www.jcu.edu.au/cts
Building performance in Cyclones
•Wind loading •Historical poor performance of houses •Seminal change in house design criteria •Building Code of Australia and Standards •Building failures during wind storms
•Tropical Cyclone Yasi •Estimate wind speeds •Damage survey •Wind damage •Performance of older housing •Storm surge damage to housing •Recommendations
David Henderson Cyclone Testing Station, James Cook University
www.jcu.edu.au/cts
Darwin - Cyclone Tracy
• Peak gust estimated 70 m/s (250 km/h Cat 4 event)
• Over 70% of houses suffered severe damage
• Some suburbs; 90% of houses destroyed
• In comparison, engineered structures performed well
www.jcu.edu.au/cts
• Traditional process – evolved from holding roof up not tying it down
• Many elements, closely spaced
• There is load sharing
• So no easily defined Load path
• They are where we shelter – so have to be secure
Why Houses – common but complex
www.jcu.edu.au/cts
Late 70’s - New building regulations
For the housing industry
•Regulations took the form of deemed to comply solutions
•Nominate member sizes and joint details
•But based on simple analysis and testing of elements
www.jcu.edu.au/cts
Need to know…
• Are they going to be safe?
The later question asked was
• Are they too safe? (i.e. too expensive)
www.jcu.edu.au/cts
• Wind tunnel tests • Loading various building
products from screws right up to whole houses
• Damage investigations • Vulnerability models
We do this by:
Load Cycles
Pd
2.0 x Pd
10200 0
TR440 (1170.2) for Qld and WA
www.jcu.edu.au/cts
Wind load distribution
Wind
Large suction at windward edge
Suction pressure on roof
Suction pressure on lee wall
Positive pressure on wall
www.jcu.edu.au/cts
(real) Wind load distribution
Pressure tap measurements at approx 400 locations on the roof of the UWO gable roofed test house.
www.jcu.edu.au/cts
Wind load distribution
Wind
Large suction at windward edge
Suction pressure on roof
Suction pressure on lee wall
Positive pressure on wall
Internal positive pressures acting in concert with external forces
Housing design standard AS4055 requires for cyclonic regions C and D, that a dominant opening is assumed in the design.
www.jcu.edu.au/cts
The Station’s work, along with people from CSIRO, Industry research labs and other Universities have all resulted in a Wealth of Standards and guides for designing and building houses to resist wind loads
Australian Building Standards:
• AS1170.2 Wind loads
• AS4055 Wind loads on housing
• AS1562.1 Design and installation of metal cladding
• HB132 “Handbook on retrofitting older housing”
• AS1684 Timber Framing
• (and lots more)
Manufacturer Literature:
• Lots of Design Manuals for framing, block work, roofing, windows, etc
www.jcu.edu.au/cts
• Safeguard people from injury caused by structural failure,
• Safeguard people from loss of amenity caused by structural behaviour,
• Protect other property from physical damage caused by structural failure, and
• Safeguard people from injury that may be caused by failure of, or impact with, glazing.
Building Code of Australia: Structural objectives
www.jcu.edu.au/cts
Cyclone track – Spaghetti diagram
BCA: Class 2 Importance level (house?)
1:500 Annual probability of exceedence
or
10% in 50 yrs prob of exceedence
www.jcu.edu.au/cts 13/35
AS1170.2-2002 Wind load standard
69 m/s (250 km/h)
45 m/s
87 m/s (300 km/h)
57 m/s
www.jcu.edu.au/cts
Cyclone Larry – domestic construction
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Thunderstorm – Northern NSW
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• Are our design standards appropriate?
• Was the design criteria (wind speed) exceeded?
• Correct implementation of design criteria?
• Appropriate materials?
• Adequate construction quality?
