Lintel Deflection or Arch Failure

It is common to find a flat or shallow arch used for carrying brickwork above an opening. The original timber frame often acts as a fortuitous lintel that adds support the arch. Such arches are sensitive to cracking due to small movements of buttressing masonry. Additionally replacement of the window frame with a uPVC unit can undermine the support and provoke masonry arch failure.

Thermal or Moisture Variations

Cracks can appear when the differing moisture or thermal movements result in tensile stresses that exceed the tensile strength of the materials used to build the wall. Helical bars are manufactured from round stainless steel wire, which is passed through a series of profiled rolls to progressively alter its shape in cross-section. The shaped wire is then forced through a twisting die to deliver a patented precision-engineered helical reinforcement bar with unique torsional elastic yield characteristics and a tensile strength that is double that of standard stainless steel.

Thor Helical reinforcing bars can form deep masonry beams that strengthen existing walls. Two parallel layers of bed joint reinforcement, each layer containing a pair of helical bars, represent a brick beam’s upper and lower flanges. The deep masonry beams can span areas of masonry failure, redistribute applied loads, and enhance the wall’s tensile, shear, and flexural capacity. Non-reinforced masonry panels are strong in compression but comparatively weak in shear and tension loads resistance. Walls can deflect and crack when subjected to increased loads and stresses. Such stresses may be induced by; localised ground movement/ subsidence, lintel failure or moisture/ temperature variations. Reinforced masonry has greater resistance to shear and tension loads as ductile steel reinforcement enhances it.

Reinforced brick masonry can strengthen masonry wherever it has lost its load-bearing capacity. It is commonly used to span areas of localised ground movement to alleviate the need for partial underpinning. In other instances, it can span between concrete pads or piles to reduce the cost of subsidence repairs. Bed joint reinforcement can also span window openings, strap external corners, stitch cracks, increase resistance to wind loading, and extend the centres of movement joints. An engineer should establish span and applied-loading to design a retrofit system to form effective deep masonry beams in existing walls. Using load tables from the BRE report on creating reinforced brick beams using Thor Helical bars, the specifier can determine the vertical distance between each pair of bars to establish the depth of the beam.

Installing lengths of strategically placed Thor Helical bars above door and window openings is a quick and easy way of creating or repairing brick arch lintels in buildings. The high tensile stainless steel bars utilise existing brickwork to form a reinforced brick lintel over a flat soldier course or curved masonry arch. Lintel failure occurs for a variety of reasons. Shallow or flat brick arches can fail due to inadequate buttressing on either side of the arch, concrete lintels tend to rotate, whist timber and steel lintels may degrade over time as rot or corrosion sets in. It is not uncommon for old timber or steel window frame to form a fortuitous lintel, which helps to support the brickwork above. When replacing these load-bearing windows and doors with non-structural uPVC units, support from the fortuitous lintel is lost, and the masonry may begin to crack as the brickwork sags.

Thor Helical bars have a long history of reinforcing and repairing brick arch lintels over openings. A section of the mortar bed is cut out immediately above the existing arch or lintel, and another is cut out further up the wall. The slots extend at least 500mm on either side of the opening. WHO-60, a polymer-modified cement-based grout, bonds a pair of spiral bars into each channel. The grout cures rapidly to create reinforced layers representing a reinforced brick beam’s upper and lower flanges. The brick beam supports the masonry above and spreads the structural loads.