07-6831 - Laserfiche WebLink

Browse Search

- Pull out force can be expressed as follows: pf=SxL Where: Pf is the pull out force. S is the strength, or retention force of the lag in lbs. per inch (from above). L is the length of thread that is imbedded in wood. Our 11 panel system above will have 38 bolts, 1/4" x 4" securing the panel frames to the roof system and into wood joists. The bohs will run through the retaining clips, having three inches of bolt length imbedded in the wood. The pull out force is calculated as follows: 260 x 3 = 780 x 38 bolts = 29,640 lb. of retention force with wood at 0.55 specific gravity. This pull out force is greater than the uplift force determined for our 11 panel . array. Fewer than 11 panels may be used per collector array, since the anchorage is proportional to the nwnber of panels in the array. Do not exceed 11 panels per array, as this will degrade performance. Pilot holes should always be drilled for lag bohs, to improve holding power. The pull out force of the thrust washeris.5 x 3.14159 x .125 x 60,000 = 11,775 lb. This pull out force exceeds the retaining clip boh strength of2209 lb. You must use tlnust washers to prevent theboh head from pulling through the clips. Where roofing materials require the use of roof jacks to allow the array to clear the shingles or tiles, roof jacks should be made and spaced according to sheet 3 of the drawing set, and installed per the framed series installation instructions. WIth blocks spaced at 24" intervals, the pull out of the stringer arrangement can be expressed as above. Applying the same formula, each block bas a retention capabilitY of390lb. x 3, or 1170 lb. The array will have an arrangement of stringers and roof jacks equal to the number of panels + 1, multiplied by the number of stringers called for in the table located on sheet 3 of the drawing set for framed series collectors. I have included a series of worksheets that calculate the uplift forces and retention forces for an array consisting of two to 11 panels, at a design pressure of 61.5 pst: This is the design pressure for coastal communities to meet the 2003 code revision. Using the reconnnended number of attachment points in the charts for the number of collectors in a given array will assure a wind - safe instaIlation.