LINTEL BEAM

Lintel is a structural member provided above the openings in masonry walls to

carry masonry and other loads coming over it.

Size of Lintel :

Width : Width equal to width of wall.

Depth : Usually taken as span rounded to the brick layer size (e.g) one brick 12

layer of traditional brick masonry measures 76 mm + 12 mm mortar. Then for a

lintel, for a width of opening up to 900 mm, one layer thickness can be adopted.

Thumb rule :

Span Lintel depth

Up to 1.20 m 150 mm

For additional 30 cm span add 2.5 cm in addition to the above thickness.

Bearing :

A minimum of 200 mm nominal bearing shall be provided for all lintels. This

should be increased for larger spans or heavy loads.

Thumb rule:

Span Bearing

0.8 to 2.40 m 200 mm

2.50 to 4.20 m 300 mm

4.30 to 6.00 m 400 mm

Reinforcement :

Since the lintels are of minor structural importance, the minimum requirements

of reinforcement specified for beams need not be strictly compiled with in lintels.

Wall thickness No. of rods usually provided

100 mm ( ½ brick) 2

200 mm (1 brick ) 3

300 mm (1½ brick) 4

Thumb rule :

For spans up to 1.20 m 2 Nos. 8 Φ RTS is enough for one brick wall.

Span Type of rods to be used

Up to 1.0 m 6 Φ MS

1.0 - 1.20 m 8 Φ RTS

1.20 - 2.0 m 10 Φ RTS

2.0 - 3.0 m 12 Φ RTS

Hanger bars :

2 Nos. 6 Φ MS or 8 Φ RTS

Stirrups :

6 Φ MS 2 legged stirrups at 150 mm to 300 mm C/C.

DESIGN ASPECTS :

i) Assume depth of lintel = span to span 10 12 ii) Effective span = clear span + d or C/C of support (bearing) whichever is less.

iii) Loading :

The lintel carries only dead load and imposed load (fixed), and very rarely it

carries an imposed load (not fixed).

iv) Bending moment :

Case- 1:

When there is sufficient height of wall above opening i.e., h > 0.866 l

This is most general case. In this case it is assumed that because of arch action

in masonry, only weight of masonry contained within equilateral triangle of sides

equal to effective span, acts as load in addition to self weight of lintel.

Height of triangle h= tan 60˚ x l/2 x 0.866 l

Load on lintel wt = weight of triangular portion of masonry

= ½ x ( 0.866 x t) x b x unit weight of masonry where

b = width of masonry wall.

Self weight of lintel/ m ws = 1 x b x t x 25 KN/m

B.M = wt x l + ws x l 2 6 8

Case -2 :When slab falls within the triangle :When a floor slab or roof slab lies within the dispersion triangle, it transmits only the load falling within the triangle. B.M. = B.M. due to triangular masonry weight + B.M. due to load w1/m transmitted by slab+ B.M. due to self weight of lintel. = wt x l + [ RA l - w1 x 2 ] + ws x l 2 6 2 8 8

Case- 3 :When the height of the wall above lintel is less than the height of the equilateral triangle :

In this case, rectangular masonry loading above the lintel up to top level of masonry and also load transmitted from slab are taken. Total load is due to rectangular masonry loading w1 + load transmitted from slab+ load due to self weight of lintel ws

B.M. = wt x l + wt x l + [ RA l - w1 x 2 ] + ws x l 2 6 2 8 8 8

TABLE

LINTEL BEAM WITHOUT CHAJJA

REINFORCEMENT DETAILS FOR 230 mm WIDTH

M20 Concrete Fe 415 Steel

Span in metre

Depth D in mm

Reinforcement Top Bottom Stirrups

0.90 120 2 – 8 # 2 – 8 # 6 Φ 2 L @ 100 C/c1.20 120 2 – 8 # 2 – 8 # 6 Φ 2 L @ 100 C/c1.50 150 2 – 8 # 2 – 8 # 6 Φ 2 L @ 120 C/c1.80 200 2 – 8 # 2 – 10 # 6 Φ 2 L @ 120 C/c2.10 200 2 –10 # 2 – 10 # 6 Φ 2 L @ 150 C/c2.50 200 2 –10 # 3 – 10 # 6 Φ 2 L @ 150 C/c3.00 250 2 – 10 # 3 – 10 # 8 # 2 L @ 200 C/c3.50 350 2 – 10 # 2 – 12 # 8 # 2 L @ 200 C/c4.00 400 2 – 10 # 2 – 16 # 8 # 2 L @ 250 C/c5.00 400 3 – 10 # 3 – 16 # 8 # 2 L @ 250 C/c