A sign of weight W is supported at its base by four bolts anchored in a concrete footing. Wind pressure p acts normal to the surface of the sign; the resultant of the uniform wind pressure is force F at the center of pressure. The wind force is assumed to create equal shear forces F/4 in the y-direction at each bolt [see figure parts (a) and (c)]. The overturning effect of the wind force also causes an uplift force R at bolts A and C and a downward force (- R) at bolts B and D [see figure part (b)]. The resulting effects of the wind, and the associated ultimate stresses for each stress condition, are: normal stress in each bolt (σu = 60 ksi); shear through the base plate (τu = 17 ksi); horizontal shear and bearing on each bolt (τhu = 25 ksi and σbu = 75 ksi); and bearing on the bottom washer at B (or D) (σbw = 50 ksi).
Find the maximum wind pressure pmax (psf) that can be carried by the bolted support system for the sign if a safety factor of 2.5 is desired with respect to the ultimate wind load that can be carried.
Use the following numerical data: bolt db = 3„4 in.; washer dw = 1.5 in.; base plate tbp = 1 in.; base plate dimensions h = 14 in. and b = 12 in.; W = 500 lb; H = 17 ft; sign dimensions (Lv = 10 ft. × Lh = 12 ft.); pipe column diameter d = 6 in., and pipe column thickness t = 3/8 in.
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Transcribed Image Text:

Sign (4.x Lt) Resultant of wind Pipe column Overturning B about x axis FH E at each bolt at each bolt Pipe column One half of over turning moment about x axis acts on each bolt pain plate Up Footing FI4 Tension TR R Compression FH 4 4