23 February, 2010

Next Meeting

Tues 20 April 2010
10.30 for 11.00


at

The Institution of Structural Engineers
11 Upper Belgrave Street
London SW1X 8BH

Previous Meetings

Presentations
Attendance
Discussion Contributions
3 October 2000 
26
 
23 April 2001
24
 
12 September 2001
21
12 September 2001
9 April 2002
22
 
24 September 2002
29
 
1 April 2003
40
 
23 September 2003
30
 
31 March 2004
32
31 March 2004
21 September 2004
25
 
6 May 2005
39
 
20 September 2005
32
 
28 March 2006
38
30 March 2006  
5 September 2006
32
 
17 April 2007
45
 
25 September 2007
30
 
15 April 2008
34
 
16 September 2008
39
 
21 April 2009
29
 
22 September 2009
24
 

22 September 2009

Parametric studies on steel connections in a sub-frame structure exposed to fire
Ying Hu
University of Sheffield

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A connection element for modelling end-plate connections in fire
Zhaohui Huang
University of Sheffield

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Modelling the Mokrsko fire test, September 2008
Florian Block
Buro Happold FEDRA

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Full Scale Fire Test on a Post-tensioned Slab
Fergal Kelly
Peter Brett Associates

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Numerical Investigations of Spalling in Concrete Exposed to Fire
Colin Davie
University of Newcastle upon Tyne

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Acceptance criteria to be used for Finite Element Analysis of structural frames
Neal Butterworth
Buro Happold FEDRA

Testing and assessment of reactive coatings to European and British standards
David Wickham
International Paint
(Akzo Nobel)

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21 April 2009

Nature and benchmarks for numerical modelling of heated structures
Martin Gillie
University of Edinburgh

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Analytical investigation of beams under high thermal loading
Martin Stadler
Technische Universität München, Germany

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Concrete in fire – perceptions and realities?
John Dowling
Corus Group

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A timeline for a solution - boundaries and fire radiation
David Fletcher
NHBC

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FE modelling of steel connections in the heating and cooling phases
George Koutlas
Corus Group – Swinden Technology Centre

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Update on intumescent coating research
Yong Wang
University of Manchester

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Nonlinear FE Simulation of Steel Structures under Extreme Loadings
Mr Z W Gong
University of Swansea

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16 September 2008

Attendance 39. There were 7 oral presentations.

Material Behaviour of High Strength Grade 10.9 Bolts under Fire Conditions
Jörg Lange

TU Darmstadt, Germany

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Experimental investigation of the robustness of common steel connections at elevated temperatures
Hongxia Yu

University of Sheffield

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Structural fire behaviour of typical steel joint asemblies
Xianghe Dai
University of Manchester

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A New Component-Based Model for Flexible End Plate Connections
Ying Hu
University of Sheffield

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Characterising Intumescent Coating Performance for Real Fire Applications
Yong Wang

University of Manchester

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Non-Linear Finite Element Analysis of Steel and Composite Joints under Fire and Extreme Loadings
Feng Wang
University of Swansea

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The WTC7 Report – A Brief Summary of the NIST Press Conference, 21 August 2008
John Dowling
Corus Group

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15 April 2008

Attendance 34. There were 6 oral presentations.

Temperature Distribution in Intumescent Coating Protected Steel Connections in Fire
Xianghe Dai
University of Manchester

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Innovative Application of Advanced Structural Fire Analysis
Allan Jowsey, Linus Lim, Alexander Heise, Barbara Lane
Arup Fire

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Behaviour of Fin-Plate Connections to CFT Columns at Ambient and Elevated Temperatures Under Shear and Bending Load
Mark Jones
University of Manchester

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An Approach for Modelling Membrane Action
and
Fire Tests on Composite Slabs, Focusing on the Behaviour of Edge Beams
Martin Mensinger

TU München, Germany

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The FRACOF Composite Slab Fire Test – The Experiment, Predictions and Results
Anthony Abu
University of Sheffield

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Fire Tests and Practical Design Method on Restrained Steel Columns
Peijun Wang
Tongji University / University of Manchester

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25 September 2007

Attendance 30. There were 6 oral presentations.

GeniSTELA - A generalised engineering methodology for thermal analysis of protected steelwork
Hong Liang
University of Edinburgh

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Experimental study of flexible end plate connections at high temperatures
Ying Hu

University of Sheffield

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Fire tests on connections to concrete filled tubular columns
Yong Wang

University of Manchester

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Automated programme for the UK graphical analysis for intumescent coatings
Hans van de Weigert

International Fire Ltd

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An embedded model for localised failure in reinforced concrete slabs
Xinmeng Yu

University of Sheffield

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Design for tensile membrane action - Comparison of TSLAB and Vulcan
Roger Plank

University of Sheffield

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17 April 2007

Attendance 45. There were 6 oral presentations.

