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:	σ_c,90d	is the design compressive stress in the contact area perpendicular to the grain
	F_c,90,d	is the the design force
	A_ef	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:	σ_c,90d	is the design compressive stress in the contact area perpendicular to the grain
	k_c,90	is a factor taking into account the load configuration, possibility of splitting and degree of compressive deformation
	f_c,90	is the design compressive strength perpendicular to the grain

The following rules are used for determination of the factor k_c,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 f_c,90,k are used for verification of pressure perpendicular to the grain:

Grade	C14	C18	C24	C30	GL28h	GL28c	GL30h	GL30c	GL32h	GL32c
f_c,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 k_c,90 is calculated according to this table:

	l₁ < 150mm	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

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