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

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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)

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Pre-80s houses

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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