ABSTRACT
Example 6.8 For a raft of size 98.4 x 39.36 ft, compute the stress at 65.6 ft depth below the center of the raft by assuming that the rectangle can be represented by an equivalent circle. The load intensity on the raft is 3133 Ib/ft2•
Solution The radius of a fictitious circular footing of area equal to the rectangular footing of size 98.4 x 39.36 ft is
~38731tRJ =98.4 x 39.36 =3873 sq. ft or Ro = ----;- =35.12 ft Use Eq. (6.21) for computing (J'z at 35.6 ft depth
65.6 Now, z I Ro = 35.12 =1.9, and rlRo= O. From Fig. 6.11, I z = 0.3
Therefore, (J'z =0.3 q =0.3 x 3133 =940 Ib/ft2•
Newmark's Influence Chart When the foundation consists of a large number of footings or when the loaded mats or rafts are not regular in shape, a chart developed by Newmark (1942) is more practical than the methods explained before. It is based on the following procedure. The vertical stress (J'z below the center of a circular area of radius R which carries uniformly distributed load q is determined per Eq. (6.21).
