Nursery Cyclone Presentation June 2013

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A summarised presentation of a study conducted by Cam Leitch and Shane Holborn for the Queensland Australia nursery industry investigating damage from cyclones (hurricanes) and high wind events.

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Nursery Cyclone Presentation June 2013

  1. 1. Cam Leitch Shane Holborn Designing structures to manage high wind loads
  2. 2. Presentation summary • Background to the project • Cyclones • Designing to withstand extreme wind • Risk levels and wind speed • Cyclone Yasi – overview of field data and observations • Critical factors for structural performance • Recommended good practice details
  3. 3. Mission is to: • Conduct quality research and testingConduct quality research and testing (Leads to(Leads to better materials andbetter materials and building practices)building practices) • Community education –a research & community educationCommunity education –a research & community education program to improve the resilience of housing to severe winds.program to improve the resilience of housing to severe winds. • Damage Investigations following severe wind events –Damage Investigations following severe wind events – essential to investigate both undamaged buildings thatessential to investigate both undamaged buildings that performed well, buildings that suffered damage (how & why?)performed well, buildings that suffered damage (how & why?) and to see if measures are needed for improvements orand to see if measures are needed for improvements or changes to construction details.changes to construction details. Vision - ToVision - To minimise loss and suffering as a result ofminimise loss and suffering as a result of severe wind eventssevere wind events Cyclone Testing Station – James Cook Uni
  4. 4. • Static or cyclic loadingStatic or cyclic loading ofof roofing, wall cladding,roofing, wall cladding, structural elements, joints, complete structuresstructural elements, joints, complete structures • UUplift, racking, flexure, pressure,plift, racking, flexure, pressure, wind drivenwind driven debrisdebris impactimpact • Wind tunnel studiesWind tunnel studies • Risk assessmentRisk assessment Testing and consulting for industry; Cyclone Testing Station
  5. 5. Previous Cyclones in Queensland (Winifred 1986)
  6. 6. Cyclone Larry – 2006
  7. 7. • Larry made landfall close to Innisfail on 20 March 2006 • Just prior to landfall, reported asJust prior to landfall, reported as a Category 5 by BoMa Category 5 by BoM • Wind gusts reaching 240 kilometres per hour • Traveling W –NW at ~ 30 kphTraveling W –NW at ~ 30 kph • Estimted $1.5 billion damage. • The costliest tropical cyclone to ever impact Australia surpassing Cyclone Tracy (1974). Cyclone Larry - 2006
  8. 8. Cyclone Ului - 2010 •Fluctuated in intensity •Weakened to category 2 before regaining category 3 strength. •21st March crossed the outlying Whitsunday Islands and made landfall at Airlie Beach, Queensland. •Damage $20 million and agricultural losses reached A$60 million.
  9. 9. Cyclone Yasi - 2011
  10. 10. •Made landfall in northern Queensland, Australia in the early hours of 3 February, 2011, causing severe damage to affected areas •The eye crossed the coastline at Mission Beach just before midnight and passed over Tully soon after. •The storm caused an estimated US$3.6 billion in damage, making it the costliest tropical cyclone to hit Australia on record Cyclone Yasi - 2011
  11. 11. Wind speed estimated from numerical models, street sign data and the occasional Anemometer 5 1 0 1 5 1 5 1 5 2 0 2 0 2 0 2 0 2 0 2 5 2 5 2 5 3 0 3 0 3 0 3 5 3 5 3 5 4 0 4 0 4 5 4 5 5 0 5 0 5 5 6 0 6 5 7 0 7 5 C a i r n s C a r d w e l l T o w n s v i l l e C l u m p P o i n t J e t t y L u c i n d a a i r n s A M O I n g h a m T o w n s v i l l e A M O G r e e n I s C a i r n s A P A I M S O R P H E U S I S F l y i n g F i s h P o i n t E t t y B a y W o n g a l i n g B e a c h S o u t h M i s s i o n B e a c h T u l l y H e a d s S o u t h J o h n s t o n e B a b i n d a I n n i s f a i l M o u r i l y a n K u r r i m i n e B e a c h B i n g i l B a y E l A r i s h S i l k w o o d T u l l y M o u r i l y a n H a r b o u r C o w l e y B e a c h M i s s i o n B e a c h B r a m s t o n B e a c h M i r r i w i n n i G o r d o n v a l e Recording wind speed in tropical cyclones
  12. 12. • Max upper bound gust speed ~240 km/h ~67 m/s • Design wind speed houses 250 km/h ~ 69 m/s • Max upper bound gust ~95% design speed Cardwell, Tully Heads, South Mission Beach • Max upper bound gust ~85% design speed Tully, Kurrimine Beach • Low Cat 4 wind speeds (mainland) - issue with what the affected community thinks went through – complacency in builders and home owners for possible future events Yasi – Estimated Wind Speeds
  13. 13. The Gap ‘Super Cell’ Brisbane 2008 More frequent, intense events - climate change predictions…..? Not just cyclones Townsville mini-tornado 2012
  14. 14. Nursery structures particularly susceptible
  15. 15. Designing to resist extreme wind events
