boominfodag 2014: presentaties ken james

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Presentaties Ken James workshop Nederlandse Boominfodag 2014

Nederlandse Boominfodag V.O.F. Postbus 8008, 3900 CA Veenendaal, T (0318) 65 44 94, F (0318) 50 68 19, [email protected]

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Workshop 1


[email protected] 11/18/2014

ENSPEC Pty Ltd UK 2014 1

Structural Analysis of Trees in Winds

Urban Trees andWind Storms

Dr Ken JamesENSPEC – Australia

2014

IntroductionAn Engineering approach to Arboriculture and trees

Topics

• Structural analysis of trees – Loaded by winds

2014 KJ

• Engineering principles

• Statics and Dynamic Methods

• Branches (Urban trees)

• The wind environment

• Measuring tree stability in winds

• Summary

Trees with branches

1. Structural analysis of TreesMethod using Engineering Principles

2014 KJ

BUILDING TREE

Engineering methods - STATICS and DYNAMICS

1. LOAD - Assess Loads on trees (Wind loads is the focus)

2. STRENGTH - Assess tree strength

3. LOADS and STRENGTHS – evaluate Failure potential

Loads and Strength

LOAD

How big is the LOAD?

Wind is the biggest load on a tree.

STRENGTH

How strong is a tree?

• Trunk

• Branch

• Root Plate

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StableNo Failure

UnstableFailure

Stability and Failure

Structural analysis of LOAD and STRENGTH

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Trunk

Root Plate

Stable

STRENGTH greater than LOAD

Failure

LOAD exceeds STRENGTH

Trunk, branch failure

2014 KJ 6

• Load exceeds branch strength



Overturning failure

2014 KJ 7

Failure - LOAD exceeds STRENGTH

Overturning Rotation about base (Moment) greater than resisting force

Stability – Tree strength greater than wind loads

2014 KJ 8

Stable trees are firmly anchored in the ground. Even in strong winds, root plate strength greater than wind loads.

2. Loads on Trees

• Load – A general term

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Wind Loads - dynamic

Leaning (gravity) - static Ice load - static

Wind loads

Self loads (weight, gravity)

Ice loads

No units

oStatic loadsoDynamic loads

Use correct terminologySpecific Engineering terms

1. Force• Tension (pulling)

• Compression (pushing)

• Bending( tension, compression and shear)

• Shear (sliding)

• Torsion (twisting)

2. Stress• Force/Area

• Axiom of Uniform Stress

Q. What is the difference betweenForce and Stress?

2014 KJ

Bending

1. ForceForce - any interaction which tends to change the motion of an object.

Nave, C. R. (2014).

• Force - units (Newtons N) (Pounds lb)

• Use kiloNewton (kN)because a Newton is small

• A carabiner is rated in kN to show the force that is safe to use. Different in different directions(like wood).

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Forces - Tension

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Tension in ropes Tension in wood

Outer fibres pull down

Tension wood

Reaction force

Compression

ZERO Tension

• in Soil

• in CRACKS



Forces - Compression

2014 KJ

Tension and compression

2014 KJ

Bending in trees

2014 KJ

Max

Min

Max

Min

Forces – Shear (sliding force)

2014 KJ

Max C

Max T

Max Shear – along centre, whole length

Shear Forces in Soil

2014 KJ

Shear – sliding forces

Important for;• Earthquakes• Soils slippage• Tree overturning failure in sandy soils

Overturning in wind, shear in sandy soil• soil slides along circular interface

Shear in wind

2014 KJ

Wind• vertical profile, example of shear

• Air layers slide over each other

• Laminar flow assumed

• Turbulence near ground (<10m)

• Do not really know wind profile?



Torsion in trees

2014 KJ

2. Stress – useful to identify failure points

2014 KJ

High Stress = Small Force/ Very Small Area

Failure occurs first at point of highest STRESSStress concentration

Could be greatest Load (Force) Or

Could be smallest area

Stress

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MEDIUM StressArea bigger

Stress – where force concentrates

HIGH Stress

Force over small AREA

Surface FAILSLOW StressLarge Area

Stress concentration (failure?)

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1. Low stressLines spaced

uniformlyacross area

2. Hole stressFlow around hole

Stress concentrationPoint of failure (initial)

Stress analysis - NASA Technology

2014 KJ

Dots on surface• movement indicates strain • Convert strain to stress• Map stress concentrations• Identify FAILURE points

Stress– branch pull down

2014 KJ

NASAbranchpull



Stress in trees

2014 KJ

Axiom of uniform stressMattheck and Breloer 1994

P13. An optimal structure has a uniform stress over the whole of its surface.

