Expansion joint: we prevent distortion of the structure. What is the expansion joint used for? What is the difference between an expansion joint and an expansion joint?
Any building structures, regardless of what material they are made of (brick, monolithic reinforced concrete or building panels), change their geometric dimensions when the temperature changes. When the temperature drops, they contract, and when the temperature rises, they naturally expand. This can lead to the appearance of cracks and significantly reduce the strength and durability of both individual elements (for example, cement-sand screeds, foundation blind areas, etc.) and the entire building as a whole. To prevent these negative phenomena, an expansion joint is used, which must be installed in appropriate places (according to regulatory construction documents).
Vertical temperature-shrinkage joints of buildings
In long buildings, as well as buildings with different amounts floors in certain sections, SNiP provides for the mandatory arrangement of vertical deformation gaps:
- Temperature - to prevent the formation of cracks due to changes in the geometric dimensions of the structural elements of the building due to temperature changes (average daily and average annual) and concrete shrinkage. Such seams are brought to the level of the foundation.
- Settlement joints that prevent the formation of cracks that can form due to uneven settlement of the foundation caused by unequal loads on its individual parts. These seams completely separate the structure into separate sections, including the foundation.
The designs of both types of seams are the same. To create a gap, two paired transverse walls are erected, which fill heat-insulating material, and then waterproofed (to prevent precipitation from entering). The width of the seam must strictly correspond to the design of the building (but be at least 20 mm).
The spacing of temperature-shrinkage joints for frameless large-panel buildings is standardized by SNiP and depends on the materials used in the manufacture of the panels (class of concrete compressive strength, grade of mortar and diameter of the longitudinal load-bearing reinforcement), the distance between the transverse walls and the annual difference in average daily temperatures for a particular region . For example, for Petrozavodsk (the annual temperature difference is 60°C), temperature gaps must be located at a distance of 75÷125 m.
IN monolithic structures and buildings constructed using the prefabricated monolithic method, the pitch of transverse temperature-shrinkable joints (according to SNiP) varies from 40 to 80 m (depending on design features building). The arrangement of such seams not only increases the reliability of the building structure, but also allows for the gradual casting of individual sections of the building.
On a note! In individual construction, the arrangement of such gaps is used extremely rarely, since the length of the wall of a private house usually does not exceed 40 m.
IN brick houses seams are arranged similarly to panel or monolithic buildings.
IN reinforced concrete structures buildings, the dimensions of the floors, as well as the dimensions of other elements, can vary depending on temperature changes. Therefore, when installing them, it is necessary to arrange expansion joints.
The materials for their manufacture, dimensions, locations and laying technology are indicated in advance in project documentation for the construction of a building.
Sometimes such seams are structurally made to be sliding. To ensure sliding in those places where the floor slab rests on the supporting structures, two layers of galvanized roofing iron are laid under it.
Temperature expansion joints in concrete floors and cement-sand screeds
When pouring cement-sand screed or arranging a concrete floor, it is necessary to isolate all building structures (walls, columns, doorways, etc.) from contact with the poured mortar throughout its entire thickness. This gap performs three functions simultaneously:
- At the stage of pouring and setting the mortar works as a shrinkage joint. Heavy wet solution compresses it as it dries gradually concrete mixture the dimensions of the poured canvas are reduced, and the material filling the gap expands and compensates for the shrinkage of the mixture.
- It prevents the transfer of loads from building structures concrete surface and vice versa. The screed does not put pressure on the walls. The structural strength of the building does not change. The structures themselves do not transfer the load to the screed, and it will not crack during operation.
- When there is a temperature difference (and they necessarily occur even in heated rooms), this seam compensates for changes in the volume of the concrete mass, which prevents it from cracking and increases its service life.
To create such gaps, a special damper tape is usually used, the width of which is slightly greater than the height of the screed. After the solution has hardened, its excess is cut off construction knife. When they settle in concrete floors shrinkage seams (if the finishing flooring not provided), the polypropylene tape is partially removed and the groove is waterproofed using special sealants.
In rooms of a large area (or when the length of one of the walls exceeds 6 m), according to SNiP, it is necessary to cut longitudinal and transverse temperature-shrinkage joints with a depth of ⅓ of the thickness of the fill. Expansion joints in concrete are made using special equipment (gasoline or electric joint cutter with diamond discs). The pitch of such seams should not be more than 6 m.
