Natural Fire Safety Concept 3 - Open Access Pages

"The development and validation of a CFD-based engineering methodology for evaluating thermal action on steel and composite structures"

Welcome to the homepages of the Natural Fire Safety Concept 3 (NFSC3) project!

This project was funded by the European Coal and Steel Community (ECSC) and ran from July 1999 to December 2002. Details of a followup project are provided at the foot of this page.

This main page contains open access information about the project for anybody with an interest in the aubject. A restricted access area is also provided the use by the project partners only


Contents


Project summary

The standard procedures for prediction of thermal actions on steel/composite structures are defined in the structural Eurocodes. In addition, recent and current ECSC research programmes (NFSC1, NFSC2) address issues related to the performance of steel structures in natural fire conditions, with a view to the development and extension of the Eurocodes methodologies.

The modelling technique of computational fluid dynamics (CFD) is being extensively used in a range of engineering disciplines for simulation of fluid flow and heat transfer processes. In the past twenty years, CFD has found increasing application in fire modelling, and this has contributed to the establishment of the discipline of fire safety engineering. However, there has so far been no coordinated attempt to exploit the potential of the technique in prediction of thermal behaviour of boundary materials due to the effects of fire in buildings. This project sought to exploit CFD techniques in developing, validating and applying a comprehensive engineering methodology for prediction of thermal actions on steel and composite structures, and to contribute to the development of the fire-related Eurocodes.

Objectives

The objective of the project was to develop an engineering methodology, exploiting the advanced capabilities of computational fluid dynamics (CFD), for determining the thermal behaviour of structural elements in steel/composite-framed buildings. Specific objectives of the project are as follows:

  • To develop a verified CFD-based engineering methodology for simulating the thermal action on steel/composite structures,
  • To apply the methodology for evaluating the effect of fire loading, ventilation and compartment construction on the thermal action on steel/composite structures,
  • To identify the essential elements of the methodology developed and provide guidance on its 'correct' use, i.e. defining the range of applicability and the sensitivity to various input parameters,
  • To apply the model for the assessment of the calibration and sensitivity of empirical design parameters, such as the convective heat transfer coefficient and safety factors used in the design guides (cf. Eurocodes EC1 and EC3).
  • To contribute to the development of the design guides.


Project team

The project team members and contact details are listed below. The photo shows some members of the team at the kickoff meeting, standing in front of one of the test rigs being used in the NFSC2 programme at BRE's large building test facility.

 

Partner

Personnel

email

Address

BRE, FRS

Dr. Suresh KUMAR

Dr. Stephen WELCH

kumars @bre.co.uk

welchs @bre.co.uk

Building Research Establishment, Fire Research Station, Bucknalls Lane, Garston, Watford, WD25 9XX, UK

Cranfield University

Prof. J.B. MOSS

Dr. Philip RUBINI

j.b.moss @cranfield.ac.uk

p.a.rubini @cranfield.ac.uk

School of Mechanical Engineering, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, UK

VTT

Simo HOSTIKKA

simo.hostikka @vtt.fi

VTT Building Technology, Fire Technology, Kivimiehentie 4, P.O. Box 1803, FIN-02044 Espoo, Finland

AGB

Dr.-Ing. Ulrich MAX

Christian LEBEDA

umax.agb @t-online.de

christian.lebeda @tuwien.ac.ut

Arbeitsgemeinschaft Brandsicherheit AGB, Au in den Buchen 90, D-76646 Bruchsal, Germany

LABEIN

Martin OJANGUREN

Jon BARCO

martin @labein.es

jon.barco @labein.es

LABEIN Technological Centre, Cuesta de Olabeaga, 16, E-48013 Bilbao, Spain

ProfilARBED - Recherches

M. Louis-Guy CAJOT

M. Mike HALLER

lg.cajot @profilarbed.lu

mike.haller @profilarbed.lu

ProfilARBED - Recherches, 66, rue de Luxembourg, L-4009 Esch/Alzette, Luxembourg


Relevant tests under NFSC2 programme

The test results of the NFSC2 programme were used during the validation phase of the project. Some of the project partners had been intimately involved in the tests conducted under this programme.

For example, BRE staff installed additional instrumentation for measuring velocities and heat fluxes in the tests performed under NFSC2 at BRE's Cardington laboratory. These tests concerned fires in a 12m x 12m compartment, where the overall rate of heat release was of the order of 30-60 MW.

