In European standards, an open-web joist refers to joists whose web is not filled with concrete.

In Iran, an open-web joist refers to joists whose web is encased in concrete, forming a T-shaped section, with only the lower flange remaining outside the concrete.

The joist without concrete in the web (NIAZIT) functions like European open-web joists; concrete does not penetrate the web, and structural performance relies on the steel system.

In the international SJI standards, joists without concrete in the web are analyzed in two scenarios:

Composite

In this scenario, the joist works in combination with the topping concrete, and the composite behavior of the slab is considered.

🔹 Reference: SJI 200-2015

Non-Composite

The joist alone carries the slab loads; concrete does not contribute structurally.

🔹 Reference: SJI 100-2020

Yes. NIAZIT joist has been tested by the Road, Housing & Urban Development Research Center and received official technical approval.

The system holds patent number 98813, valid until 1415 (Iranian calendar).

• Standard 543 and its updates 82, 94, 151: Guidelines for designing and executing joist and block slabs

• National Standard ISIRI 1-2909: Joist truss and joist for joist-block slabs – specifications and testing

• National Standard ISIRI 12977: Open-web joist – specifications and testing (specific to Chromit joists)

No. According to ISIRI 1-2909, trussed joists with ceramic footing are prohibited; only concrete-footed trussed joists are allowed.

No. Current Iranian standards only cover joists with concrete-filled webs forming T-sections.

No. Due to patent and technical approval, production without official licensing is illegal.

⚠️ Important Legal Notes

Any modification of the joist by other manufacturers is illegal and invalid.

“NIAZIT” is a registered brand name but is also commonly used in the market to refer to joists without concrete in the web.

A composite joist is a system where steel and concrete simultaneously share the bending and shear loads.

Both create a composite section during concrete pouring, but their analysis, design assumptions, and structural behavior differ significantly.

It is a colloquial and market term in Iran, used outside the ISIRI 12977 standard and Publication 543.

Open-Web Joist (Chromit):

According to Publication 543 – Clauses 2-3-1, 6: Spans over 7–8 m should be double.
ISIRI 12977 – Clause 4-4: Joists longer than 7.5 m must have continuous male plate along their length.
Top flange: symmetric double flange; bottom flange: male plate for spans over 6.5 m.

 
NIAZIT Joist (Non-Concrete Web):

Top flange is selected as a beam from the start.
Bottom web is calculated according to required section.
Long spans up to 16 m can be executed as single joists without doubling.

Depending on usage, span length, and load, spacing ranges from 50 to 75 cm.
Doubling is not required.
If spacing increases, appropriate measures for the topping slab must be applied.

• Short spans: 5 cm
• Long spans: 6 cm
• Minimum concrete grade: C20

Open-Web Joist (Chromit):

Part of shear resisted by concrete web, rest by zigzag reinforcement.
Issues: improper vibration, cracking, web failure, rebar unable to carry full shear.
Result: web failure (8–12 cm), shear system collapse, deflection, increased risk of slab collapse.

 
NIAZIT Joist (Non-Concrete Web):

Middle members act independently, without concrete dependency.
Elastic and recoverable behavior after earthquake.
High seismic resistance; joists return to original position.

According to SJI 200-2015, joist height is determined based on span-to-depth ratio and architectural slab thickness.
Typically 20–35 cm for standard spans.

Parts not in contact with concrete → anti-corrosion coating
Parts embedded in concrete → no coating needed
According to SJI, coating non-concrete-exposed members prevents corrosion.

Purpose: prevent temperature-induced cracks
Minimum bar: #6
Spacing: 25 cm, ~2 cm below slab surface
According to SJI, thermal bars only need to be perpendicular to joists.

According to SJI 200-2015, negative moment reinforcement is not required in joists without concrete in the web.
Reason: hinged end connection, top flange not attached to girder, or double-end shear connector in concrete frame.

Controls tensile and compressive forces at joist ends
According to SJI: designed with engineering software and shear analysis
Strap or angle can be used; angle preferred for larger polar moment of inertia

Plain bar (AI): better weldability, lower tensile strength
Deformed bar (AII): higher tensile strength, lower weldability
According to SJI: actual bar tensile strength considered in calculations

Yes, according to:
ISIRI 12977 Clause 5-2-5-5
Publication 543 Clause 2-2-2-5, Part 5
Connecting two profiles by splice at any flange location is permitted.
For tensile members: butt weld splice with minimum resistance 1.14Fy × A (A = total spliced section).
Example: For bottom flange 4.2 cm² (12×4 mm strap), #10 rebar can be used as equivalent in splice.

Rib / mid-span tie:
Provides lateral support for joists
Reduces sinusoidal vibrations and slab deflection
Increases overall slab stiffness
According to ISIRI 12977 and Publication 543, technically necessary and recommended.

Joist camber: seen when plaster/concrete applied directly, mid-rebar curvature, improper seating
Result: gradual deflection of joist
In NIAZIT slabs: special design and proper connection, deflection controlled within code limits, practically no camber effect.

Performance similar to steel frame fire protection
If polystyrene (EPS) used as formwork: suspended ceiling with 5 cm gap below mandatory
Implementation responsibility lies with owner and supervising engineer

Yes, for ease of installation, labor reduction, and accessibility
Technical requirements: minimum density 12 (Std. 11108)
Fire requirement: flame spread ≤ 15 mm in 20 sec
Non-compliance: plaster cracking, EPS deterioration
Suspended ceiling mandatory for fire safety

ETABS has Steel Joist Design option for joists without concrete in the web.
Training limitation: joists can be modeled like standard steel joists, replacing dead load DL = 320 kg/m²

Concrete-bottom joists:
Std. 1-2909, Clause 1-3 → CO₂ only allowed for top rebar
Std. 1-2909, Clause 9-1 → certified welder required
CO₂ welding must be in closed, wind-free environment

Steel joists (Chromit & NIAZIT):
Std. 12977 Cl. 8-1, Pub. 543 Cl. 2-2-2-5 Part 4, SJI 200-2015 Cl. 3.3
Electrode welding mandatory, CO₂ not permitted

Slab diaphragm stiffness depends on: structural system type, dimensions, lateral load elements, frame rigidity, slab thickness/type, number of stories
Displacement control per Iranian Code 2800
According to Pub. 543 Appendix 2, Part 11-B and 10th Building Code (2022), defined for composite beams, no recalculation required

Short spans (≤5 m) and low-rise buildings → conventional block joists common
Other cases: reduced concrete, no negative/udca bars, long spans, fewer columns, smaller beams/columns/foundation
Result → economical, lighter, cost-effective

No. Removing web concrete → reduced dead load
Top flange: composite performance like Chromit
Bottom flange: tensile force carried by steel
Result: NIAZIT joist lighter than Chromit

 Three main factors:
1️⃣ Dead load → reduces beam/column/foundation size
2️⃣ Materials → joist, formwork, concrete, rebar, shoring, accessories
3️⃣ Labor cost
Sum of three → real criterion for slab system selection

Main difference: type of formwork and installation cost
Not in the NIAZIT joist itself

Pricing: based on plan & m²
By kg → low transparency, weight tolerance, scale differences
Transparent method: final cost per m²

• Depending on order volume: 3–10 working days

• Production capacity: >5000 m²/day, facility >2000 m²

• Includes: manufacturing, assembly, anti-corrosion, full product preparation