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:

 

check_01

or based on the factor of safety as:

check_02

 

 

 

where:

 

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:

check_03

 

 

where:

 

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.

 

 

 

pianta_fondazione_02

 

 

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:

 

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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:

 

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

 

 

 

check_06

 

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,

 

 

 

fondazione_circ

 

Método de cálculo de las dimensiones equivalentes de una cimentación sometida a carga no baricéntrica

 

 

 


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