B 80
[Subsidiary]
CAP. 123]
Building (Construction) Regulations
[1985 Ed.
Stiffness of members.
L.N. 294/76.
(a) both steel and concrete are elastic within the range of the permissible stresses and the modular ratio is equal to 15;
(b) at any cross-section plane sections remain plane; and
(c) all tensile stresses are taken by the reinforcement except that the concrete may be assumed to resist diagonal tension within the limits of shear stress specified for concrete in regulation 116.
132. (1) Reinforced concrete members shall possess adequate stiffness to prevent such deflexion or deformation as might impair the strength or efficiency of the structure or produce cracks in finishes or in partitions.
(2) For all normal cases it shall be assumed that the stiffness will be satisfactory if
(a) in the case of members with steel stresses not more than 125 MPa, the ratio of span to overall depth does not exceed the values given in Table XXXII; and
(b) in the case of members with steel stresses greater than 125 MPa, the ratio of span to overall depth does not exceed 90 per cent of the values given in Table XXXII.
Simply supported
Continuous
Cantilever
TABLE XXXII
Permissible values of ratio of span to depth of beams and slabs
(1)
(2)
BEAMS--
Ratio of span to overall depth
20
25
10
SLABS-
30
35
Spanning in 1 direction
(i) simply supported
(ii) continuous
Spanning in 2 directions
(i) simply supported
(ii) continuous
Cantilever
30
35
40
12
(3) (a) For the purposes of calculating bending moments in continuous structures, the moment of inertia shall be estimated by considering--
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