Eccentric Footing Design Excel Sheet

Eccentric Foundations

Pad foundations are small concrete pads which sit beneath the columns to spread the force over a larger area. They need to be large enough so that the bearing pressure beneath the foundation does not exceed the bearing capacity of the underlying soils.

Small pad foundations are usually arranged around the column or load point in the centre. This is the most efficient way of spreading the load as any eccentricity in the arrangement of the footing causes higher bearing pressures at one side of the foundation.

However there are some cases where the column cannot be placed centrally on the footing. This can occur when columns are close together or where there is a restriction on the size of the foundations in one direction. For example this commonly occurs when a building is placed very close to another building or close to a land boundary or topographical feature.

Similarly pad foundations are usually symmetrical because this again is the most efficient way of spreading the load from the column. However in some cases footings must be built asymmetrically when a natural or man-made boundary interferes with the footprint of the foundation. This often happens when a new foundation must be built close to an existing footing. In some cases a re-entrant corner needs to be included which will increase the bearing pressures beneath the foundation.

The calculation of the bearing pressures beneath an eccentric or asymmetrical footing is much more complex than for a symmetrical foundation with a central load point. In most cases it is no longer practical to complete these calculations by hand, a simple spreadsheet such as the CivilWeb Eccentric Footing Design Excel Sheet can be used to complete the calculations.

CivilWeb Eccentric Footing Design Excel Sheet - Inputs

First the designer must input the loading conditions and the geometrical parameters for the foundation. In most cases for eccentric foundations some or all of the geometrical inputs are set by the site conditions and cannot be changed by the designer. The CivilWeb Eccentric Footing Design Excel Sheet allows the designer to analyse a foundation of any size and shape. A handy dynamic drawing of the foundation is included so that the designer can see exactly what they have input. This eliminates any risk of any confusion with the inputs. The designer can input the loading conditions to include axial, horizontal and moment forces in both directions. This covers any likely loading conditions.

Next the designer must input the soil properties. The CivilWeb Eccentric Footing Design Excel Sheet simply uses a maximum allowable bearing capacity input for the strength of the underlying soils. For most eccentric foundation designs this simplified analysis will be suitable. The bearing capacity of the soil must be determined from site testing before the design is finalised. A simple spreadsheet program such as the CivilWeb Soil Bearing Capacity Calculation Suite can be used for this analysis.

In the majority of conditions the bearing capacity will be sufficient in order to ensure that the foundation does not settle more than 25mm. However in some clay soils consolidation settlement caused by increased pore water pressure can continue for years even when the bearing capacity of the soil has not been exceeded. In these cases a separate settlement analysis may be prudent, particularly for structures which are susceptible to settlement. A simple spreadsheet such as CivilWeb Foundation Settlement Calculator Spreadsheet can be used to complete a consolidation settlement analysis.

When the loading, geometry and soil details have been input, the CivilWeb Eccentric Footing Design Excel Sheet can complete the analysis of the proposed foundation. The spreadsheet can complete this analysis according to either BS EN 1997 or BS 8004. The spreadsheet then presents the designer with the bearing pressures underneath the foundation which are used to determine whether the foundation is suitable or not. The spreadsheet completes all these calculations instantly so the designer can very quickly alter the dimensions of the foundation to achieve a valid design.

Once the foundation dimensions have been finalised, the CivilWeb Eccentric Footing Design Excel Sheet can now be used to complete the design of the reinforcement. This can be done in accordance with either BS EN 1992 or BS 8110. The spreadsheet uses the loading information to calculate the maximum bending moments and shear forces acting on the foundation. This is then used to design the reinforcement. The spreadsheet includes unique reinforcement picker tools which show the designer exactly which combination of reinforcement bar size and spacing is best suited.

The CivilWeb Eccentric Footing Design Excel Sheet then provides a handy summary of the designer information so the designer can quickly check that the design is valid. Then the spreadsheet produces a detailed drawing of the proposed foundation which the designer can use for the construction of the foundation.

CivilWeb Eccentric Footing Design Excel Sheet

The CivilWeb Eccentric Footing Design Excel Sheet completes the complex calculations required for eccentric foundations. This includes foundations of any shape and with the loading column in any position on the foundation. These calculations are generally too complex to complete by hand and this powerful spreadsheet completes them instantly. This allows a fully optimised, fully compliant eccentric foundation design to be completed in minutes, saving many hours of design work on every eccentric foundation design.

The CivilWeb Eccentric Footing Design Excel Sheet can be purchased here for only £20.