Every industry undergoes major transformations with technological advancements, and the construction industry is no exception. One such achievement is the widespread use of various types of concrete joists to create structures with high durability and stability. Today, this has made it possible to construct high-rise buildings without concerns about height-related challenges. These joists, by significantly enhancing the strength of roofs compared to the past, play a crucial role in elevating construction standards.
A concrete joist, also known as a block joist, is one of the most important and widely used components in the building industry. These joists are made from rebar and concrete and are produced as prefabricated elements; this feature improves both the speed and accuracy of construction project execution.
In the production process of a concrete joist, one steel reinforcement bar is placed in the upper section, and two steel bars are placed in the lower section. Then, several reinforcement bars are connected in a zigzag pattern to both the upper and lower sections. This structure significantly increases the resistance and strength of concrete joists.
The extensive application of concrete joists in construction is due to their unique properties. Thanks to their ability to bear heavy loads and distribute them uniformly, these joists play a vital role in the construction of towers and tall structures. Furthermore, using concrete joists enhances the durability and stability of the structure and also enables optimization of construction time and costs. These characteristics have made concrete joists a top choice for construction projects.
Block joists are divided into two main types:
Truss concrete joists consist of a concrete heel and a steel truss. The truss, which is a triangular structure, can withstand both tensile and compressive forces, and its use in the joist is essential for achieving the required strength and robustness. The components of this type of joist are as follows:
Each of these rebars plays a specific role in reinforcing the joist, and their diameter varies depending on the structural requirements and the length of the joist. Typically, rebars with diameters of 8, 10, 12, 14, and 16 millimeters are used. The bottom tensile rebars bear tensile forces, the top rebars resist compressive forces, and the zigzag rebars are used to generally reinforce the truss and distribute forces evenly. This combination of rebars helps enhance the strength and stability of the joist against various forces.
Concrete alone is not strong enough for constructing a roof and may crack or break. Therefore, combining concrete with rebar and steel wire is essential. In pre-stressed concrete joists, steel wires (with a diameter of 5 millimeters) are used. The number of these wires is determined based on the joist’s length and the amount of pressure applied.
The wires are placed under tension to increase the load-bearing capacity, enabling them to withstand heavy pressures. These joists are manufactured in factories following specific regulations and standards, which leads to higher quality and strength. Being prefabricated, these joists speed up construction in large-scale projects.
The concrete used in pre-stressed concrete joists is of grade C35 with a strength of 1750 to 1900 Newtons per square millimeter. Using pre-stressed concrete joists can reduce the overall project costs, which has increased demand and expanded their application in the construction industry.
Two lower reinforcement bars or rebars of the truss that bear the pressures from bending moments and the dead load of the roof.
Bears the weight of the joist and the dead load of the roof, and if it is higher than the surface of the blocks, it helps control the thermal shrinkage of the roof.
Helps bear the bending force and dead load of the roof and ensures continuity between the tensile member of the truss and the covering concrete.
If the two lower tensile rebars are insufficient to bear the maximum bending moment at the mid-span, additional rebars must be placed inside the metal truss. These extra rebars are called reinforcing rebars.
Covers the rebars for fire protection, with a width between 10 to 16 centimeters and sufficient height to encase the rebars.
Block joists are considered one of the most important and functional elements in roof construction. By reinforcing concrete joists with rebar, the inherent weakness of these components against tensile forces is compensated. This feature has enabled the use of concrete joists in large projects and high-rise structures. Their widespread application in the construction industry is so significant that they must also be used on load-bearing walls and horizontal beams in brick buildings.
Concrete joists perform very effectively in steel roofs, brick frames, reinforced concrete structures, and buildings exposed to tensile forces. Due to their high resistance and strength against tension, these joists are among the most widely used materials in the construction industry.
Concrete joists, thanks to their engineered design and high-quality materials, provide excellent resistance against lateral forces such as wind and earthquakes, which significantly enhances building safety and durability.
Installing and executing concrete joists does not require specialized skills, and experienced workers can perform the task by following simple guidelines. This leads to reduced labor costs.
Using props during roof construction, due to proper load distribution and reduced material consumption, lowers overall construction costs.
Block joists are lightweight, making them easier to transport, which reduces costs.
Using various types of blocks—such as polystyrene, cement, and clay blocks—between the joists significantly decreases concrete consumption. This feature not only reduces material costs but also helps lower the overall weight of the structure.
These advantages demonstrate the effective role of concrete joists in improving efficiency, reducing costs, and increasing safety in construction projects.
Concrete joists are loaded in three stages:
Bearing the load from their own weight during transport and installation.
Bearing the dead load of the roof (weight of the joist, blocks, and in-situ concrete) and construction loads between the main supports during roof execution.
After the removal of temporary supports, bearing the dead and live loads during the operational phase.
These stages ensure that the joists maintain the necessary strength and stability during every phase of construction and building use.
Observing these points not only increases the service life of block joists but also contributes to the overall improved performance of the structure.
For optimal purchase and selection of concrete joists, consulting with engineers and construction specialists is essential. It is advisable to procure the required joists directly from manufacturers to get the best price and quality by eliminating intermediaries. The price of concrete joists fluctuates continuously due to the use of raw materials such as rebar, cement, ironware, and concrete.
To receive an accurate price quote for concrete joists, you can contact our experts and consultants and provide details such as the size and type of top and bottom rebars, the thickness of the zigzag, the concrete strength grade, the joist height, the joist length, and the size of the reinforcing rebars. With this information, our experts can inform you of the price per meter and per piece of the joist. This process ensures that you obtain the required joists at the best possible price and quality.
The concrete joist is a primary component in projects involving concrete-framed buildings, widely used in roofs due to its high strength and ease of installation. The types of concrete joists include truss joists and pre-stressed concrete joists. Truss joists are reinforced with steel rebars and concrete, while pre-stressed concrete joists utilize pre-stressed rebar and steel wire. Industrial joists help reduce concrete consumption, lower installation costs, and increase resistance against lateral forces like wind and earthquakes, thus ensuring improved efficiency and safety of structures.
