Strip Footing Design Excel Spreadsheet

Strip Foundation Design

A strip foundation is defined here as a long and narrow concrete foundation which supports loadings from a number of linear columns or load points. This is sometimes call a grade beam. This spreadsheet cannot be used to design wall footings accommodating a linear universally distributed load. For this our Wall Footing Design Spreadsheet can be used.

Strip foundations are very commonly used for warehouses and other long structures with a large number of closely spaced or lightly loaded columns or loading points. In these cases the columns are so closely spaced that individual footings would begin to merge anyway, so a continuous long narrow strip foundation is more appropriate.

Strip foundations work in a similar fashion to any other concrete spread foundation. The concentrated loadings from the small columns are transferred into the concrete strip foundation which spreads this loading out over a larger area. The strip foundation must be wide enough to spread the load sufficiently that the bearing capacity of the underlying soils is not exceeded.

CivilWeb Strip Footing Design Excel Spreadsheet - Inputs

First the designer must input the loading details. This includes the size and spacing of the columns or load points acting along the length of the strip foundation. These spacings and loadings are usually determined as part of the superstructure design and cannot be easily altered by the foundation designer. The spreadsheet can be used to analyse up to  16 different load points such as columns. These 16 load points can be placed anywhere along the strip foundation and can be any size. They can include axial, horizontal and moment loads in both directions to analyse any possible loading conditions.

Next the designer must input a trial length and width for the proposed strip foundation. The CivilWeb Strip Footing Design Excel Spreadsheet will analyse this trial foundation size and determine whether it is valid or not. The designer can take this trial size from similar projects or from experience. It can be modified after the initial analysis is done to optimise the design. The spreadsheet also creates a helpful dynamic drawing of the proposed strip foundation which shows the designer exactly what is being analysed. This avoids any risk of confusion over the purpose of the inputs.

Next the designer must input the soil design parameters. The CivilWeb Strip Footing Design Excel Spreadsheet analyses the foundation simply against a maximum allowable bearing capacity for the underlying soils. The soil bearing capacity can be input from typical values or from experience for preliminary design. Before final design the maximum allowable bearing capacity of the soil must be checked with onsite soil testing. An easy to use spreadsheet such as the CivilWeb Soil Bearing Capacity Spreadsheet can be used to complete the detailed soil bearing capacity analysis for use with the final design.

The maximum allowable bearing capacity generally limits the maximum settlement to 25mm. Some clay soils however can settle more than this even when the bearing pressures beneath the foundation do not exceed the bearing capacity of the soil. Strip foundations can also be susceptible to differential settlement where the long strip spans areas of different soils. In these cases a separate settlement analysis can be undertaken using a simple design spreadsheet such as the CivilWeb Foundation Settlement Calculator Spreadsheet.

After the designer has input the loading, geometric and soil design information the CivilWeb Strip Footing Design Excel Spreadsheet calculates the bearing pressures beneath the foundations and checks whether these exceed the bearing capacity of the soil or not. The spreadsheet completes the analysis in accordance with either BS EN 1997 or BS 8004. The spreadsheet also presents the results of the analysis using unique analysis tools which show the designer exactly where the design can be optimised.

After the designer has optimised the strip foundation dimensions, the CivilWeb Strip Footing Design Spreadsheet then designs the reinforcement required. The spreadsheet calculates the maximum bending moments and shear forces acting on the foundation. This can then be used to design the reinforcement. The spreadsheet includes unique reinforcement picker tools which show the designer exactly which combination of reinforcement bar sizes and spacings are best suited to this particular foundation.

The CivilWeb Strip Footing Design Spreadsheet finally presents the designer with a handy summary of the design information, highlighting any areas where the design is not sufficient. The spreadsheet also draws a dynamic foundation reinforcement drawing which the design can use for the construction phase of the project.

CivilWeb Strip Footing Design Excel Spreadsheet

The CivilWeb Strip Footing Design Excel Spreadsheet completes all the calculations required to complete a strip foundation design in accordance with BS EN 1997 or BS 8004. The spreadsheet includes a number of unique design tools which allow the designer to complete a full optimisation of the design in minutes, saving many hours of work on every strip foundation design.

The CivilWeb Strip Footing Design Excel Spreadsheet can be purchased here for only £20.