Dynamic Loading of Trees
Measuring Root Plate
Movement
Ken James
ENSPEC
Introduction
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Structural analysis to assess stability of trees in winds
Static and Dynamic Methods
Measuring trees response – trunk, and root plate
New instruments to measure Root Plate Tilt
Case studies
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Structural Analysis
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An engineering approach
Measure forces and strengths of structure
Measure stability (movement at the base)
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Stability and Failure
Trees are stable if they are
stronger than the loads they
experience.
If
LOAD exceeds STRENGTH
FAILURE OCCURS
Biggest load is WIND
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Structural failure
Load exceeds strength
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Trunk, branch failure
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Root plate failure
Inspections – visual
Can we measure something?
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Current methods of structural analysis
STATIC
• Tree pull (Germany)
DYNAMIC
• Forestry modeling
• Urban trees – very little.
• Wind loads – need data
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Static pull test
KJ
CUGE 2010
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Static Pull – Germany 2010
Elastometer
Trunk
Inclinometer
Root Plate
Inclinometer - tilt
Two instruments
1. Inclinometer (Argus)
Euro1000
2. Tilt sensor (accelerometer)
US$130
Both accurate to 1/100th degree
Elastometer
• Tree Quinetic system
• Wifi links to computer
Munich Pull Test, 2010
Tree pull tests – Ohio 2010
Ultimate test to failure
Success or failure?
Tipping Curve
• Limit for Static test taken as
40% of failure load
• This translates to
TILT ANGLE OF 0.25 Deg
Failure taken as 1.00 degree TILT
If TILT can be monitored in winds
then TILT below 1.00 Deg
indicates STABILITY
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Static Tree Pull - Brisbane
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Load Cell
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New Instrument
Accelerometer
Can use as a tilt sensor
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New Instrument to measure Tilt
Accelerometer
Three axes
• X horizontal
• Y horizontal
• Z vertical
Responds to
• ACCELERATION
• VIBRATION
REMEMBER
GRAVITY – a force that causes
acceleration vertically
down towards the Earth
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Accelerometer - microchip
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Small , sensitive, cheap
Miniature lever arm vibrates
3 in X,Y,Z directions
Gravity pushes on X and Y (Static angle)
No gravitation effect on vertical Z axis
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Tilt Sensor
Accelerometer can be used
as a tilt meter
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Tilt Sensor
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Exploded view
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On board battery, logging
USB connection to computer
On/Off button at rear
Software sets sample rate, logging details and time
Issues still with time accuracy, temperature drift, reliability
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Tilt Sensor, holder and tree
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Turn on sensor – blue light flashes
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Position on tree
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Sample
output
BLACK N/S
RED E/W
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Case studies
Tree stability after bush fires
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Tree stability
Victoria
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Tree leaning along water course
Is it stable?
Should it be kept or removed?
Bush fire damage from Black Saturday
fires (7 Feb 2009)
• Wet period undermined bank.
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Tree measured for one month
Several large wind periods
Root plate moves but very little
Tree considered stable and remains
Must monitor again in 6 months
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Sensor on tree at base
• Red circle shows tilt sensor
at base of tree
• Sensor measures root plate
angle continuously at 20 Hz.
• On board battery
• Logs data to text file
• Change sensor for
continuous monitoring
Limit to
• Battery life
(4 days continuous)
• Memory capacity (1MB)
• Need wifi and feedback that
it is working
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Sensor hidden
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Security of sensor
Vandalism or theft
Bark hides sensor
Keeps sun off sensor
• Temperature variations
cause readings to drift.
• Not a big problem as wind
data can be seen
• Inconvenient and needs
upgrade
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Two sensors, base and 4 m
4m height
• Max tilt 0.48 deg
Root Plate
• Max tilt 0.14 deg
Tree consider within limits of stability during monitoring period.
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Brisbane Trees
• Pull tests
• Monitoring root plate movement
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Pull test, tilt sensor response
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Ficus macrophylla, Davies Park, Bris.