Why failures?
www.jcu.edu.au/cts
Cyclone Yasi – effects on Buildings
www.jcu.edu.au/cts
Tropical Cyclone Categories (Not the same as the Saffir-Simpson scale used in North America)
Cyclone
Category Gust Wind Speed
(10 m height in open terrain)
1 < 125 km/h < 35 m/s
2 125 – 170 km/h 35 - 47 m/s
3 170 – 225 km/h 47 - 63 m/s
4 225 – 280 km/h 63 - 78 m/s
5 > 280 km/h > 78 m/s
www.jcu.edu.au/cts
www.jcu.edu.au/cts
Wind speed estimated from numerical models, street sign data and the occasional Anemometer
5
1
0
1 5
15
1
5
20
20
20
2
0
2
0
25
25
2
5
30
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
• TC Yasi Double Holland Wind Model by Bruce Harper (GHD/SEA)
• Using AWS-calibrated parameters supplied by Lou Mason (UTAS/AMC)
• All winds are “over-water” without any terrain or topographic effects.
Recording wind speeds in Tropical cyclones
www.jcu.edu.au/cts
Estimated wind speeds
• Max gust speed estimated at 240 km/h
• (Design wind speed houses 250 km/h)
• Max gust ~95% design speed Cardwell, Tully Heads, South Mission Beach
• Max gust ~85% design speed Tully, Kurrimine Beach
Potential for complacency in community and industry
Cat 4 wind speeds (mainland)
www.jcu.edu.au/cts
Street Survey - Three category Damage Index
No Roof (R) Openings (O) Walls (W)
0 None none none
1 Gutters downpipes debris not pierced debris not pierced
2 Debris damage to roof debris pierced debris pierced
3 lifted < 10% windows/doors leaked Carport /verandah damage
4 lost roofing < 50% Windward broken < 30% One wall panel fallen
5 lost battens < 50% frames lost < 30% > 1 wall panels fallen
6 lost battens > 50% Windward broken 30%-70% racking damage, cladding attached
7 lost battens > 50% and lifted
rafters
Windward broken > 70% racking damage and lost cladding
8 lost battens > 50% and
damaged tie-down
Windward broken > 70% and suction
loss
only small rooms intact
9 lost roof structure > 50%
including ceiling
100% broken / missing no walls remaining
www.jcu.edu.au/cts
Damage Data
Post 80s (current construction) • <3% major roof damage • ~30% all roller doors damaged • But many houses had water ingress
Pre 80s (older housing) • >12% major roof damage • ~2% damaged by large debris • May have hidden damage
www.jcu.edu.au/cts
Post-80s housing (current construction)
www.jcu.edu.au/cts
Pre-80s houses
www.jcu.edu.au/cts
Improving future for Pre-80s housing
• Roof space inspections should be undertaken to look for partial or hidden failures of connections within the roof.
(not just intensity/peak of event but also duration)
• Tie-downs up to date – Whenever roof is off – look deeper / every 10 years?
• General information on upgrading structural performance in existing houses can be found in Standards Australia Handbook HB 132.2.
www.jcu.edu.au/cts
Maintenance of all buildings
• Regular structural maintenance
• Looking for corrosion, rot, UV degradation, etc – Applies to all housing (not just old)
– Whenever roof is off – look deeper: every 10 yrs?
