Steel brace design to EC3

Design method

Unless explicitly stated all brace calculations are performed in accordance with the relevant sections of BS EN 1993-1-1:2005 (Ref. 1) (herein abbreviated to EC3) and the associated National Annex.

A basic knowledge of the design methods for braces in accordance with the design code is assumed.

Classification

No classification is required for braces in tension.

Braces in compression are classified according to Table 5.2 as either: Class 1, Class 2, Class 3 or Class 4.

Class 4 sections are not allowed except for angle (single and double) and tee sections.

Axial tension

An axial tension capacity check is performed according to clause 6.2.3.(1)

The following points should be noted:

Clause 6.2.3 (3) - is not considered
Clause 6.2.3 (4) - is not considered
Clause 6.2.3 (5) - is not considered

Axial compression

An axial compression capacity check is performed according clause 6.2.4.(1)

Compression buckling

If axial compression exists, the member is also assessed according to clause 6.3.1.1(1) for flexural buckling resistance about both the major and minor axis i.e. N_b,y,Rd and N_b,z,Rd over the buckling lengths L_yy and L_zz and where required the torsional, or flexural-torsional buckling resistance, N_b,x,Rd.

For single and double angles (both equal and unequal) there is also a compression buckling check about the v-v axis, over the buckling length L_vv. For single angles, L_vv is the system length L, while for double angles L_vv is L/3.

All section types are checked for flexural buckling. It is only hollow sections that do not need to be checked for torsional and torsional-flexural buckling.

Different effective length factors can be applied for flexural buckling in the major and minor axis. For single and double angles an effective length factor can also be applied in the v-v axis. The default effective length is 1.0L in all 3 cases. You are expected to adjust the effective length factor (up or down) as necessary.

The torsional and torsional flexural buckling effective length factor (1.0L) can not be changed.