Two-Way Shear in Continuous Footings
The calculation for two-way shear in continuous footings is similar to the calculation for spread footings described in Section 4.10.2 and is performed for each column and/or wall on the footing. As with spread footings, the continuous footing check is performed assuming that the column is at the center of the slab, thus using the interior condition described in ACI 318-14 3.4.2.3. Edge and Corner two-way shear checks are not currently performed. Unlike spread footings, the soil force acting within the assumed punching failure plane of the continuous footing is not subtracted from the required punching shear capacity in RAM Foundation. This will produce a slightly more conservative design for continuous footings as compared to spread footings.
Two-way shear checks are performed slightly differently for different supported elements. The special conditions are handled as follows:
Columns at the End of Walls
Checks are made for the wall and end columns individually using each member's forces.
Brace and Column Forces
Columns with braces framing into them are checked as one member. The brace and column forces are combined and the two-way shear check is performed using the column dimensions.
The two-way shear check is not performed for the case in which the brace is supported directly on the foundation without a column at the same location. This is due to a lack of information regarding the connection of the brace to the foundation.
Brace Framing into a Wall
In this case the wall dimensions are used considering only the wall forces. Even though the brace forces are used for the analysis and design of the footing, the two-way shear check cannot be performed due to a lack of information regarding the connection of the brace to the wall and size of the brace's effective area on the foundation.
Columns at the End of Walls
In the case where a partial wall frames into a column the larger of the two members is used to define the perimeter of member and the combined load of the partial wall and column are used for the two-way shear check.
In the case where the partial wall does not frame into a column the two-way shear check that is performed will be on the partial wall only.
In both cases it is possible that the two-way shear check will be un-conservative because the supported members may be an edge member but it will only be checked as an internal member.