Question 11.11: Consider the same situation as Prob. 11.10, except that ther...

Geotechnical Earthquake Engineering

Consider the same situation as Prob. 11.10, except that there is a 2 by 2 pier group. The piers are spaced 3 pier diameters (centerline to centerline). Determine the downdrag load on the pier group.

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Since there are 4 piers in the 2 by 2 group and assuming each pier is separately subjected to a downdrag load, or:

Q_{D}=(4)(179)=716 kips

The second downdrag condition is to use Eq. (11.17), or:

$Q_{D}=4 B L_{1} s_{u}$ (11.17)
B = 3 times the diameter + 2r = (3)(3) + (2)(1.5) = 12 ft

Q_{D}=4 B L_{1} s_{u}=(4)(12)(40)(500)=960,000 lb =960 kips

Hence the governing condition would be assuming the downdrag over the entire perimeter of the pier group, or $Q_{D}=$ 960 kips

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