danny hopkin research engineer - redbook · danny hopkin - fire performance of engineered timber...
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Fire performance of engineered timberDanny HopkinResearch Engineer
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Content
• What is engineered timber? Why use it?• Research drivers
– Why are we interested in E.T.?• DCLG- Fire performance of SIPs
– What is a SIP?• Summary• Forward look
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What is engineered timber?• Any form of timber element not formed from
a continuous solid piece of wood.– Categories:
• Light timber (UK)• Large section (Scandinavia)
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Examples?
• Light timber frame:– Engineered floor joists/studs– Structural Insulated Panels (SIPs)
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Examples?
• Large section timber:– CLT – LVL– Glulam
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Why use it?
• Structural drivers:– Less defects– Less material for equivalent stiffness
• Construction drivers:– Easier to work with– Less time on site– Prefab = Less skilled labour
• Environmental drivers:– Less waste– Better thermal performance
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Why are we interested?• Research drivers:
– Redundancy = Fire Resistance (FR)• Excess material is a good thing• Removing material reduces inherent FR
– Improved thermal performance means:• Introduction of combustible insulation• Different fire dynamics• Mechanisms for fire spread
– Structural integrity• Type of failure (predictable? sudden?)
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The outcome
• 2 year CLG funded research project into the fire performance of SIPs and engineered floors.
• 7 full scale natural fire experiments• 20+ laboratory fire tests• Development of numerical models (thermal
& structural)
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STRUCTURAL INSULATED PANELS
(DCLG) The performance in fire of
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What is a SIP?
• Prefabricated lightweight units• Used as a principal load bearing element
– External & internal walls– Roofs– Floors (rarely)
• Sandwich construction comprising two structural veneers bonded to a light weight insulating core
70 to 250 mmFace layers
Insulated core
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What is a SIP? (2)
• SIPs currently approved for use up to 4 storeys in the UK (limited by FR)
• Can be viewed as a single structural element or an entire system
• Typically residential applications • Increased use in commercial applications
i.e. hotels, schools, offices. • Can be used as infill panels on multi-storey
framed structures.
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What is a SIP? (3)• SIPs assembled on site to form volumes• In the UK SIPs almost exclusively OSB PUR/PS
composites• Traditionally adopted with an engineered timber floor plate
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Project objectives• To determine how SIPs & EFJs fail when
exposed to a ‘realistic’ fire scenario.– 60 mins FR ≠ 60 min survivability in a real
fire• Hypotheses:
– (a) SIPs- combustible veneer & combustible core forming a structural composite……………..Not good!
– (b) EFJs- less redundant material…….sudden brittle collapse
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Objectives contd…
• Typical SIP system could not be defined by a single large scale fire test so we did 4!
• Target to represent multi-occupancy vs. single dwellings and EPS vs. PUR insulants
• Overarching objective- establish how the system fails.
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What did we do?
• 4 x full scale fire tests on SIP buildings– F1- 60 min EPS building– F2- 30 min EPS building– F3- 60 min PUR building– F4- 30 min PUR building– All with I section joist floors
• FR 30- Designed to fail• FR 60- Designed to survive burnout• How? Fire severity designed as 60 min equiv.
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EPS
PUR
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What did we do? (2)• Additional 3x full scale natural fire tests on
engineered floors– (J1) Traditional solid floor– (J2) I joist floor– (J3) Truss steel web floor
• Comparative performance
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The fires:
• 7 experiments conducted between Jan and Dec 2009
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What did we find out? (F1-F3)• Buildings survived burnout* without
collapse.• Passive fire protection stayed in place for
the duration of the experiment• Nominal deflection of the floor plate• But some interesting ‘post experiment
findings’*Fire brigade intervened after 80ish min to
accelerate cooling
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F1 and F3• Outcome generally positive but….
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What did we find out? (F2-F4)
• Mismatch between PFP spec and fire design….failures.
• Imminent floor collapses in both cases (terminated to save instruments etc)
• Extensive damage to wall panels and involvement of insulation
• Identification of system redundancy which prevented major collapse
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F2 & F4
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Summary of findingsEngineered floors:
– fail in a more sudden and brittle manner than ‘traditional’ joist floors
– have little inherent fire resistance. What does exist is afforded by the membrane mechanism whereby joists are tied together via MDF sheathing
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Summary of findings (SIPs)• Where PFP is appropriately specified and
installed: no failures and compartment is capable of surviving burnout without collapse or significant deformation (subject to exemplary workmanship)
• Where thermo-plastic insulants are used i.e. PS, significant damage/loss of composite action can occur as a result of heat transfer through internal linings without direct exposure
• However collapse didn’t occur due to redundancy i.e. alternative load paths through timber ring beams, corner studs and intermediate timber studs.
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SIPs…• Without studs whole building collapse would
have occurred.
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Concerns of stakeholders- myths and facts
Engineered floors fail in a more brittle/catastrophic manner than solid timberPotential for unseen fire spread (more pronounced in PUR panels)Potential for re-ignition after FRS intervention.
x SIP structures are not robust (they are if solid timber is present)
x Increased fire spread due to service penetrations (insufficient oxygen present)
x Pool fires as a result of melted EPS (low volume of polymer present)
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Forward look• Timber is here to stay• Buildings will get higher• Detailing and workmanship becomes more critical• Potential for site fires to become more common• Solutions?
– Invest in research– Promote performance based design
• The standard fire test is only a yard stick.• What about real fires?• What about system interactions?• Buildings in fire fail at interfaces.
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Thanks for your time
• Danny Hopkin MEng AIFireE– [email protected]– +441923664662– http://www.lboro.ac.uk/cice/people/engine
ers/90.html