Flat Slab Performance in Accidental Fires
David Fletcher

NHBC

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Membrane Action of Concrete Floor Slabs at Ambient and Elevated Temperature
Bok Man Chan
University of Manchester
The concept of membrane action has been adopted to explain the ultimate load carrying capacity of floor slabs above the traditional yield-line load at ambient and elevated temperatures. However, the detailed distribution of membrane forces within the concrete and reinforcement components of the slab has not been fully investigated. This research project extends the investigation of membrane action in concrete slabs to fully understand the development of the internal forces. A finite element model has been developed to simulate horizontally unrestrained, isotropic reinforced, concrete slabs. Both shell elements and solid elements were used at ambient temperature and solid elements were used at elevated temperature to accurately represent the highly non-linear temperature distribution through the depth of the slab. The models have taken into account the smear crack concept with thermal, geometric and material nonlinearity. Two types of smooth bars, mild steel reinforcement and stainless-steel reinforcement, with different diameters and spacing of bars in rectangular and square slabs were simulated. The effect of the membrane action within the slabs due to different reinforcement ductility, reinforcement content and aspect ratio of the slab, were also investigated. Numerical results were validated against a number of small-scale slab tests carried out at the University of Manchester and were shown to provide very good predictions. It has been concluded that the distribution of the in-plane stress and through-depth stress of the slabs, subjected to large displacement at ambient temperature is similar to the slabs at elevated temperature. The magnitude is different due to the different applied load and weakening of the material due to elevated temperatures. Numerical studies show clearly the need to model the tension softening curve of the concrete with an accurate estimate of the fracture energy and maximum tensile strength. It is expected that the conclusion of this research project will be used for further development of design codes and guidance.

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Assessing the Safety of Tall Buildings in Multiple Floor Fires
David Lange, Charlotte Roben and Asif Usmani
University of Edinburgh
With increasing acceptance and use of performance based design methodologies, the question of the safety of tall buildings in a multiple floor fire will sooner or later need to be addressed. Particularly so in cases where the occurrence of such a scenario is deemed to have an unacceptably high probability. A simple stability assessment method for tall buildings subjected to multiple floor fires is proposed. This method would allow structural engineers to obtain an indication of the upper bound collapse mechanism for tall buildings in multiple floor fires without the need to use complex and labour-intensive computer models. It can also be used to provide bounds on the results of a more comprehensive computational analysis and aid the interpretation of the output, thus helping to avoid errors. This method is strictly only applicable to tall buildings which can be idealised as two dimensional frames. However as many tall buildings tend to be rather regular in plan, the method could be used quite generally, at least for preliminary assessment.

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Informal Update on the Eurocode NAs (including NCCI for EC1 as PD 6688-1-2)
Roger Pope
BCSA

Cooling Behaviour of Structures after a Fire
Martin Gillie
University of Edinburgh

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Experimental Investigation of Fin Plate Connection Behaviour at Elevated Temperatures
Hongxia Yu
University of Sheffield

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Modelling Intumescent Coating Behaviour in Fire
Jifeng Yuan
University of Manchester
This research aims to provide a robust scientific footing to model intumescent coating performance under various fire exposure conditions, to help develop fire engineering design methods suitable for application under different fire conditions. A mathematical model has been established to investigate the fire protection performance of intumescent coatings. In the model, once some basic chemical characteristics and physical properties of the intumescent coating has been quantified, the fire performance of this kind of intumescent coating exposed to different external heat conditions (Cone-calorimeter, standard fire, parametric fire, etc) can be determined. In the mathematical model, the governing equations are based on energy and mass conservation, and the model is solved by using the Finite Difference Method (FDM). Heat transfer, heat generation (from chemical reaction), and mass transfer (production of volatile gases and their movement) models form the basis of the model. Arrhenius equation is used to describe chemical kinetics of coating decomposition (typically including three parts: melting, blowing, and charring), which in turn is responsible for expansion. An important aspect of this research is to develop and examine a thermal conductivity model for the expanding porous intumescent coating foam, which should not only include pure conduction in air, but also radiation through the voids of the porous foam. The main objective of this research is to identify the main fundamental parameters that are responsible for describing the intumescence performance with sufficient accuracy under different fire conditions.

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5 September 2006

Attendance 32. There were 7 oral presentations.

Behaviour of Cellular Beams and Composite Slabs at Ambient and Elevated Temperatures
Siamak Bake Mohamadi
University of Manchester

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The Development of Finite Elements for 3D Structural Analysis in Fire
Chaoming Yu
University of Sheffield

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The Suitability of Fire-Field Modelling for Enclosure Fires involving Complex Solid Fuel Loads
Stuart Winter
University of Manchester
Research on the use of Computational Fluid Dynamics to model closed car-park and compartment fires is presented. The Fire-Field model FDS (Fire Dynamics Simulator) is used to simulate closed car-park fires and successful comparisons with simulations performed as part of the European Commission report on such fires are made. The car fire assumptions used in these simulations, and consequently the conclusions drawn from their output, are critically assessed. An alternative modelling approach for car fires in fire-field simulations is outlined by the author. The simulation of full-scale compartment fire tests using FDS is also considered and a model representing the important processes of wooden crib burning is presented. The practical application of such models is discussed.

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High Temperature Material Laws of High Strength (S460) Steel
Jörg Lange
TU Darmstadt

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3D Interpolation Method for the Determination of the Contribution of Intumescent Coatings to the Fire Resistance Performance of Structural Steelwork Protected with Intumescent Coatings
Hans van de Weijgert
International Fire Consultants

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Download article (PDF (547kb)

A Component-Based Connection Model for Steel Framed structures in Fire
Florian Block
Buro Happold

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Design Fires for Structural Fire Analysis - Approving Authority Status Quo
Samantha Foster
Arup Fire

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28 March 2006

Attendance 38. There were 6 oral presentations.

Technical Update on the Torre Windsor Fire, Madrid
Roger Pope
BCSA

(The slides contain currently restricted material, and cannot be downloaded yet.)

