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Compression perpendicular to the grain in supports

Design of compression perpendicular to the grain in supports is based on the chapter 6.1.5 of EN 1995-1-1:

The design compressive stress in the contact area perpendicular to the grain is calculated using the formula (6.4):

\sigma _{c,90,d}=\frac{F_{c,90,d}}{A_{ef}}

where:

σc,90d

  • is the design compressive stress in the contact area perpendicular to the grain

Fc,90,d

  • is the the design force

Aef

  • is the contact area perpendicular to the grain. The length of the contact area is increased by 30mm in accordance with 6.1.5(1) on both ends of the support, providing that the distance from another joint or member end is longer than this value.

Final verification corresponds to the expression (6.3):

\sigma _{c,90,d} \leq k_{c,90} f_{c,90}

where:

σc,90d

  • is the design compressive stress in the contact area perpendicular to the grain

kc,90

  • is a factor taking into account the load configuration, possibility of splitting and degree of compressive deformation

fc,90

  • is the design compressive strength perpendicular to the grain

The following rules are used for determination of the factor kc,90:

  • The value 1.5 is used for solid timber providing that the distance from the nearest joint is longer than 2h (where h is the height of supported member).
  • The value 1.75 is used for glued laminated timber providing that the distance from the nearest joint is longer than 2h (where h is the height of supported member). The length of the support shall be shorter than 400mm.
  • The value 1.0 is used in other cases

Different procedures are used for certain national annexes:

SS EN 1995-1-1 (Sweden)

Following values of partial factors are used for verification of pressure perpendicular to the grain:

\gamma _{M}=1.0 ; k_{mod}=1.0

This procedure can be used in cases when increased deformations in supports have no significant impact on the system’s stability and mechanical resistance. Otherwise, the procedure according to EN 1995-1-1 shall be used.

NS EN 1995-1-1 (Norway)

Verification of pressure perpendicular to the grain is based on "Rapport 86: Compression perpendicular to the grain, a recommendation" (released by Norsk Treteknisk Institutt in February 2013).

Following values of the characteristic compressive strength perpendicular to the grain fc,90,k are used for verification of pressure perpendicular to the grain:

Grade

C14

C18

C24

C30

GL28h

GL28c

GL30h

GL30c

GL32h

GL32c

fc,90,k [MPa]

4.3

4.8

5.3

5.7

5.3

5.3

5.5

5.5

5.7

5.7

The factor kc,90 is calculated according to this table:

l1 < 150mm

l1 < 150mm

a ≥ 100mm

a < 100mm

l ≥ 150mm

1.0

1.0

1.0

150mm > l ≥ 15mm

1.0

1,0+(150-l)/170

1,0+a(150-l)/17000

15mm > l

1.0

1.8

1,0+a/125

where:

l1

  • is the distance from the nearest joint

l

  • is the length of the support

a

  • is the distance from the member end