In case uplift occurs, a part of the foundation base does not participate in transferring pressure to soil. Such phenomenon can be allowed for under the foundation of columns that are loaded with moments resulting from live loads, with the exception of dynamic loads.
- ACI \ BS 8004:1986 \ CSA
A condition limiting eccentricity is not available for the codes mentioned. If such an analysis is required, it is necessary to check this value manually.
- DTU 13.12 / Fascicule 62 Titre V
A measure which defines the foundation uplift for the code Fascicule 62 Titre V. This is the effective footing-soil contact area expressed as percentage with respect to the total foundation area. The default criteria of the percentage foundation-soil contact area are as follows.
- ULS: 10 %,
- SLS (for a frequent combination): 100 %
- SLS (for a rare combination): 75 %.
These values comply with the requirements of the code Fascicule and may be modified as needed.
The document DTU 13.12 does not impose any particular requirements for foundation uplift. However, you can impose limitations for the contact area analogously to the code Fascicule 62 Titre V. Code combinations according to DTU 13.12 frequent and rare combinations are not distinguished in SLS. Only two limits are accessible here: separately for ULS and separately for SLS.
- EN 1997-1:2004 and ENV 1997-1:1994 (EC 7)
Eurocode 7 imposes special requirements for foundations with a large load on eccentricity (6.5.4). It is possible to design a foundation considering the limit condition for a position of the force resultant of 1/3 of length or width 6.5.4 (1).
Due to the danger connected with foundation uplift, it is possible to introduce a more rigorous condition for the positon of resultant, which prevents uplift (1/6 of length or width) which corresponds to the core of section. This condition may be applied in design of foundations for structures of higher importance.
These limitations are defined in the Geotechnical Options dialog on the General tab.
- PN-81/B-03020
The Polish code divides ULS loads into two groups:
- Long-term loads.
- Total loads.
For each load group a position of load resultant to the foundation base may be determined. Defining an eccentricity for long-term loads greater than that for total loads is disallowed.
The following limitations for the location of eccentricity may be applied to these groups.
Core 0
Location of eccentricity at core 0 ensures that such a foundation base shape is selected so the load on eccentricity for unidirectional bending does not exceed 1/30 of the dimension of the foundation base. In this case of distribution of stresses under the footing, studies allow for the application of a simplified calculation method as for the axial load combined with an additional safety factor.
Note: Calculations in the module are always performed in an exact way.Core I
Core 1 prevents a gap under the foundation base, which indicates uplift. In this case the eccentricity may not exceed the values A/6 and B/6 so the neutral axis does not intersect the foundation base.
For the foundation of industrial hall columns loaded with overhead traveling cranes, the resultant of design forces for dead, live, short- and long-term loads may not overstep the core of foundation base 2.3 d.
Core II
The generalized core has been introduced due to the limitation of allowable gap under the foundation when uplift of the footing base occurs 2.3 a. The code allows for the gap between the ground and the foundation base. The range of which may not be greater than half of the distance C', between the straight line that extends parallel to the neutral axis and passes through the centroid of the whole base, and the outermost point of the base which lies opposite to the point at which the maximum stress value q rmax occurs. Therefore, the allowable, relative value of a gap for core II equals 0.5 and results from the C/C' ratio. For a simple case of eB = 0, C = A/4, a C' = A/2.
- SNiP 2.02.01-83
A condition limiting eccentricity is not available for the code mentioned. If such an analysis is required, it is necessary to check this value manually.