fv 180 psi (for DFL#2) F'vn 311.04 psi F'vn > fvu Works Beam works