Attention! When filling heated floor elements with mortar, shrinkage joints are installed to the entire depth of the screed.
Expansion joints in foundation blind areas and concrete paths
Foundation blind areas, designed to protect the foundation of a house from the harmful effects of precipitation, are also susceptible to destruction due to significant temperature changes throughout the year. To avoid this, seams are installed to compensate for the expansion and contraction of concrete. Such gaps are made at the stage of construction of blind area formwork. Transverse boards (20 mm thick) are attached to the formwork around the entire perimeter in increments of 1.5÷2.5 m. When the solution has set a little, the boards are removed, and after the blind area has completely dried, the grooves are filled with damping material and waterproofed.
All of the above also applies to the arrangement of concrete paths on the street or parking spaces near own home. However, the step of deformation gaps can be increased to 3÷5 m.
Materials for arranging seams
Materials intended for arranging seams (regardless of type and size) are subject to the same requirements. They must be resilient, elastic, easily compressible and quickly recover their shape after compression.
It is designed to prevent cracking of the screed during its drying process and compensate for loads from building structures (walls, columns, etc.). Wide choose sizes (thickness: 3÷35 mm; width: 27÷250 mm) of this material allows you to equip almost any screed and concrete floors.
A popular and easy-to-use material for filling deformation gaps is a cord made of foamed polyethylene. On construction market There are two varieties of it:
- solid sealing cord Ø=6÷80 mm,
- in the form of a tube Ø=30÷120 mm.
The diameter of the cord must exceed the width of the seam by ¼÷½. The cord is installed in the groove in a compressed state and filled with ⅔÷¾ of the free volume. For example, to seal 4 mm wide grooves cut in a screed, a Ø=6 mm cord is suitable.
Sealants and mastics
Various sealants are used to seal seams:
- polyurethane;
- acrylic;
- silicone.
They come in both one-component (ready-to-use) and two-component (they are prepared by mixing two components immediately before use). If the seam is of small width, then it is enough to fill it with sealant; if the gap width is significant, then this material is applied on top of the laid cord made of foamed polyethylene (or other damping material).
Various mastics (bitumen, bitumen-polymer, compositions based on raw rubber or epoxy with additives to impart elasticity) are used mainly for sealing external expansion gaps. They are applied on top of the damping material placed in the groove.
Special profiles
IN modern construction expansion joints in concrete are successfully sealed using special compensation profiles. These products come in a variety of configurations (depending on application and joint width). For their manufacture, metal, plastic, rubber are used, or several materials are combined in one device. Some models in this category must be installed during the process of pouring the solution. Others can be installed in the groove after the base has completely hardened. Manufacturers (both foreign and domestic) have developed a wide range of the lineup such devices, both for outdoor use and for indoor installation. The high price of the profiles is compensated by the fact that this method of sealing gaps does not require their subsequent waterproofing.
In custody
Correct arrangement of temperature, expansion, expansion and settlement joints significantly increases the strength and durability of any building; parking spaces or garden paths With concrete covering. When using high-quality materials for their manufacture, they will last for many years without repair.
Expansion joints
An expansion joint is a joint at least 20 mm wide that divides the building into separate compartments. Thanks to this dissection, each compartment of the building receives the possibility of independent deformations.
Depending on the purpose, expansion joints are divided into three main types:
– temperature-shrinkage joints are installed to avoid the formation of cracks and distortions in the external walls of buildings due to differences in air temperatures outside and inside the building. Seams of this type cut the structures only of the ground part of the building - walls, floors, coverings and ensure the independence of their horizontal movements relative to each other. In this case, foundations and other underground parts of the building are not dissected, since temperature differences for them are smaller and deformations do not reach dangerous values.
The distances between temperature-shrinkage joints are assigned depending on the climatic conditions of the construction site and the material of the external walls of the building. For example, in residential buildings this distance is 40 ¸ 100 m for brick walls and 75 ¸ 150 m for walls made of concrete panels (the lower the outside air temperature at the building construction site, the smaller the distance between expansion joints). The building compartment located between two temperature-shrinkable seams or between the end of the building and the seam is called temperature compartment or temperature block;
– sedimentary joints are provided in cases where unequal and uneven settlement of adjacent parts of the building is expected. Such settlement can occur with differences in heights of individual parts of the building of more than 10 m, with different loads on the foundation, as well as with heterogeneous soils under the foundations.
