Check limit load (SLU)

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Check limit load (SLU)


The vertical bearing capacity of the foundation soil is verified according to the theory of limit states using the following inequality:



or based on the factor of safety as:







σ-extreme design contact stress at the footing bottom


Rd-design bearing capacity of foundation soil


γRV-coefficient of vertical bearing capacity of foundation


SFv-safety factor for vertical bearing capacity



Extreme design contact stress at the footing bottom is assumed the form:






V-extreme design vertical force


Aef-effective area of foundation



Effective Area

When solving the problem of eccentrically loaded foundations the program offers two options to deal with an effective dimension of the foundation area:




a rectangular shape of effective area is assumed

circular shape of effective area is assumed


Rectangular shape


A simplified solution is used in such cases. In case of axial eccentricity (bending moment acts in one plane only) the analysis assumes a uniform distribution of contact stress σ applied only over a portion of the foundation l1, which is less by twice the eccentricity e compared to the total length l.







Determination of effective area in case of axial eccentricity




An effective area (b*l1) is assumed to compute the contact stress, so that we have:




In case of a general eccentric load (foundation is loaded by the vertical force V and by bending moments M1 and M2 the load is replaced by a single force with given eccentricities:



The size of effective area follows from the condition that the force V must act eccentrically:





Circular  shape

A circular foundation subjected to a vertical load applied with an eccentricity e=Md/Nd can be regarded as an equivalent fictitious foundation with a centrally applied load (Figure), as suggested by Meyerhof (1953) and Vesic (1973). In this case,the area of the fictitious foundation, A', can be calculated as:


The aspect ratio of the equivalent rectangular area can also be approximated as the ratio of the line lengths b to l, as shown in Figure that is,






Calculating method of the equivalent dimensions of a circular foundation subjected to a non-barycentric load.




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