1985 Ed.]
Building (Construction) Regulations
[CAP. 123
B 109
[Subsidiary]
(1) based on the tensile reinforcement,
Mr = Ast Pstla
(2) based on the resistance to crushing of the concrete in compression,
Mr = Pcb bd12⁄4
where-
la = is the lever arm, which may be taken as d1 - 3 Ast Pst⁄4bpcb
Ast = is the area of tensile reinforcement;
Pst = is the permissible tensile stress in the reinforcement;
Pcb = is the permissible compressive stress in the concrete in bending;
b = is the breadth of the section; and
d1 = is the effective depth to the tensile reinforcement;
(3) where it is necessary for the resistance moment to exceed Pcb⁄4 bd12, compressive reinforcement should be provided so that
Mr = Pcb bd12⁄4 + AscPsc (d1 - d2)
where
Asc = is the area of compressive reinforcement;
Psc = is the permissible compressive stress in the steel, or 380(1 - dn⁄do)MPa, whichever is the lesser;
dn = is the depth of the concrete in compression; and
d2 = is the depth to the compressive reinforcement.
The area of tensile reinforcement shall be such that the stress in the steel does not exceed the permissible stress.
164. (1) The resistance moment when compressive reinforcement is not provided may be assumed to be the lesser of the 2 values calculated from the following equations:
(a) based on the tensile reinforcement,
M1 = AsPu(d1
L.N. 294/76.
Simplified formulae for T-beams or L-beams in load factor method.