Flexure Capacity

Last updated: February 01, 2022

The continuous footing flexure capacity is calculated in the same manner as the spread footing. The flexure capacity of the footing is checked from face of column to face of adjacent column or edge of slab.

The required flexure capacity for a section perpendicular to the footing's major axis is recovered from the Finite Element analysis on the beam elements.

The required flexure capacity for a section perpendicular to the footing's major axis is calculated by defining effective transverse design strips. The column design strips are defined as follows:

For columns remote from the footing ends: The column strips are calculated as 3 w/4 + 9d/4on either side of the column center line.
For columns at the ends of the footing another check needs to be considered: 3 w/4 + c

The effective width is taken as the sum of the minimum values of the equations above for either side of the column.

where

w	=	Column Width parallel to footing local major direction
c	=	Distance from column face to footing end
d	=	Depth of footing from top surface to centerline of flexural reinforcement parallel to the footing minor axis direction.

Continuous Footing Section Locations for Transverse Flexure Reinforcement

The total soil stress under the critical section B' is then recovered from the spring forces. The required moment capacity for the column for transverse reinforcement is calculated as:

Moment arm: L' = w₁ - w & w₂ - w
Total Force on section: $q_{u l t} = \frac{Total Spring Force}{B \times B^{'}}$
Moment Capacity: $M_{u} = \frac{q_{ult {(L^{'})}^{2}}}{2}$

The process is repeated for all columns and all the regions between columns.

The continuous footing's provided flexure capacity is calculated using the same method outlined in "Flexure Capacity" for Spread footings.

The same method is used for areas between adjacent column effective width areas. In both the column effective width areas and the areas in between, if there is any part of the critical area in tension, the program checks to see if the load on the uplift portion of the footing using the footing slab self weight and surcharge controls the value of M_u.

Note: The footing is analyzed for moments in the columns producing moments along the continuous footing major axis. The moments on the columns that produce moments along the continuous footing minor axis are not considered in the analysis. If it is found by the engineer that the footing minor axis moments are significant, they will need to be considered separately by the engineer for footing overturning stability and flexural capacity of the transverse reinforcement.