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Interflam 2016 - Design at the interface

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A structural fire engineering strategy for an expressed Cor-Ten frame

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Interflam 2016 - Design at the interface

  1. 1. Design at the interface A structural fire engineering strategy for an expressed Cor-Ten frame Dr. Danny Hopkin – Associate Director
  2. 2. Scope • What interfaces? And why? • Our project; • The challenges we faced; • The lessons we learned; & • Convention.
  3. 3. Fire safety engineering Structural engineering Structural fire engineering The interfaces What? Who? How? An interface between disciplines The interfaces between facets of competence
  4. 4. 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 Competence – A prerequisite for success
  5. 5. 4 Pancras Square For an industrial buildingAn industrial site
  6. 6. The building • A 10 storey office – 46 m in height; • Predominantly a concrete frame – cast insitu & PT; • Architectural feature – external Cor-Ten frame; • A huge Cor-Ten transfer structure; • Tricky interfaces.
  7. 7. A successful solution A melange of competing goals, obligations & constraints, of varying intelligibility
  8. 8. The life safety goal • "Stability for a reasonable period"; • Consistency of risk – Kirby, et. al; • Overall reliability requirement of 97%; • Active reliability contribution of 93%; • Passive reliability requirement of 49%; • All 50% have the potential to fully develop. 0 20 40 60 80 100 0 50 100 150 200 Fractile(%) Height (m)
  9. 9. Fire manifestation 0% 20% 40% 60% 80% 100% 220-230 310-320 370-380 430-440 490-500 550-560 610-620 670-680 730-740 790-800 850-860 910-920 970-980 1070-1080 1260-1270 Percentile(-) Peak steel temperature (°C)
  10. 10. Thermal conditions • A lack of guidance – Law & O’Brien – SOA; • Steady state analysis – overly conservative; • A need to quantify transient behaviour; • Consider the impact of wind; • Quantifying thermal gradients, etc., key.
  11. 11. Thermal conditions Side 1 Side 2 Rear Front A 0.75 0.75 0.96 0.41 B 0.67 0.67 0.95 0.40 C 0.86 0.86 0.98 0.57 0.00 0.20 0.40 0.60 0.80 1.00 Relativeproportionofcompartment temperature(-) Elevation of element 0 200 400 600 800 1000 1200 0 30 60 90 120 150 180 210AST(°C) Time (min) Fire Compartment Sides Rear Front - BS EN 1991-1-2 Annex B as a ‘scalar’ - Benchmarked against CFD models - Adequately conservative. Element orientation influences exposure:
  12. 12. • Location ‘manages’ exposure; • Sections still very hot; • Concrete filling, where practicable; • Shielding, where permissible; & • Otherwise, plate sizing. Fire Floor Floor Above 120 mins 180 mins 240 mins Managing temperature
  13. 13. Materials – Cor-Ten • Cor-Ten is not a typical material; • The scale of the section is not typical; Peak Temperature (°C) Yield Strength Reduction (MPa) Residual Yield Strength (MPa) 700 30 325 800 60 295 900 90 265
  14. 14. Structural response • Two key areas: • Vierendeel transfer; & • Columns • Other complications: • Connections; • PT; • Bi-metallic corrosion & PFP.
  15. 15. Vierendeel behaviour -4000 -3000 -2000 -1000 0 1000 2000 3000 0 5000 10000 15000 20000 Axialforce(kN) Time (s) • Expansion governed; • Very sensitive to TFs; • Doesn’t deflect excessively; • Plastic strain  tension; • A building that needs to ‘breathe’; • Matching ‘actual’ vs. ‘idealised’.
  16. 16. Column behaviour • Concrete filling; • Explored rebar vs. T; • T more ‘buildable’; • UC 254x127x84 (S355); • Actions influenced by curvature & slab ‘push-out’; • Sensitivity to vertical fire spread explored; -150% -100% -50% 0% 50% 100% 150% 0 30 60 90 120 150 180 InnerTeeUtilisation(%) Time (min) BF WEB_C TF MAX Min
  17. 17. Lessons & key points • Struct. Eng. understood their responsibility & limits; • “Stability for a reasonable period” not FR120 + sprinklers; • They understood the expertise req’d & delegated; • Those responsible for delivery were involved in design. • Quantification of the goal -> rational basis -> rational process; • Thermal tools are inadequate for external exposure; • Cor-Ten does not behave like regular carbon steel; • Bigger is not always better; • A need to be pragmatic about what you can’t fully quantify.
  18. 18. Design by convention
  19. 19. Skill & care • Successful fire engineering doesn’t end when a report is issued….
  20. 20. Acknowledgements • Co authors – D. Illingworth, E. O’Loughlin, B.McColl & S. Anastasov; • Design team – Eric Parry Associates, BAM, Grontmij • Client – Argent; & • AHJ – Camden LABC, London FB and BRE (reviewer).
  21. 21. Thanks for your time "If you always do what you've always done, you'll always get what you've always got.“ - H. Ford • Danny.Hopkin@trentonfire.co.uk • http://uk.linkedin.com/in/dannyjhopkin • https://twitter.com/DannyHopkin • http://www.slideshare.net/DannyHopkin

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