BYL Rainham CPD - Structural Design for Fire Safety - Nov 15
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Dr. Danny Hopkin is the head of fire engineering at Trenton Fire Ltd, a fire and risk consultancy firm. He has a background in structural engineering and fire safety. In this presentation, he discusses the history and development of fire resistance standards and testing. He then talks about modern building trends, challenges with performance-based fire engineering, and the importance of competence and multidisciplinary collaboration in fire safety design. As an example, he summarizes the fire safety design process for a complex building with unusual structural and fire safety considerations.
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BYL Rainham CPD - Structural Design for Fire Safety - Nov 15
- 1. Dr. Danny Hopkin CEng MIFireE MIMechE PMSFPE Head of Fire Engineering Trenton Fire Ltd.
- 2. Who am I? Struct. Eng. graduate, Joined the BRE (2007-2011), Doctorate “Fire resistance of engineered timber”, Chartered Fire/Mech Engineer, Fire engineering nerd: – Chair IFE FR SIG, IStructE FESG – Member BSI B/525/5 & FSH/24 Lead a team of 12 FEs across 2 offices
- 3. Trenton Fire Ltd Fire & risk consultancy, Specialist & independent, Facilitators and not barriers to successful design; – Code consulting, – Advanced performance based design. Committed to making sure our design’s are implemented as intended; – Engagement with main contractors – Site visits, etc. Award winners
- 4. Overview Fire resistance – A quick history lesson Modern buildings – Where are we going? Rising to the challenge – Competency – Success – Engineering Designing at the interface Questions
- 5. ‘Fire resistance’ A history lesson
- 6. 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
- 7. 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
- 8. 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”.
- 9. 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… Key question – will this continue?
- 11. Where are we going? Into cities & up
- 12. Timber is on the rise
- 13. Sustainability
- 14. 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?
- 15. Accidental & variable load-cases Wind – performance based assessment Seismic – performance based assessment Fire?............................
- 16. Lame substitutions* Fire safety engineering Structural engineering Structural design for fire safety * Credit Dr. Guillermo Rein (Imperial College)
- 17. Lame substitution of the 1st kind Structural engineer is replaced by pseudo-science Fire safety engineering Failure at x°C
- 18. Lame substitution of the 2nd kind Fire engineer is replaced by pseudo-science Structural engineering Temperature Time Failure at x mins
- 19. Lame substitution of the 3rd kind Both engineers are replaced by pseudo-science Temperature Time Failure at x°C
- 20. Fire – apathetically…. Solution – protect all steel members to a 120 minute standard for a limiting temperature of X°C Engineering…..Done!
- 21. “intended to provide guidance for the more common building situations…” Prescriptive FR – a health warning “need to take into account the particular circumstances of the individual building…”
- 22. Progress - reviewing what is built vs. tolerability of performance achieved The path to contemporary guidance
- 23. The apathy part…
- 24. Rising to the challenge Modern Buildings
- 25. Competence Low-rise buildings Medium-rise High-rise or complex structures A competent builder? A structural engineer? Specialist structural engineering input? Structural fire safety?
- 26. Requirements for success* What? Who? How? Regulations Responsibility Skill & Care *Credit: Neal Butterworth
- 27. Challenges
- 28. Challenges
- 29. Successful FR design Defining goals (Regulation & aspirations) Assessing the appropriateness of a prescriptive solution & delegation of responsibility Skill to deliver performance in tangible terms: – Quantifying the design goals, – Defining what the fires might look like, – Computing how hot the structure might get, – Ensuring adequate structural performance in fire Care to ensure that the designer’s intentions are achieved in practice
- 30. 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…
- 31. Design at the interface 4 Pancras Square
- 32. 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
- 33. 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
- 34. Competency revisited… Regulations Responsibility Skill & Care Structural engineers understood they were responsible for ensuring “stability for a reasonable period” in fire Those responsible for construction were engaged at an early stage and became familiar with the requirements Design team understood that the fire performance demands were beyond their competency & delegated
- 35. 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 passive (structural system) contributions ‘Scale’ Frequency Consequence ‘Risk’ Outcome – building designed to resist fires equivalent to 60 minutes of furnace exposure (or 60 minutes of fire resistance)…
- 36. Defining the fires 6 fires selected as a design basis that were at least representative of the 97th percentile confidence limit Fires were ‘realistic’ not pseudo representations Fire safety engineering
- 37. Thermal exposure to Cor-Ten 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
- 38. Managing external member temperatures 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
- 39. Structural response – performance limits & lessons Aims – Stability! – Prevention of excessive deformation Lessons – Expansion governed – Cooling phase critical – Bigger is not always better Displacement (m) Structural engineering
- 40. 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!!!)