3. Strength - trees and wood

Difficult to get values in the field• Trunk• Branches• Root plate (and soil)

• Structure of wood - complex 3D

2014 KJ

3. Strength – Root Plate

2014 KJ

Strength of roots and Soil• Inspections – visual

• Can we measure something?

• Tilt of root plate - degrees

STABLE

UNSTABLE

5. STATICS and DYNAMICSMethods of structural analysis

Trees and Wind

• Wind Force (kN)

• Height of force (m)

• Overturning at baseMoment = Force x height

= kN . m = kNm

2014 KJ

How to interpret kNm scale

10 50 100 500Small big v. big huge

5. What’s in Statics

2014 KJ

STATICS

• Spring (k)

• Force (constant)

Pull in Static Pull test

Push in winds

Tipping curve

Static Pull – Germany 2010

ElastometerTrunk

InclinometerRoot Plate



Static test – to failure

• Biomechanics Week, 2010

• Testing to failure using static pull

• Aim to establish limits of test, when failure occurs?

• Sometimes failure of trunk (as above), sometimes in root plate

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Tree Pull TestWind load approximated by a STATIC Pull

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Limit for Static test

• Limit taken as 40% of failure load

• This translates to TILT ANGLE OF 0.25 Deg

Ref: Wessolly & Erb 1998

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• Maximum load taken as failure point

• Failure occurs above 1.00 deg. TILT

• Probably 1.5 to 2.5 degree

Hypothesis

If TILT can be monitored in winds then TILT below 1.00 degree indicates STABILITY.

Tipping Curve

KJ CUGE 2010 34

Static pull test results Brudi 2002

Stress inside the trunk (wood)A measure of the wood material propertiesslope of line is important (F=k.x) Brudi 2002

Overturning values (rootplate)

320 kNm, 640 kNm(moment at base)

Beech is • stiffer than Horse chestnut (slope)

• stronger than Horse chestnut (stress max)



Compare Static Pull – Wind Load

Static pull East

Static Pull North

Static Pull Results

Static Pull North

Static Pull East

Eucalyptus 27m (2009)

Compare Static Pull – Wind Load

2014 KJ

Wind Load (measured )James 2010

600 kNm

Wind Force 10 times static pull



Example of resultsStatic Pull 60 kNm (tree starts creaking, 1 ton pull)

Wind Load 600 kNm ( tree still stands)

1 ton pull



Static test – not for all trees

• Moreton Bay Fig, Brisbane, Australia, 2014

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6. What’s in DynamicsDynamics includes;

1. Spring (k)

2. Mass (Inertial forces) (m)

3. Damping (energy dissipation) (c)

4. Force (varies with time)

Dynamics in trees - must consider

MASS – the size of a tree and branchesBig trees respond differently to small trees

DAMPING – ENERGY dissipationBranch sway provides damping in wind.

2014 KJ

Force(t)

Dynamic Analysis – includes MASSFree Undamped Vibration

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Mass (m)• Oscillates back and forth

Dynamic MODEL

MASS (m)SPRING (k)

Tf

Tm

k

oo

o

1

2

2

Natural periodNatural frequency

2m

Tk

Dynamics terms - Frequency

2014 KJ

Frequency – number of vibrations per second (HERTZ) Hz.Period – time for one cycle to repeat (seconds)

Large (40m) - slow 0.2 5Medium (25m) 0.3 3Small - fast 1 1

TREE SIZE Frequ. Period(Hz) (Sec)

Dynamics - Damping

2014 KJ

Damping (c)

• ENERGY Dissipation

• Careful - do not to say energy is “used up” because physics theory says that is not possible.

• Energy can neither be created nor destroyed (Newton’s 2nd Law of Motion)

• so Wind Energy must go somewhere.

• Usually not well understood

• In trees, little information available

• Could help trees survive by preventing large sways

• BRANCHES may be important

Dynamics - Damping

2014 KJ

Damping (c)

• ENERGY Dissipation

• Careful - do not to say energy is “used up” because physics theory says that is not possible.

• Energy can neither be created nor destroyed (Newton’s 2nd Law of Motion)

• so Wind Energy must go somewhere.

