Two-Way Shear Capacity

Last updated: February 01, 2022

The calculation for two-way shear on continuous footings is similar to the calculations for spread footings and is performed for each column and wall on the footing.

The calculation of the controlling design shear is calculated as follows:

V_{u_x} = V_{t_x} (1 + \frac{1.5 M_{u m a j}}{V_{t_x} C_{\min}})

BS8110: Part 1, Equation 25

V_{u_y} = V_{t_y} (1 + \frac{1.5 M_{u \min}}{V_{t_y} C_{m a j}})

V_u = min(V_{u_x}, V_{u_y})

BS8110: Part 1, Section 3.7.6.2, Note 2

where

V_t	=	Design Shear at column face
M_umaj	=	Design moment transferred from the slab to the column at the connection in the major direction
C_maj	=	Length of the side of the perimeter considered parallel to the axis of bending. Major side for bending in minor direction
M_umin	=	Design moment transferred from the slab to the column at the connection in the minor direction
C_min	=	Length of the side of the perimeter considered parallel to the axis of bending. Minor side for bending in major direction

Note: A two-way shear check is carried out assuming an "interior" column that is far from any slab edges. If the supported column is close enough to the footing edge or corner, the user will need to do supplemental checks to confirm that the footing capacity is acceptable.

The correction for the soil reaction below the column or wall is not performed for continuous footings. This will produce a slightly more conservative design for continuous footings as compared to the spread footings. As with spread footing, the continuous footing check is performed assuming that the column is in the center of the slab. Edge and corner two-way shear checks are not currently performed.

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.

Braces And Column Forces

Columns with braces framing into them are checked as one member. As the brace and column forces are combined the two-way shear check is performed using the column dimensions.

No two-way shear check is performed in the case where the brace is directly supported 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 only the shear wall is checked using only the shear 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 required size of the brace's effective area on the foundation.

Partial 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.