Mat Footing Design per Canadian A23.3 2019

Mats are designed to service and ultimate load cases/combinations.

Workflow

Either:
- Imports a superstructure model from STAAD.Pro. This brings in the support reactions and column/pedestal data from that model into SFA
or
- Start with a blank model in SFA, define the locations of column supports (if any) and assign the column sizes and loads acting on the foundation through those columns.
Create a mat foundation job and choose the code as Canadian (A23.3-2019). Select the load combinations (categorized into Service and Ultimate) for which the mat should be analyzed and designed.
Specify any additional loads on the mat if any - point loads, area loads, etc. Generate load combinations if needed. (Load combinations from the SS model can also be imported through Step (1)
Define the mat boundary and mesh it to produce a finite element model of the mat. Specify the mat thickness to be used for analysis as well as for design.
Specifies soil supports and/or pile spring supports.
Performs the FE analysis of the mat.
Create a moment envelope which is a set of discrete points where the concrete design of the mat will be performed.
Perform the flexure and punching shear checks. The program will recommend a bar arrangement for flexure for the longitudinal and transverse directions for the top and bottom surfaces. In the event of insufficient thickness as a singly-reinforced section, a failure will be shown.
Perform moment capacity checks for a desired bar diameter and spacing.

Design for flexure:

Moments used in the design are based on the results of the FE analysis of the mat.
After retrieving the moments per unit width at the various points defined by the envelope, the program transforms them to the longitudinal and transverse directions of the mat, includes the Wood-Armer effects if the user chooses to include them, and the resulting values form the basis of the design.
At each location, for each direction and surface, the maximum value from amongst all the selected load cases is used in the reinforcement calculation.
The procedure used in the design of each envelope point is similar to that for an isolated footing, with the "width" of the section set to one metre.
Details of the design are reported in tables in the "Slab designer" page of the program, for a one metre width.

Design for oneway shear

Design for twoway (punching) shear

The procedure used in the design for twoway shear is similar to that for an isolated footing. One difference is that the upward force from the soil supports beneath the column are not subtracted from the downward force from the column. Thus, a higher force than appropriate is used in the design. This produces a more conservative result than expected. UBM effects are considered in a manner similar to that for the isolated footings.
The reduction in punching shear capacity per Section 13.3.4.3 and 13.3.4.4. of the code for mats whose thickness exceeds 300 mm is currently not performed.

Design for the pile punching through the mat.

SFA does not check the punching action of piles through the mat for foundations that are supported on piles.

The following results are available for viewing through the program’s calculation reports.

Summary of minimum/maximum nodal displacements from the FE model
Summary of minimum/maximum plate element stresses and moments from the FE model
Summary of maximum soil pressures from the various service load cases/combinations.
Contact Area report for each service load case/combination. A loss of contact will be evident through a value that is less than 100%
Report of Sliding and overturning check for each service load case/combination.
Static equilibrium mismatch report in the event of instabilities that cause overturning or sliding.
Pile reaction summary for service and ultimate load cases/combinations.
Details of the flexure design checks for the longitudinal and transverse directions for top and bottom surfaces.