The flexural capacity of the footing is calculated for the
section at the concrete column edge or modified base plate edge and is
expressed as:
|
| Equation 4-17 |
|
| Equation 4-18 |
The top reinforcement
ATsis
only required to meet flexural capacity and bar spacing requirements. It is not
checked for minimum reinforcement area requirements per Section 7.12.2.1
The bottom reinforcement
AsB
is required to meet flexural capacity and bar spacing requirements as well as
the requirements of Section 7.12.2.1 as described below. When top reinforcement
is required the minimum reinforcement area takes into consideration both the
top and bottom reinforcement in a given direction.
| As,min =
0.002bh for fy = 40 ksi
| ACI 318-14 8.6.1.1 |
| As,min =
0.0018bh for fy = 60 ksi
| ACI 318-14 8.6.1.1 |
|
for fy > 60 ksi
| ACI
318-14 8.6.1.1 |
The reinforcement spacing is also limited to
| Smax = 18
in
| ACI 318-14 7.12.7.2.2 |
| Smax = 5 x
Footing Thickness
| ACI 318-14 7.12.7.2.2 |
Note: ACI 318-14 24.3.2 is
not implemented because it relates to crack width controls and may not have any
impact on corrosion so it is considered not to be applicable for foundations.
In calculating the required footing moment at the face of
the column,
RAM Foundation establishes an applied stress
prism bounded by the soil stress area. Note that this stress prism could
reflect either a stress generated from soil pressure (acting upward on the
footing), a stress generated from the footing self-weight plus a uniform
surcharge (acting downward on the footing), or a combination of both. A unique
stress prism is generated for each concrete load combination used in the
design.
The moment is calculated by treating the soil stress area as
a cantilever beam supported at the column face. If any portion of the soil
stress area is in uplift (not in contact with the soil), a check is done to
determine if the uplift component of the loading produces a greater moment at
the face of the column than the soil pressure component of the loading. If it
does, the required moment will be used to size/check top reinforcement for the
footing. Otherwise, the moment will be used to size/check bottom reinforcement.
The flexure capacity of the footing is considered to be
acceptable when adequate reinforcement is provided in the footing to satisfy
Equation 4‑19 on all sides of the column.
|
| Equation 4-19 |
Flexure Critical
Sections for Major Moment
Flexure Critical
Sections for Minor Moment
