B 50
[Subsidiary]
CAP. 123] Building (Construction) Regulations
[1985 Ed.
(c) the height measured from the base to the top of the chimney shaft, shall not exceed the least width of the base multiplied by...
(i) 10 times if the shaft be square;
(ii) 12 times if the shaft be circular or polygonal;
(d) the thickness at its top and for 6 m below its top shall be at least 225 mm and it shall be increased by brick for every additional 6 m, or part thereof, measured downwards:
Provided that-
(i) any cap, cornice, plinth, string course or other departure from plain brickwork; and
(ii) any internal lining,
shall be additional to the thickness of the brickwork required by this paragraph;
(e) any internal lining shall not be bonded with the brickwork. (f) any metal used in connexion with the construction of the shaft shall be properly protected against corrosion;
(g) any footings which may be provided at the base of the shaft shall spread all round at base by regular offsets and the space enclosed by such footings shall be filled in solid with concrete.
(2) Every chimney shaft built of reinforced concrete shall comply with the relevant provisions of Part XII for the structural use of reinforced concrete and shall comply with the following provisions-
(a) the concrete shall be not inferior to that designated Grade IIIA in regulation 19:
(b) the reinforcement shall be in accordance with the requirements of regulation 20 and the concrete cover shall be not less than 40 mm thick;
(c) the concrete stresses shall not exceed the maximum permissible stresses in regulation 116 or 157 if special or designed mixes are used:
(d) the stresses in the reinforcement shall not exceed 60 per cent of the maximum permissible stresses in regulation 117 or 158;
(e) due account shall be taken of the effect of temperature stresses; and
(f) any lining which may be provided to the shaft shall not be taken as contributing to the strength of the shaft.
(3) If built of mild steel shall be constructed of steel plates not less than 5 mm thick and properly stayed and protected against corrosion.
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