Connections of Unprotected Steel Members to Fire Walls
Alexander Heise
Arup Fire
It is common practice to design single storey warehouse or industrial structures for fire, with very limited or no fire protection. Structural failure of these forms of single storey buildings in a fire situation is tolerated, traditionally based on the low risk to the life safety of building occupants these structures are deemed to create. This originates from a typically limited occupancy with multiple means of escape, and as such a rapid evacuation time. However traditionally the risk to the life safety of fire fighters has not been considered in the design, and this is resulting increasingly in external and therefore limited fire fighting in these forms of structure. Therefore the concept of property protection and business continuity through protection of contents has become an increasingly important concept in design. It is then essential to maintain compartmentation within these large volume spaces in order to limit fire spread and resulting damage to the overall contents of the building and the extent of structure.

What this means is that the large fire walls provided to sub-divide these space, cannot be damaged when the unprotected steel structure fails. As a consequence, the unprotected steel structure is usually erected independently from the fire wall, preventing the use of the load bearing capacity of the fire wall in the structural design concept. This results in the need for additional columns and bracing. This paper presents an alternative concept to this standard approach allowing connections of unprotected steelwork to fire walls. Two different design concepts for these connections are presented, which prevent damage to the fire wall when unprotected steel members connected to the fire wall fail. These two design concepts can be combined enabling the designer to find the most cost effective solution for the connection.

The first option is a design concept based on maximum load bearing capacity of bolts. The maximum reaction forces limited by the load bearing capacity of bolts are calculated using design values for the upper limit of the load bearing capacity of the bolts. A complete design concept will be presented including combination values for additional loads and design values to determine the resistance of the fire wall in the fire situation. The statistical parameters of the bolts determined on the basis of 3000 tests collated from literature and bolt producers will be explained. The statistical parameters for additional loads and resistance will be described in detail. The design values for the maximum load bearing capacity of the bolts and the design resistance for the fire wall is determined using the FORM-Method. The determination of combination values considering additional loads in the fire situation using the Borghes-Castanheta method, will also be discussed.

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Modelling of a Fully Developed Natural Fire in a Large Compartment
Yulian Spasov
Corus Group - Swinden Technology Centre

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The Contribution of Intumescent Paint to the Fire Resistance of Structural Steelwork
Hans van de Weijgert
International Fire Consultants

Download paper describing the method (PDF 500kb).

Download presentation slides (PDF 165kb)

Fire Protection in High Rise Buildings - Are We Doing Enough?
Neal Butterworth
Buro Happold FEDRA

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Spalling of Concrete Elements in Fire
John Purkiss
University of Aston

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20 September 2005

Attendance 32. There were 4 oral presentations.

Finite Element Analysis of Concrete Filled Steel Columns in Fire
Jun Ding
University of Manchester
Concrete filled steel columns are widely used all over the world, due to their significant advantages in construction speed and high fire resistance. This paper presents the results of a finite element study to simulate the fire performance of concrete filled steel columns exposed to the standard fire condition. The current structural fire resistant design standards such as EC 4 Part 1.2 and BS 5950 Part 8 provide simplified and approximate methods to calculate the fire resistance of these members, but their range of application is limited and there is still a lot of uncertainty over their accuracy. Finite element analysis offers the possibility of accurately simulating the behaviour of this type of columns, including non-uniform temperature distributions and geometric and material non-linearity in fire. The objectives of this study are to validate the finite element simulations for both heat transfer and structural analyses, both being conducted using a general finite element analysis package ANSYS. The temperature distribution within a composite column cross section is analysed by using a 2- D model, while a 3-D model is used to simulate the structural behaviour of the column in fire. The results from the finite element analyses were compared with a number of fire test results and were found to agree well with the available test results. A numerical parametric study was carried out to investigate the sensitivity of simulation results to different assumptions with regard to the effect of initial displacement, meshing of the cross-section and concrete stress-strain relationship at elevated temperatures.

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The Behaviour of Fin Plate Steel Connections in Fire
Marwan Sarraj
University of Sheffield

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The Insurers' View
Dave Sibert
Fire Protection Association

The Madrid Fire 12/02/05
Paul Jenkins
London Fire Brigade

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6 May 2005

Attendance 39. There were 4 oral presentations.

Quantitative comparison of Fire Dynamics Simulator and parametric fire curves with compartment fire test data
Nicholas Pope

University of Manchester
This presentation gives a comparison of two parametric fire modelling techniques (Eurocode 1, and the BFD curve method) and one field model (Fire Dynamics Simulator) against large scale post-flashover test data. Using a method of the product moment correlation coefficient, it is shown that the BFD curve predictions are most closely representative of reality. For the computational test data, two grid resolutions are adopted in the FDS field model, the finer of which having comparable results in terms of regression analysis to the BFD method. Both the field model and the BFD curve method were found to give better predictions compared to the Eurocode method over the duration of the test. However, a direct comparison of the maximum gas temperatures shows the field model to be poorer in its predictive capability than the parametric methods, under-predicting the maximum gas temperatures. In addition, a more in-depth analysis of the FDS predictions indicates that by considering simply average compartment temperatures the more inaccurate spatially-specific temperature predictions were disguised. This study provides useful quantitative data on the three techniques presented and discusses more general issues concerning fire modelling.