• Usually not well understood

• In trees, little information available

• Could help trees survive by preventing large sways

• BRANCHES may be important



Trees and winds (Dynamics)

2014 KJ

• WIND LOAD – BIGGEST on trees

• 6 -10 times greater than

STATIC loads (James 2010)

• Dynamics of Branches

• Wind comes in gusts

• Speed is never constant

• Direction keeps changing

• Branches sway out-of-tune

• Sway is complex to analyse

Dynamics of Poles/beams

2014 KJ

SINGLE DEGREE OF FREEDOM – SDOFONE WAY OF SWAYING ONLY

Beam ModesDynamic sway

2014 KJ

Beams and Columns

Dynamic Beam Mode 2 and 3Swiss Impact tests

2014 KJ

Energy from impact mass, simulate rock slides2nd mode, top breaks offThis does not happen in wind because 1st mode dominant

Deflection shape Frequency

Swiss impact base.avi - Swiss impact top.avi

2014 KJ

Trees, branches and mass damping

Branch masses sway “out of tune”, no regular harmonic motion, but complex interaction of branches

Damping Components

1. Aerodynamic – drag forces (quasi-static)

2. Visco-elastic – internal, soil, root plate interaction

3. Mass damping – oscillating branch masses

4. Crown collisions - forestry

Normal speed x3 speed

Complex dynamic sway

2014 KJ

Pole as a tree Branch on a trunk

Trunk dynamics Branch dynamicsNo Branches two branch modes.avi



Branch DynamicsNASA technology (USA)

2014 KJ 2014 KJ

Real wind loads on trees(James and Kane 2008)

Ref: James, K.R. 2010 A dynamic structural analysis of trees subject to wind loading.

PhD Thesis – University of Melbourne. - Free Download

Summary – Statics and DynamicsSTATICS

• Spring (k)

• Force (constant)

Pull in Static Pull test

Push in winds

2014 KJ

Dynamics includes;

1. Spring (k) (k)

2. Mass (Inertial forces) (m)

3. Damping (energy dissipation) (c)

4. Force (varies with time)

2014 KJ

THE END

[email protected]

Ken James 2014 KJ 53

Biomechanics Map

Ken James 2014 KJ 54

Biomechanics Models



Tree Sensor live

2013 KJ 55

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Workshop 2


11/18/2014

1

12014 KJ

Measuring tree stability in winds.(Tilt of tree root plate)

Dr Ken JamesENSPEC – Australia2014

Measuring Tree Stability

• How is tree stability in winds measured?

• New InstrumentsTree Motion Sensor (TMS)

• How it works

• How to use it on trees

• Results

• Interpretation

• Issues

2014 KJ 2

2.1 Wind Loads on Trees

• Overturning at Base

• Measure Tilt Angle (degrees)

2014 KJ 3

Trees and wind loads

2014 KJ

• WIND LOAD – BIGGEST on trees (6 to 10 times STATIC load)(James 2010)

• Wind comes in gusts

• Speed is never constant

• Direction keeps changing

• Wind load causes overturning at base

WIND LOAD TILT (angle at base)

Tree stable if tilt within some limit!

Stable trees – Tilt of root plate low

Tree stable

Tilt of root plate stays within some max value or a “limit”

Even in strong winds

2014 KJ 5

Tree overturns

Tilt or root plate goes beyond the “limit of stability”

Stability – Tree is stronger than wind loads

2014 KJ 6

Stable trees are firmly anchored in the ground. Even in strong wind, tilt of root plate remains within limits of stability.

11/18/2014

2

Tilt of tree root plate

New Instruments and

How to use them on a tree.

2014 KJ

New Instruments to measure tilt

2014 KJ

Measuring tilt of root plate in winds.

Reference: James, K.R., Hallam, C., and Spencer, C. 2013. Measuring tilt of tree structural root zones under static and wind loading. Journal of Agricultural and Forest Meteorology, Vol. 168, 160-167.

Root plate tilt – 2 cases(Nield and Wood 1999)

Root plate flexes and rotates about centre line of trunk at ground level.

Entire root plate well anchored in ground

ie. a stable tree

INSTRUMENTS USED HERE

At what tilt angle does failure begin?

2014 KJ 9

Rotates about hinge point at the edge of root plate.

Tree uproots and falls over.