– Check condition of connections, main members
– Replace/Update where necessary
www.jcu.edu.au/cts
Loss of secret-fixed cladding and pierced fixed cladding Poor installation
Roof Cladding
Screws not
correctly fixed
into timber purlin
Screw spacing
greater than
manufacturer
requirements
www.jcu.edu.au/cts
Roof tiles
• Fixing of ridge and part tiles
• Anchorage for C3, C4 sites
• AS 2050 fixes needed – Real fixings for ridges
– De-rating wind class for sarking
www.jcu.edu.au/cts
Sheds
– Design for dominant openings
– Detail all components including compression bracing and foundations
– Design for correct wind rating
www.jcu.edu.au/cts
Doors
Required: • Acknowledgement that Wind
ratings for doors exist (Specification /certification)
• All forces on supports to be resisted including wind lock tensions
www.jcu.edu.au/cts
Dominant openings
• AS4055 already using dominant openings
• AS/NZS1170.2 allows protection of openings
– Doesn’t address large debris impact
– Problems with hardware
www.jcu.edu.au/cts
Windows and doors
• Doors and windows are part of the building envelope
• Need to be able to resist wind loads
www.jcu.edu.au/cts
Wind-borne debris
• Small
– Tiles
• Medium
– Battens
– Sheets
• Large
– Roofs
– Sheds
– Big consequences
www.jcu.edu.au/cts
Strong compartments • Increased protection for occupants against large debris
– ~1/3 to 1/2 of large debris released hits other houses
– Recognise envelope can be damaged
– Extra protection in strengthened small rooms
• Increased protection for occupants against extreme events
www.jcu.edu.au/cts
Wind-driven rain • Entry of water to internal space
– Through windows, doors (seals designed for serviceability winds)
– Problems for carpets, contents
• Entry of water to roof space – Through vents, broken soffits, valley gutters
– Problems for ceilings, wall linings
• Consequences – Mould, corrosion, rot (amenity)
– Replacement of linings (structure)
– Homelessness
• New standard for waterproofing at ultimate wind speeds?
• Selection of more durable materials?
www.jcu.edu.au/cts
Wind finds weakest link
If we are to avoid failures in high wind events, it is important to ensure that;
• Appropriately designed and tested products, components and fixings are used
• Good product info and training is available on use/installation
• And the information is carefully followed
www.jcu.edu.au/cts
Structural storm tide damage
• Total height ~ 5 to 6m above AHD
• Height of water above HAT ~ 2 to 3m
www.jcu.edu.au/cts
Storm Tide in TC Yasi • Significant, but could have been much worse
• Height of building relative to surge important
• Not much margin for error
>600 above floor a problem for most houses
www.jcu.edu.au/cts
Storm Tide – Guidelines for planning and building (recently published by QLD Reconstruction Authority)
• Wind, water and waves at the same time
• Level all important – Water height
– Wave height
• Flow-under design – water and debris – details
• Flow-through design – water and debris – details
To Conclude: • The wind finds the weakest link.
• Failure of a single element can lead to the
progressive failure of the structure.
• Our houses are where we shelter – they
have to be secure.
• But MUST evacuate if threat of Storm Tide
• Continued community Education
and Awareness is required
www.jcu.edu.au/cts
end
www.jcu.edu.au/cts
Repairs after TC Larry
• Checked performance of houses repaired after TC Larry – Limited sample size
– Innisfail and Kurrimine Beach
– Smaller or similar loads
www.jcu.edu.au/cts
Internal pressure does the work
Windward door failure leads to intern + extern pressures working together
Example from Dubbo thunderstorm
www.jcu.edu.au/cts
Construction type
• Lightweight cladding
• Unreinforced masonry
• Reinforced masonry
www.jcu.edu.au/cts
Height of water through buildings
• <200 mm
• >600 mm
• >1 m
www.jcu.edu.au/cts
Storm Tide
Astronomical Tide Level
High Tide
Low Tide
Mean Sea Level
Storm Surge Height
Wave Set Up
Highest Water Level Breaking Waves
Currents
www.jcu.edu.au/cts
Education / Training / Information
• New construction – Correct detailing requirements to match/exceed min design wind load – Materials of appropriate durability – Doors, windows, roller doors, hardware
• Maintenance – Roof space inspection for partial damage / deterioration – Whenever roof off, then check, maintain, upgrade
• Curriculum – Engineers, designers, certifiers – Wind Classifications, detailing – Trades – need to match details to wind classification
• Community education – Need for maintenance – Clean up potential debris – Build to minimise risks – topography, storm surge – Evacuation / in-house shelters