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:=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 />T.he procedure to determine the Unirac SolarMount series <br />railitype and rail span uses standard beam calculations and <br />structural engineering methodology. The beam calculati0ns <br />are based on a simply supported beam conservatively, ignoring <br />the reductions allowed for supports of continuousbeams 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, pner. See Part I (Procedure <br />to Deterniine the Design Wind Load) for more information on <br />calculating the Design Wind Load. <br />3. Please Note: The t:erms rail span and footingspacing <br />are interchangeable in this document. See Figure 3 for <br />illustrations. <br />4. To use Table 8, the Dead L.oad for your specific installation <br />must be Iess 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 />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 />Loadl, S (psf), Design Wind Load, pnet (p€f) 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 (psf)= 1.00 + 1.061 (downforce case 1) <br />P 040 = 1.OD! + 1.Opnet (downforce case 2) <br />POR,0 = 1.OD + 0.759 + 0.7*net (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) (Positive.for downforce, negative <br />for uplift) <br />11ie maximum Dead Load', D (psf), is 5 psfbased 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. Ille reduction is a flinctimi of the roof <br />slope, Exposure Factor, Importance Factor and -Iherrnal Factor. <br />Please refer to Chapter 7 ofASCE 7-05 for more information, <br />Figure 3. Rail span andfooting <br />spacing are interchangeable.>%*> -/4--6 <br />%.4.. <br />h.». <br />21 e -- <br />./3,C> <br />- as' .--KNX- -/ <br />-ST;:4. --- <br />-*- -:444 +/1. ' <br />./. 1 r <br />,-- :./ 4/0,58%,-S>C / <br />93/B b%/ \6\#fe re#/ <br />qail 4 - -.AO @CO <br />V,044 OP->1 - <br />Coot :$$£-<2.r<®ac/4 --#/ .N*%3 <br />Phse <br />Note: Modules must be centered symmetrically on <br />the rails (+/- 2 *), as shown in Figure 3. <br />10