Deformation Joints in Buildings

Simple example: the coefficients of thermal expansion for steel and wood differ significantly. This explains the mechanical failure of wooden beams located in cold roof spaces, secured with standard bolts or rebar without thermal breaks. To address this and other issues, deformation joints are used in common construction practices.

Below is a complete list of problems where this element 'works' and helps maintain the structural integrity of the entire building:

• seismic activity of the Earth's crust;
• ground settlement, rise in groundwater levels;
• structural deformations;
• sudden changes in ambient air temperature.

Depending on the nature of the problem, all deformation joints are classified as thermal, shrinkage, seismic, and settlement joints.

Thermal Deformation Joint

Structurally, a deformation joint is a cut that divides the entire building into sections. The size of the sections and the direction of division—vertical or horizontal—are determined by engineering design and calculations of static and dynamic loads.

To seal the cuts and reduce heat loss through deformation joints, they are filled with elastic thermal insulation, most commonly special rubberized materials. This division increases the overall structural flexibility of the building, preventing thermal expansion of individual components from causing destructive effects on other materials.

Typically, a thermal deformation joint runs from the roof to the foundation, dividing the building into sections. It is not necessary to divide the foundation itself, as it lies below the frost penetration depth and is not exposed to the same negative effects as the rest of the structure. The spacing of thermal deformation joints depends on the type of building materials used and the geographical location of the site, which determines the average winter temperature.

Settlement Deformation Joint

The second major application of deformation joints is compensating for uneven ground pressure in buildings of varying height. In this case, the taller (and heavier) part of the building exerts greater pressure on the soil than the shorter part. This can lead to cracks in walls and foundations. Similarly, uneven ground settlement beneath the foundation area may also cause structural issues.

To prevent wall cracking in such cases, settlement deformation joints are used. Unlike the previous type, these joints divide not only the building but also its foundation. Often, a single building requires multiple joint types. Combined joints are known as thermal-settlement joints.

Anti-Seismic Deformation Joints

As their name suggests, these joints are used in buildings located in seismically active zones. The principle is to divide the entire structure into 'cubes'—enclosures that are structurally stable on their own. Each such cube must be bounded by deformation joints on all sides and all faces. Only then will the anti-seismic joint function effectively.

Along anti-seismic joints, double walls or double rows of load-bearing columns are constructed, forming the primary structural support for each individual enclosure.

Shrinkage Deformation Joint

Shrinkage deformation joints are used in monolithic concrete frames, as concrete naturally shrinks slightly in volume during curing due to water evaporation. These joints prevent cracks that could compromise the load-bearing capacity of the monolithic frame.

The purpose of such a joint is to gradually expand as the monolithic structure hardens. Once curing is complete, the formed joint is fully sealed. Special sealants and waterproof gaskets are applied to shrinkage and all other types of deformation joints to ensure long-term watertightness and durability.