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Base plate in compression

The resistance of concrete in compression is defined according to EN 1993-1-1 by the following formula

Base dimensions

Where is:

βj

  • The factor, that is applied in case that the characteristic strength of grouting is higher than 20% of the characteristic strength of concrete and the grouting thickness is smaller than 20% of minimum base dimension. The value of the factor is 2/3.

fcd

  • The design value of concrete strength in compression

kj

  • The concentration factor

The factor kj is calculated using expression

Where is:

a, b

  • The dimensions of base

a1, b1

  • The effective dimensions

h

  • The height of a base

The values a1 and b1 are calculated using following expressions

The assumption is, that the stress is distributed uniformly under the active area. This area consists of the column cross-section and surrounding are with maximum distance c from the edge of the cross-section. The thickness c is given by formula

Where is:

t

  • The thickness of the base plate

fy

  • The yield strength

fj

  • The concrete resistance in compression

γM0

  • The partial safety factor

The active areas for column web and flange

The active area under the base plate

Stiffness

The deformation between base plate and concrete surface for force F is calculated using expression

where the shape factor α depends on material characteristics. Following formula is used for concrete foundation and steel base plate according to (Wald, Sokol; 1996)

Where is:

δr

  • The teformation under the stiff base plate

α

  • The shape factor

Ec

  • The modulus of elasticity of concrete

L

  • The plate length

ar

  • The width of effective base plate

The stiffness is calculated in accordance with EN 1993-1-8 using formula

The effective width of T-stub ar can be replaced for elastic deformations by the following width (ed.Weynand; 1999):

Where is:

tw

  • The web thickness of effective T-stub

t

  • The thickness of base plate

References

Wald F., Sokol Z.: Proposal of the Stiffness Design Model of the Column Bases, Connection v Steel Structures II, Behaviour, Strength, and Design, ed. Bjorhovde, Colson, Zandonini, Pergamon Press, London 1996, p. 237 - 249, ISBN 0-08-042821-5.

COST C1: Column Bases in Steel Building Frames, ed. K. Weynand, EC, Brussels 1999.

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