Download presentation slides (PDF 430kb)

Analysis of reinforced concrete buildings In fire
Zhaohui Huang
University of Sheffield
A non-linear finite element, developed for three-dimensional modelling of beam-column elements of general cross-sections in fire conditions, will be described. Because of the changes in material properties and the large deflections experienced in fire, both geometric and material non-linearities are taken into account in this formulation. The cross-section of the beam-column is divided into a matrix of segments, and each segment may have different material, temperature and mechanical properties. The more complicated aspects of structural behaviour in fire conditions, such as thermal expansion, cracking or crushing of concrete, and progressive change of the constitutive properties of materials with temperature, are modelled. Since it is possible to offset their nodes by pre-determined distances the elements can easily be combined with shell or plate elements to model concrete floor systems in fire. A high-deflection numerical example using linear elastic material is presented to demonstrate the accuracy at high deflections of the elements. A full-scale standard fire test on a composite slim-floor beam has been modelled to show the capabilities of the element. Finally detailed 3D analyses of a reinforced concrete structure subject to standard fire conditions are carried out.

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Global effects of fire on long span, truss based floor systems used in multi-storey buildings
Graeme Flint
University of Edinburgh

Fire safety on board ships: Lessons from the past - systems for the future
Hans van de Weijgert

International Fire Consultants
Shipowners and shipyards, electrical engineers, naval architects and classification societies are all confronted with fire safety aspects of cable and pipe transits. Trouble free maintenance, low cost installation, lower overall costs, protection of human life and international regulations often turn out to be conflicting as it comes to fire safety. And what about fire safety during the construction process itself? The recent fire on board the Diamond Princess at a yard in Nagasaki shows that fire safety deserves attention throughout the lifetime of the ship – from the moment the ship's design is on the drawing-board right through till its final voyage.

This lecture focuses on the principles behind type approval certificates for fire safety devices such as cable and pipe transits. Based on these regulations and on the lessons we have learned from daily practice, new technologies and systems have been developed that fulfil the demands of all parties.

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21 September 2004

Attendance 25. There were 4 oral presentations.

Effects of Heating on Long Span Truss based Structures
Graeme Flint andAsif Usmani
University of Edinburgh

The ODPM Compartmentation Project
Tom Lennon
BRE

Download presentation slides (PDF 794kb)

Component Testing of Column Compression Zones at High Temperature
Florian Block
University of Sheffield

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An Experimental Study of the Compressive Performance of Structural Panels with Cold-Formed Thin-Walled Perforated Steel Channels
Bashar Salhab
University of Manchester

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31 March 2004

Attendance 32. There were 5 oral presentations.

Design of composite columns under high temperatures with special consideration of imperfections
Anja Urbach
TU Darmstadt
Composite columns use the insulation properties of the concrete to reach high fire resistance without additional fire proofing. The design of these columns for a fire is influenced by the imperfections due to uneven distribution of thermal stresses and geometric inaccuracies.

The first problem is to find the temperature distribution over the cross section, assuming that this distribution is constant over the columns length. This can be calculated with normal FEM software.

Based on the exact material laws for steel and concrete under temperatures up to 1000 degrees Celsius the second step is made. By variation of the curvature and the strain of the centre line, incorporating the material laws and adding the thermally induced stresses the interaction between moment, curvature and normal force is calculated.

The axial buckling load is defined as the intersection point of the strain dependent Euler buckling load calculated with the tangent modulus of the stress-strain relationship and the course of the resistance to axial compression of the total cross section against the strain.

The calculation of the moment-curvature relationship gives also the stiffness distribution over the column length which will allow calculating the column’s collapse load by a second-order analysis including geometrical imperfections.

The calculations are based on the advanced calculation models of the Eurocode 4 Part 1-2

Download presentation slides (PDF 1.0Mb)

Tensile membrane action of thin, lightly reinforced concrete floor slabs under large deflection and at elevated temperatures
Samantha Foster
University of Sheffield

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Numerical simulation of composite floor slabs under fire condition
Can Tesar
ETH Zurich
In-plane forces in reinforced concrete slabs are caused by large deflections. Under fire condition this membrane action increases the load-carrying capacity of composite floor slabs dramatically. A tailor-made finite element program \textit{SlabFem} is being developed to
investigate the structural behavior and the load-carrying-mechanism of heated composite floor slabs. The basic concepts of the program - including the material laws and the elements models - are shown. The numerical modeling of the shear connection between beam and slab elements is presented in detail.

The seventh Cardington full-scale fire test on the composite frame
Tom Lennon
BRE

Performance-based structural fire engineering design - a sceptic's view
David Fletcher
NHBC

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23 September 2003

Attendance 30. There were 7 oral presentations.

Fire Resistant Design Criteria of Tall Building Structures
Y C Wang

Manchester Centre for Civil and Construction Engineering

This paper argues that the structural fire resistant design criteria of tall building structures should be considered differently from those embedded in the current design philosophy where only stability of the structure in fire is considered. The potential repairability issue should be addressed at the design stage by conducting a potential risk assessment. This risk assessment may determine the acceptable extent of fire damage to a tall building that the fire resistant design team should aim to achieve.

