Evolution of Open Web Steel Joists
December 16, 2024
Interview with the Inventor of OWSJ
November 6, 2025
✨ NIAZIT Joist Installation Guidelines (NIAZIT OWSJ Roof System) ✨
Installation on Reinforced Concrete Frames
The use of transverse ties (bridging) is mandatory. Each tie consists of two rebars with a minimum diameter of 12 mm: one placed on the bottom chord and one below or on the top chord, parallel to each other and perpendicular to the joists, connected using soft binding wire.
For spans shorter than 3 m, installing temperature reinforcement and tying it to the joist (T‑section) is sufficient; transverse ties are not required.
For spans of 3–5.5 m, use one row of transverse ties; for spans greater than 5.5 m, use two rows. The spacing between adjacent ties shall not exceed 2.5 m.
Shrinkage and temperature reinforcement shall be installed at 25 cm spacing, perpendicular to the joist direction, using 6, 8, or 10 mm diameter rebars.
When temperature ties are used, they must be kept in tension to prevent protrusion during concreting and to restrain joist movement.
For larger spans in concrete structures, due to compressive forces in fresh concrete, the use of one or two rows of temporary props during concreting is recommended.
The NIAZIT roof system does not require U‑bars (odka) or negative moment reinforcement.
NIAZIT joists do not require web concrete; approved blocks may be used adjacent to internal elements.
Installation on Steel Frames
Transverse ties are mandatory and consist of two rebars (minimum 12 mm) welded to the joists, placed on the bottom and top chords, perpendicular to the joist direction.
For spans less than 3 m, temperature reinforcement welded to the joist (T‑section) is sufficient; transverse ties are not required.
Use one row of ties for spans of 3–5.5 m and two rows for spans greater than 5.5 m; maximum spacing is 2.5 m.
Shrinkage and temperature reinforcement at 25 cm spacing using 6, 8, or 10 mm rebars. Up to 4.5 m spans, tying with wire is acceptable; for larger spans, welding to the top chord is mandatory.
Temperature ties must be tensioned to prevent displacement during concreting.
No bearing reinforcement or negative moment bars are required in the NIAZIT system.
Web concrete is not required; approved blocks may be used.
Installation on Load‑Bearing Walls
Transverse ties (two rebars ≥12 mm) welded perpendicular to the joists are mandatory.
For spans below 3 m, temperature reinforcement welded to the joist (flat bar and T‑section) is sufficient; hidden transverse ties are not required.
One row of ties for spans of 3–5.5 m and two rows for spans above 5.5 m; spacing ≤2.5 m.
Shrinkage and temperature reinforcement at 25 cm spacing with 6, 8, or 10 mm rebars. Wire tying is sufficient up to 4.5 m; beyond this, welding to the top chord is mandatory.
Temperature ties must be tensioned to prevent movement during concreting.
For spans greater than 5 m, one row of temporary props is essential to prevent joist torsion during concreting.
No bearing or negative moment reinforcement is required.
Web concrete is not required; approved blocks may be used.
