1985 Ed.]
Building (Construction) Regulations
[CAP. 123
B 63
[Subsidiary]
(f) the surface and edges of the flange of the steel section shall
have a concrete cover of not less than 50 mm; and
(g) the casing is effectively reinforced with wire to BS 4482: 1969 of at least 5 mm diameter, and the reinforcement shall be in the form of stirrups or binding at not more than 150 mm pitch, and so arranged as to pass through the centre of the concrete cover,
the least radius of gyration (ky) may be deemed to be equal to 0.2 (b+100) mm and the radius of gyration (k...) shall be deemed to be equal to that of the uncased section:
Provided that in no case shall-
(i) the said stress exceed 1 times the maximum permissible stress on the uncased section of that column or strut; and
(ii) the ratio (l/k) of that uncased section exceed 250.
(4) In compound or built-up sections formed with different thicknesses of high yield stress structural steel, the maximum permissible stress for the whole of the section shall be taken as that for the greatest thickness of material used.
99. The maximum permissible stresses and the increases permitted thereon specified in regulations 97, 98 and 100 for beams, girders, columns and struts and all their connexions may be increased by 25 per cent when the calculations are based on all loads including wind load:
Provided that-
(a) the said stresses and increases are not exceeded when the calculations are based on all loads other than wind load; and
(b) the increase permitted by this regulation shall not apply to the stresses specified in regulations 97 (in respect of slab bases and parts in bearing only), 101 and 106.
100. (1) Members subject to both axial compression and bending stresses shall be so proportioned that the quantity
Stress due to wind.
Combined stresses.
Fa
fa fbe Fbe
fo
Fa
does not exceed unity at any point,
where fa = the calculated average axial compressive stress; total permissible axial stress on columns and struts:
fbe
Fbe
= total permissible compressive flexural stress in extreme fibres of beams and girders.
(2) Members subject to both axial tension and bending stresses shall be so proportioned that the quantity
the maximum resultant compressive stress due to bending about both principal axes; and