Most failure has already occurred by 4°Coutts 1986

INSTRUMENTS NOT FOR USE HERE

2. Overturning Tree1. Stable Tree

2014 KJ

Tilt sensor – location on tree

Tilt sensor at ground level

All trees have flexible root anchorage, not just poorly rooted trees, (Nield and Wood 1999)

Rotation point of a STABLE tree well anchored in the ground

TMS at ground level

2014 KJ 11

Assume: A well anchored tree, roots flex in the groundWind will cause tree to tilt at centre of root plate, at ground level

New Instrument

Tree Motion Sensor

• a tilt sensor (accelerometer inside)

• 20 readings per second

• Accurate to 1/100th degree (0.01°)

• Records data

• Self powered (20 days)

• Memory card & USB interface

• Simple to attach on a tree

• GPS – location of tree recorded

• Compass – direction of wind

122014 KJ

Ref: James, et al. 2014. Measuring tilt of tree structural root zones under static and wind loading. Journal of Agricultural and Forest Meteorology, 160-167.

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3

Accelerometer - microchip

• 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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TMS sensors – charging batteries , Group of 10

2014 KJ 14

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Measuring dynamic root plate tilt

Control - 3m height

Used to check that WIND has blown

HIGH TO AVOID VANDALISM

BASE – on Root Plate

Used for Stability data

MUST BE AT GROUND LEVEL

TMS on Tree

2014 KJ 16

Use data for Tilt (Stability Assessment)

ControlChecks that tree has experienced wind loading (only)Not for stability assessment

172014 KJ

Monitoring a tree

Base - attach TMS

GROUND LEVEL

Tree had roots cut

Council manager wanted to know if tree was unstable.

TMS attached before a strong wind.

Turned on, wait for wind.

Control - 3m on TRUNK

Adjust horizontal

Record TMS number

Record tree details

182014 KJ

Control – to check wind at the tree

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192014 KJ

Turn on TMS – start logging

Use spanner to touch end contacts to turn on and off.

1. Turn on TMS by touching two contacts.

RED light shows start up

TMS light turns

GREEN shows battery OK.

TMS ready.

2. Touch contacts to activate LOGGING.

TMS light turnsRED/ORANGE

TMS looks for GPS

Light flashes GREEN (10) then goes out

TMS logging (20 days)

Retrieve TMS after storm

2014 KJ

1. Turn off TMS by touching two contacts.

RED light shows then turns off.

Remove from tree

Take back to office

How to get tilt data from TMS

1. Remove from tree

2. In office, unscrew end,take out micro SD card

3. Put SD card into computer

4. Upload to TreeSensor

5. Report generated

REPORT

TREESENSOR.COM - Login

2014 KJ 22

Create accountLOGIN

Upload dataReport preparedDownload report (1 hr)

Stand-alone program option available.

Program - Tree Sensor live

2013 KJ 23

See data live from TMS

Retrieve data

View tilt graphs

Analyse data (Excel)

Create Reports

2014 KJ 24

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5

Tilt dataReport automatic from TreeSensor

2014 KJ 25

Results

Results from tilt monitoring

2014 KJ

Instrument data - after winds

2014 KJ

Max tilt = Max WindMax. tilt = 0.49°

“within the limits of stability”

18 July to 8 August 2014, Brisbane.

Tilt data – 20 daysMax. tilt = 0.49°

TILT DATA

WIND DATA

Tilt during a wind gust

• Base Tilt - used for stability assessment (max = 0. 0.13°)• Control (4m) - to show strong wind has blown (max = 0. 0.38°)• Tilt bigger at 4m, both sensors record tilt accurately as tree sways in wind.

Base

Control

Tilt data replay

2014 KJ 29

Root pate tilt during wind gust – max tilt = 0.72°

At present only quoting maximum tilt value during wind storm.

Separate (N/S) & (E/W) tilt Resultant tilt TreeTilt data after winds

2014 KJ

CONTROL

Wind (RED)

BASETilt data

Base tilt value = 0.14° - “within the limits of stability”Control – shows strong wind has blown

11/18/2014

6

Spruce Tilt -1.49°

2014 KJ

• Maximum tilt recorded so far

• Tree obviously moving in the ground

• Did not fail

• Data helped decision to remove tree

Wind 70 km/h

Tilt in wind – Spruce 1.49°

SpruceExample of tilt from a wind gust.

Wind SW, tree tilts to NE

What are the limits of stability?