- 41. Care…
- 42. Thanks – Questions? Danny Hopkin – 07894483449 – Danny.Hopkin@trentonfire.co.uk – http://uk.linkedin.com/in/dannyjhopkin – https://twitter.com/DannyHopkin – http://www.slideshare.net/DannyHopkin
Editor's Notes
- To introduce the idea of how structures can be designed better to resist fire, there is a need to understand where we’ve come from, what we do and what approaches purport to deliver… We can begin to see how current approaches become increasingly challenging to apply in the modern world… Need to begin to think about how we evolve our thinking to cater for increasingly complex buildings, in terms of minimum levels of competency, requirements for successful design, etc. Then I will run through a brief case study & answer some questions…
- We’ve heard the history of how the concept of materialised and why? It should also now be clearer as to what it actually delivers and how this might begin to diverge from current ambitions…
- We build more with timber, the ambition is to build higher with timber…. Murray Grove in London at 10 storeys used to be the world’s tallest timber frame building. Soon the world’s first 40 storey timber building will be complete.
- Achieving a sustainable building is a key goal for most clients. This means influencing material choices and their thermal performance, which all impact upon fire development and fire performance…
- Structural fire resistance is delivered at the interface of two disciplines. Perhaps the best articulation of how we will approach the design of these future challenging buildings is that of the lame substitutions proposed by Dr. Guillermo Rein at imperial college, London. Designing at the interface is tough, as it requires two disciplines to work together.
- For a moment I shall wear my fire engineer’s hat, and you will be the proxy of the structural engineer. I’ve no interest in understanding your structure, so instead I dilute the problem, first from a complex structure to a single element and then, in lieu of trying to understanding this element, I’ll assign a temperature at which I consider it might fail.
- Next, I will wear my structural engineers hat and you shall be the proxy of the fire engineers. Again, I’ve not interest in understanding your discipline, fires are complicate, so I will dilute all of the possible manifestations of a fire and massage them into a single time-temperature curve….the standard fire curve.
- Then there is the 3rd kind, where both parties are replaced by pseudo-science. Where neither the structure’s performance or the fire’s characteristics are represented in any realistic form. This, unfortunately, is what some might suggest is representative of how fire resistance is dealt with…
- If we follow the path of the progression of our guidance, we see that disasters shape its evolution, not science. In their current manifestation, ADB, etc., are an example of a series of rules born out of surveys of buildings considered to be adequately safe.
- If we are to try and do things better, we need to look at: competency – specifically, competency that is commensurate with the complexity of the project… What it means to deliver a successful design in the context of structural fire safety… Delivering solutions at the interface of two disciplines that traditionally don’t work well together…
- First, lets consider competence. More specifically, who might be competent to do what? If we draw analogies with structural engineering…. We are all likely comfortable placing our trust in the experience of a competent builder in the delivery of a house, We are likely to accept we need specialist input, say a structural engineer, when the project gets more complex, As we get more complex, specialist specialists are likely to be required? People with seismic expertise for instance. Structural design for fire safety? We might appoint a fire engineer – but what does the fire resistance section of the strategy say?
- In terms of delivering a successful design, on the face of it, it’s really quite simple. You need to have three things. Firstly a clear definition of what it is that needs to be achieved, secondly making someone responsible for achieving it, and finally the knowledge and know how to achieve it.
- We have everything we need to be successful,… good clear regulations, an industry with the skill & ability, clear responsibility for decisions… The challenges are at the interfaces…
- In the case of structural design for fire safety…
- In summary, successful design hinges on having the right people, with the right level of competency undertaking the right tasks. As an industry, we have everything in place to do this….and it is done better than any other country in the world.