Download presentation slides (PDF 1.6Mb)

Analysis of Catenary Action in Steel Beams Under Fire Cocnditions
Yingzhi Yin
Manchester Centre for Civil and Construction Engineering

This presentation investigates the large deflection behaviour of a steel beam under fire conditions taking into consideration the effect of the catenary action provided by the surrounding structures. After validating the capability of ABAQUS against available experimental results of fire tests, a numerical parametric study is conducted with parameters investigated including beam span, load ratio, uniform and non-uniform temperature distributions, different levels of axial and rotational restraint at the beam ends and the effect of lateral torsional buckling on axially restrained beams. It is concluded that the existence of horizontal axial restraint can significantly affect a beam's survival temperature in fire. The development of catenary action in a steel beam at large deflection can help the beam to hang to the surrounding structure and prevent the runaway deflection. Clearly, fire engineering design will need to consider the effect of axial forces in the beam on the adjacent structure. A simplified hand calculation method is then developed to model the beam behaviour at elevated temperatures, which may be adopted as a design calculation method. The proposed method can be used to predict the mid-span deflection and the catenary force of a heated steel beam, which are the main concerns of steel structure fire engineering design.

Download presentation slides (PDF 1.1Mb)

CFD Modelling of Large Compartment Fires
Nicholas Pope
Manchester Centre for Civil and Construction Engineering

The modelling of compartment fires has, over the last twenty years, evolved from simple hand calculations to zone models, and now to field models. The basis of field models is the area of physics called computational fluid dynamics (CFD). Much of the validation work done on such complex models has often been confined to the analysis of plumes or small scale fires. The major reason for this is in testing on the small scale the input parameters and output measurements are able to be measured relatively accurately. Using the large scale test facilities at Cardington, large scale compartment fire data was analysed using the Fire Dynamics Simulator - a Large Eddy Simulation CFD package developed at NIST in USA. The results of this large scale testing were compared directly with the equivalent results predicted by the CFD model. These predictions need to be understood in terms of the limitations and approximations applied not only by the user but by the underlying physics of the model itself.

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Fire Resistance: Implications for Regulations and Standards of the September 11 Terrorist Attacks on the World Trade Center
Tom Lennon
BRE
Following the initial shock, horror and outrage at the nature and scale of the attack on the twin towers on the 11th September 2001, thoughts have turned to ways in which such an event can be prevented in the future, or, if this is not possible, on ways in which the consequences of such an event can be minimised. For engineers the complete collapse of the twin towers and the manner of the collapse has led to much reflection on the nature and purpose of the design and regulatory process. The balance between risk and consequence is one that all designers consider either explicitly through a risk assessment process or implicitly through interpretation of the regulations and design codes and standards. The nature of the terrorist attack where the building was subjected to firstly a large impact force followed, almost immediately, by the combustion of many tons of highly flammable aviation fuel is not a normal design situation. However, the consequences of failure of the twin towers or of any tall building accommodating large numbers of occupants in a crowded urban environment are such that complete collapse should be avoided under all conceivable design scenarios. If this is not possible then the building should survive for a period sufficient to evacuate all building occupants and those in the immediate vicinity. This paper will consider the concept of fire performance and fire resistance in terms of traditional prescriptive fire design and in relation to performance based fire engineering design. Results from a series of full scale fire tests carried out on real buildings at BRE's whole building test facility will be used to look at the effectiveness of fire engineering design methods.

Download presentation slides (1. PDF 0.7Mb) (2. PDF 2.5Mb)

Risk-based Approaches in Fire Safety Engineering
Craig English
WSP Group

a) Absolute risk in fire (comparison of failure probability in fire with that for accidental loads at ambient temperature).

b) Comparative risk. Comparison of performance of design alternatives with code compliant solutions.

c) Correlating evacuation times with structural failure times.

A New Approach to Specifying Fire Resistance Requirements for Regulatory Purposes
Brian Kirby
Corus Group

Application of a new limit state design method to the Cardington tests
Neil Cameron

University of Edinburgh

A new method for the design of concrete slabs has recently been developed at the University of Edinburgh and presented at a previous STIFF meeting. The method has been used to analyse four of the six Cardington fire tests. In comparison with the experimental results the theoretical results agree well. They show that in three of the four tests there was considerable spare load carrying capacity.

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1 April 2003

Attendance about 40. There were 4 oral presentations, plus a General Discussion session.


24 September 2002

Attendance 29. There were 5 oral presentations, plus a General Discussion session.

Utilising academic research in consultancy: a case study
Barbara Lane & Susan Lamont
Arup Fire
The presentation will address the collaboration between academia (Edinburgh University) and consultancy (Arup) and the resulting benefits to the construction industry. Brief details of the collaboration will be provided. A detailed summary of recent project work carried out at Arup relying on this collaboration will be developed. The non-linear analysis of composite-steel frame construction for specific projects will be addressed. The assumptions made when developing the building model, plus some results and consultation will also be presented for discussion. A way forward for progressing the integration of such complex analysis with practical design but particularly in the context of the approvals process will be suggested. The intent being to initiate some debate as to a sensible means of developing quality design solutions based on complex analysis but in a way that a quality review by the local authorities can take place. The main aim being to enhance the reputation of the fire engineering profession.

