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  • When concrete has dried it is a dull, light grey colour. Some think that a concrete lintel exposed for its full depth on the external face of brick walls is not attractive. In the past it was for some years common concrete Practice to hide the concrete lintel behind a brick arch or brick lintel boot lintel built over the opening externally.

    lintel A modification of the ordinary rectangular section lintel, known painted with as a boot lintel, was often used to reduce the depth of the lintel itumen exp0se(j externally. Figure 93 is an illustration of a section through the head of an opening showing a boot lintel in position. The lintel is boot-shaped in section with the toe part showing externally. The toe is usually made 65 mm deep. The main body of the lintel is inside the ‘”^lining wa^ where it does not show and it is this part of the lintel which does most of the work of supporting brickwork. Some think that the face of the brickwork looks best if the toe of the lintel finishes just 25 or 40 mm back from the external face of the wall, as in Fig. 94. The brickwork built on the toe of the lintel is usually j B thick for open­ings up to 1.8 m wide. The 65 mm deep toe, if reinforced as shown, is capable of safely carrying the two or three courses of |B thick brickwork over it. The brickwork above the top of the main part of the lintel bears mainly on it because the bricks are bonded. If the opening is wider than 1.8 m the main part of the lintel is sometimes

    ■ boot made sufficiently thick to support most of the thickness of the wall

    lintel over, as in Fig. 94.

    Fig. 94 Boot lintels Fig 95

    The brickwork resting on the toe of the lintel is built with bricks cut in half. When the toe of the lintel projects beyond the face of the brickwork it should be weathered to throw rainwater out from the wall face and throated to prevent water running in along soffit or underside, as shown in Fig. 93.

    When the external face of brickwork is in direct contact with concrete, as is the brickwork on the toe of these lintels, an efflores­cence of salts is liable to appear on the face of the brickwork. This is caused by soluble salts in the concrete being withdrawn when the wall dries out after rain and being left on the face of the brickwork in the form of unsightly white dust. To prevent the salts forming, the faces of the lintel in direct contact with the external brickwork should be painted with bituminous paint as indicated in Fig. 93. The bearing at  ends where the boot lintel is bedded on the brick jambs should be of the same area as for ordinary lintels.

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  • Composite lintels are stressed by a wire or wires at the centre of their depth and are designed to be used with the brickwork they support which acts as a composite part of the lintel in supporting loads. These comparatively thin precast lintels are built in over openings and brickwork is built over them. Prestressed lintels over openings more than 1200 mm wide should be supported to avoid deflection, until the mortar in the brickwork has set. When used to support blockwork the composite strength of these lintels is considerably less than when used with brickwork.

    Non-composite prestressed lintels are made for use where there is insufficient brickwork over to act compositely with the lintel and also where there are heavy loads.

    These lintels are made to suit brick and block wall thicknesses, as illustrated in Fig. 92. They are mostly used for internal openings, the inner skin of cavity walls and the outer skin where it is covered externally.

    Fig. 92 Prestressed lintels

     

    Precast, or prestressed lintels may be used over openings in both internal and external solid walls. In external walls prestressed lintels are used where the wall is to be covered with rendering externally and for the inner leaf of cavity walls where the lintel will be covered with plaster.

    Precast reinforced concrete lintels may be exposed on the external face of both solid and cavity walling where the appearance of a concrete surface is acceptable.

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  • The word ‘precast’ indicates that a concrete lintel has been cast inside a mould, and has been allowed time to set and harden before it is built into the wall.

    The words ‘situ-cast’ indicate that a lintel is cast in position inside a timber mould fixed over the opening in walls. Whether the lintel is precast or situ-cast will not affect the finished result and which method is used will depend on which is most convenient.

    It is common practice to precast lintels for most normal door and window openings, the advantage being that immediately the lintel is placed in position over the opening, brickwork can be raised on it, whereas the concrete in a situ-cast lintel requires a timber mould or formwork and must be allowed to harden before brickwork can be raised on it.

