NSC 29
February 18
GRADES S355JR/J0/J2
RAINHAM STEEL
Head Office: 01708 522311 Fax: 01708 559024 Bury Office: 01617 962889 Fax: 01617 962921
email: sales@rainhamsteel.co.uk www.rainhamsteel.co.uk
Beams • Columns
Channel • Angle
Flats • Uni Flats
Saw Cutting
Shot Blasting
Painting • Drilling
Hot & Cold Structural
Hollow Sections
RAINHAM STEEL Proud sponsors of BOXNATION Channel of Champions
Technical
is much less than that at the corners of square and rectangular
sections (about 10% in the worst case) and there is consequently
no restriction on the choice of cold formed circular hollow
sections, even with the presence of a gross stress concentration.
Designers will also remember that BS EN 1993-1-8:2005
Clause 4.14 and Table 4.2 imposes restrictions on welding
near cold formed zones. The table is entitled ‘Conditions for
welding cold formed zones and adjacent material’ and gives
maximum thicknesses based on an r/t ratio or strain due to cold
forming. Unhelpfully, the radius considered in the clause is the
internal radius of the corner, whereas the product standard
BS EN 10219-2 uses the external radius (external corner profile).
The corresponding r/t values and limiting thicknesses are given
in Table 6 (below right).
The clause therefore prohibits welding within 5 times the
wall thickness of the corners of many square and rectangular
cold formed sections, unless the steel is “fully killed Aluminiumkilled
steel (Al ≥ 0.02%)”, with limits on carbon (C ≤ 0.18%,),
phosphorous (P ≤ 0.02%) and sulphur (S ≤ 0.012%). Alternatively,
tests must have been carried out to show that welding is
permitted.
Table A1 in Annex A of the product standard indicates the steel
is fully killed steel with a minimum 0.02% of total aluminium.
The table gives the chemical composition of the steel and
includes maximum percentages by mass of carbon (C ≤ 0.22%),
phosphorous (P ≤ 0.03%) and sulphur (S ≤ 0.03%). The material
therefore satisfies the requirement for fully-killed aluminium
killed steel but allows the percentage of carbon, phosphorous
and sulphur to fall outside the limits specified in Table 4.2.
This restriction prohibits the adoption of a welded end plate or
base plate for most rectangular and square cold formed hollow
sections which comply with the product standard but do not
meet the tighter requirements for carbon, phosphorous and
sulphur in Table 4.2.
Design detail Thickness range
(mm)
Temperature
adjustment
(°C)
Maximum
thickness
(mm)
no fatigue; external steelwork,
welded very severe, high design
stress (>0.5fy ) no gross stress
concentration, S355J2H
0 < t ≤ 6 -181 5
6 < t ≤10 -145 9
10 < t -124 13
Table 4: Detail classed as welded very severe (equivalent to -30 °C in NA.1)
Design detail Thickness range
(mm)
Temperature
adjustment
(°C)
Maximum
thickness
(mm)
no fatigue; external steelwork,
welded severe, high design
stress (>0.5fy ) no gross stress
concentration, S355J2H
0 < t ≤ 6 -171 6
6 < t ≤10 -135 11
10 < t -114 16
Table 5: Detail which is classed as welded severe (equivalent to -20 °C in NA.1)
Product standard
thickness range
(mm)
Product standard
tolerances based
on R
Table 4.2
Corresponding r/t
Table 4.2 “worst
case” maximum
thickness (mm)
0 < t ≤ 6 1.6T to 2.4T 0.6 to 1.4 not given
6 < t ≤10 2.0T to 3.0T 1.0 to 2.0 6
10 < t 2.4T to 3.6T 1.4 to 2.6 6 (out of range)
Table 6: Maximum thickness for welding related to the product standard
/Welding
/Simple_connections#Flexible_end_plate_connections
/Simple_connections#Column_bases
/www.rainhamsteel.co.uk
link