The following table summarises some information on these tests (updated 24/4/02):

Test number

1

2

3

4

5

6

7

8

Date of test

4.2.99

1.4.99

27.5.99

25.8.99

21.10.99

11.11.99

6.1.00

17.2.00 

Fire load type

W

W

W+P

W

W+P

W

W+P

W+P

Boundaries

I

HI

HI

HI

HI

I

I

I

Opening

F

F

F

F+B

F+B

F+B

F+B

F

Peak T_gas (C)

1120

1290

1330

1337

1347

1332

1273

1326

Peak T_steel (C)

-

-

-

-

1220

1301

1245

1196

Peak velocity (m/s)

10

12

16

-

n/a

-

-

-

Peak flux (kW/m2)

155

255

270

340

n/a

280

270

250

Key:

W = 100% wood

W+P = 80% wood, 20% plastic (by calorific value

I = compartment lining - insulating

HI = compartment lining - highly insulating

F = opening at the front only

F+B = openings at both front and back

 
As can be seen in the above table, peak measured temperatures exceeded 1300oC in five tests, this measurement being supported by the observation of total heat fluxes of up to 350 kW/m2 and velocities of over 15m/s.

These values are somewhat higher than those observed in typical full-scale compartment fire tests and can be attributed in part to the highly insulating walls, the inclusion of plastic in the fuel and the short residence times (due to high flow rates).

For illustrative purposes, photos from the ECSC NFSC2 test series are displayed below, showing the lighting of the fire (Test 7) and early growth phase of the fire (Test 1) respectively.


Results

A robust CFD-based engineering modelling methodology has been developed for evaluating thermal action on steel and composite structures. The methodology has been validated by using a systematic approach of progressive verification and validation, starting with simple fire scenarios and proceeding to more complex but practical scenarios. To ensure reliability and robustness of the methodology, every partner has contributed to the model verification and validation exercise and have managed to reproduce reasonably satisfactorily the results for each scenario. Some partners have used a selection of zone and CFD models for this purpose.

Illustrative results, comparing the model predictions with the Large Compartment fire test, are shown below:


Recommendations

Draft recommendations have been prepared covering the treatments of a range of relevant parameters in the simpler Eurocodes methodologies. The main parameters of interest are the convective heat transfer coefficient, the various emissivities, including both “fire” and “member” emissivities, the configuration factor, the effective radiative flux and the general form of the governing heat exchange equations which draw all of these factors together.

A further set of recommendations have been developed as draft “best practice” guidance for the engineering methodology developed within the current project. These extend to:

  • scope - area of application, e.g. localised fire, or post-flashover fire; requirements and applicability, e.g. domain size/computational limits/cell size/accuracy balance; transient versus pseudo “steady-state” and distributed burning;
  • fire/structural specific issues, such as smoke, high-temperature material properties, moisture/intumescence effects, ventilation control, fuel chemistry, etc.;
  • detailed guidance on the use of CFD codes from the practitioner’s point of view, covering the determination of conservative bounds on solutions (e.g. by assuming adiabatic boundaries), choice of physical models, numerical modelling issues, guidance on the modelling process as a procedure, including sensitivity studies etc., validation work and finally some relevant case studies, perhaps based on the validation test cases studied within the scope of the current research.

More details will be provided in due course once these are approved by the ECSC F6 committee.


TRA-EFCT Workshop

The fifth (and final) annual workshop of the "Targeted Research Action - Environmentally Friendly Construction Technologies" was held in Rimini, 11-12 October 2001 (
http://www.tra-efct.com/workshop). The following contributions were prepared for the workshop, since the current ECSC "NFSC3" project is classified under the TRA network in the "Steel cluster".

The technical contribution prepared for this meeting summarises most of the work done on the project up to that date [Word version; zipped poster].

The technical contribution prepared for the fourth annual workshop held in Prague, 11-12 October 2000 describes earlier work on the project [Word version; zipped poster].


Further work

A follow-up project is currently under negotiation with the Research Fund for Coal and Steel.

The overall objective of the proposed project is to develop an integrated engineering methodology for determining the structural performance of steel/composite-framed buildings in natural fires. The methodology will be both fundamental and comprehensive, exploiting the advanced capabilities of both computational fluid dynamics (CFD) for predicting the thermal behaviour and finite-element (FE) models for determining the mechanical response of the structure. Systematic validation of the methodology will be carried out considering test data from full-scale fire tests. The methodology will be applied to test cases and impact assessment undertaken. Design guidance will be developed as appropriate.

More detailed information on this new project will be posted here in due course.


They were initially set up by S.Welch at BRE, January 2000
Last updated July 2003
Copyright (c) BRE 2003