Rice. 3.67. Schemes for installing expansion joints in buildings:
A– temperature-shrinkable;
b– sedimentary:
1 – above-ground part of the building;
2 – underground part (foundation);
3 – expansion joint
Sedimentary seams vertically dissect all structures of the building, including its underground part. This allows for independent settlement of individual volumes of the building. Settlement seams provide not only vertical, but also horizontal movements of dismembered parts, so they can be combined with temperature-shrinkage seams. This type of expansion joints is called temperature-sedimentary;
– anti-seismic seams are provided in buildings located in earthquake-prone areas. The anti-seismic seam, like the sedimentary seam, divides the building along its entire height (above-ground and underground parts) into separate compartments, which are independent stable volumes, which ensures their independent settlement.
In Fig. Figure 3.67 shows diagrams of the arrangement of expansion joints in buildings.
Every structural element of a building carries a certain force load during its work in the structure. Moreover, it is not always associated with seismic vibrations or the weight of the building as such. The problem of construction physics itself is already long time represents uneven expansion different materials when heated and their narrowing when cooling.
Eg:
The thermal expansion coefficients of metal and wood differ several times. This justifies mechanical destruction wooden beams located in the cold under-roof space, which are secured using conventional studs and fittings without thermal break. To solve this and some other problems, the construction of expansion joints is used in general construction practice.
Below we present full list problems when this element “works” and helps maintain the structural integrity of the entire building:
- seismic activity of the earth's crust;
- soil settlement, rise of groundwater;
- force deformations;
- sudden change in ambient temperature.
Depending on the nature of the problem being solved, all expansion joints are divided into temperature, shrinkage, seismic and sedimentary.
Temperature expansion joint
Structurally expansion joint is a section that divides the entire structure into sections. The size of the sections and the direction of division - vertical or horizontal - is determined design solution and power calculation of static and dynamic loads.
To seal the cuts and reduce the level of heat loss through expansion joints, they are filled with an elastic heat insulator, most often these are special rubberized materials. Thanks to this separation, the structural elasticity of the entire building increases and the thermal expansion of its individual elements does not have a destructive effect on other materials.
As a rule, a temperature expansion joint runs from the roof to the very foundation of the house, dividing it into sections. It makes no sense to divide the foundation itself, since it is located below the depth of soil freezing and does not experience this negative impact like the rest of the building. The spacing of expansion joints will be influenced by the type of used building materials And geographical location object that determines the average winter temperature.
In statically indeterminate systems of reinforced concrete buildings and structures, in addition to the forces from external loads additional forces arise as a result of temperature changes and concrete shrinkage. In order to limit the magnitude of these forces, temperature-shrinkage seams are installed, the distances between which are determined by calculation.
The calculation may not be done for structures of the 3rd category of crack resistance at design low temperatures outside air above minus 40° C, if the distances between expansion joints do not exceed the required values given in the SNiP table. In any case, the distances between the seams must be no more than:
150 m for heated buildings made of prefabricated structures;
90 m - for heated buildings made of prefabricated monolithic and monolithic structures.
For unheated buildings and structures, the indicated values must be reduced by at least 20%. To prevent additional forces from occurring in case of uneven foundation settlements (sections of different heights, complex ground conditions etc.) provision is made for the installation of sedimentary joints.
It should be noted that sedimentary seams cut through the structure to the base, and temperature-shrinkage seams only to the top of the foundations. Sedimentary seams at the same time play the role of temperature-shrinkage seams.
Schemes of expansion joints
The width of the temperature-shrinkable seam is usually 2...3 cm, it is specified by calculation depending on the length of the temperature block and the temperature difference.
Key points in the temperature calculation problem
Expert opinion.
Uncertainty with the rigidity characteristics of the base in the horizontal direction - for example, given the rate at which the thermal load is applied, a fair amount of rheology may occur. Friction on the soil will be different in different areas of the foundation depending on the pressure on the soil in these areas. Local damage to waterproofing - can it happen and should it be taken into account? What about local zones of plasticity in soils? Well, the plus I mentioned backfilling. Variation of the rigidity characteristics of the base in the horizontal direction can repeatedly change the forces from temperature loads. With piles it is even more difficult.
