Expansion joints are considered essential in any construction project or material selection due to several factors., such as seismic or thermal effects that can cause contractions or expansions. Its main function is to control these movements, allowing the materials to move freely and thus avoiding the formation of cracks or fissures.
These joints are implemented in various elements of the building structure, including the structure itself, the soils, the walls, the facades, decks and roofs. Among the most common are contraction and expansion joints.. It is crucial to follow the guidelines established by the regulations to determine the appropriate distances between expansion joints in each specific situation..
Since expansion joints can occur in a variety of shapes and situations in building construction, It is important to briefly address some of the most relevant types.
Expansion joints in structures
The CTE requires the installation of an expansion joint in buildings to avoid continuous elements of more than 40 m in length, and thus do not consider thermal actions (DB-AE 3.4.1).
To achieve this meeting, The double pillar technique will be used with an approximate separation of about 5 cm between them, creating independent structural elements. Another valid option is the installation of brackets.
To avoid the need for double pillar structures, that can complicate the layout of garages or homes, Stainless structural pins can be used to transfer these forces..
In the case of joints in concrete walls, The detail attached in the Library of construction details for concrete structures of Cypecad will be followed.
- Structural joints: They will be arranged according to the specific needs of the building in terms of its structural joints..
- To separate vertical elements, like hormigón walls or pillars, of the concrete slab, We will use a material that absorbs expansion, like expanded polystyrene.
- Expansion joints will be established every 20 The 25 meters long, which will cross the entire thickness of the slab. The opening must be wide enough to prevent unwanted deformations caused by expansion of the concrete.. Likewise, to avoid obstructions by dirt or dirt, The opening will be sealed with a compressible material.
- Regarding shrinkage or contraction joints, Its installation is recommended in areas of 15 a 20 square meters and in places where the pavement is restricted by very rigid elements, as sinks, manholes, pillars, among others. This prevents the spontaneous formation of these joints.. In these rigid elements, The placement of a previously mentioned separation joint is also recommended..
Expansion joints in factories, unlike conventional expansion joints, They do not need to cross the entire thickness of the slab. In general, They are made by means of a radial cut.
As established in the Basic Document SE-F Factory of the CTE in its Section 2.2 about “Movement joints”, These gaskets are installed to allow for thermal expansion, moisture shrinkage, the creep, the retraction, as well as to accommodate bending deformations and the effects of internal stresses caused by vertical or lateral loads. All this is done in order to avoid damage to the factory structure. It is important to consider the distances indicated in the table 2.1 for supported factories.
These distances apply to buildings with a rectangular or concentrated floor plan.. In the event that the plant is asymmetrical, with L-shaped wings, U, etc., whose lengths exceed half of those indicated, The joints will be located near the points where they are. Whenever feasible, joints will be designed with overlap.
Expansion joints in factories
In accordance with the Basic Document SE-F Factory of the CTE, in your section 2.2 about “Movement joints”, the need to install movement joints is established to allow thermal expansion, due to humidity, creep, retraction, as well as to accommodate bending deformations and the effects of internal stresses caused by vertical or lateral loads. These joints will be placed respecting the distances indicated in the table 2.1, specifically designed for buildings with a rectangular or concentrated floor plan.
In the event that the plant has an asymmetrical configuration, with L-shaped extensions, U u otras, whose dimensions exceed half of the indicated distances, The joints will be located near the joining points of these extensions.. What's more, whenever feasible, These joints will be designed with overlap to guarantee their effectiveness.
To hide expansion joints in the building, it is suggested to duplicate the partitions, placing one for each structure. This will prevent the joints from being visible. Between the two partitions you can add a polystyrene plate, fixed to one of the partitions using glue points.
Expansion joints in paviments
We can find various types of joints, just like in the slabs.:
- Structural joints: They will be installed according to the arrangement of the structural joints present in the building.
- Separation boards with factories: To hide them, skirting boards will be used.
- Expansion joints: The choice of material to use (terrazzo, marble, stoneware, madera, etc.) as well as the level of traffic to which the pavement will be exposed (residential, commercial or industrial) will influence this case. Installing terrazzo in a home is not the same as in a hospital. In general, in homes, some joints of approximately 2 mm between the tiles are sufficient to absorb the expansions and contractions of the pieces. Nevertheless, as mentioned earlier, Each situation is unique and requires a specific analysis.
Expansion joints in flat roofs
At the design stage, Three different types of joints can be identified.
The structural roof joints must coincide with the structural expansion joint of the building. In this case, It is advisable to raise two parapets to separate the different decks. The width of these joints should be approximately 5 cm, matching the width of the structure.
Roof expansion joints must be left every 15 meters maximum or on surfaces of approximately 50 m2. For these meetings, a width greater than 3 cm and must be made with expansive material as a top finish. In the case of asphalt fabrics, whether to use a finished romo. It is important that these joints coincide with ridges or hips to guarantee correct drainage of water..
Finally, Movement joints must be made in the encounters with vertical elements such as bibs. In this case, you can choose to run double factory, where the fabric will rise up the inner bib, or place a single factory and add vertical insulation. This allows the cover to move independently of the exterior façade..
Tipo crets
During the structural design stage, the need to use pillars or double walls can be avoided, as well as support brackets, by installing stainless structural pins or crets, which can transfer the necessary efforts.
The use of expansion joints is crucial to prevent the formation of unwanted cracks and their consequent damage., such as loss of tightness and corrosion.
In particular, Article 3.4 of the basic Structural Safety document Actions in Building establishes that in conventional buildings with structural elements of concrete or steel, thermal actions can be dispensed with if expansion joints are installed so that there are no continuous elements of more than 40 meters long.
In the case of floors and walls with restricted mobility, The inclusion of expansion joints reduces the need for reinforcement to control the width of the cracks. Therefore, specifying these joints in floors and walls with movement restriction is usually an unavoidable measure.
Design Advantages of Crets Pins
CRET dowels simplify both the design and implementation of expansion joints by addressing the previously mentioned challenges.. This system offers the following advantages:
- Simple setup: CRET dowels replace brackets and half-wood joints, reducing free clearance and eliminating the need to prepare more complex formwork and reinforcements.
- Elimination of bending pillars or walls: It is not necessary to alter the structure of columns or walls on both sides of the expansion joint. This is especially beneficial in phased construction and maximizes usable floor space..
- Hassle-free installation on site: CRET dowels come with built-in plates with holes for easy attachment to formwork. What's more, include stickers indicating proper orientation, thus avoiding the need for additional work or drilling in the formwork.
Installation
In the first stage, CRET sheaths/females are fixed to the formwork with at least two nails diagonally, with the upper face marked with the word “ALTO”, to allow concrete to be poured on the first side of the joint once the necessary reinforcement has been placed.
Once the concrete has set, The formwork is removed and the joint filling material is introduced. (like rock wool, I THINK BM, etc.), The dowels are then placed in the respective sleeves/females and the necessary reinforcement is provided before pouring the concrete in the second part of the joint..
Sealed
Regardless of the nature of the board, all must ensure adequate sealing, that it is not superficial and that it has the correct depth.
In cases where the depth is excessive, the joint can be filled with a compressible insulating material.
The final sealing finish must be elastic, with the capacity to deform or compress up to a 25%, and must be resistant to adverse weather conditions.
It is important to carry out periodic inspections of this material, both on facades and roofs, to ensure proper maintenance, since in these areas it is completely exposed.
