B 96
[Subsidiary] Footings.
Method of design for flat slab construction.
Definitions and notation for flat slab construction.
CAP. 123] Building (Construction) Regulations [1985 Ed.
144. (1) The bending moments at any section of a footing for a reinforced concrete column or wall shall be taken to be the moment of the forces over the entire area on 1 side of the section. The critical section for bending in the footing shall be taken at the face of the column or the wall.
(2) (a) Subject to sub-paragraph (b) the reinforcement provided to resist the bending moments specified in paragraph (1) shall be distributed uniformly across the full width of the section.
(b) In rectangular footings for columns, the reinforcement parallel to the short edge should be more closely spaced near the column.
(3) The critical sections for shear shall be taken to be at a distance from the column face equal to the effective depth of the footing.
(4) The critical section for local bond stress shall be taken to be the same section as the critical section for bending moment at the face of the column or wall.
145. Flat slabs may be designed—
(a) as continuous frames analysed by the elastic theory in the manner described in regulation 155; or
(b) by the empirical method described in regulation 156,
and shall comply with regulations 146 to 154.
146. (1) In regulations 147 to 156–
"flat slab" means a reinforced concrete slab with or without drops, supported generally without beams, by columns with or without flared column heads:
"panel" means the rectangular part of a flat slab enclosed by the centre lines joining 4 adjacent columns;
"drop" means the part of a flat slab which is thickened throughout an area surrounding the column or column head; and
"column head" means an enlargement at the top of a column which is designed and built to act monolithically with the column and flat slab.
(2) In regulations 147 to 156-
L1 is the length of the panel in the direction of the span;
L2 is the width of the panel at right angles to the span;
Ln is the average of L1 and L2;
Dc is the diameter of the column head or column, where no column head is provided;
ts is the thickness of the slab;
td is the thickness of the drop; and
q is the total load per unit area on the panel.