Practice Question: Find Crane outrigger Base Spreader thickness

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Solution

Answer: C) 10 inch 

The spreader RC block shall work to spread the area of the pressure to be on a larger area, so the final pressure on the soil will be less than the bearing capacity.

The minimum required area of the pressure:     
\[= \frac{Applied\ load}{Bearing\ capacity }= \frac{20 \ kip \times1000 }{1500 \ psf} = 13.33 ft^2\]

Minimum width of the pressure:

\[= \sqrt{13.33} = 3.65 ft = 43.8\ inch\]

Vertical Pressure Distribution = 1:1 so every 1 ft in thickness will increase the width by 2 ft.

The required minimum thickness:

\[= \frac{(43.8-24)}{2} = 9.9\ inch\]

So, minimum thickness is most nearly = 10 inch 
 

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