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Gabor Palotas

Arches & Lintels - 2.2

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    UNIT 1 - Traditional Arches & Lintels

    • Traditional Arches & Lintels

      COURSE 2 / MODULE 2 - ARCHES & LINTELS / LESSON 1 - TRADITIONAL ARCHES & LINTELS

    • (Title correction!) Spanning items of openings are curved or horizontal load-bearing structures installed above a wall opening. They bear the load above the opening and transfers it to the supporting structure underneath.

      1. Lintels: straight-lined spanning structures of openings

      The most ancient forms of lintels were made of wood or stone, either as simple beams or as a series of beams across the span. In structural terms, they are bent structures where the upper belt is subjected to compressive forces and the lower belt to tensile forces.

      Stone lintels

      The tensile strength of stone is extremely low, so it is not economical as a bent structure. It means that spans of greater width can only be achieved with an exceptionally high structural height, which is not an economical solution. 

      Timber lintels

      In contrast, timber beams are considered highly efficient as bent structures, and therefore, they have traditionally been the most commonly used straight-lined lintels. Timber lintels are square cross-sectioned, hewn, or sawn wooden beams laid in mortar or mud mortar on both sides of the opening, giving the lintel elements suitable bearing. For wider walls, several beams should be placed side by side, leaving ventilation gaps between them to prevent decay. Lintels were also exposed to extend their lifespan and were less frequently whitewashed, painted, or timber-clad.

      Steel lintels

      In the 19th century, additional materials appeared that performed the function of lintels economically. One is the steel beam, mainly built of I- or U-section beams or from their alignment. The beams must be bolted together at one-metre intervals in the aligned arrangement. The required bearing width for steel beams is 1.5-2 times the beam height, typically placed in traditional, small-element brickwork. Under the beams, the bricks are placed in cement mortar or cast in concrete for structural reinforcement. 

      Bricks are often placed between the steel beams, with a protective coating over the beams. Alternatively, you can also plaster the beam with a mesh around it to protect the steel from corrosion. Also, the space around the beams can be filled with concrete by either shuttering the entire cross-section or forming a lintel casing. Aesthetically, it was particularly favourable to use a brick course of the same material as the brickwork, suspended on a steel wire fixed to the concrete back section.

      2. Arches: curved spanning structures of openings  

      Arches are a special form of lintel originally-constructed of stone or brick using a wooden template to support the structure. Over the centuries, different forms of arches have evolved. What they all have in common is that they are subjected to a curved, compressive force at the supports, resulting in horizontal force components in addition to the vertical ones at the supports. Their origins are usually attributed to the Romans, who used the semicircular arch (also known as the round arch, being the purest arch form) in a very versatile and widespread way.

      Stone arches

      Stone arches were typically formed in stone walls. Roughly carved, slightly wedge-shaped natural stones can be used to create straight or semicircular arches over small openings. Precision-carved stones are required to form arches of any shape. Some examples include semi-circular arches or round arches, segmental, three-centred, parabolic, rampant, three-pointed, acute, round horseshoe, ogee, trefoil, or flat arches.

      Brick arches

      Brick arches can be made in various shapes, using uniform or various reveal widths. The arches are built in a bonded manner, the same way as pillars. Typically, we use bricks without carving and with wedge-shaped mortar joints. However, large curvature arches with a small radius can only be masoned with wedge-shaped carved elements. In this case, joints with almost parallel sides are created between the wedge-shaped bricks. Arch masonry is only possible using templates. The bricks should be laid symmetrically from both sides of the impost until the two sides meet. The ribs should not be removed until the mortar has set. 

