Steel brace design to BS 5950

Tekla Structural Designer
2021
Tekla Structural Designer

Steel brace design to BS 5950

 

Design method

Unless explicitly stated all brace calculations are in accordance with the relevant sections of BS 5950-1:2000 (Ref. 2).

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 Clause 3.5 as either: Class 1, Class 2, Class 3 or Class 4.

Class 4 sections are not allowed.

Hollow sections

The classification rules for SHS and RHS relate to “hot-finished hollow sections” only (“cold-formed hollow sections” are not included in this release).

Axial Tension

An axial tension capacity check is performed according to clause 4.6.

Brace tension capacity is calculated according to section type as follows:

A. Hollow sections (CHS, RHS, SHS): Gross area capacity
B. Angle, Channel, Tee sections:

Reduced effective net area capacity

(Clauses 4.6.3.1 and 4.6.3.2)

C. I/H and any other sections: Effective net area capacity (Clause 4.6.1)

Notes:

  1. For section types B and C listed above, an Effective net area (Ae) should be entered either as a percentage of the gross area (Ag) or as an absolute value. The default is to use 100% of Ag, and an absolute value cannot be used if autodesign is also selected.
  2. The 'Geometry' property needs to be selected manually if autodesign is also selected, otherwise the 'Geometry' property does not appear visible.

Axial compression

An axial compression capacity check is performed according clause 4.7.

If either an Angle (single or double) or Channel or Tee section has been selected as the brace member then a 'Connection at each end' property box appears which allows selection of an appropriate Clause from Table 25 of the BS code to describe the connection type.

The default Clauses from Table 25 are as follows:

Single Angle 4.7.10.2a
Double Angle 4.7.10.3d
Channel 4.7.10.4b
Tee 4.7.10.5b

Notes:

  1. Clauses 4.7.10.2b, 4.7.10.2c, 4.7.10.3b, 4.7.10.3c, 4.7.10.3d and 4.7.10.3e only apply to Bolted connections so in these cases 'Bolted' should be selected in the 'Connection' property box. ('Bolted' is the default connection.)
  2. For Angle (single and double), Channel and Tee sections the Effective Length Factors will be auto-completed according to the connection Clause selected but these Factors can be changed if required. For Angle (single and double) sections the length Lv-v is always assumed to be L/3 and the Effective Length Factor v-v will act on this Lv-v.
  3. For single Angle sections the longer leg is assumed to be the connected element unless 'Short attached' is checked on the Size page of the dialog.
  4. For double unequal Angle sections, whichever leg is not the back-to-back leg is assumed to be the connected element when connection Clauses 4.7.10.3a and 4.7.10.3b are selected, and vice versa with Clauses 4.7.10.3c, 4.7.10.3d and 4.7.10.3e

Compression buckling

If axial compression exists, the member is also assessed according to clause 4.7 with all relevant sub-clauses.

The default effective length in each axis is 1.0L.

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