There is much confusion regarding the Fire design of composite slabs, specifically relating to span conditions and reinforcement requirements.
A composite slab achieving the minimum concrete cover above the top of the deck will achieve a 30 minute fire rating without further verification (see Product Data Sheets for more details).
Where the fire period is greater than 30 minutes there are two methods for Fire Design:
UK NCCI (Simplified Method)
Can be used where the slab is continuous over supports. The deck contribution is considered along with top mesh reinforcement and can be used for designs up to 2hr fire period.
EC Standard (Fire Engineering Method)
The resistance is based on loose bar & mesh only, the deck contribution is not considered. Can be used for both single and continuous spans with up to 4hr fire period.
- Where the slab and reinforcement are continuous, the minimum requirement is top mesh reinforcement only, subject to exact span and load criteria (large spans or loads may not be achievable with mesh only
- For single span slabs where the reinforcement is discontinuous, the slab will require loose bar in the troughs and top mesh fabric
SMD Elements® Design Software gives you the option of checking composite slabs using both design methods.
For more information on this topic, see our TGN Section 5.3 specifically relating to Fire Design.