LINTELS

DEFINITION

     A lintel is a horizontal member which is placed across an opening to support the portion of the structure above it.  The function of a lintel is just the same as that of an arch or a beam. However the lintels are easy and simple in construction. For an arch, or a beam. However the lintels are easy and simple in construction. For an arch. Special centering or form work is required. However the arches are suitable under the following circumstances:
1.       Loads are heavy,
2.       Span is more,
3.       Strong abutments or supports are available.
The ends of Lintels are built into the masonry and thus the load carried by lintels is transferred of the masonry in jambs. At present, the lintels of R.C.C are widely used to span the openings for doors, windows, etc in a structure. In generals, it should be seen that the bearing of lintel i.e. the distance up to which it is inserted in the supporting wall, should be the minimum of the following three considerations. Wall should be the minimum of the following three considerations.
1.       100 mm or
2.        Height of lintel; or
3.       One-tenth to one-twelfth of the span of lintel.
In this chapter, the topic of lintels will be discussed in detail.

MATERIALS FOR LINTELS

The common materials used in the construction of lintels are as follows:

1.       Wood or timber lintels

2.       Stone lintels

3.       Brick lintels

4.       Steel lintels

5.       Reinforced cement concrete lintels.

1)      Wood or timber lintels: These lintels consist of pieces of timber which are placed across the opening.  The timber lintels are the oldest types of lintels and they have become obsolete except in hilly areas or places where timber is easily available.

A single piece of timber can be used as a lintel or built-up sections may be formed as shown in fig. 18-1 and fig. 18-1, three timber pieces are bolted to serve as a lintel.  Bolted to serve as a lintel. Fig. 18-2 shows a wood lintel composed of two timber pieces and two distances of packing pieces.  The bolts are provided through the packing pieces as shown if the timber lintels are strengthened by the provision of mild steel plates at their top and bottom, they are known as the Fetched lintels.

The important features of wood lintels are as follows:

I)A bearing of about 150 mm to 200 mm should be provided on the wall and the ends of lintel should be placed on mortar so as to create a level and firm bearing.

II)The width of lintel should be equal to the thickness of the opening and the depth of lintel should be about 1/12 to 1/8 of the span with a minimum value of 80 mm.

III)The wood lintels are liable to be destroyed by fire and also are liable to decay, if not properly ventilated. Hence sound and hard timber like teak should be used in the construction of wood lintels and a coat of suitable preservative should be applied.

IV)The wood lintels are comparatively weak and relieving arches of brick or stone should therefore be provided as shown in fig 17-5 and fig. 17-14.

V)The wood lintels help in securing the beads of frames of timber doors and windows.

Vi)If wood lintel is to be sued for larger spans, it is necessary to design it as a timber beam simply supported at its ends.

2)      Stone Lintels: These lintels consist of slabs of stones which are placed across the openings. The stone lintels may be formed of a single piece or more than one piece. The stone lintels are not generally favoured  mainly due to the following reasons:

I.The stone possesses low tensile resistance. Hence the relieving arches are to be provided when the span exceeds I m. Otherwise the depth of stone lintel becomes considerable. The depth of stone lintel should be at least one mm per ten mm length of the opening.

II.The stone cracks when subjected to the vibratory loads. Hence the stone lintels should be used with caution where shock waves are likely to occur frequently.

III.It is difficult sot obtain a good stone of required depth. Hence the stone is not available. Moreover the stone which are to be used for lintels. Are to be properly dressed on site of work. This will increase the cost of work

3)      Brick Lintels :  These lintels consist of bricks which are generally placed on end or edge as shown in fig. A better way of providing and of a brick lintel is shown in fig. 18-4 The important features of brink  lintels are as follows :

I.The bricks should be well –burnt, copper-coloured, free from cracks and with sharp and square edges.

II.A temporary wood support, known as a turning piece, is used to construct a brink lintel.

III.In order to maintain the appearance of brickwork, a brink lintel should have a depth equal to some multiple of brick courses.

IV.It is found that the bricks having frogs are more suitable for the brink lintels. It is due to the fact that the forge, filled with mortar, form keys between different layers and thus the shear resistance of brink lintels.  Results in overall increases of the strength of brink, lintel.

V.A brick lintel is a weak form of construction and hence it is suitable up to a span of I mm with light loading for greater. Spans and slightly heavy

a)A brick lintel with reinforcement, as shown in fig. 11-41, may be provided.

b)A steel angle or steel flat bar of length equal to brick lintel, may be provided at the bottom of lintel. The exposed surfaces of steel angle or steel. Angle or steel flat bar may be suitably painted so as to make them inconspicuous. )

4)     Steel Lintels: These lintels consist of steel angles or rolled steel joists. The formed is used for small spans and light loading and the latter is used for large spans and heavy loading. A steel lintel becomes useful when there is no space available to and heavy loading. A steel lintel becomes useful when there is no space available to accommodate the rise of an arch.  The steel joists may be used singly or in combination of two or three units.

       When used singly, the steel joist is either embedded in concrete or gladded with stone facing to match with the width of opening. When more than one unit are placed side by side, the tube stone facing to match with the width of opening. When more than one units are placed side by side, the tube separators are provided to keep the still joists in position.  Side by see, the tube separators are provided to keep the steel joists in position.

 The joists are usually embedded in concrete to protect the steel corrosion and fire. The steel collapses quickly due to fire and hence the casing of concrete make the steel more fire-resistant.

5)     Reinforced cement concrete  Lintels : These lintels consist of the reinforced cement concrete and they have replaced practically all other materials for the lintels  The R.C.C Lintels are fire proof, durable , strong, economical and easy to construct  No relieving arches are necessary when the R. C.C Lintels are adopted.

                 The usual concrete mix for R.C.C lintel is 1:2:4 i.e. I part of cement, 2 parts of sand and 4 parts of aggregates by volume. The plain concrete lintels can be used puts a span of about 800 mm. But some form of reinforcement is necessary in the R.C.C lintels as plain concrete is weak in tension. The amount of reinforcement depends on lintels as plain concrete is weak in tension. The amount of reinforcement depends on the span of lintel, width of opening and the total load to be supported by the lintel. The span of lintel, width of opening and the total load to be supported by the lintel.

       R.C.C. Lintel for an opening of span 1 meter and of width 1/1/2 bricks. The projection, in the form of weather shed, can be easily taken out from lintels weather shed throws the rain water away from the wall. 

      The R.C.C. Lintels may be pre-cast of cast-in-situ. The pre-cast R.C.C lintels are convenient for small span up to 2 meters or so and they are economical as the same mould can be used of prepare a number of lintels. The pre=cast R.C.C lintels increase the speed of construction and allow sufficient time for the curing before fixing. 

                One precaution of be taken in case of pre-cast. R.C.C. lintels is that the top of lintel should be properly marked with tar of paint this will help I placing the lintel correctly.  Fore cast-in-situ R.C.C lintels, the centering is prepared. Reinforcement is placed and concreting is done as usual.

 When finishing is to be done or where appearance is not of importance, the surface of R.C.C. lintel can be kept exposed. Otherwise a rebate may be provided in the lintel and the surface can be suitably finished. Surface can be suitably finished.  Rebated boot lintel over an opening in a cavity wall. This arrangement helps in improving the quantity of concrete. A flexible D.P.C. should quantity of concrete. A flexible D.P.C should be provided. And the toe of boot lintel should be strong enough to bear the load of wall above it.