8.1 Bending: UB sections, UC sections and parallel flange channels
4.2.5.2
(a) Moment capacity, assuming shear load is low (<60% of the shear capacity):
| Mcx = py Sx |
but ≤ 1.2 py Zx |
for Class 1 (plastic) and Class 2 (compact sections) |
| Mcx = py Sxeff |
but ≤ 1.2 py Zx |
for Class 3 (semi‑compact sections) |
4.2.5.1
If the moment capacity is governed by 1.2 py Zx the values in the tables have been printed in italic type because higher values may be used in some circumstances. This limit is only appropriate for simply supported beams and cantilevers. For other cases, a general limit of 1.5 py Zx should be applied; a full explanation is given in AD195 [13].
(b) Where the shear load is high (>60% of the shear capacity), the values should be checked and reduced, if necessary.
(c) The moment capacity Mcx has been based on the section classification given but it should be noted that this classification applies to members subject to bending about the x‑x axis only
Note: None of the universal beams, universal columns or parallel flange channels in grade S275 or S355 are slender under bending only.
4.3.6.4 (c)
4.3.6.7
(d) Buckling resistance moment, Mb
| Mb = pb Sx ≤ Mcx |
for Class 1 (plastic) and Class 2 (compact sections) |
| Mb = pb Sxeff ≤ Mcx |
for Class 3 (semi-compact sections) |
| pb |
has been obtained for particular values of λLT = u v λ $w0.5 |
4.3.6.9
4.3.6.7
4.3.6.8
4.3.6.8
where:
| β w |
= 1.0 |
for Class 1 (plastic) and Class 2 (compact sections) |
| |
= Sxeff / Sx |
for Class 3 (semi-compact sections) |
| λ |
is the slenderness = LE/ry |
| u |
is a Buckling parameter (as defined in the code) |
| v |
is a Slenderness factor (as defined in the code) |
Table 19
(e) The buckling resistance moments, Mb, have been based on:
- The effective length, LE, given at the head of the tables.
- Section classification as above.
8.2 Bending: Hollow sections
8.2.1 Circular and square hollow sections
4.2.5.2
(a) Moment capacity assuming shear load is low (< 60% of shear capacity):
| Mc = py S |
but ≤ 1.2 py Z |
for Class 1 (plastic) and Class 2 (compact sections) |
| Mc = py Seff |
but ≤ 1.2 Py Z |
for Class 3 (semi‑compact sections) |
| Mc = py Zeff |
|
for Class 4 (slender sections) |
4.2.5.1
If the moment capacity is governed by 1.2 py Z the values in the tables have been printed in italic type because higher values may be used in some circumstances. This limit is only appropriate for simply supported beams and cantilevers. For other cases, a general limit of 1.5 py Z should be applied, a full explanation is given in AD195 [13].
4.2.5.3
(b) Where the shear load is high (>60% of the shear capacity), the values for Mc should be checked and reduced, if necessary.
(c) The section classification is given in the tables but it should be noted that this classification applies to members subject to bending only. For square hollow sections all section classifications are possible under pure bending. None of the circular hollow sections are slender under pure bending.
(d) The second moment of area (I) is repeated in the tables as it is required for deflection checks.
4.2.3
(e) Shear capacity
| Pv = 0.36 py A |
for circular hollow sections |
| Pv = 0.6 py(D/2D)A |
for square hollow sections |
8.2.2 Rectangular hollow sections
(a) Moment capacity
The values of Mcx and Mcy have been calculated as for circular and square hollow sections (Section 8.2.1).
Table 11
(b) The section classification given in the tables applies to members subject to bending only about the appropriate axes. Sections can be slender for pure bending about the x-x or y‑y axis in both S275 and S355 because the d/t ratio of the flange is greater than 40ε for hot-finished sections and 35ε for cold-formed sections. It should be noted that a section may be slender when bending about the y‑y axis and not slender when bending about the x‑x axis.
4.3.6.1
Table 15
(c) The limiting length, Lc, is the length above which lateral torsional buckling should be checked.
(d) The second moment of area (I) is repeated in the tables as it is required for deflection checks.
