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:1: U NI RAC Unirac Code-Compliant Installation Manual SolarMount 1 <br />Part II. Procedure to Select Rail Span and Rail Iype <br />[2.1.] Using Standard Beam Calculations, Structural Engineering Methodology <br />The procedure to determine the Unirac SolarMount series <br />rail type and rail span uses standard beam calculations and <br />srnictural engineering methodology. The beam calculations <br />are based ona simply supported beam conservatively, ignoring <br />the reductions allowed for supports of continuous beams over <br />multiple supports. Please refer to Part I for more in formation <br />on beam calculations, equations and assumptions. If beams <br />are installed perpendicular to the eaves on a roo f steeper than <br />a 4/12 pitch in an area with a ground snow load greater than <br />30psf, then additional analysis is required for side loading on <br />the roof attachment and beam. <br />In using this document, obtaining correct results is <br />dependent upon the following: <br />1. Obtain the Snow Load for:your area from your local building <br />official. <br />2. Obtain the Design Miind Load, phet· See Paft I (Procedure <br />:to Determine the Design Wind Load) for more information on <br />--Eilailififirthe-Design Wind Load. <br />3. Please Note: The terms rail span and footing spacing <br />are interchfingeable in this document. See Figure 3 for <br />illustrations. <br />4. Touse Table 8 and Table 9 the Dead Load fpr your specific <br />installation must be less than 5 psf, including modules and <br />Unirac racking systems. lf the, Dead Load is greater than 5 <br />psf, see your Unirac distributor, a local structural engineer or <br />contact Unirac. <br />The following prorprlure w·111 gliirle yoil in selpang a I Jnirar <br />rail for a flush mount installation. It will also help determine <br />the design loading imposed by the Unirac PV Mounting <br />Assembly that the building structure must be capable of <br />supporting. <br />S lep 1 . Delel·11111,e Llic-Tblut Deaisil Ludd <br />Figure 3. Rail span andfooting <br />spacing are interchangeable. <br />02 <br />The TotaIDesign Load, P (p.0 is determined using ASCE 7-05 <br />2.4.1 (ASD Method equations 3,5,6 and 7) by adding the Snow <br />Loadz, S (psf), Design Wind Load, pnez (psj) from Part I, Step 9 <br />and the Dead Load (ps,O. Both Uplift and Downforce Wind <br />Loads calculaced in Step 9 of Part l must be investigated. Use <br />Table 7 to calculate the Total Design Load for the load cases. <br />Use the maximum absolute value of the three downforce cases <br />and the uplift case for sizing the rail. Use the uplift case·only <br />for sizing lag bolts pull out capacities (Part II, Step 6). Use the <br />following equations or Table 7. <br />P (ps.0 = 1.OD + 1.OSI (downf6rce case 1) <br />P (ps.0 = 1,OD + 1.Opnet (downforce·case 2) <br />P (ps.0 = 1.013 + 0.7531 + 0.75pnet (downforce €ase 3) <br />P.(p€Q = 0.60 + 1,_Qpnet (uplift) <br />D = Dead'Load (psj) <br />S = Snow Load 0]43 <br />pnet = Design Wind Load (psD (Positivefor downforce, negative <br />for Llplift) <br />Ihe maximum Dead Load, D (psD, is 5 psfbased on market <br />research and internal data. <br />1 Snow Load Rcductzon - Th: snow load can be reduced according <br />to Chapter 7 ofASCE 7-05. Theireductionis afunction ofthe roof <br />slope, Exposure Factor, fmportance Factor and Thermal Factor, <br />Please refer to Chapter 7 Of ASCE 7-05for more informal·ion. <br />Ai. <br />P io <br />Note: Modules must be centered symmetrically on <br />the rails (t/- 2.9, asshown in Figure 3. <br />1 <br />10