Behaviour of Restrained Columns in Fire
Yong Wang

Manchester Centre for Civil and Construction Engineering
University of Manchester
A restrained column, forming part of a complete structure, can have many types of structural interaction with the adjacent structure. As a result, the loading and boundary conditions of the restrained column in fire will be different from those at ambient temperature. At present, only Eurocodes offer a limited amount of design guidance on the effective length of continuous columns in fire. The objectives of this research, supported by the EPSRC, are to provide experimental information to evaluate how bending moments and effective lengths of restrained steel and concrete filled columns change under fire conditions. In total, 34 fire tests, including 18 tests on restrained steel columns and 16 tests on restrained concrete filled columns, have been carried out. Parameters investigated include type of beam to column connection, level of column axial load and amount of initial column bending moment. The results of this investigation suggest that for fire limit state design, the design bending moment of a restrained column may be taken as that caused by the reactions of the connected beams acting eccentrically. The results of this study also validates the design recommendation on steel column effective length in Eurocode 3 Part 1.2. For concrete filled composite steel and concrete columns, the design recommendation on column effective length in Eurocode 4 Part 1.2 is acceptable if there is no local buckling in the steel tube. However, if local buckling occurs, the position of local buckling should be considered as a pin. Further research is necessary to determine when and where local buckling occurs.

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Behaviour of Pre-cast Hollow-Core Slabs in Fire
Tom Lennon

BRE
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A New Method to Estimate the Ultimate Load Capacity of Composite Floors in Fire
Neil Cameron
University of Edinburgh
A new method for determining the ultimate load capacity of composite floors systems in multi-storey building fires is presented. Collapses of composite frame buildings in fire are an extremely rare event therefore the manner of structural failure is not well understood. One of the main contributions to the robust performance of such structures is due to the tensile membrane mechanism in the composite deck slab. The research group at Edinburgh has discovered that the development of tensile membrane mechanism in fire is much more reliable relative to ambient conditions. This is because a large amount of thermal strain allows composite floor systems to assume highly deflected shapes while limiting the magnitude of damaging tensile mechanical strains, thereby retaining the ability to carry loads for much longer. If the load capacity available through the tensile membrane mechanism could be reliably quantified, then it may not be necessary to apply protection to all beams leading to significant cost savings.

Component-Based Steel Connection Model
Ian Burgess
University of Sheffield
This presentation reports on the experimental furnace testing and development of simple analytical models intended to initiate the development of a Component Method for modelling of steel beam-to-column connections in fire conditions. The main objective was to investigate the behaviour of tension and compression zones of end-plate connections at elevated temperatures. A series of experiments was carried out. Simplified analytical models of the component behaviour have been developed, and validated against the tests and detailed finite element simulations. The simplified models seem very reliable for this very common type of joint. The component models developed have produced moment-rotation curves which correlate well with the results of previous furnace tests on complete connection behaviour in fire. The principles of the Component Method can be used directly in either simplified or finite element modelling, without attempting to predict of the overall joint behaviour in fire. This will enable semi-rigid behaviour to be taken into account in the analytical fire engineering design of steel-framed buildings, for which it is inadequate simply to consider the degradation of the ambient-temperature moment-rotation characteristics of a joint without taking account of the high axial forces which also occur.

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9 April 2002

Attendance 22. There was one oral presentation, plus a General Discussion session.

On the application field of OZone V2
Jean-François Cadorin
Université de Liège
The computer code OZone V2 has been developed to help engineers in designing structural elements submitted to compartment fires. The code is based on several recent developments, in compartment fire modelling on one hand and on the effect of localised fires on structures on the other hand. It includes a single compartment fire model that combines a two-zone model and a one zone model. It takes into account the localised effect of a fire on a structural element with the help of the Hasemi's model. It is thus a pre- and post-flashover model. It calculates the temperature of a steel section submitted to that compartment fire and, finally, evaluates the fire resistance of simple steel elements, according to EC3.

The methodology implemented in the tool OZone V2 is first briefly presented. Some important sub-models are also described (combustion model, wall model).

Some limitations of the zone model approach are first quoted and some improvements made in OZone are explained.

Comparisons of the code with full-scale fire tests are then presented. These comparisons enable to find some limits to the application field of the code. A particular emphasis will be given on large openings and on burning rates.

Download Ozone Report 2002-003 (PDF438kb)

OZone is available from http://www.ulg.ac.be/matstruc/en/index.html

General Discussion : Collapse of the World Trade Center Towers

The following abstract was sent by Ali Nadjai of The University of Ulster, who was unfortunately unable to be present on the day:

Ali Nadjai
University of Ulster

The structure integrity of the World Trade Center depends on the closely spaced columns around the perimeter. Lightweight steel trusses span between the central elevator core and the perimeter columns on each floor. These trusses support the concrete slab of each floor and tie the perimeter columns to the core, preventing the columns from buckling outwards.

The buildings survived the impact of a plane, although a significant number of perimeter columns on several floors of the building were completely destroyed, but failed under fire. The high temperature fires from burning aviation fuel and plane debris softened the steel core of the structure. Eventually, the loss of strength and stiffness of the materials resulting from the fire combined with the initial impact have caused the collapse of the towers.

Codes and their supervision need urgent investigation and updating, for the safety of all those who live and work in tall buildings, both here and around the world.

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12 September 2001

Attendance 21. There were 3 oral presentations, plus one extra contribution during the Discussion session.

Update on Codes and Standards
Roger Pope
BCSA
A review of the current situation on development of codes and standards relevant to steel construction in fire.

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A Comparison of Structural Behaviour in Response to a Short-Hot Fire and a Long-Cooler Fire: Part II
Susan Lamont
University of Edinburgh
At the last STIFF meeting we presented the differences in structural behaviour of a small generic composite steel frame in response to two fires. This highlighted a new phenomenon in the primary beam of the frame, which could not be explained adequately at the time. The initial behaviour was as expected with axial compressions developing in all beams as the heating regime progressed and beams expanded against supports. However in both fire scenarios, but at two different temperatures, there was a sudden sharp reduction in compression in the primary beams accompanied by a sharp increase in deflection of the composite floor. This phenomenon was not noted in the modelling of any of the Cardington tests. This presentation will describe this behaviour further and attempt to explain the reasons behind this apparent `instability' and its effect on the surrounding structure.

