Expansion joints in reinforced concrete

An essential element in reinforced concrete construction is the expansion joint. The longevity and structural integrity of concrete structures depend on these joints. Without them, the natural movements and temperature fluctuations of time could cause serious harm to buildings, bridges, and other concrete constructions.

Despite being robust and long-lasting, concrete is susceptible to expansion and contraction in different temperatures. If this movement is not controlled, it may result in cracking and other types of damage. Because expansion joints are made expressly to absorb these kinds of movements, structural problems can be avoided when concrete expands and contracts.

The importance of expansion joints is increased in reinforced concrete. These structures are stronger because of the steel reinforcement, but it also affects how the concrete responds to stress. In order to prevent undue stress on any one component and lower the chance of damage, expansion joints that are positioned correctly aid in the distribution of forces within the structure.

One of the most important aspects of concrete construction is knowing where and how to put these joints. The size of the structure, the kinds of loads it will support, and the environmental conditions it will encounter are just a few of the many variables that engineers and builders need to take into account. They guarantee the long-term soundness and functionality of the concrete structure by meticulously designing and constructing expansion joints.

What is an expansion joint?

This is the project-provided vertical (horizontal) plane fragmentation of the building structure, which compensates for stresses in the supporting frame and results in modifications to the geometric dimensions and relative positioning of the reinforced concrete. These joints determine how elastic mobility should be designed into buildings. They are separated into temperature, shrinkage, structural, settling, and seismic categories based on the stress they are meant to offset.

In order to control the natural movement of concrete structures brought on by variations in temperature, moisture content, and other environmental conditions, expansion joints in reinforced concrete are crucial. These joints let concrete to shrink and expand safely, preventing structural damage and cracking. The longevity and integrity of buildings, bridges, and other infrastructure are guaranteed by engineers through the use of expansion joints in the design and construction of concrete elements. The longevity and functionality of reinforced concrete are contingent upon the appropriate positioning and upkeep of these joints.

The largest distances between expansion joints in reinforced concrete structures

Expansion joints, the distance between which is determined in relation to crack resistance values, are placed between buildings, the framework of which consists of pre-stressed products of the first and second groups in terms of resistance to cracking. Within a single heated building, the spacing between cuts shouldn’t be greater than:

  • for prefabricated structures – 150 m;
  • for prefabricated monolithic and monolithic structures – 90 m.

20% is subtracted from the given values if the building is not heated.

Structures that extend along the facade and cross-section are divided into distinct blocks by expansion joints. The dimensions are not calculated when the design numerical parameters are less than the corresponding indicators from Table 1 (at air temperatures of -40 degrees Celsius and above). The latter is acceptable if the structure consists of both non-stressed and pre-stressed products, each of which belongs to the third group in terms of crack resistance. Table 1 displays the maximum distances between deformation disconnectors that can be omitted in reinforced concrete structures.

The distance between seams in single-story reinforced concrete buildings can be extended by 20% in comparison to the information presented in Table 1. When building vertical ties in frame structures located in the center of a distinct block, the table data are also applicable. By positioning these ties along the edges of the block, the work of the frame becomes more similar to a solid structure when typical deformations are taken into account.

How are they performed?

A structure’s temperature-shrinkage (sedimentary-seismic) section can be created by combining the shrinkage and thermal (sedimentary and seismic) joints. The building is divided into two sections: the first splits it into equal parts along the length and width from the roof to the top of the foundation. In reinforced concrete, a vertical section of floors and walls with a width of 20 to 30 mm provides the permitted deformation. Hydrophobic material that is elastic is present in this empty space. The proper opening is formed by installing paired columns and beams in adjacent sections of nearby buildings.

Even when blocks in a building are joined by an insert span, a settlement joint is still installed in buildings with blocks installed in different soil types and heights. By inserting bitumen-impregnated wooden blocks into the formwork, the thermal expansion of the reinforced stone in the blind area is offset by fragmentation up to a 2-meter step. The formwork’s wall abutment is made movable and hermetic. When a room’s area surpasses 30 m2, shrinkage deformations in concrete floors can occur.

Cracks appear when concrete expands during the hardening process. Material breaks can pass along the made cuts or beneath them in the depth when the screed’s surface is cut to a depth of 1/4 to 1/2 of the height. A screed area can be as long as six meters on one side and as wide as one:1.5 on the other. Dampers that account for material shrinkage and thermal horizontal expansion are installed in structural joints of concrete poured at different times and in joints made of different materials laid in the floor.

Along the room’s perimeter, insulation joints divide the concrete screed from the walls for the entirety of its height. Elastic materials are inserted into the cut, or it is left empty. In a similar vein, cutting the joint isolates the screed on the floor from columns and stairwells. Joints divide monolithic floor slabs from the structure’s supporting frame. Finding the width of a typical floor element is aided by calculations.

These kinds of fragments are poured into interfloor ceilings. Elastic waterproofing materials and compounds are used to fill the voids, which are then sealed. Expansion joints also separate strip foundations into independent elements over their whole height. They have to offer dependable waterproofing as well as load and stress compensation. The project determines the quantity and frequency of foundation sections. The type of soil determines the foundation’s cutting step.

For instance, 15 m on heaving ones and 30 m on slightly heaving ones. Seam sealants need to be able to hold their elasticity and tightness over time. Internal and external wall vertical structures divide them into compartments by forming horizontal sections.

The compartment height is up to 20 meters for load-bearing facade walls and up to 30 meters for internal walls. Within these frame apertures, a spoon is positioned, twice encased in the pacli material and sealed with clay. The range of their width is 3 mm to 100 cm, depending on the kind of seams.

Topic Description
What are Expansion Joints? Expansion joints are gaps or spaces in concrete structures that allow for movement caused by temperature changes or other factors, preventing cracks.
Why Use Expansion Joints? They prevent damage by absorbing stress from thermal expansion and contraction, keeping the structure intact.
Materials Used Common materials include rubber, foam, or flexible sealants that can compress and expand as needed.
Installation Proper placement and sizing are crucial to ensure effectiveness, typically placed at regular intervals or around sections prone to movement.

When it comes to the resilience and lifespan of reinforced concrete structures, expansion joints are essential. These joints stop ugly and possibly dangerous cracks from forming by allowing concrete’s natural expansion and contraction. This prolongs the service life of pavements, bridges, and buildings while also improving their structural integrity.

Concrete that has expansion joints installed and designed correctly is guaranteed to be resilient to changes in temperature and other environmental stresses. This is especially crucial in areas with severe weather since concrete can expand and contract significantly due to heat. The stresses resulting from these movements could cause structural failures in the absence of these joints.

To guarantee that expansion joints continue to function properly, regular upkeep and inspection are necessary. These joints’ ability to accommodate movements may be compromised over time by the deterioration of the materials used in them. Ensuring the overall health of the structure is protected by timely expansion joint repairs and replacements.

It is a wise and proactive move to include expansion joints in the design of reinforced concrete structures. We can create resilient structures that require fewer expensive and frequent repairs by recognizing and addressing the inherent characteristics of concrete. In the end, this careful planning results in a more dependable and safe infrastructure.

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Anna Vasilieva

Journalist with a technical education, specializing in construction topics. I can explain complex technical topics in simple and accessible language.

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