2014 KJ

When does a tree begin to fail? Tilt range degrees

Is there a range of tilt that is “within some limit of stability?”

Tilt values from Static Tests

2014 KJ

Tipping curve

for

Static Pull test

Wessolly and Erb 1998

0.25° limit of STATIC TEST?

40% of failure load

Failure above 1°

Tilt values in WindsTilt in winds much greater than Static Test

2014 KJ

Tilt angle

Results from TMS

(2 years data)

O.25° limit of STATIC TEST?

1.49° Max TMS value

Tree still standing but moving in wind

1.00° limit of Stability

0.60° limit (roots break, Coutts 1986)

95% tree below 0.60° in all storms

Max 1.49°

Approx 8 trees

0.65°- 0.88°

95% below 0.60°

Tilt RangesLow, Medium, High

2014 KJ

Tilt angle

1.49° Max TMS value

1.00° limit of Stability

0.60° limit (roots break, Coutts 1986)

ow 0.60° in all storms

O.25° limit of STATIC TEST?

HIGH

MEDIUM

LOW

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7

Microphone in soil (0.60°)First roots breaking detected at (0.60°)

Static test Coutts 1983

2014 KJ 37

0.60

Lowtilt

High tilt above 1°

Static Pull - Small and large treesAre results the same?

2014 KJ 38

Norway spruce – Switzerland (Lundström, Jonsson & Kalberer 2007)

Large tree H=39 m, DBH=69 cm

Small tree H=16 m, DBH=16 cm

Tipping curveCan the results be scaled up and down?Do large and small trees have the same

tipping curve?

Cannot scale up results from small trees

Static Pull - Small and large trees

2014 KJ 39

Large tree Small tree Load (kNm) 850 11Tilt at peak 4° 14°(77 times bigger LOAD than small tree)

4°

11

850

14°

(Lundström, Jonsson & Kalberer 2007)

Initial Failure point - 1°

2014 KJ 40

Failure has only just begun at 1 degree Slope of curve changes (point 2) (Lundström, Jonsson & Kalberer 2007)

1° 1°

High tiltHigh tilt

High tilt above 1°

Limits of stability – tilt angle

2014 KJ

Tilt range degrees

Tilt Range DegreesHigh above 1

Medium 0.60 -1

Low below 0.60

Minimum wind speed 40 km/h

Values for initial failure, stable tree, well anchored in the ground.

Failure

2014 KJ

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8

How do trees fail in wind?

Hale et al. 2010

2014 KJ 2014 KJ

Failure is “not all at once”

Nelson, New Zealand, storm

Stress concentrationsRoot plate failure1

2014 KJ

Stress concentrationsRoot plate failure2

2014 KJ

Components of Failure (Static)

2014 KJ 47

1°.6

1st thing to fail

1st failure, soil under root plate

• Coutts 1983, 1986

2014 KJ 48

• Crack appears first under root plate(under 1° of tilt)

• Soil has no tension strengthso crack opens in one direction but in other direction there is considerable compressive strength.

• After crack wind causes rocking

• Water enter crack (if it rains)

• Progressive (fatigue) failure occurs

• After some time, final failure and tree falls

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9

Tree pull (small tree)

2014 KJ

NASA treepull

Fatigue Stress

2014 KJ

Repeated cyclic loading can cause failure at lower stress than a direct force (pull or push)

1. Repeated cyclic loading of a foot during running can cause stress fracture in bones.

2. Repeated cyclic loading by waves and notch stress caused ship to split.

3. Repeated cyclic loading by wind may cause roots to progressively fail until tree overturns.

Trees in wind stormTropical storm, Brisbane, Australia -27 Jan 2013.

2014 KJ 51

3. Failed treeJacaranda, New Farm Park, Brisbane

After

Before

Stable and Un-stable treeTMS data examples

2014 KJ 52

Tilt response of two trees over a 20 hr period during a storm – 27 Jan 2013.

Tree failure measured over 10 hrsStorm - 27 Jan 2014

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Jacaranda, New Farm Park, Brisbane, Australia

Jacaranda after failure Failed root plate

Tilt data over 10 hours prior to failure

0 4 6 10

2.00

1.00

Tilt on 3 adjacent trees

2014 KJ 54

0.25 degrees - limit Static Pull1 degree – limit for stability ?

0.25 deg.