    Lintels are cast in situ, that is in position over openings, if a precast lintel would have been too heavy or cumbersome to have been easily hoisted and bedded in position.

    Precast lintels must be clearly marked to make certain that they are bedded with the steel reinforcement in its correct place, at the bottom of the lintel. Usually the letter “T or the word ‘Top’ is cut into the top of the concrete lintel whilst it is still wet.

    Prestressed concrete lintels

    Prestressed, precast concrete lintels are used particularly over internal openings. A prestressed lintel is made by casting concrete around high tensile, stretched wires which are anchored to the concrete so that the concrete is compressed by the stress in the wires. (See also Volume 4.) Under load the compression of concrete, due to the stressed wires, has to be overcome before the lintel will bend.

    Two types of prestressed concrete lintel are made, composite lintels and non-composite lintels.

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  • Since Portland cement was first mass produced towards the end of the nineteenth century it has been practical and economic to cast and use concrete lintels to support brickwork over openings.

    Concrete is made from reasonably cheap materials, it can easily be moulded or cast when wet and when it hardens it has very good strength in resisting crushing and does not lose strength or otherwise deteriorate when exposed to the weather. The one desirable quality that concrete lacks, if it is to be used as a lintel, is tensile strength, that is strength to resist being pulled apart. To provide the necessary tensile strength to concrete steel reinforcement is cast into concrete.

    For a simple explanation for the need and placing of reinforcement in concrete lintels suppose that a piece of india rubber were used as a lintel. Under load any material supported at its ends will deflect, bend, under its own weight and loads that it supports. India rubber has very poor compressive and tensile strength so that under load it

    will bend very noticeably, as illustrated in Fig. 90. The top surface of under $& ruDber becomes squeezed, indicating compression, and the lower load rubber surface stretched, indicating tension. A close examination of the india lintel rubber shows that it is most squeezed at its top surface and progressively less to the centre, and conversely most stretched and progressively less up from its bottom surface to the centre of depth.

    A concrete lintel will not bend so obviously as india rubber, but it will bend and its top surface will be compressed and its bottom sur­face stretched or in tension under load. Concrete is strong in resisting compression but weak in resisting tension, and to give the concrete lintel the strength required to resist the tension which is maximum at its lower surface, steel is added, because steel is strong in resisting tension. This is the reason why rods of steel are cast into the bottom of a concrete lintel when it is being moulded in its wet state.

    Lengths of steel rod are cast into the bottom of concrete lintels to give them strength in resisting tensile or stretching forces. As the tension is greatest at the underside of the lintel it would seem sensible to cast the steel rods in the lowest surface. In fact the steel rods are cast in some 15 mm or more above the bottom surface. The reason for this is that steel very soon rusts when exposed to air and if the steel rods were in the lower surface of the lintel they would rust, expand and rupture the concrete around them, and in time give way and the lintel might collapse. Also if a fire occurs in the building the steel rods would, if cast in the surface, expand and come away from the concrete and the lintel collapse. The rods are cast at least 15 mm up from the bottom of the lintel and 15 mm or more of concrete below them is called the concrete cover.

    Fig. 90 Bending under load

     

    Reinforcing rods

    Reinforcing rods are usually of round section mild steel 10 or 12 mm diameter for lintels up to 1.8 m span. The ends of the rods should be bent up at 90° or hooked as illustrated in Fig. 91.

    The purpose of bending up the ends is to ensure that when the lintel does bend the rods do not lose their adhesion to the concrete around them. After being bent or hooked at the ends the rods should be some 50 or 75 mm shorter than the lintel at either end. An empirical rule for determining the number of 12 mm rods required for lintels of up to, say, 1.8 m span is to allow one 12 mm rod for each half brick thickness of wall which the lintel supports.

