This document discusses structural fire safety in modern buildings. It provides a brief history of fire resistance testing and standards, noting that the concept was developed over 100 years ago in response to large fires. It then discusses emerging trends in modern building design, including taller timber buildings and structures with unusual features that may be sensitive to fire. The document advocates for a performance-based approach to structural fire engineering rather than solely relying on prescriptive standards. It summarizes a case study of a mixed-use building with an unusual structural frame where structural fire engineering was used at the design phase to explicitly define fire safety goals and model structural response to fires.

1. Structural fire safety & modern
buildings
Dr. Danny Hopkin CEng MIFireE
Head of Fire Engineering, Trenton Fire Ltd.

2. Overview
Fire resistance – A quick history lesson
Modern buildings – Where are we going?
Rising to the challenge
Designing at the interface
Questions

3. ‘Fire resistance’
A history lesson

4. FR – A need identified
Origins – 1900s (Gales, et al., Bisby & Maluk)
– Intended as a temporary practice correction after the
Baltimore and San Francisco conflagrations
– Flooding of market place with proclaimed ‘fire proof
materials’
– A lack of trust in ‘private testing’
– A need to independently benchmark performance

5. FR – A level playing field
Emergence of federal and municipal
testing laboratories
No ‘standardised’ test method/criteria
Ira Woolson – NFPA (1903) – A need
to:
– “unify all fire tests under one single
standard and remove an immense
amount of confusion within the fire testing
community”
The concept of fire resistance is born
The ‘test fire’ defined by anecdotal
evidence of NY FF

6. FR – 112 years on….
At the 1917 NFPA annual meeting, Woolson stated that; “we
want to get it as nearly right as possible before it is finally
adopted, because, after it is adopted by these various
associations, it will be pretty hard to change it”.

7. Structural fire resistance
Tests whether an isolated structural
element does not violate particular
performance criteria after a set
period of time in a furnace.
Deflection limit span/20
It cannot ever be a measure of
survivability in a real fire.
However, it hasn’t served us too
badly…

8. A divergence
Future trends

9. Where are we
going?
Into cities & up

10. Timber is on the rise

11. Emerging trends - UK
263 towers (>20
storeys) proposed in
London…
There will be features
that are ‘unusual’ or
sensitive to fire…
How will we approach
their design?

12. Accidental & variable load-cases
Wind – performance
based assessment
Seismic – performance
based assessment
Fire?............................

13. Fire – apathetically….
Solution – protect
all steel members to
a 120 minute
standard for a
limiting temperature
of X°C
Engineering…..Done!

14. The apathy part…

15. Rising to the challenge
Modern Buildings

16. What are we trying to achieve?
Legally – B3 – “stability for a reasonable period”
Holistically –
– Business continuity?
– Resilience?
– Insurability?
– Aesthetics?
Delivering a solution that meets aspirations, fulfils
obligations, in cognisance of the constraints

17. Fire safety
engineering
Failure at x°C
Structural
engineering
Temperature
Time
Failure at x°C
With thanks to G. Rein
(Imperial College)

18. Challenging the adequacy of the
‘magic numbers & golden rules’
Assessing the appropriateness of a prescriptive
solution
Where necessary delivering performance in
tangible terms:
– Explicit performance goals
– Defining what the fires might look like,
– Computing how hot the structure might get,
– Ensuring adequate structural performance
considering fire as a load case
Structural fire engineering

19. Something in common?
All considered unusual
(un-common)
SFE integral
More resilient
All have features
sensitive to fire that
prescriptive design
wouldn’t capture
Some more cost
effective than…

20. The right process, the right solution
Tabulated/prescriptive fire solutions are
not invalid, they’re just not a panacea,
The key questions:
– Do we only care about life safety?
– Can the fire be appropriately represented by a
furnace exposure?
– Can the structural response be adequately
represented by isolated element behaviour?
Answers direct the path to a solution…

21. Design at the interface
4 Pancras Square

22. The building
Not an especially tall building,
but unusual
10 storeys + roof garden
46m in height
Retail use at GF, office
elsewhere
Structural Cor-Ten frame
PT concrete floor slabs
Internal steel composite
columns

23. Key design challenges
An ‘architectural
structural frame’,
Inability to protect Cor-
Ten,
Key structural elements
were located outside the
fire compartment,
Limited international
experience – Cor-Ten
Discipline integration

24. Explicit definition of the goal
What is ‘acceptable’ performance?
– Building designed to withstand 97% of ‘real’ fires,
– A large proportion addressed by virtue of sprinkler
protection
– The remainder must be resisted by the passive
(structural system)
‘Scale’
Frequency
Consequence
‘Risk’

25. Defining the fires
Monte Carlo simulation (10,000 fires sampled)
Large compartments – a need to consider both
travelling and post-flashover fires
6 fires selected as a design basis that were at
least representative of the 97th percentile
confidence limit
Fire safety
engineering

26. Thermal exposure to Cor-Ten
Hand calculations
informed by EC1-1-2
CFD modelling
(FDS)
Aim – defining
temperatures and
thermal exposure for
‘external’ elements
0
200
400
600
800
1000
1200
0 30 60 90 120 150 180
AST(°C)
Time (min)
CFD results
Design methodology (solid)
Fire safety
engineering

27. Managing external member
temperatures
Finite element
analysis of
temperature
development
Thermal ‘load-
case’ for structural
analysis
Mitigation
measures 0
100
200
300
400
500
600
700
0 60 120 180 240 300
Temperature(°C)
Time (min)
Top flange
Web
Bottom Flange
Shielding Plate
Fire safety
engineering

28. Structural response
– performance limits & lessons
Aims
– Stability!
– Prevention of excessive deformation
– Materials stay within ‘ductile’ strain limits
Lessons
– Expansion governed
– Cooling phase critical
– Bigger is not always better
Displacement (m)
Structural
engineering

29. Fire safety
engineering
• Successfully define the fire fully
• Quantify exposure at the building perimeter
• Properly quantify structure temperatures
• Complete disregard for thermally induced stresses
• Interactions not captured
Structural
engineering
• Failure temperature of the structure can be defined….
• Some ‘system’ interaction, i.e. thermal expansion,
redistribution, etc.
• The fire is ill-defined, heat transfer poorly captured
• Sensitivity to cooling doesn’t manifest (critical!!!)

30. Thanks
Danny Hopkin
– 07894483449
– Danny.Hopkin@trentonfire.co.uk