Fire safety engineering of structures

DRAFT

Introduction

The relevant Building Fire Safety Regulations and Procedures in Hong Kong may be referred to HKU website: http://www.arch.hku.hk/teaching/firesafety.html.

The fire resistance period (FRP) in HK is specified in Section 6 and Table 2 of Code of Practice of Fire Resisting Construction 1996 (FRC).

A number of different approaches to ensure fire safety, which includes:

·        A prescriptive approach (deemed-to-satisfy rules)

·        A performance based approach to address a particular part of the design with the rest of the design following a prescriptive based approach

·        A full performance based approach

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(a) Prescriptive method defines a structural fire design fairly in terms of the materials used, shape and size of structural elements, thickness of fire protection materials and construction details etc.
PNAP 192 & FRC table A to F: Fire resisting material.
PNAP 195 & MOE: Provision of means of escape
CoP FSI: Fire service installation of equipment
PNAP 87 & BO 21(6)(d): Permanent Water Supply to Fire Service Installations
PNAP 182, MOA & B(P) 41, 41A, 41B, 41C & 41D: Means of Access for Firefighting and Rescue in Buildings
PNAP 202: Application of fire safety codes
PNAP 212 & Fire Safety (Commercial Premises) Ordinance: Prescribed commercial premises when floor area exceeds 230m². 
PNAP 302 & Fire Safety (Buildings) Ordinance: For composite building or domestic building

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Concrete

Three methods for design of concrete for fire resistance:

A. Tabulated data

B. Fire test
C. Fire calculation

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A. Tabulated data
Control of cover, finish and minimum dimension of elements:
(i) For BS8110-2, estimation of concrete cover:-
C ave = (A1C1 + A2C2 + ...) / (A1 + A2 +...)
where A1, A2,... = Area of reinforcement; C1,C2,... = Cover / distance from heated faces
(ii) In FRC 1996, consideration of design of fire resisting elements: -
Column/beam - exposure condition, steel ratio and minimum dimension (table E);
Steel column/beam - concrete cover, finish or gypsum board (table D)
Slab/stair - minimum dimension and concrete cover (table C & F)
Wall - Steel ratio & cover (table A) and finish (table B)
(iii) Applied finish for additional protection. i.e. gypum or gypum plaster board (Table B & D of FRC)
(iv)  Additional requirement for high strength concrete of grade greather than 60D according to s4.3 of CoP of Concrete 2004. The Buildings Department may impose the following conditions in approval letter
B. Fire test
(i) A quality assurance proposal is to be submitted with sufficient preliminary test results to confirm that reliable and consistent concrete can be produced. This should include a detailed assessment of the concreting materials, the mix design and the quality control procedures of the batching plant. In this respect the designed mean resistance to crushing shall initially exceed the specified resistance to crushing by a margin of not less than 12 MPa.
(ii) Adequate facilities are to be provided on site, for sampling the fresh concrete, making, curing and storing the test cubes.
(iii) An experienced and competent person is to be provided full time to supervise the whole work so as to ensure compliance with the approved plans.

(iv) All concrete arriving onsite shall come from a concrete supplier registered under the Quality Scheme for the Production and Supply of Concrete (QSPSC).

(v) Sampling of fresh concrete, making, curing, storing and compression testing of concrete test cubes should be carried out in accordance with the methods specified in CS 1:1990 by a laboratory accredited under HOKLAS for the particular test concerned. Both sampling and test results should be reported on a HOKLAS Endorsed Certificate and submitted within 21 days after sampling and/or testing.

(vi) At least one sample of concrete shall be taken from every ready mixed vehicle arriving on site. If concrete is site batched one sample shall be taken from every 10m³ of concrete produced.
(vii) Insitu core testing to the completed structure shall be carried out. Tests for compressive strength of concrete cores should be carried out in accordance with the method specified in CS1: 1990, by a laboratory accredited under HOKLAS for the particular test concerned. Test results should be reported on a HOKLAS Endorsed Certificate and submitted within 21 days after testing.
(viii) Qualified site supervision of the drilling of concrete core samples, by an experienced and competent person, should be provided. The person supervising the drilling of core samples should be indepedent from the contractor.
(ix) Details of any subsequent revision of the mix design are to be submitted.
(x) Consent to commence the work will not be granted until the following documents have been submitted and found satisfactory.
·        the quality assurance proposal and confirmation of the mix proportion to be adopted;
·        proposals for the onsite facilities for sampling of fresh concrete and making, curing and storing the test cubes;
·        the name of the laboratory accredited under HOKLAS, which will carry out the onsite and laboratory sampling and testing work;
·        the name and professional details of the person who is to supervise the works on a full time basis; and

·        proposal for insitu core testing of the finished concrete structure.