Queries on BS 8110-2:1985 Section 4 Fire resistance requirements on structural concrete covers in co

[ksniresh.jkbgmail.com]

Dear ENG-TIPS members,

(1) I would like to humbly request clarification on Section 4. Fire resistance of BS 8110-2:1985 (Page 25-3Cool (see attached page highlighted in red). I have attached the slab section and other relevant documents for your reference and ease of understanding.

(2) The following is stated in Section 4.1.4 Surfaces exposed to fire (Page 25)(see attached page highlighted in red)

"The surfaces exposed to fire in the standard test of the element are as follows:

walls: one side
floor: soffit
beams: sides and soffit
columns: all sides (fully exposed) or one or more sides (protected by adjacent walls)"

(3) Further to the above, the following is stated in Section 4.2.3 Cover to main reinforcement (Page 27)(see attached page highlighted in red)

"a) Floor slabs. Cover is the average distance from the soffit or the heated face...."

(4) My queries are:
(i) If the source of fire is on top of the floor slab, would the top of slab be considered as the 'heated face' as mentioned in Section 4.2.3? Or the Section 4.2.3 refers to the soffit of floor slab only regardless of the source of fire?

(ii) The majority part of Section 4 emphasizes more on the soffit of slab rather than top of slab when it comes to fire resistance requirement for floor slabs. Does this mean that only the concrete cover of soffit of slab need to comply with the fire resistance requirement, and the concrete cover of top of slab does not need to comply with the fire resistance requirement?

(5) I truly appreciate if you could clarify this matter.

Thank you very much.

Kind Regards,
Niresh

 

[rapt]

Normally the surface above the fire is the heated surface.

The top surface of the slab does not get anywhere near as hot as the bottom of the slab above.

The only time top steel is normally expected to be exposed would be a top corner/edge bar where the fire can come up the side of the member.