FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

Volume II DESIGNING THE FOUNDATION 10
EXAMPLE 10.3. PIER FOOTING UNDER GRAVITY LOAD (concluded)
COASTAL CONSTRUCTION MANUAL
Illustration A. Site layout
Find: The appropriate square footing size for the given gravity load.
Solution: The square footing size can be found using Equation 10.5:
L = 1.5 ft
The IRC requires a minimum of 2-in. projection for spread footing. Moving to the next minimum
standard footing size, a 24-in. x 24-in. x 12-in. square footing to resist the gravity loads should
be used.
Example 10.3 and Example 10.4 model the conditions where the pier and footing only resist axial loads that
create no moment on the footing. In those states, the soils are equally loaded across the footing. When a pier
and footing foundation must resist lateral loads (or must resist gravity loads applied at some distance Δ from
the centroid of the pier), the footing must resist applied moments, and soils below the footing are no longer
stressed equally. Soils on one side of the footing experience compressive stresses that are greater than the
average compressive stress; soils on the opposite side of the footing experience stresses lower than the average.
10-41