Since the lateral area of the foundation is negligible, A for the 

 installation equals 6.83 square feet. 



F, = 60 * 6.83 = 410 pounds 

 d 



Effective lateral force due to sloping bottom, 



F. = W * tan i = (135 + 500) * tan 6° = 67 pounds (3) 

 l sub 



Checking that, 



F. + F^ < 1/2 * W . (4) 

 l D — sub 



W 

 sub _> 2 * (67 + 410) = 954 pounds, therefore, must add weight 



Try simply thickening strip footings, use 9/16 inch, 



W sub = 135 + ( 2 * L - B ) * 34 = 1040 pounds 

 Checking 



F. = 1040 * tan 6° = 109 (3) 



i 



F. + F, = 519 < 1/2 * 1040, which is satisfactory (4) 

 id — 



Check for keys, for sand, 



F = 0.3 * 1040 = 312 pounds (5) 



F. + F, = 519 > 312, therefore need keys 

 id 



d = 0.17 + 0.05 * B = 0.25 feet 

 e 



For sand this value is reduced by a factor of 3; therefore, the required 

 depth of the keying edge equals 1 inch. 



Overturning Moment 



For this installation, the average height of the area projected 

 laterally, 



z n = 1/2 * z = 3.42 feet 

 1 max 



23 



