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eUN\RAC Unirac Code-Compliant Installation Manual SolarMount <br />Part IL Procedure to Select Rail Span and Rail Type <br />[2.1.] Using Standard Beam Calculations, Structural Engineering Methodology <br />Theprocedure to determine the Unirac SolarMount series <br />rail type and rail span uses standard beam calculations and <br />structural engineering methodology. The beam calculations <br />are based on a 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 information <br />on beam calculations, equations and assumptions. If beams <br />are installed perpendicular to the eaves on a roof 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 yourlocal building <br />official. <br />2. Obtain the Design Wind Load, p,jet. See Part I (Procedure <br />to Determine the Design Wind Load) for more infofmation on <br />calculating the Design Wind Load. <br />3. Please Note: The terms rail span and footing spacing <br />are interchangeable in this document. See Figure 3 for <br />illustrations. <br />4. To use Table 8, the Dead Load for your specific installation <br />must be less than 5 psf, including modules and Unirac packing <br />systems. If the Dead Load is greater than 5 psf, see your <br />Unirac distributor, alocal structural engineer or contact <br />Unirac. <br />The following procedure will guide you in selecting a Unirac <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 strueturemust be capable of <br />supporting. <br />Step 1: Determine the Total Design Load <br />Figure 3. Rail span andfooting <br />spacing are interchangeable. <br />/ <br />The 7btal Design Load, P (Psf) is determined using ASCE 7-05 <br />2.4.1 (ASD Method equations 3,5,6 and 7) by adding the Snow <br />Loadl, S (psf), Design Wind Load, pnet (psf) from Part I, Step 9 <br />and the DeadLoad (psf). Both Uplift ahd Downforce Wind <br />Loads calculated in Step 9 ofPart 1 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;t:he <br />following equations or Table 7. <br />P;(#99 - 1.OD + 1.Dsl (doWnforce case 1) <br />P (AO = 1.019 + 1.Ophet (downforce case 2) <br />P 00€0 = 1.OD + 0.7491 + 0.75pha (downforce case 3) <br />P (psf) = 0.6D + 1.Opnet tuplift) <br />D = Dead Load (psf) <br />S = Snow Load (psf) <br />pnet = Design Wind Load (psf) (Positivefor downforce, negative <br />for uplift) <br />The maximum Dead Load·, D (Dsf), is S psfbased on market <br />research and int€rnal data. <br />1 Snow Load Reduction - The snow load can be.reduced according <br />to Chapter 7 of ASCE 7-05. The reduction is a function ofthe roof <br />slope, Exposure Factor, Importance Factor and Thermal.Factof. <br />Please refer to Chapter 7 of ASCE 7-05 for more information. <br />B <br />r' en <br />9 4 <br />0ot 4 -\ <br />P.. <br />Note: Modules must be centered symmetrically on <br />the rails (+/- 29, as shown in Figure 3. <br />10