Mat Foundation Design Spreadsheet

Mat Foundations

A mat foundation consists of a large slab which accommodates many different columns or load points. In many cases a mat foundation will accommodate all the columns of the structure on one single foundation.

Mat foundations are commonly used in areas with poor soil. In these cases the low bearing capacity of the soil leads to individual foundations for each column which overlap with each other. In this case individual foundations can be joined together to form mat foundations.

Mat foundations are good at spreading loads over a wide area and so they are commonly used for foundations on soft soils with a low bearing capacity.

Mat Foundation Design

Mat foundation design is similar to the design of any foundations. The mat foundation must be sufficiently large as to spread the total load over a large enough area so that the maximum allowable bearing capacity of the soil is not exceeded.

The design of mat foundations is slightly complicated by the fact that the foundations can be considered as either rigid or flexible. Smaller, thicker mat foundations can be taken as rigid because the deflection of the mat foundation under the design loads will not be significant. However, very large mat foundations can have significant deflections in some cases which will affect the maximum bearing pressures created beneath the foundations. The CivilWeb Mat Foundation Design Excel Sheet includes design spreadsheets for both rigid and flexible mat foundations.

Once the dimensions of the mat foundation have been set, the foundation itself can be designed. Mat foundations are designed in a similar manner to any reinforced concrete foundation. The maximum bending moments and shear forces are determined, and then the reinforcement is sized to suit these forces.

Mat Foundation Design Spreadsheet - Inputs

Firstly the geometry and the loadings of the columns are determined. Usually this is determined by the superstructure design and cannot be significantly altered by the designer without redesigning the superstructure. The designer can input up to 32 point loadings, from columns for example. The designer can place the loadings anywhere on the foundation to suit any possible loading condition. The load points can include axial, horizontal and moment forces in both directions.

Next the designer can input the soil properties. The CivilWeb Mat Foundation Design Excel Sheet simply requires a maximum allowable bearing capacity to be entered for the soil. The designer can take this value from experience for preliminary design though a detailed bearing capacity calculation will be required for final design. This can be done using a simple spreadsheet such as the CivilWeb Soil Bearing Capacity Calculation Excel Suite.

Then a trial size is set for the mat foundation. This trial geometry will be checked by the spreadsheet for validity. The trial size can be set from experience of similar foundations. The spreadsheet will then show the designer if the proposed mat foundation is valid or not and if the dimensions can be optimised. Bearing pressure calculations are carried out in accordance with either BS EN 1997 or BS 8004.

In most cases the design of the mat foundation will be suitable so long as the maximum allowable bearing capacity of the soil is not exceeded. However in some soft clay soils consolidation settlement can continue for years after the structure is completed. In these cases it can be prudent to undertake a separate settlement analysis as well. A simple spreadsheet such as the CivilWeb Foundation Settlement Calculator Spreadsheet can be used for this.

Mat Foundation Design Spreadsheet - Reinforcement Design

The CivilWeb Mat Foundation Design XLS now calculates the maximum bending moments and shear forces present in each direction in the mat foundation. These are then used to detail the required reinforcement in accordance with either BS EN 1992 or BS 8110.

The CivilWeb Mat Foundation Design XLS includes unique reinforcement design tools which make the design and optimisation of the reinforcement simple. The designer is presented with a graph showing exactly which combination of bar size and spacing is best suited to the design.

CivilWeb Mat Foundation Design Spreadsheet

The CivilWeb Mat Foundation Design Spreadsheet contains all the tools required to complete a fully optimised, fully compliant mat foundation design in minutes. The designs can be completed in accordance with either BS 8004 and BS 8110 or BS EN 1997 and BS EN 1992. The CivilWeb Mat Foundation Design Spreadsheet completes all the calculations instantly saving the designer many hours on every mat foundation design. The spreadsheet also includes unique design analysis tools which allow the designer to optimise the mat foundation design at a glance.

Buy the CivilWeb Mat Foundation Design Spreadsheet now for only £20.