Wall ties are used to connect the interior wall through the insulating material (and the air-gap clearance) with the exterior wall and to make them a single coherent unit.
Outline of a threeply wall:
Wall ties are considered to be “flexible” due to the engineering specifications of a threeply wall.
The interior part of the wall is facing the room, thus its temperature and geometry are not subject to considerable fluctuations. Which is not the case with the exterior wall: in summer it can warm up to 70ºС, while in winter it can cool down to minus 40-50ºС. Temperature fluctuations change geometry of the wall. The interior wall remains steadfast while the exterior wall “moves”, therefore the wall ties bend (thus the wall ties are considered to be “flexible”). For this reason stability of wall connection and therefore reliability of the whole construction object depend on the specifications of the raw materials used for production of wall ties.
Safety and Energy Performance of the Buildings.
Construction rules and regulations SNiP II-22-81 “Masonry and Reinforced Masonry Constructions”, art. 6. 31 stipulate that: “Wall ties should be produced of corrosion-resistant steel or steel with corrosion prevention treatment as well as polymer materials.” Composite materials are used as polymer materials, i.e. basalt and fiberglass reinforced plastic.
According to this SNiP it is dangerous to use wall ties made of rebar that is not corrosion-resistant, rebar produced of ferrous materials as well as wire, because corrosion of these materials may cause destruction of exterior walls and thus impairs safety of the building. Such state of the building is hazardous, and it is no longer safe to live in the building, because the building or a part of it can fall down. It takes time and investment to repair dangerous buildings, which is impractical and unprofitable.
Composite wall ties are widely used in the Russian Federation. Wall tie is a bar with a round cross-section, which has sand bulges on both ends. These bulges serve as anchors (linkage) that allow to fix the wall tie in masonry joints. Sand anchors ensure stable linkage with the construction mortar and provide additional corrosion prevention in the alkaline environment of the concrete. To create an air-gap clearance a rebar spacer made of impact-resistant and frostproof material is used. Air-gap clearance ensures natural ventilation of the exterior face wall.
For construction of a threeply wall the length of the wall ties is calculated according to the following formula:
L = 90 mm + Т (+40 mm)+ 90 mm, where
L — length of the wall tie;
90 mm — embedment depth of the ends of the wall tie;
Т — thickness of the heat insulating material;
40 mm should be added, if there is an air-gap clearance in the wall.
Thus energy performance and safety of the building as well as further operating costs depend on the correct choice of the material used for production of wall ties.