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8 Trees – Cathedral Lane, Taggerty VIC

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Tree 5 Max tilt 0.60°All other trees – tilt below 0.20°NOTE SCALE S DIFFERENT

One tree moves more than the others

8 trees together• Tree 5 has a peak tilt of 0.60°.• Tree 4 - next 0.26°

• Variance shows divergence from avg.• represents energy from the wind.• Shows tree 5 moves more than the other

trees all the time• Future – may be useful (Research only now)

2014 KJ 56

Variance

Maxima

0.60°

Issues• VibrationsTMS accelerometer records vibrations

Earth quakes

Trains, big trucks

Earth works

Blasting

People kicking

• SecurityStealing (disguise, cover)

• FailureDoes not predict failure

Confirms that a tree is “within limits of stability”

2014 KJ 57

Vibrations – not wind data

• Train passing at regular intervals give false maximum.

Data on tree stability Summary

New instruments, Tree Motion Sensor

• tilt of tree root plate in winds

• Provides data on stability

• Limits of stability – tilt angle

• Does not predict failure

• Used to confirm stability

2014 KJ 60

Tilt Range DegreesHigh above 1

Medium 0.60 -1Low below 0.60

Minimum wind speed 40 km/hValues for initial failure, stable tree, well anchored in the ground.

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11

Thanks for listeningTHE END

Repeated pulling testResults can vary

2014 KJ 62

Previous studies

• Wind throw is a dynamic process and the static pulling method may not accurately represent the actual dynamic forces on trees and root systems under natural wind loading. (Coutts 1986)

• Trees have been observed to blow down at wind speeds considerably lower than those predicted by static pulling. (Hassinen et al. 1998).

• How trees fail under natural wind conditions has never been verified in field experiments due to lack of measurements during damaging storms (Hale et al. 2010).

• the simulation of static loading by tree pulling alone is not enough to explain the mechanical stability of trees (Peltola 2006).

2014 KJ 63

Stress and fatigue on trees in wind

2014 KJ

Repeated cyclic load

may cause failure at lower stress than

a direct force(pull or push)

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Workshop 3


ISA Rhode Island 24-29 July 2009

1

KJ 1

Wind loads on TREES and the influence of BRANCHES

Dr Ken James

ENSPECMelbourne, Australia

Introduction

1. Focus is on large open grown trees (above 10m)

with many branches

2. Size matters in winds – because branches move

3. Research – models of Trees (Simple to complex multi-modal)

4. Role of branches – Dynamics of MASS(inertia) and damping

5. Damping- aerodynamic, viscoelastic and mass damping

6. Form of tree is critical - effect of branch removal?

7. Wind loading on branches – upwards?

KJ 2014 KJ 2

3.1 Trees and Branches

Shape and size vary

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Small Slender Large OPEN GROWN GIANT

Open grown Trees

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• Emphasis here on the biomechanics of open grown trees rather than

small trees, slender in forests or plantations, or GIANT trees.

• Distinction is NOT based on SPECIES but on their FORM

• Why?

OPEN GROWN TREES usually have considerable BRANCH mass.

• Term OPEN GROWN TREES is used rather than URBAN TREES,

because the BIOMECHANICAL PRINCIPLES are not unique to urban trees

but rather to all trees of the open grown form.

Small Slender Large OPEN GROWN GIANT

Why study Open grown Trees?

• Wind loads become large in storms

• Large dynamic forces occur as branches sway

• Dynamic forces due to branch sway caused by MASS (inertia forces)

• Dynamic forces caused by DAMPING (prevent dangerous sways)

• Failure in urban areas may cause damage to people or property

• Liability issues?

Characteristics of the trees that are studied in this Dynamics workshop

OPEN GROWN trees typically found in Urban areas

• 10 to 60 m in height (this is not exact but is a guide)

• For trees of this height the proportion of branch mass to trunk mass is important

• Branches are a major portion of the total tree mass

• In winds, sway is dominated by branch dynamics

KJ 2014 KJ 5

3.2 Dynamics – must consider SIZE and branches

2014 KJ

Trees are not all the same

4 Categories

1. Small

2. Slender

conifers, plantation, forestry

3. Large open grown

Urban trees, with branches

4. GIANT


2

2014 KJ

Small trees – Drag (constant)

Drag is DOMINANT here1. Aerodynamic drag forces on leaves is the main force

2. Proportion of other dynamic responses are small

(small inertia forces because mass is small)

3. Drag is effectively a constant force (Static)

4. No Dynamic motion even though air is moving

In Dynamics• results from small trees may not automatically scale up

and apply to larger trees.

