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:F UNIRAC Unirac Code-Compliant Installation Manual SolarMount <br />Part II. Procedure to Select Rail Span and Rail Type <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 />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 your local building <br />official. <br />2. Obtain the Design Wind Load, pnet. See Part I (Procedure <br />to Determine the Design Wind Load) for more information 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 racking <br />systems. If the Dead Load is greater than 5 psf, see your <br />Unirac distributor, a local 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 structure must be capable of <br />supporting. <br />Step 1: Determine the Total Design Load <br />Figure 3. Rail span andfooting <br />spacing are interchangeable. <br />The Total Design Load, P (P€f) is determined using ASCE 7-05 <br />2.4.1 (ASD Method equations 3,5,6 and 7) by adding the Snow <br />Loadi, S (psf), Design Wind Load, pnet (psf) from Part I, Step 9 <br />and the Dead Load (psf). Both Uplift and Downforce Wind <br />Loads calculated in Step 9 of Part 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 the <br />following equations or Table 7. <br />P Gsf) = 1.OD + 1.09 (downforce case 1) <br />P (psf) = 1.OD + 1.Opnet (downforce case 2) <br />P Oqf) = 1.OD + 0.759 + 0.75pnet (downforce case 3) <br />P (psf) = 0.6D + 1.Opnet (uplift) <br />D = Dead Load (psf) <br />S = Snow Load (psf) <br />pnet = Design Wind Load (psf) (Positive for downforce, negative <br />for uptift) <br />Ike maximum Dead Load, D (Dsf), is S vsfbased on market <br />research and internal 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 Factor. <br />Please refer to Chapter 7 of ASCE 7-05 for more information. <br />Nd <br />B <br />Rail <br />Page <br />Note: Modules must be centered symmetrically on <br />the rails (+/- 29, as shown in Figure 3. <br />0 <br />10