Technical
the relevant temperature well outside the range covered by the
tables in BS EN 1993-1-10 and PD 6695-1-10.
The SCI’s recent publication P419, Brittle fracture: selection of
steel subgrade to BS EN 1993-1-10 addresses the acknowledged
conservatism in the standard for structures where fatigue is
not a significant design consideration and presents tables of
limiting material thicknesses for this circumstance. However, the
tables do not extend to the much lower temperatures indicated
when considering the adjustments for the high strains resulting
from cold forming. SCI has produced values for the relevant
temperatures and these are given in Table 2 for S355J2 material
(the common steel grade for hollow sections).
As an example consider a cold formed section of steel
grade S355J2 with thickness in the range 0 to 6 mm used in an
external building environment where fatigue is not a design
consideration, with a high design stress (σEd > 0.5fy ), no gross
stress concentration and with a welded detail classed as “Welded
very severe”.
Temperature adjustments are given in Table 3:
From Table 2, the limiting thickness of the cold formed section
is 5 mm. Limiting thicknesses for sections in the higher thickness
ranges in the product standard are given in Tables 4 and 5 for
details classed as “welded very severe” and “welded severe”.
Table 5 also applies to a detail which is classed as “welded very
severe” and has a design stress of less than 0.3fy .
An examination of the sizes in the Blue Book shows that
certain sections should not be used if the attributes of a
connection detail correspond to those in Table 4. If the detail
corresponds to the description in Table 5, there is no restriction
on the catalogue sizes which could be used.
The strain involved in cold forming circular hollow sections
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Material S355J2 Stress level 0.75fy
Temperature (°C) -70 -80 -90 -100 -110 -120 -130 -140 -150 -160 -170 -180
Thickness (mm) 54 40 30 32 18 15 12 10 8 7 6 5
Table 2: Limiting thicknesses for low temperatures
Thickness
Range (mm)
External
corner profile
C1 and C2 or R
Maximum
strain
%
strain
0 < t ≤ 6 1.6T to 2.4T T/(2×1.6T – T) = 1/2.2 45.5
6 < t ≤10 2.0T to 3.0T T/(2×2.0T – T) = 1/3.0 33.3
10 < t 2.4T to 3.6T T/(2×2.4T – T) = 1/3.8 26.3
Table 1: Strain due to cold forming
Adjustment (Tmd + ΔTr) ΔTRD ΔTRg ΔTRT ΔTRσ ΔTRS ΔTε ΔTεcf Total
Temperature (°C) -15 -30 0 0 0 0 0 -136 -181
Table 3: Temperature adjustments for determining limiting thickness
/Steel_material_properties#Toughness
/Fatigue_design_of_bridges#The_mechanism_of_fatigue
/Design
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/Steel_construction_products#Structural_hollow_sections