Nonlinearity of reinforced concrete, its rather “long-term” rigidity characteristics - what will be the change in the deformation diagram of reinforced concrete at a loading rate that is characteristic of temperature loads? I am already silent about all the other subtleties of modeling the nonlinear properties of reinforced concrete - at a minimum, it is necessary to model with solids in order to take into account the reduction, including the shear stiffness of all elements, especially massive ones, which are concentrators.
Uncertainty with the temperature loads themselves. In reinforced concrete, even without these loads, numerous cracks will open, and even more so taking into account the temperature. And not only the rigidity of the frame will decrease, but also the loads themselves, because the area of the elements itself decreases (due to the formation of cracks), which is not taken into account by the methods known to me.
Thus, I believe that a full-fledged temperature calculation of reinforced concrete frames is currently a guess, and the only thing you need to trust is design experience, reflected in particular in the recommended distances between temperature blocks.
Settlement expansion joint
Second important application expansion joints is compensation for uneven pressure on the ground during the construction of buildings of varying number of storeys. In this case, the higher part of the building (and, accordingly, heavier) will press on the ground with greater force than the lower part. As a result, cracks can form in the walls and foundation of the building. A similar problem can arise from soil settlement within the area under the foundation of a building.
To prevent cracking of the walls in these cases, sedimentary expansion joints are used, which, unlike the previous type, divide not only the building itself, but also its foundation. Often in the same building there is a need to use seams various types. Combined expansion joints are called temperature-sedimentary joints.
Antiseismic expansion joints
As their name suggests, such seams are used in buildings located in seismic zones of the Earth. The essence of these seams is to divide the entire building into “cubes” - compartments that are themselves stable containers. Such a “cube” should be limited by expansion joints on all sides, along all edges. Only in this case will the anti-seismic seam work.
Along the anti-seismic seams, double walls or double rows of support columns are installed, which form the basis load-bearing structure each individual compartment.
Shrinkage expansion joint
Shrinkage expansion joints are used in monolithic concrete frames, since concrete, when hardening, tends to slightly decrease in volume due to the evaporation of water. The shrinkage seam prevents the occurrence of cracks that disrupt bearing capacity monolithic frame.
The point of such a seam is that it expands more and more, parallel to the hardening of the monolithic frame. After hardening is complete, the resulting expansion joint is completely caulked. To impart hermetic resistance to shrinkage and any other expansion joints, special sealants and waterstops are used.
Expansion joints in buildings are installed to reduce loads on structural elements in places of predicted deformations that occur due to temperature fluctuations, seismic influences, uneven soil settlement and that can cause dangerous loads.
Depending on the purpose, expansion joints can be divided into temperature, sedimentary, seismic and shrinkage.
In a hot pagoda, when heated, the building expands and lengthens; in winter, when cooled, it contracts; these temperature deformations lead to the appearance of cracks.
Expansion joints divide the above-ground structure of the building vertically into separate parts, which ensures independent horizontal movement of individual parts of the building. In foundations and others underground elements buildings are not satisfied with expansion joints, since they are in the ground and are not subject to significant changes in air temperature.
Installation of expansion joints in external walls of buildings:
A, B - with dry and normal operating modes; B, D - with wet and wet modes;
1 - insulation; 2 - plaster; 3 - jointing; 4 - compensator; 5 - antiseptic wooden slats 60x60 mm; 6 - insulation; 7 - vertical joints filled with cement mortar.
The distance between expansion joints is determined depending on the wall material and temperature indicators construction area.
Expansion joints of external walls must be water- and airtight and frost-proof, for which they must have insulation and reliable sealing in the form of elastic and durable seals made of easily compressible and non-crumpling materials (for buildings with dry and normal operating conditions), metal or plastic expansion joints made of corrosion-resistant materials (for buildings with damp and wet conditions).
Settlement expansion joint
Settlement joints are taken into account in cases where different and uneven settlement of adjacent building elements is expected. Separate adjacent parts of the building may differ in number of floors and length. In this case, the higher part of the building, which will be heavier, will press on the ground with greater force than the lower part. Such uneven soil deformation can lead to cracks in the walls and foundation of the building.