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Root Plate Tilt under wind (East)
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Root Plate Tilt under wind (150 s)
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Trunk and Root Flare (Flexibility)
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Trunk and Root Flare (Flexibility)
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Comparing Strain and tilt data
Tilt data
• Red E/W
• Black N/S
Strain data
• Red E/W
• White N/S
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Manna Gum, E. viminalis,
Marysville, Vic
Botanical Name
Common Name
Tree Height metres (approximately)
Tree Spread metres (approximately)
Diameter at Breast Height (DBH)
E. viminalis
Manna gum
39 m
15 m
830 mm
Trunk
Strainmeter
Root Plate
Tilt Sensor
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Dynamic tree response in wind gust
Trunk
response
Root Plate
response
Eucalyptus viminalis
Height
DBH
Slenderness
Manna Gum
42 m
1670 mm
25
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Dynamic tree response in wind gust
Trunk
response
Root Plate
response
Eucalyptus viminalis
Height
DBH
Slenderness
Manna Gum
42 m
1670 mm
25
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Dynamic tree response in wind gust
Trunk
response
Root Plate
response
Eucalyptus viminalis
Height
DBH
Slenderness
Manna Gum
42 m
1670 mm
25
Brisbane 2011 Mar
50
Dynamic tree response in wind gust
Wind change
• Start northerly, change to southerly
Compare trunk and root plate response
• Similar dynamic response over 30 min
• Both show wind loads on tree
• Dynamic at 20 Hz
• Root plate moves 0.10 degrees
• Considered stable
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Dynamic tree response in wind gust
Wind data
Eucalyptus viminalis
Height
DBH
Slenderness
Manna Gum
42 m
1670 mm
25
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Summary - Tree stability
Tree stability recorded
• Dynamic measurements over 4 weeks
• Wind loads measured
• Wind speeds measured
• Tree considered stable in this period because root plate
tilt data indicates very little movement
(Max measured is 0.10 degrees).
• Tipping limit 0.25 degrees, failure at 1.00 degrees
REFERENCE - Wessolly, L., and M. Erb. 1998. Handbuch der Baumstatik und
Baumkontrolle. Patzer Verlag, Berlin, Germany.
• Data on file for later reference (legal, liability?)
• No guarantee, tree is a biological structure and may fail.
Eucalyptus viminalis
Height
DBH
Slenderness
Manna Gum
42 m
1670 mm
• Monitor again (6 months, 12 months?)
• Over time changes will be detected.
25
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Highest Tilt Data
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Max Tilt Data
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All trees monitored over same period
Trees tilt response 0.14 to 0.44 deg
Tree#9 tilt 0.84 deg max during gust
Tipping curve suggests failure at 1.00 deg
• This tree is moving in the root plate more
than any other tree monitored.
• Report generated so managers can make
decisions on future program.
• No immediate target as road is a remote
location
• Regular monitoring recommended
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Summary
100 trees
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Trees showing high tilt
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Kinglake, Victoria
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Gordon’s Bridge Rd
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Tree #1
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Tree#5
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Compare root plate
response
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Marysville, Vic, Australia
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Marysville, Victoria
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Marysville Caravan Park
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16 trees
Manna gum, all 0ver 30 m
Cabins directly under trees
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Marysville Caravan Park
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Wind Data 1
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Wind Data 2
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Wind Data 3
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Wind Data 4
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Wind Data 5
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Wind Data 6
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Castella Rd, Vic - Map
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9 trees
Tilt sensors monitor root plates
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Castella Rd, Vic - Trees
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Castella Rd, Vic – Weather data
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Castella Rd Tree6.1
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Castella Rd Tree6.2
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Castella Rd Tree6.3
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Castella Rd Tree6.4
• Gust from W
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Castella Rd Tree6.5
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Castella Rd Tree6.6
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Castella Rd Tree7.1
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Castella Rd Tree7.2
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Castella Rd Tree7.3
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Castella Rd Tree7.4
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Castella Rd Tree7.5
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Castella Rd Tree7.6
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Gust from West
Tree #4
and
Tree #6
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Castella Rd - Summary
Tree#1
23
820
28
0.14
S
19/02/2011
Tree#2
24.5
700
35
0.06
S
19/02/2011
Tree#3
15
430
35
0.05
SW
18/02/2011
Tree#4
23
480
48
0.13
SW
19/02/2011
Tree#5
23
550
42
0.09
SW
19/02/2011
Tree#6
17
270
63
0.31
E/W
19/02/2011
Tree#7
16
270
59
0.16
SW
19/02/2011
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