  16. 16. AS/NZS1170.2-2011 Wind regions Region C 69 m/sRegion C 69 m/s Region A 45 m/sRegion A 45 m/s Region D 88 m/sRegion D 88 m/s Region B 57 m/sRegion B 57 m/s Regional Wind SpeedsRegional Wind Speeds
  17. 17. Tropical cyclone categories CycloneCyclone CategoryCategory Maximum Gust SpeedMaximum Gust Speed CentralCentral PressurePressure (hPa)(hPa) Damage PotentialDamage Potential (m/s)(m/s) (km/h)(km/h) 1 25 – 3525 – 35 90 – 12590 – 125 >990>990 Negligible house damageNegligible house damage 22 35 – 4735 – 47 125 – 170125 – 170 970970 –– 985985 Minor house damageMinor house damage 33 4747 –– 6363 170170 –– 225225 950950 –– 965965 Some roof & structural damageSome roof & structural damage 44 63 – 7863 – 78 6969 225 – 280225 – 280 250250 930930 –– 945945 Significant roof and structuralSignificant roof and structural damagedamage 5 >78>78 >280>280 <925<925 Extremely dangerous withExtremely dangerous with widespread destructionwidespread destruction Region C Design Wind Speed in open terrain at 10m height for “standard” structures (houses)
  18. 18. Critical Wind Loading Parameters Modify this wind speed to account for the following: 1. Topographic Effects (Wind speeds-up on hills) 2. Height of Structure (Taller structures have higher wind speeds) 3. Shielding by other buildings or terrain (normally trees are not counted, as the leaves are assumed to be stripped in a severe cyclone. However, at lower wind speeds, trees can act as a wind break). on hills increasing over the ocean in the suburbs near the coast decreasing on hills increasing over the ocean in the suburbs near the coast decreasing
  19. 19. Designing to Resist Wind Events Design Wind Action < Actual Capacity of the Structure •Design Wind Action - Pressures (and forces) applied depends on the actual wind speed of the cyclone that impacts the – NO control over this •Actual Capacity of Structure - The structure should be designed to resist a selected “Design Wind Speed”. This is chosen so the risk of this design wind speed being exceeded is relatively low – We choose (VD) to manage the risk of failure •Design wind speed means the design gust wind speed for the area where the building is located, calculated in accordance with AS/NZS
  20. 20. Risk Levels and Wind Speed The probability (risk) of having a cyclone with at least a certain wind speed reduces as the wind speed increases. Wind engineers specify the risk of occurrence in any one year as being the “Annual Probability of Exceedance”, expressed as a ratio (e.g. 1:250, equiv to 1/250 or 0.4%) The risk of a cyclone occurring in each year is independent of what happened the year(s) before. A structure that will be used for a longer time (ie a larger Design Life), will have an increased risk of exposure to being impacted by a cyclone with at least the selected design wind speed, over the longer time frame.
  21. 21. Risk Levels for Different Design Life from AS/NZS1170.0 (2002) Design Working Life Importance Level Annual Probability of Exceedance for Wind Design Cyclonic Non- Cyclonic Less than 6 months 1 1/250 1/25 2 1/250 1/100 5 Years 1 1/250 1/25 2 1/250 1/250 25 Years 1 1/250 1/50 2 1/250 1/250 50 Years 1 1/250 1/100 2 1/500 1/500
  22. 22. Importance Levels for Different Structures Consequence s of Failure Description Importanc e Level Comment Low Low consequence for loss of human life, or small or moderate economic, social or environmental consequences 1 Minor structures (failure not likely to endanger human life) Ordinary Medium consequence for loss of human life, or considerable economic, social or environmental consequences 2 Normal structures and structures not falling into other levels High High consequence for loss of human life, or very great economic, social or environmental consequences 3 Major structures (affecting crowds) 4 Post-disaster structures (post-disaster functions or dangerous activities) from AS/NZS1170.0 (2002)
  23. 23. Yasi Damage to Nursery Structures Loss of covers to Igloos
  24. 24. Yasi Damage to Nursery Structures Shade house footing damage
  25. 25. Yasi Damage to Nursery Structures Destroyed potting shed and shade house damage
  26. 26. Yasi Damage to Nursery Structures Unrepaired damage remains in an almost totally devastated business
  27. 27. Review of Field Practice Cable Guyed Structures View of a typical cable-guyed structure
  28. 28. Shade cloth blown off cables after TC Yasi Review of Field Practice Cable Guyed Structures
  29. 29. Cable Guyed Structures Recommended plans and bay sizes/dimensions
  30. 30. Cable to Column Top Details Cable Guyed Structures
  31. 31. Horizontal cables clamped to round bar welded to top of interior column Cable Guyed Structures External column
  32. 32. Cable Guyed Structures - footings Footing failures to a Cable Guyed Structure Some general points about foundations: •Each type of footing for a particular structure should be purpose designed (do not copy footing sizes from other areas where factors such as the design loads and soil type are likely to be different). •In general terms, footings in sand will usually be larger than those in clay. •The sides of footings should be close to vertical, wherever feasible. •Extend the tops of footings at least 75 mm above finished ground level and provide a slope to the top surface.
