Keywords: Opening, jamb, head of openings, ledge, niche, monolithic lintel, prefabricated lintel

The openings in the walls and partitions are designed to illuminate the room with daylight and to connect the adjacent spaces or outer environment with the interior of the building.
The wall openings are divided according to their purpose:

• Window openings that perform lighting and room ventilation functions
• Door openings that function as a room entry and room connection
• Gate openings which are used for vehicle entry
• Passes are openings without filling
• Other openings such as niches

All openings have head of openings and jambs. The jamb is the lateral surface of the opening in the wall. The jamb may be straight or craned. The head of opening is the construction above the opening. The window openings also have the window sill (window ledge). The window ledge is the bottom part of the niche and the entire lining under the window, that is, the wall from the floor to the window. The niche is usually a decorative recess in the strength of the building's brickwork. Door and gate openings have a threshold at the bottom or they are without a threshold.

The lintel must be placed over the openings. The lintel must be able to transmit the load from the adjacent part of the ceiling and walls to the vertical support along the opening.

Requirements for the lintel:

• Static requirements - Load transfer to support
• Compositional - In the case of assembled lintels, the dimensions must correspond to the compositional dimension of the vertical structures and ceilings
• Thermal insulation requirements - to ensure the minimization of thermal bridges

Loads of lintels may be equally continuous (e.g. reinforced concrete slab) or with the group of solitary loads (e.g. beams). According to the position of the load, there are one-sided load eccentricity (the peripheral wall) and a load-sided (at the middle of the wall). Depending on the shape of the centerline, the head of opening can be straight (pressed or bent) or arched (strain dependent on pressure or flexural pressure).

The lintels must ensure the transfer of loads to the adjacent supports. The loading effect on lintels is not constant, but usually triangular. The size of the displacement angle depends on the stiffness of the wall and its height above the lintel. Thermal bridges must be excluded in peripheral structures. Modern lintels made of reinforced ceramic blocks or porous concrete have the supporting function and thermal insulation function.

According to the technological implementation, the lintels may be monolithic or prefabricated. Prefabricated lintels can be stone or brick, from steel beams or from ceramic block beams. Prefabricated translations are reinforced concrete or lightweight concrete.

The direct stone lintels are made up of precisely placed bevelled blocks and connected by stoneware clinch. The arched stone lintels consist of stone vaults of different shapes and sizes. Due to the great difficulty in realizing the stone lintels and due to the insufficient thermal insulation of the stone, at present, the stone lintels are not used in new constructions.

The lintels from stone blocks should have upper and lower obverses horizontal. The lintel line is wedged from both sides and closed with a central voussoir, the joints are straight or oblique.

The direct reinforced lintels use tape steel to transfer the tensile stresses in the lower face. Arched lintels into the foot are either common bricks with a wedge of mortar or sliced conical bricks. The static effect of the lintels is similar to the vaults, with a span of about 3.0 m. The head joint formed by the wedge of the mortar has a minimum width of 8 mm and a maximum of 20 mm. Joints wider than 20 mm are wedged by flat fragments of bricks or roof tiles. The crushed bricks must have a minimum thickness of 45 mm.

Simple brickwork head of openings is done as a reinforced brick lintel. It is made as a straight vault made of hard bricks and reinforced in the joints by a 20/1 - 30/2 mm strap taking the pull at the bottom of the lintel.

The brick strip is vaulted in the wall thickness on the wooden, or mortar, shoulders. It is suitable for smaller spans and for the head of openings without indentation. The masonry is done from the foot towards the center. The direction of the joint is controlled by a template or a lath. The slope of the raised or recessed foot is determined by a center angle, preferably 30 °.

The steel lintels from rolled I-beams are used for heavy loads and large spans (up to 6 meters) as well as for renovations. The advantage of steel lintels is their ability to transfer loads immediately. The supporting length is affected by the overall length of the beam and the load, but at least 150 mm.

The lintels from steel beams are made of rolled profiles laid on concrete or stone bed foundation. The embedded traverses are either concreted or encircled by bricks and wrapped in ceramic or rag-mesh and plastered (fire protection). These lintels should be additionally insulated by thermal insulation to avoid the thermal bridge.

Ceramics have the low tensile strength and thus ceramic lintels are complemented by the reinforcement in ceramic blocks. Ceramic shaped brick acts as a lost formwork. And also forms a suitable base for plastering. Ceramic lintels parts are manufactured in various shapes. The ceramic parts are placed vertically into a prepared bed of cement mortar (supporting length 150 to 300 mm). In the perimeter walls, they are combined with a thermal insulator.

Lightweight concrete lintels can be made from porous concrete, ceramsite concrete and other materials. The lintels from lightweight concrete can be box, roller, segment or arc.

The lintels from lightweight concrete are used in most cases for brickwork made of blocks of the same material. Flat load-bearing porous concrete lintels are supporting elements reinforced by welded concrete reinforcement. They have excellent thermal insulation properties and are therefore a suitable supplement to massive masonry made of aerated concrete without changing the underlying material for plastering and with minimal thermal bridges.

Prefabricated reinforced concrete lintels are assembled from prefabricated rod-shaped elements of which it is possible to compose multipart lintels. The lintels are made in lengths from 1.2 to 3 meters. The supporting length of the lintels is given by the width of the lintel, but not less than 150 mm. Prefabricated reinforced concrete lintels can be loaded immediately after installation.

Monolithic reinforced concrete lintels are applicable for any load range. The advantage of monolithic lintels is their shape and dimensional variability. The disadvantage is considerable labor, the need for formwork and the possibility of loading until the concrete is hardened. Monolithic lintels may act as a single beam over one or a continuous beam over multiple openings. If the head of the opening is closely related to the ceiling structure, the monolithic lintel can be associated with the reinforced concrete rim. Support of monolithic lintel should be at least 7,5% clearance opening (minimum 200 mm). The reinforcement of the translation must correspond to their static effect.