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A Simplified Model of Heated Steel Beams at Large Deflection
Ahmed Allam
Arup Fire
This presentation introduces a simplified model for a heated steel beam at large deflection taking into consideration the effect of the catenary action provided by the surrounding cold structure. This model can be used to predict the mid-span deflection, and the tensile axial force induced by catenary action, of a heated steel beam. This tensile axial force at large deflection can lead to integrity failure, and consequent fire spread, if sufficient strength and ductility are not designed into key elements such as beams and connections. However, provided that this can be done in particular cases, then it may be possible to prove much greater real fire resistance than is estimated by the simple calculation methods currently used. The study highlights the effect of the axial horizontal restraint which can be provided by the surrounding cold steel frame on the behaviour of the heated beam at large deflection. However for heated steel beams in steel construction catenary action, which may help the beam to hang to the surrounding structure, can prevent the runaway deflection when the tensile axial force of the beam has been overcome. The prime objective of this study is to study computationally and analytically how different levels of restraint from surrounding structure, via catenary action in beams, can affect the survival of steel framed structures in fire.

Mechanical Properties of Grade 8.8 Bolts at Elevated Temperatures
Buick Davison
University of Sheffield

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23 April 2001

Attendance 24. There were 4 oral presentations.

Rotationally Restrained Steel Columns in Fire
Faris Ali
University of Ulster
The presentation discusses the outcomes of the experimental investigation on the performance of rotationally restrained steel columns in fire. Half scale steel columns (within steel frames) where tested in fire under two values of rotational restraint 0.18 and 0.93. Each case of rotational restraint was tested under four loading levels 0.2, 0.4, 0.6 and 0.8. The presentation discusses the test methodology and the main results and compares the results with a case of axially only restrained columns in fire. A method of calculating the effective length of fixed end columns is also discussed.

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Behaviour of Steel Beam-to-Column Joints: Test Results of the Compression Zone at Elevated Temperatures
Spyros Spyrou
University of Sheffield
This presentation is an update on a test program being carried out at the University of Sheffield, which investigates the behaviour of steel beam-to-column joints at elevated temperatures and seeks to use the component approach to model the overall structural response. The behaviour of the compression zone is under investigation and a comparison of the experimental results with a simplified mathematical model is presented.

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Theoretical Approach for Concrete Masonry Walls Subjected to Fire
Ali Nadjai
University of Ulster
Use of theoretically based methods has gathered momentum in the last two decades, especially with the advances in computer technology. Computing power enables detailed evaluation of a dynamic transient process. The aim is to generate the fire process and develop a representative computer model. With sound knowledge of material properties and the effects of temperature, then computer models are capable of recreating the effects of material degradation and subsequent thermo-structural response. Analysis can be very complex and specialised, and designers may be unable to understand the intricacies of tools such as finite element. Unless thermal effects on material properties are thoroughly understood then computer models will be flawed. For example before Anderberg [1] no one understood the significant influence of transient strain on concrete response, theoretical models prior to this time therefore did not truly represent total strain response. Even today there is still very limited data available on material property response with temperature. One must also understand the effects of interaction of various parameters. The simultaneous combined effects of load and temperature acting in concrete specimens produce significantly different response than the additive effects applied separately.

This paper describes the development of one such approach, a mathematical model to predict the deflection response of axially loaded concrete masonry walls in fire situations. To validate the theoretical model a comprehensive suite of experimental tests was conducted on walls of varying slenderness ratio and different load. The methodology used for the experimental testing was unique in that ½ scale walls were used, requiring an enhanced fire curve to generate thermal similitude in model and prototype. The theoretical model considers internal equilibrium of axial forces and moments and generates an equivalent linear strain and associated strain gradient (curvature) from total strains through the wall cross section. The effect of load and load eccentricity are incorporated by computing linear stress distribution though the section using conventional structural mechanics. The combined effects of temperature and stress are considered at discrete points through the wall and are integrated through the section to compute the resultant wall curvature and subsequent deflection. The model under pins the significant influence of Load Induced Thermal Strain (LITS) on deflection response.

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A Comparison of Structural Behaviour in Response to a Well-Ventilated and an Under-Ventilated Fire
Susan Lamont
University of Edinburgh
During fires in highly redundant composite steel framed buildings the structural behaviour is dominated by the thermal regime. This has been highlighted in numerous publications by researchers in recent years (Huang et al 1999, Rotter et al 1999, Usmani et al, 2001).

This presentation describes the impact of a well-ventilated fire and an under-ventilated fire on a generic composite steel frame building. Well-ventilated fires will reach high temperatures but the duration of the post-flashover phase will be short. In contrast under-ventilated fires will achieve much lower maximum temperatures but the duration of the post-flashover phase will be notably longer.

When exposed to these fires the structure will respond in two distinct ways both thermally and structurally. During the well-ventilated fire the unprotected steel reaches temperatures similar to the fire atmosphere. The lightweight concrete because of its much lower thermal conductivity and the short fire exposure reaches temperatures only marginally higher than at ambient. Thus a high gradient exists over the depth of the composite section. In contrast the under-ventilated fire (extended post-flashover duration) allows the concrete slab much longer to respond to the heating regime. In this second scenario both the steel and the concrete achieve considerable temperatures and the mean overall temperature of the composite section is high. Therefore, we have two distinct situations, one in which there is a high gradient leading to structural performance influenced by thermal bowing and a second scenario where the mean temperature of the composite section is high and the behaviour of the structure is dominated by thermal expansion effects.

