Flexural Failure of Ice - What we have Learnt from Confederation - - PowerPoint PPT Presentation

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Flexural Failure of Ice - What we have Learnt from Confederation Bridge T.G. Brown - Department of Civil Engineering, Schulich School of Engineering, University of Calgary. - IFN Engineering Ltd. Outline Confederation Bridge and Ice

SLIDE 1

Flexural Failure of Ice - What we have Learnt from Confederation Bridge

T.G. Brown

Department of Civil Engineering,

Schulich School of Engineering, University

f Calgary.
IFN Engineering Ltd.

SLIDE 2

Outline

 Confederation Bridge and Ice in Northumberland Strait.  The monitoring programme.  Ice force measurement.  Observations related to flexural failure.  Flexural failure loads, measurements and predictions.  Sidebar – ridges.  Conclusions.

SLIDE 3

Confederation Bridge

SLIDE 4

Confederation Bridge

SLIDE 5

Confederation Bridge

SLIDE 6

Ice in Northumberland Strait

SLIDE 7

Ice in Northumberland Strait

Synthetic Aperture Radar Image of Ice in Northumberland Strait, 1988.

SLIDE 8

Typical Ice Conditions

SLIDE 9

Why is Confederation Bridge a good site for ice observations?

Ice is present for 100 to 120 days every year
Each pier “sees” something like 3000 km of ice a year.
Which means that each pier encounters something of

the order of 9000 ridges a year.

Ice floe diameters typically to 2 km but we have seen
ne floe measuring 5 km by 8 km
Level ice thicknesses to about 1 meter

SLIDE 10

Why is Confederation Bridge a good site for ice observations?

Ice speeds have been measured to 1.6 m/sec
Ice is wind and tidal current driven, hence

much pressure in plane of ice cover

Ridge keel depths have been measured to 16

m.

Consolidated ice thicknesses measured to 2.5

m.

SLIDE 11

Monitoring Programme Elements

Ice forces were the controlling lateral load condition
Bridge designed to a Beta factor of 4.25 for single path load

systems – annual probability of failure of ~10-7

Uncertainty regarding design ice forces:

– Estimates ranged from 16 to 33 MN for unfactored 100-year design force!!

– Measure ice forces – Measure ice pressures – Observe behaviour of ice against piers – Measure related ice and environmental parameters

SLIDE 12

Measurements

Confederation Bridge, we measure:

– Tilt response of piers, and – Acceleration response of piers

Advantages:

– Highly accurate – Dynamic sensitivity

Disadvantages:

– Response contaminated by structure response to ice and other dynamic load effects – Attenuation of tiltmeter signal at frequencies >2 Hz

– How to calibrate? – Measure pressures – View interactions

SLIDE 13

Kinematic Instrumentation

Biaxial Tiltmeter Accelerometers

SLIDE 14

Ice pressures

14m
10m
9m
5m
1.575m

0m 1.575m Each Panel 1m by 2m (Typ.) Cone Panels Tapered to Match Conical Surface

SLIDE 15

Behaviour

Closed-Circuit TV
Time-lapse recording
Focus on two piers
Initially analogue
Now digital

SLIDE 16

Kinematic Instrumentation

Sensor Locations +24.56m +3.20m 10.0 m. 4.0 m

52° 78°

Group 4 Spare Group 3 Sensor Locations +24.56m +3.20m 10.0 m. 4.0 m

52° 78°

Group 4 Spare Group 3

SLIDE 17

Calibration

SLIDE 18

Calibration

SLIDE 19

Then the rope broke!

Video taken during the pull test in 1997

showing the rope breaking.

SLIDE 20

And we got:

0.1
0.08
0.06
0.04
0.02

0.02 0.04 0.06 0.08 0.1 135 140 145 150 155 160

SLIDE 21

Ice Flexural Behaviour

SLIDE 22