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Summary Table 2 in Annex A summarizes the procedures for verifying the centre.

 

1.1 - Calculation of the eccentricity

 

The torsor of the forces (Md;x , Md;y , Vd , Hd ) must be calculated at the center of the foundation and at the base of the footing. When the foundation is subjected at a time, the resulting load is not centered, we speak of the eccentricity of the load. The value of this shift depends on the combination of shares considered. Thus, it is necessary to calculate it for each given combination of actions. Table 7 illustrates the torsor of the forces for the different types of footings.

 

With:

Md: calculation value of the moment about the axis perpendicular to B;

Vd: calculation value of the vertical component of the efforts;

Hd: calculation value of the horizontal component of efforts;

Md;y: calculation value of the moment about the axis perpendicular to width B;

Md;x:  calculation value of the moment about the axis perpendicular to the length L.

 

Table 7: Calculation of eccentricity according to the type of footing

 

1.2 - Checks at the ELU

 

For combinations of actions at the ELU, the inequalities in Table 8 should be checked.

Table 8: Inequalities to be checked at the ELU for an eccentric load, depending on the shape of the footing [Forms 9.5.1, 9.5.2, and 9.5.3]

 

Where the eccentricity of the load exceeds one-third of the width of a spread footing or 30 % of the diameter of a circular footing, special precautions must be taken with regard to the stiffness of the supporting soil, to the detailed verification of the calculation values of the actions and to the definition of the position of the edge of the foundation taking into account the construction tolerances. If precautions are not taken, tolerances of up to 0.10 m on footing dimensions should be used [9.5 (2)].

 

If the eccentricity of the load is too great, the execution tolerances have a significant impact on the sizing. In this case, the footing should be shifted unfavorably by 10 cm in the plan, changing the forces for some loading cases, leading to an increase in eccentricity.

Otherwise, the impact of execution tolerances is low, so execution tolerance should not be taken into account in the justifications.

 

1.3 - Verifications to ELS

 

For combinations of actions with ELS almost-permanent, frequent or characteristic, the inequalities in Table 9 should be checked.

Table 9: Inequalities to be checked at ELS for an eccentric load, depending on the shape of the footing [Forms 13.3.1 to 13.3.6]