Welcome to the Official Website of NIAZIT Roof Industrial Group
Exclusive Manufacturer of NIAZIT Open Web Steel Joist (Concrete-Free Web System)
Exclusive Manufacturer of NIAZIT Open Web Steel Joist (Concrete-Free Web System)
NIAZIT Roof Industrial Group, under the leadership of Engineer Mohammad Niazi, has been operating for over two decades in the production of joists without concrete infill in the web. Through continuous effort and its unique capabilities, the group has successfully executed more than 5 million square meters of roofing across various regions of the country. Consequently, the company has secured a significant share of civil and construction projects and has become a recognized and reputable name in the industry, reflecting the quality and reliability of its services.
The NIAZIT Open Web Steel Joist system is an advanced form of European-style open web steel joists. The overall joist configuration is patented under registration No. 98813 and is exclusively owned by Engineer Mohammad Niazi. This system is derived from the SJI 200-2015 specification, in which the joists do not include concrete within the web. Composite behavior is provided by the concrete topping slab acting compositely with the joist top chord and/or shear studs installed on the top chord.
In this type of joist, the top chord consists of a T-section, while the web members are composed of discontinuous vertical and diagonal reinforcing bars. Each member can be analyzed individually, both before and after concrete curing. The bottom chord is constructed using steel straps, providing the necessary structural performance.
Unlike conventional open web joists in Iran (commonly known as Kromit), where concrete must fully penetrate the web, NIAZIT joists do not rely on a T-shaped concrete section and feature a different design for the web members. Consequently, the design criteria and limitations of concrete-free web joists, i.e., NIAZIT, differ from those of conventional open web joists in Iran, including the following aspects:
1- In the upper edge section, a shield section is used instead of a corner, which not only optimizes the performance of the upper edge during concreting, but also makes the radius of gyration symmetrical in two directions.
2. In NIAZIT joists, due to compliance with the length-to-depth ratio, there are no restrictions on span length, allowing implementation over long spans.
3. In areas where the joist is not encased in concrete, zinc-chromate anti-corrosion coating is applied.
4. If the block or formwork support is not placed on the bottom chord of the joist, the governing factor for the bottom chord becomes the minimum calculated cross-sectional area rather than the minimum plate width.
| Type of materials | DL | Type of materials | DL |
| Web Concrete | 0 | Slab Concrete + Joist Weight + Triangular Concrete | 165 |
| Polystyrene Block (EPS) | 5 | Plaster and Finish Coat | 50 |
| Levelling Lightweight Aggregate | 37 | Levelling Lightweight Aggregate | 21 |
| SUM = 320 (kg/m2) | |||
Since the dead load of the NIAZIT Roof System is lower than that of various conventional roof systems—including joist-and-block slabs, steel deck roofs, open web steel joists, and composite slabs—it can be readily substituted for existing roof systems in Iran without requiring structural reanalysis.
Due to the elimination of concrete in the joist web, the dead load of the roof is reduced by 80 to 100 kg/m², resulting in a total dead load of 320 kg/m².
When the dead load of the NIAZIT Roof is considered during structural design, the total material usage in the foundation, beams, and columns is reduced by at least 15 to 20%.
Unlike conventional open web joists (Kromit), NIAZIT joists can be used as single units in long spans.
Since this system does not require U-shape reinforcement or negative moment bars, the consumption of reinforcing steel is reduced by 2 to 3 kg per square meter of roof.
The special design of this type of joist allows for the construction of long spans up to 16 meters without any issues.
In the design of this type of joist, in addition to accounting for tensile and compressive forces, the human sensitivity factor (5 Hz) is considered in the calculations, ensuring that the roof remains vibration-free even in long spans.
Due to the special design and arrangement of the NIAZIT joist web members, the joist does not experience long-term deflection, allowing direct application of plaster and finishing materials beneath the roof.
The elimination of concrete in the joist web allows the roof to be implemented using a variety of permanent and temporary formworks, enabling easy replacement of existing roof systems.
Due to improper vibration of the concrete within the web during installation of conventional Kromit joists, their seismic performance is often compromised. In contrast, NIAZIT joists, while eliminating web concrete altogether, feature an internal component design that provides optimized performance under seismic loading.