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Skydiving shows Drag (constant)

Drag• Drag is effectively a constant force

• No Dynamic motion

Small Tree motion

Not wise to extrapolate results to larger trees

Gilman et al 2008.

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Wind 110 mph

• Many studies in forestry on

trees and wind using dynamic analysis.

• Use simple (Pole) Model of a tree

(no branches)

• Conclude there is harmonic sway

• Calculate percent damage of forest

• Do not assess individual tree damage

NOTE

• very slender trunk

• Trunk is the main moving mass

• small proportion of branch mass

• Are open grown trees the same? Do the results in wind apply to open grown trees?

2014 KJ

Slender trees in windForest and Plantation trees

• Dynamics like a vibrating pole(Rudniki et al. 2001)

Giant Trees

2014 KJ

Trunk MASS has major effect – Inertia resists Wind Force

Motion - tree moves so slowly that wind gusts have little effect

- STATIC methods applicable here.

Trunk Mass and InertiaGiant Forest Trees

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Trunk mass HUGE so tree sways slowly

One sway = 20 seconds

(Period = 20s, frequency = 1/20 = 0.05 Hz)

Wind gusts have little effect because;

• Gusts come faster

(period about 3 to 5 s, frequency = 0.3 Hz)

ie. frequencies do not match

• Gusts push on only part of the big tree at

any one time. (aerodynamic admittance function)

• Trunk MASS has huge INERTIA which

resists motion (and wind gusts)

• STATIC methods applicable here.


3

Giant Forest Trees

2014 KJ

Trunk MASS has major effect – Inertia resists Wind Force

Motion - Trunk moves so slowly that wind gusts have little effect

- Branches also move but their contribution is small.

KJ 14

3.3 Models used in Dynamics Research

of Trees and Wind

Complex

Dynamic models

• James et al. 2006

• Spatz 2007

• Theckes et al. 2011

• De Langre 2011

Simple

Dynamic models

• Greenhill 1888

• Bruchert et al. 2003

• Guitard and Castera 1995

• Leigh 2014

Simple Tree models

KJ 2014 KJ 15

Spatz 2000, Bruchert et al. 2003 Guitard and Castera 1995

Tree as a pole

After Greenhill 1881Tree as a pole with canopy as rigid attached masses

distributed vertically along trunk.

How Dynamic Models represent

trees and wind

KJ 2014 KJ 16

Tree Simple model mass, spring, damper

Mass – mass is concentrated at one point

Spring – material properties (of the trunk)

Damping – energy dissipation stops the motion

Wind – force varies with time (this moves the mass)

Displacement – this is what is modelled,

the output of a model can be checked with the real structure

How Dynamic Models represent

trees and wind

KJ 2014 KJ 17

Tree

no damping with damping

Simple model mass, spring, damper

Simple tree models

• Single degree of freedom motion (SDOF), this

means only one possible sway motion.

• No branches in the model

• This model must have harmonic sway or a

regular frequency of sway

• Motion is back and forth in a regular pattern

What is missing?

• Branches as separate swaying masses

• Inertial forces as branches sway

• Damping effects of branches

• Does not simulate real trees in the field

• Complex sway options are missing.

KJ 2014 KJ 18

Leigh 2014

Low Cycle Fatigue Failure of

a Sitka Spruce Tree in Hurricane Winds


4

Complex Tree models

KJ 2014 KJ 19

Tree Two branch

models

Many branch

models

De Langre 2007

Fractal branches

Theckes et al. 2011

Spatz et al. 2007

James et al. 2006

Finite

Element

Mattheck 1990

Moore and Maguire 2008

KJ 2014 KJ 20

Complex sway – two massesTwo masses = Two solutions

Multi Degree of Freedom System (MDOF)

KJ 2014 KJ 21

Dynamics – two branches

Two branches

Two solutions

1. Branches move together 2. Branches move apart

Many masses, many solutions, as in trees with many branches

Two Branch Models

• Spatz et al. 2006, 2007

KJ 2014 KJ 22

Area under curve = ENERGY

Two Branch Models


KJ 2014 KJ 23

Two branches - dynamics


KJ 2014 KJ 24


5

Architecture changes frequencies

of sway

• De Langre 2007

KJ 2014 KJ 25 APR08 2014 KJ 26

Mass model - James et al. 2006

- with dynamic branches

Multi-modal branch dynamics

KJ 2014 KJ 27

James 2006, 2010 Spatz et al. 2007

PracticalResults from winds in trees Theory

Two masses

James 2006, 2010

Tree sway spectrum in wind

Shows many frequencies around single peak

Branch Dynamics

2014 KJ

Finite element analysis

KJ 2014 KJ 29

Moore and Maguire 2008

Leigh 2014

• Complex structural analysis

• combines best of all methods

• Structure divided into a web of elements

• Each element analyzed

• Good for stress analysis

• Used in mechanical design, human skeleton

• Limited for trees so far.