    Fig. 91  Ends of reinforcing rods

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  • As an alternative to the use of steel lintels reinforced concrete lintels may be used to support the separate leaves over openings. This construction may be used where the appearance of a concrete lintel over openings in fairface brick is acceptable and where an outer leaf dense concrete 0f brick or block is to be rendered to enhance protection against rain  penetration or for appearance sake. insulation board ^ ranSe of precast reinforced concrete lintels is available to suit the in cavity carried widths of most standard door and window openings with adequate down to head anowance for building in ends of lintels each side of openings. For use with fairface brickwork the lintel depth should match the depth of brick course heights to avoid untidy cutting of bricks around lintel ends.

    penetration or for appearance sake. insulation board ^ ranSe of precast reinforced concrete lintels is available to suit the in cavity carried widths of most standard door and window openings with adequate down to head anowance for building in ends of lintels each side of openings. For use with fairface brickwork the lintel depth should match the depth of brick course heights to avoid untidy cutting of bricks around lintel ends.

    Fig. 81 Concrete lintels

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  • Most loadbearing brick or blockwork walls over openings, where the cavity insulation is continued down to the head of the window or door frame, are supported by steel section lintels. The advantage of these lintels is that they are comparatively lightweight and easy to handle, they provide adequate support for walling over openings in small buildings and once they are bedded in place the work can proceed without delay. Because of their ease of handling and use these lintels have largely replaced concrete lintels.

    The lintels are formed either from mild steel strip that is pressed to shape, and galvanised with a zinc coating to inhibit rust, or from stainless steel. The lintels for use in cavity walling are formed with either a splay to act as an integral damp-proof tray or as a top hat section over which a damp-proof tray is dressed. Typical sections are illustrated in Fig. 78.

    The splay section lintels are galvanised and coated with epoxy powder coating as corrosion protection and the top hat section with a galvanised coating. For insulation the splay section and top hat section lintels are filled with expanded polystyrene.

    The top hat section steel lintel is built into the jambs of both the inner and outer leaf to provide support for both leaves of the cavity wall, as illustrated in Fig. 79. The two wings at the bottom of the lintel provide support for the brick outer and block inner leaves over the comparatively narrow openings for windows and doors. Where the cavity is partly filled with insulation it is usual to dress a flexible dpc from the block inner leaf down to a lower brick course or down to the underside of the brick outer leaf. The purpose of the damp-proof course or tray is to collect any water that might penetrate the outer leaf and direct it to weep holes in the wall.

    The splay section lintel is built into the jambs of openings to provide support for the outer and inner leaf of the cavity wall over the

    brick outer leaf and openings, as illustrated in Fig. 80. Where the cavity is filled with 50 mm cavity filled insuiatjon there is no need to build in a damp-proof course or tray.

    block inner leaf Any water that might penetrate the outer leaf will be directed towards the outside by the splay of the lintel.

    Unless the window or door frame is built-in or fixed with its external face close to the outside face of the wall, the edge of the wing of the lintel will be exposed on the soffit of the opening. In handling and building in, there is a possibility that the edge of this wing might suffer damage to the protective galvanised coating. On the external face of a wall, water may penetrate the zinc coat and cause corrosion of the steel below. Rust very quickly spreads around the initial fracture of the protective coating. It is worthwhile making the comparatively small outlay on a stainless steel lintel as insurance against a possibly much larger expenditure on replacement of a corroded galvanised steel lintel.

    Fairface brickwork supported by steel lintels may be laid as horizontal course brickwork or as a flat brick on edge or end lintel.

    Fig. 79 Top hat lintel Fig. 80 Splay lintel

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  • The metal angle iron that brick rests on, especially above a window, door, or other opening.

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  • (1) A beam placed perpendicular to joists, and to which joists are nailed
    in framing for a chimney, stairway, or other opening.
    (2) A wood lintel.
    (3) The horizontal structural member over an opening (e.g., over a door or window).

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