Compressive Stress
Given:
a 6400# weight is supported by an 8" x 8" post.
Determine:
a. the compression stress in the 8" x 8" post
b. the bearing stress between the post and the steel plate
c. the bearing stress between the steel plate and the concrete.
Solution:
a. The compressive force in the post is distributed over a cross-sectional
area of 64 square inches: 6400 pounds/ 64 in2 = 100 psi
b. The stress at the point between the post and the steel bearing plate
is dictated by the smallest area being loaded. The post is smaller than
the plate, so it is the critical surface. The stress between the two is
again 6400 pounds divided by 64 square inches for a total stress of 100
psi.
c. The stress between the plate and the concrete floor is also determined
by the smallest area. In this case it is the 10" x 10" plate.
The load remains the same 6400 pounds but it is now distributed over an
area of 100 square inches. The resulting stress is 64 psi, a clear reduction
in the stress.