The Flexure or moment capacity of the footing is taken at column edge (or modified base plate edge. The Flexural capacity of the footing is:
|
| Equation 5-3 |
where
|
z
| = | d - 0.45x |
|
0.111d ≤ x
| = |
Equation 5-4
|
The area of flexure reinforcement As is subject to the following limits:
| As, min≥ 0.0024bh for fy = 250N/mm2 | BS8110: Part 1, Table 3.25 Part c |
| As, min≥ 0.0013bh for fy = 460N/mm2 | BS8110: Part 1, Table 3.25 Part c |
| As, min≥ 0.0013bh for all other values of fy | |
The reinforcement spacing is also limited to
| Smax≤ 3d ≤ 750mm | BS8110: Part 1, 3.12.11.2.7 limited by clause b |
| Smin> (hagg + 20)/dd+ dd | BS8110: Part 1, Section 3.12.11.1 |
Note: hagg is taken as 20 mm. If the minimum reinforcement spacing needs to be larger to accommodate constructability related issues then the user will need to set a larger minimum spacing in the Reinforcement tab of the Design Criteria dialog box.
The ultimate moment on the footing is taken as the moment produced from the total soil stress on one side of the column times the distance from the centroid of the soil stress to the critical section. If there is any part of the critical shear area in tension, the program checks to see if the moment from the uplift portion of the footing using the footing slab self weight and surcharge controls the value of Mu.
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.
Flexure Critical Sections for Major Moment
Flexure Critical Sections for Minor Moment