  33. 33. Footing NOT extended far enough above ground Cable Guyed Structures - footings
  34. 34. Cable Guyed Structures - footings Horizontal cables clamped to round bar welded to top of interior column
  35. 35. Cable-guyed structure with winder to roll up cloth Review of Field Practice Cable Guyed Structure with roll-back cloth
  36. 36. Review of Field Practice Cantilever Post Structures General view of cantilever post structure, fitted with top rails
  37. 37. Cantilever Post Structures Details for typical cantilever post structure
  38. 38. Install extra bolt to pipe clamp Cantilever Post Structures
  39. 39. Review of Field Practice Temporary Structures Temporary- Low Cost Structure
  40. 40. Bent columns to cantilever post structure Review of Field Practice Cantilever Post Structures
  41. 41. Review of Field Practice Hoop or Igloo Structures Hoop and “Igloo” structures
  42. 42. Damaged structures Review of Field Practice Hoop or Igloo Structures
  43. 43. Hoop Structures Hoop Structures
  44. 44. oop Structures – Avoid Mullion Failure Good Practice to use a bolt through clamps to end mullions
  45. 45. Igloo Structures Typical “Igloo” Structure
  46. 46. End Wall and Roof Bracing to Typical “Igloo” Structure Good Practice to use Roof Bracing to provide support at the top of every Mullion (End Wall Column) Top of Mullion should be supported by Roof Bracing Igloo Structures
  47. 47. Roof Bracing – Should support Mullions Diagonal pipe wall brace Diagonal pipe wall brace Crossed tension wire bracing Crossed tension wire bracing Top of Mullion NOT supported Good Practice to provide support to top of mullions Igloo Structures - Provide Support to Mullions
  48. 48. loo Structures – Struts to Roof Bracing Buckling to struts between structural frames Struts between frames failed by buckling
  49. 49. Critical wind loading factor for shade houses Choice of shade cloth
  50. 50. Choice of Shade Cloth •Shade cloth normally chosen for its “Shade Factor” •However wind load on cloth controlled by its porosity. •Some evidence that wind uplift (load perpendicular to the surface) is significantly reduced on porous cloth •Anecdotal evidence suggests that shade cloth of no more than 30% shade appeared to fare better in severe wind events.
  51. 51. Critical Factor for Shade houses Choice of Shade Cloth 70% and 30% shade cloth
  52. 52. 16mm Quad Net cloth Critical Factor for Shade houses Choice of Shade Cloth
  53. 53. Recommended Good Practice Details Clips to Shade Cloth Clips - connect cloth to support cables Good Practice to provide adequate connections from cloth to support wires
  54. 54. Critical Factors for Performance 1.Design - select an appropriate Design Wind Speed (usually set by regulation) and commission an engineer to perform a structural design to ensure that all of the members and connections can withstand the calculated wind loads 2.Construction quality and detailing - build the structure to comply with the design 3.Regular inspection and maintenance - set up regular inspection and maintenance schedules for structures. 4.Planning and preparation of your response well prior to an event The wind finds the weakest link
  55. 55. • Building resilience – long term factors to consider for your business • Notes for new nurseries – design, layout and construction • Before the cyclone – how to prepare in advance of a cyclone or storm • During the cyclone – what to do during the event • After the cyclone – what to do directly after • After the disaster checklist – a tool to assist in the assessment of damage for insurance purposes • Contacts and resources – a list of references for further information and specialist support • Emergency contacts card – which you can fill in and give to your staff. Extension pack
  56. 56. •Develop plans to prepare, respond and recover from disasters whether they be storms, cyclones, floods •Think about your property its layout and individual considerations like location and topography •Make sure everyone knows the plan and their role within it •Allow for the significant value of the plants to be protected by the structure •Think about broader disruptions – no power or water •Talk to your insurer – know what is and is not covered Building resilience

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