--- url: https://qsteelcad.com/en/blog/light-steel-floor-rules-2027 language: en alternate: https://qsteelcad.com/blog/hafif-celik-doseme-kurallari-2027 updated: 2026-11-06 publisher: RENMAE Teknoloji ve Yazılım LTD. ŞTİ. --- # Light steel floor rules 2027: deflection table, 8 Hz and web stiffeners A floor is now calculated not only for strength but also for deflection and vibration. We have collected the limits in Section 7 of the regulation, the 8 Hz requirement and the stiffener plate rules in one place. ## Short answer Section 7 of the 2027 light steel regulation treats the floor together with strength, deflection, vibration and diaphragm behaviour. For general use the maximum deflection is L/200. The floor natural frequency must be at least 8 Hz and the joist span/depth ratio at most 18. If these cannot be met, joist spacing is tightened and bridging members are used. ## Key points - Maximum deflection is L/200 for general use, L/250 under live load only. - The floor natural vibration frequency must be at least 8 Hz. - The joist span/depth ratio is at most 18. - A web stiffener is needed if h/t > 180 or the shear stress exceeds 80%. - If openings exceed 3%, the floor is modelled as a shell element. In a light steel floor, comfort is often the limit, not capacity. The joist carries the load but bounces when you walk on it, or it cracks the finish. That is why Section 7 of the regulation puts load capacity, deflection, vibration and connections under the same heading. The lower limits of Section 2 for material apply here as well. ## What are the deflection limits? Short-term and long-term deflections are checked according to Table 7.1 as appropriate to the intended use. For deflection checks, the load combinations in Section 15.1 of the Turkish steel structures regulation (ÇYTHYE 2018) are used. | Member or use case | Maximum deflection | | --- | --- | | General use (floor, joist) | L/200 | | Under live load only | L/250 | | Supporting infill walls or brittle finishes | L/300 | | Floor resting on members that show no ductility | L/360 | | Horizontal drift at stud top in single-storey buildings | H/300 | | Per storey height in multi-storey buildings | Storey height / 300 | | Roof beams (no insulation, non-brittle) | L/250 | | Roof beams (carrying brittle finishes) | L/300 | ## What is required for vibration? Depending on the intended use of the building, vibrations must not adversely affect occupant comfort. The regulation asks for three things here: the floor system is analysed with a finite element model, the floor natural vibration frequency is at least 8 Hz, and the span/depth ratio of the joists is not greater than 18. If these conditions cannot be met, joist spacing is arranged at less than 40 cm to limit vibration, and at least two bridging members are used between joists. In floors with trapezoidal sheet decking, the sheet is screwed to the joists at no more than 15 cm spacing. To reduce vibration, an acoustic insulation felt, a rubber sheet or a viscoelastic layer can also be placed under the decking. ## When is a web stiffener needed? Local web crippling can occur in the end zones of floor joists. The regulation ties web stiffener plates to conditions against this: - They are provided in members where the web height/thickness ratio is h/t > 180. - They are mandatory if the shear stress exceeds 80% of the design shear strength. - The wall thickness is at least that of the web member. - They are fixed to the web with a bolted connection. - The distance between stiffeners is the smaller of s ≤ 4h or s ≤ 500 mm. - The minimum width is 2 cm. ## Does the platform versus balloon framing difference matter? Platform and balloon framing systems can be used where the floor system meets the walls. If balloon framing is used, the bending effect caused by eccentricity in the load transfer from the floor joist to the stud is taken into account in the stud calculations. So the choice is not only about ease of erection; it also changes the stud calculation. ## What are the diaphragm requirements? For the overall stability of the structure, lateral loads are transferred through the floors by rigid diaphragm action. Section 7 repeats the overstrength factor D from TBDY, the connection calculation and the collectors. When the 3% opening limit is exceeded, the floor is modelled as a shell element and the load transfer mechanism is shown. Joist bearing is at least 40 mm. Read next: [Floor and roof diaphragms: who delivers the load to the braced wall?](https://qsteelcad.com/en/blog/floor-and-roof-diaphragms) ## Additional rules for connections and the roof Section 7.6 requires the connections of floor members to each other and to the main load-bearing members to be designed according to Section 8 so as to transfer shear and moment. Connection details between the sheathing elements and the steel profiles are detailed for shear force transfer. Blocking and bracing members give the floor system stiffness. In the top sheathing, the stiffness needed for stability under the roof must be provided by bracing members or additional beams. > At altitudes above 400 metres, ice loads are considered in the roof load calculation in addition to the snow loads in TS 498 (Section 7.6). ## What to look at for floors in QSteelCAD The program does not calculate deflection or vibration. Joist span, spacing and section can be read from the model; the calculation is done by the project engineer. For ceiling panels built in Automatic roof, check the spacings against your own setting. ## Frequently asked ### What is the deflection limit in a light steel floor? L/200 for general use and L/250 under live load only. It is L/300 if the floor carries brittle finishes and L/360 if it rests on members that show no ductility. ### What should the vibration frequency of a light steel floor be at least? The regulation requires the floor natural vibration frequency to be at least 8 Hz. ### What is the minimum joist bearing in mm? 40 mm. This value is the same in TBDY 2018 10.5(e) and in the 2027 regulation. ### What is the maximum joist spacing? The regulation gives no general spacing; if the vibration conditions cannot be met, it requires joist spacing of less than 40 cm and at least two bridging members. ## Related solutions - [Automatic roof](https://qsteelcad.com/en/solutions/automatic-roof)