Sedimentary joints dissect vertically all the structures of the building, including its underground part - the foundation.
Schemes for installing expansion joints in buildings:
A - sedimentary; B - temperature-precipitation:
1 - expansion joint; 2 - underground part (foundation) of the building; 3 - above-ground part of the building;
If it is necessary to use expansion joints in one building different types, if possible, they are combined in the form of so-called temperature-sediment joints.
Antiseismic expansion joint
Anti-seismic joints are installed in buildings constructed in earthquake-prone areas prone to earthquakes. They divide the entire building into compartments, which in the design represent independent stable volumes. Along the lines of anti-seismic seams, double walls or double rows of support columns are installed, which form the basis of the supporting structure of each individual compartment and ensure their independent settlement.
Layout of seismic belts in buildings with stone walls and design of anti-seismic belts outer wall:
A - facade; B - section along the wall; B - plan of the outer wall; G, D - inner part; E - detail of the plan of the anti-seismic belt of the outer wall;
1 - antiseismic belt; 2 - reinforced concrete core in the wall; 3 - wall; 4 - floor panels; 5 - reinforcement cage in the seams between the floor panels;
Shrinkage expansion joint
Shrinkage expansion joints are made in monolithic concrete frames, since concrete decreases in volume during hardening due to water evaporation. Shrinkage joints prevent the occurrence of cracks that impair the load-bearing capacity of the monolithic concrete frame. After hardening is complete, the remaining shrinkage expansion joint is completely sealed.
In brick walls, expansion joints are made in quarter or tongue-and-groove. In small-block walls, adjacent sections are joined end-to-end and are additionally protected from blowing by steel expansion joints.
Expansion joints in brick walls:
A - c brick wall, abutment into tongue and groove; B - in a brick wall, a quarter connection; B - with a compensator made of roofing steel in a small-block wall;
1, 2 - gasket; 3 - steel compensator; 4 - blocks;
Temperature changes, humidity, climate in general, seismicity and dynamic loads are factors that often lead to deformation of the structure. To prevent changes in the volume of building materials (expansion or contraction due to temperature differences) or subsidence of elements (due to errors in or insufficient soil reliability) from leading to the destruction of the entire structure, it is advisable to use an expansion joint.
Types of expansion jointsDepending on what type of deformation is necessary to prevent, seams are classified into temperature, shrinkage, anti-seismic and sedimentary.
Used to prevent horizontal changes. When calculating industrial building with frame design diagram seams are placed at least every 60 m for heated and 40 m for unheated buildings. As a rule, expansion joints only affect above ground structures, while the foundation is less susceptible to temperature differences.
A sedimentary expansion joint is necessary to prevent cracks from appearing in structural elements as a result of the fact that the load is distributed unevenly or the soils are weak and some elements sag. Unlike an expansion joint, a sedimentary joint also separates the foundation.
Anti-seismic expansion joints in buildings located in areas with increased seismic activity are practically necessary. Due to them, the building is divided into blocks that are essentially independent of each other, and therefore in the event of an earthquake, the destruction or deformation of one block will not affect the others.
If your structure consists of monolithic reinforced concrete walls, a shrinkage expansion joint is necessary. The fact is that concrete tends to shrink and decrease in size - that is, a wall poured directly at the construction site, and not assembled from reinforced concrete panels, will certainly decrease in volume, forming a gap. For comfort further work a shrinkage joint is made before pouring the next wall, and after the concrete has dried, the seams and gaps are sealed.
Seam sealing and insulation
It is very important to pay special attention to this aspect: the seams must be well protected from exposure external factors. For this purpose they are used different kinds insulation and filler. Polyurethane or epoxy sealants are a good option: they have high hardness and are not very elastic; another variant -
use of polyethylene foam cord followed by sealing with sealant. Another option is to fill the expansion joint. And the expansion joint in the wall, filled with mineral wool, must be sealed with an elastic mass that is resistant to weather conditions and protects the filler from moisture and dampness. In addition to fillers, the seam can be protected using a profile or strip of a suitable size.
Seam sizes
The width of expansion joints varies from 0.3 cm to 100, depending on the type of joint, as well as the operating conditions of the building. Expansion joints reach 4 cm (narrow), and shrinkage joints are medium (4-10 cm) and wide (10-100 cm).