This presentation looks at a composite generic steel frame designed to comply with EC4 Part 1.1. Petterson’s (1976) temperature-time curves are adopted to describe the two fires. Heat transfer to the concrete and protected edge beams is calculated using the adaptive finite element heat transfer code HADAPT (Usmani and Huang 1994, Lamont et al 2000) and unprotected steel temperatures are calculated using the appropriate equations in EC3 Part 1.2.

The behaviour of the frame is analysed during a well ventilated and an under ventilated fire and the key features of response are highlighted. Some preliminary conclusions are made about the most detrimental heating regime.

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3 October 2000

Attendance 26. There were 7 oral presentations.

Modelling of the Cardington Demonstration Fire Test using ABAQUS/Explicit
David O'Callaghan
Corus STC
This presentation covers some of the modelling issues and incorporates some of the understanding gained from previous tests to carry out a simulation of the office fire demonstration test. This test differed somewhat from previous tests and included such differences as heated edge beams, a two-bay fire compartment and different fire loading. Results are presented from a number of simulations with various modelling assumptions, with each showing differences in behaviour.

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Testing of Restrained Columns in Fire
Beilei Hu
University of Manchester
The presentation will address an experimental programme for restrained columns in fire, which is funded by EPSRC. It involves the types and dimensions of tested specimens, physical modelling of boundary conditions and the details of the furnace. It will also discuss the possible numerical modelling which will be carried out at a later stage of the project based on the experimental studies.

Natural Fire Safety Concept: Full Scale Tests, Implementation in the Eurocodes, and Development of a User-friendly Design Tool
Tom Lennon
BRE, Garston
The purpose of this presentation is to summarise BRE's role in an ongoing research programme to develop a new concept for design based on natural fire behaviour. The object of the research is to move away from a reliance on the standard fire curve to a more rational approach taking into account all the influences on fire growth and development. The project is due to finish shortly. This is the second phase of a European collaborative project funded by the ECSC. The global approach to fire safety was formulated in the first phase (NFSC1) and a one-zone model (OZONE) was developed to predict fire behaviour and heat transfer to structural members. However, no tests were carried out during this first phase to validate the design approach. BRE's role was to carry out a series of large-scale tests to look at post-flashover behaviour. Complementary experimental programmes were carried out by other partners to investigate localised fire behaviour and the reliability of active measures (sprinklers). The output from the research will be a validated model for predicting compartment fire behaviour, and the implementation of the results into the Eurocodes.

Modelling Studies of the Cardington BS Corner Test
Martin Gillie
University of Edinburgh

The Influence of Surrounding Cool Structure on the Behaviour of Composite Buildings in Fire
Zhaohui Huang
University of Sheffield
Of the six large-scale fire tests carried out on the full-scale composite building at BRE Cardington, the Restrained Beam Test was subject to very high restraint from the surrounding cool structure, while the BRE Large Compartment Test was subject to no restraint at all. Comparing these two tests it can be found that the influence of surrounding cool structure on the structural behaviour of the fire compartment is important and should be investigated in more detail. Because the cost of such tests is very high it is becoming increasingly important to have analytical methods which can predict the behaviour of structures when subjected to fire conditions. In this paper a typical composite steel framed building is set up using VULCAN and a series of analyses are carried out based on several locations of fire compartment, in order to get a better understanding of the interactions between cool and hot structure. A number of different fire scenarios, for example the Standard Fire and typical natural fires, are applied. The results are compared with Eurocode 4 limits, and some conclusions on current fire engineering design codes for composite structure are highlighted.

Investigation of Tensile Membrane Action in Composite Slabs in Fire Using a Grillage Analogy
Ahmed Allam
University of Sheffield
It has become apparent recently that the ultimate survival of composite framed buildings in fire is to a large extent controlled by the ability of the concrete slabs covering the fire compartment to sustain their loading when acting as tensile membranes at very high deflections. These occur when temperatures are very high, so that exposed steelwork has lost almost all of its strength. The membrane action is a geometrically non-linear behaviour whose exact nature depends on the supporting conditions which can be maintained around the boundaries of the fire compartment, and on the in-plane restraint imposed by surrounding structure. In the development of design principles based on the ultimate maintenance of compartmentation against fire spread it is important that this form of structural action, and its modelling, should be fully understood, so that it can be designed-in to buildings as part of an integrated fire engineering design approach. The simplest level is to model the slab as a beam grillage using non-linear beam elements. Initially, simply supported and fixed-edge slabs are studied. This is extended to heated slabs with different levels of horizontal restraint stiffness from adjacent structure, and to multi-bay slab systems. Finally a comparison is made of these simplified grillage systems and high-deflection slab behaviour.

Behaviour of Steel Beam-to-Column Joints: Test Results of the Tension Zone at Elevated Temperatures
Spyros Spyrou
University of Sheffield
This presentation is an update on a test program being carried out at the University of Sheffield, which investigates the behaviour of steel beam-to-column joints at elevated temperatures. Using the image acquisition and processing technique a total of twenty-five tests, within the tension zone, and a comparison with a simplified mathematical model will be presented.

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