FORM and SHAPE of TreeBiggest effect on dynamics - Branches

KJ 2014 KJ 30

• Material properties – small effect on tree dynamics.

• In contrast, small morphological variations can produce

extreme behaviors such as;• very little or

• nearly critical dissipation of stem oscillations.

• FORM or SHAPE of tree greatest effect on dynamics

• BRANCHES dynamics has the greatest effect

Sellier and Fourcaud 2009


6

KJ 2014 KJ 31

Form and shapeBranches and dynamic wind loading

Branch dynamics biggest effect

Tree is a collection of branches (Shigo)

Branches provide damping to dissipate

wind energy

Prevent dangerous sway occurring

Branches act individually to balance the

whole tree

What is the effect of removing a branch?

ie. pruning

windtrees2.avi

KJ 32

COMPLEX

tree sway

No regular harmonic motion, but complex interaction of branches

Damping – aerodynamic, viscoelastic, mass damping

No movement upwind from zero point (yellow)

James 2010

KJ 33

3.4 Role of Branchesmedium size, open grown trees

Branches can dominate open grown trees structure

Melbourne, Botanic Gardens

Damping

• dissipates ENERGY

• Usually the most difficult dynamic parameter to describe

In trees damping components include

• Aerodynamic (drag)

• Visco-elastic (internal, roots, soil)

• Mass damping (branch masses swaying out-of-time with each other)

• Crown collisions

ENERGY transfer from

WIND to TREE (James 2010)

KJ 2014 KJ 34

3.5 Examples of dynamics and structures

Tuned mass damped Structures

Buildings

Poles

Bridges

| Mass damper KJ 36

Taipei 101 – tallest building

Mass

damper


7

KJ 37

Tuned mass

damper730 tonnes

Ball mass sways opposite to building mass

in winds

Dampens wind energy

Reduces movement 40%

KJ 38

Tuned mass damper

No damping - bridge

KJ 2014 KJ 39 KJ 2014 KJ 40

Open Grown or urban trees

No damping - tree

KJ 2014 KJ 41 KJ 42

No mass damping, US - style

• No mass damping

• Energy not dissipated

• Arborist becomes the dynamic mass

• SAFETY

• Energy transferneed to understand this

• New ideas/methods?


8

KJ 43

Branch movement upwards?

Shigo (1991)

• Suggested upward

breaking of branches

occurs

• observed broken fibres

at end of branch

KJ 44

Wind forces on branches!

up or down?

Burnley, Melbourne, April 2008

KJ 45

Branch sway - Eucalyptus saligna

Wind direction

Branch sway left and UPWARDS

KJ 2014 KJ 46

Pruning limbs

KJ 2014 KJ 47

Pruning - comment

James Urban 2008 Up by roots.

Pruning trees – Gilman et al. 2008

KJ 2014 KJ 48

Research supporting recommendations for pruning trees to reduce

wind damage is almost nonexistent in the primary literature.


9

Pruning trees – Gilman et al. 2008

KJ 2014 KJ 49

•No difference in movement among reduced, raised, structurally

pruned, and lion’s tailed trees;

•No statistical differences in trunk movement among pruning types at

the lower wind speeds.

•Thinning the outer edge of the crown was one of the least effective

pruning types for reducing trunk movement in wind.

Caution:It may not be wise to extrapolate these results to larger trees using the

trees tested here to represent branches or parts of a larger structure.

KJ 2014 KJ 50

Removing branches may not be

good!

KJ 2014 KJ 51

Pruning farm trees

KJ 2014 KJ 52

Remove branches more sway occurs

• Branch mass damping removed

• Sway increases

• Dynamics magnifies response of tree

• May need to rethink some pruning options

Summary - Role of Branches

1. Branches influence dynamics

damping, mass (inertia)

2. