iclr webex: observations from the june 17, 2014 angus tornado (slides)
DESCRIPTION
On Thursday, July 3 ICLR conducted a webinar entitled ‘What can we do to mitigate tornado damage: Observations from the Angus tornado.’ The session was led by Dr. Greg Kopp, Professor in the Faculty of Engineering, Western University. At approximately 5:20 p.m. June 17, an EF2 tornado tore through a subdivision in the town of Angus, Ontario, located just west of Barrie. According to media reports 102 houses were damaged, many severely. First thing the morning of June 18, Western University engineering’s Storm Damage Assessment Team, led by Dr. Kopp, was on the ground to work with Environment Canada to assess and rate the tornado. The team also worked to map the storm track and document damage to 85 homes, 11 of which had complete roof failures. The team found several code deficiencies in Angus, including missing toe-nails and, in some cases, missing wall-to-floor connections. Dr. Kopp led a discussion on the team’s findings and presenting on how tornado damage to homes can be mitigated.TRANSCRIPT
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Observa(ons from the Angus Tornado, 2014 June 17
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Observa(ons from the Angus Tornado, 2014 June 17
Gregory A. Kopp
Boundary Layer Wind Tunnel Laboratory, Faculty of Engineering, Western
[email protected] @gregoryalankopp
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Objec(ves of Presenta(on • Overview of damage in Angus • PaCerns of damage/EF-‐Scale raGngs • Comparisons with damage observaGons
from the 2009 Vaughan Tornadoes • Discussion about miGgaGng tornado
damage
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Damage track of the Angus Tornado
Preliminary track courtesy of Environment Canada
Most of the damage was in this neighbourhood
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Summary of Damage to Houses 101 houses with damage were iden(fied in Angus:
The bulk of the damage was down 2 streets; worst debris was in the backyard between the streets.
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Summary of Damage to Houses 101 houses with damage were iden(fied in Angus:
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Summary of Damage to Houses
…views from the backyards, between these two streets
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Summary of Damage to Houses
Red = houses with roof-‐to-‐wall-‐connecGon failures (ie, roof is gone) Green = roof sheathing (ie, small part of roof is gone) Yellow = everything else.
The bulk of the damage was along two streets; however, the major structural roof damage (~22 houses) was along only one street
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Summary of Damage to Houses – Structural Roof Failures
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Summary of Damage to Houses – Structural Roof Failures
Angus….7 houses in row!
Internal pressures do not seem to have played the same role as they did in the two 2009 Vaughan tornadoes because of the wind direcGons involved.
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Imagine turning a house upside down…
hanging weights off the roof…
and shaking it…
WHAT DOES THE WIND DO TO A HOUSE:
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Wind Induced Pressures on the Roof of a House
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Internal Pressuriza(on oWen leads to roof failures
Peak internal pressures depend on several parameters…basically the posiGve wall pressure is transferred into the interior volume
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Large windward wall opening – internal pressurizaGon – roof failure
VAUGHAN, 2009
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These were the correct nails… but there are only 2, not 3
VAUGHAN, 2009
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The neighbour’s house… very minor shingle damage
VAUGHAN, 2009
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Summary of Damage to Houses – Structural Roof Failures
Incorrect toe-‐nailed, roof-‐to-‐wall-‐connecGons were prevalent
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Full-‐scale tests at the “3 LiCle Pigs” project
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Summary of Damage to Houses – Structural Roof Failures
Lab tests of toe-‐nailed connecGons
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-.,!./!0'++!12.,!,+'2)3!
Our preliminary analysis suggests that 2 missing nails per connec(on reduces the failure inducing wind speed by about 40%
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!!!!!!!!
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4../!2$#55!!!!6!2.)7('%+)8!&.(()&2%.(!1'/2)$!0%298$'0'+!/$.:!2.,!,+'2)!%(!+';!2)523<!!-9)!;#%+8%(=!&.8)!$)>#%$)5!?!('%+5!2.!&.(()&2!)'&9!$../!2$#55!2.!29)!2.,!,+'2)!./!29)!0'++5<!
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Summary of Damage to Houses – Structural Roof Failures
In contrast, inexpensive hurricane clips roughly double the capacity. Our analysis of the Vaughan Tornado suggests that these would have kept the roofs on in these events.
We are s(ll analyzing the wind speeds that may have caused these failures.
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Barrie Tornado, 1985
2-‐storey, hip roof
2-‐storey, gable roof
Analysis of Roof Damage
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Looking at this Barrie photo...
• Peak coefficient for hip roof is about 0.8. For a two storey gable it is about 1.2 (50% larger)
• Hip roofs have larger capacity due to connecGons on all 4 walls, compared to two walls for gable.
• These two factors lead to about a 40% difference in failure wind speed, all else being equal.
Analysis of Roof Damage
… although the damage is clearly DOD-‐6, we are s(ll analyzing the wind speeds that may have caused the Angus roof failures.
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EF-‐Scale and Degrees of Damage (DOD) for Houses
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Summary of Damage to Houses – Cladding Red = shingles; Green = siding; Yellow = everything else
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Summary of Damage to Houses – Cladding
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Summary of Damage to Houses – Cladding
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EF-‐Scale and Degrees of Damage (DOD) for Houses
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Vehicles – the overturned U-‐Haul truck
Vehicles are not included in the EF-‐Scale …but they were in the original Fujita Scale
Correla(ons of damage – shingles, garage doors, sheathing
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Damage observa(ons near overturned U-‐Haul truck
RepeGGve shingle damage (> 20% of roof)
Some garage doors blown in
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Damage observa(ons near overturned U-‐Haul truck
RepeGGve shingle damage (> 20% of roof)
Some garage doors blown in
Roof sheathing – 1 or 2 panels
LOOKING IN OTHER DIRECTION
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Damage observa(ons near overturned U-‐Haul truck
Vehicles are not included in the EF-‐Scale… but they were in the original Fujita Scale (Fujita, 1981)
120 – 180 km/h
180 – 250 km/h
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The overturned U-‐Haul correlates with DOD-‐4: 130 – 187 km/h This falls into the EF-‐1 range
Damage observa(ons near overturned U-‐Haul truck
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Wind tunnel tests of U-‐Haul trucks
Range is about 140 – 200 km/h, but most likely to be at lower
range because of wind direc(on. This is remarkably consistent
with DOD-‐4…but perhaps lucky, given the uncertain(es!
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Wind-‐borne debris Goderich, ON, F3, August 2011
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Wind-‐borne debris
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Wind-‐borne debris
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Large opening in envelope – internal pressure – roof failure
OPENINGS IN THE WALL VAUGHAN, 2009
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DEBRIS IMPACTS -‐ Neighbour’s garage roof landed on this house
VAUGHAN, 2009
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Wind-‐Borne Debris Impacts
ROOF
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Wind-‐Borne Debris Impacts
ROOF
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Wind-‐Borne Debris Impacts
Holding the roof structure on houses will reduce the damage at adjacent houses
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Wind-‐Borne Debris Impacts Red = debris impacts; Yellow = everything else.
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Wind-‐Borne Debris Impacts Preliminary analysis: Red = debris impacts; Yellow = everything else.
Debris impact damage is strongly correlated with Structural Roof Damage
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Wall Failures
This type of “uncharacterisGc” failure indicates issues with construcGon
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Wall Failures
This type of “uncharacterisGc” failure indicates issues with construcGon
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For Want of a Nail
For want of a nail the shoe was lost. For want of a shoe the horse was lost. For want of a horse the rider was lost.
For want of a rider the message was lost. For want of a message the baCle was lost. For want of a baCle the kingdom was lost. And all for the want of a horseshoe nail.
Ques(ons? [email protected] @gregoryalankopp
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Acknowledgements
ICLR & NSERC: for providing funding for this research, and for on-‐going support
Environment Canada: Dr. David Sills, Peter Kimball, Mitch Meredith
UWO research team/students: Sarah Stenabaugh, Emilio Hong, Chieh-‐Hsun Wu, Derek Stedman