B 94
[Subsidiary]
Permissible loads on columns.
L.N. 294/76.
CAP. 123] Building (Construction) Regulations
[1985 Ed.
(12) In floor or roof systems where the ribs run in one direction only, stiffeners of minimum 75 mm width between ribs for the full depth of the rib shall be provided for clear length of rib greater than 4 m and at intervals not exceeding 4 m.
143. (1) (a) The permissible axial load Pc on a column reinforced with longitudinal bars and lateral ties shall not exceed that given by the following equation:
Pc = Pcc Ac + Psc Asc
where Pcc is the permissible stress for the concrete in direct compression;
Ac is the cross-sectional area of concrete excluding reinforcing steel;
Psc is the permissible compressive stress for column bars; and
Asc is the cross-sectional area of the longitudinal steel.
(b) Where helical reinforcement is used, the permissible axial load Pc on a column shall not exceed that given by the equation in sub-paragraph (a), or the following equation, whichever is the greater:
Pc = Pcc Ac + Psc Asc + 1.85 Pcc Acc
where Acc is the cross-sectional area of concrete in the core excluding the area of longitudinal reinforcement; and
As is the equivalent area of helical reinforcement (volume of helix per unit length of the column), and
Pcc Acc + 1.85 Pcc As shall not exceed 0.5 fcu Ac, where fcu is the works resistance to crushing of the concrete at 28 days.
(c) The permissible combination of direct load and bending moment to which a column may be subjected shall be determined on the basis of the elastic theory, with a modular ratio of 15 and the permissible stresses in bending given in regulations 116 and 117.
(d) The load on a column subject to both direct load and bending moment shall not exceed that permissible for an axially loaded column.
(e) The permissible load on a reinforced concrete column, having a ratio of effective length to least lateral dimension between 15 and 36, shall not exceed the appropriate permissible load in sub-paragraph (a), (b), (c) or (d) multiplied by the coefficient appropriate for each ratio of