      While a semi-circular arch (round arch) can span 6-8 metres, the maximum span with a straight arch is only around 1.40 metres. The flat arch should be slightly curved, with a rise of 2-4 centimetres, to allow the structure to settle. Boards or planks should support the arch during construction. Flat arches can be made in two different designs:

      • Radial gap formation

      • Parallel gap formation: in this case the central part must be filled with wedge-shaped bricks

  • UNIT 2 - Modern Lintels

    • Modern Lintels

      COURSE 2 / MODULE 2 - ARCHES & LINTELS / LESSON 2 - MODERN LINTELS

    • 1. Precast Reinforced Concrete Lintels

      Precast reinforced concrete lintel beams are manufactured in fixed sizes and are ready for installation. They can be installed quickly, do not require formwork, and their material and dimensions match the building systems in which they are used. A disadvantage is that they can only be installed in exterior walls if additional thermal insulation is provided—ideally placed on the exterior side or aligned with the window/door (or!) frame. Another drawback, due to the fixed sizes, is their limited flexibility: because these components are typically prestressed, cutting them to size is strictly prohibited.

      Block-height lintels with immediate load-bearing capacity

      Block-height precast reinforced concrete lintels match the height of the masonry blocks within the given system and the course height of walls built from these blocks. Earlier designs still in use today are simple trapezoid-shaped reinforced concrete structures made with prestressed reinforcement. The number of such elements placed side by side must match the required thickness of the wall. These lintels do not need to be supported or undergo additional procedures; once placed, they can be loaded immediately.

      Reinforced concrete lintels of block height with clay formwork are designed to be combined with clay hollow blocks. A C or (or!) U-shaped clay formwork surrounds the load-bearing, prestressed reinforced concrete core. Only whole blocks should be placed in the bearing width of the lintel. They may only be laid in a conventional mortar bed; their installation with adhesive foam or thin-bed mortar is prohibited.

      Block-height lintels with silicate formwork have also been developed for aerated concrete block systems. These lintels must be laid in masonry mortar with a minimum bearing of 20 centimetres. The U-shaped silicate formwork lintel is positioned with its legs facing downward during masonry work.

      Tension zone lintels

      Tension zone precast reinforced concrete lintels with a block height of 6–12 centimetres provide only the lower, tensioned section of the final lintel. The compression zone above the lintel must be constructed on-site, either by adding masonry or by pouring concrete. When using clay formwork lintels, the upper reinforced concrete sections are set into U-shaped clay formwork grooves. The typical heights of the elements are 6.5 or 8.5 centimetres.

      The compression zone can be constructed using small-element solid bricks or, in the case of partition walls, clay or concrete hollow blocks. The lintels must have a minimum bearing of 12.5 centimetres and be put in a conventional mortar bed at the supports. Clay formwork lintels must be supported until the compression zone becomes load-bearing, with a maximum span of 1 metre between the supports.

      U-shaped Monolithic Reinforced Concrete Lintels (lintels!)

      Both clay and aerated concrete block systems include a U-shaped lintel product that aligns with each system's dimensions. The U-shaped elements form a continuous, permanent formwork for the cast-in-situ, reinforced concrete core. These elements must be assembled from separate pieces, so they can only be set up and poured with concrete when adequately supported. 

      The clay U-shaped elements are typically 23.8 centimetres long and joined together with masonry mortar, providing a minimum bearing of 12 centimetres. A custom-sized formwork piece must be cut to fit the bearing area thus avoiding cracks arriving from a protruding position. Before concreting, insulation boards must be placed inside the U-sections adhered to the outer leg of the U shape.

      Typically, the aerated concrete U-shaped formwork elements are 60 centimetres long and must be installed with a minimum 20-centimetre bearing. The elements must be joined together with adhesive mortar.

      2. Monolithic reinforced concrete lintels

      The considerable advantage of monolithic reinforced concrete lintels is that they can be made in any size, with individually-sized reinforcement and cross-section. Their disadvantage is that they require more on-site work: supported formwork, iron installation and on-site casting and then removing the formwork. It may be an advantage if the proximity of the ring beam allows it to be shuttered and concreted together with the ring beam. The lintels should be designed with a reduced cross-section for external walls, leaving room for additional thermal insulation.

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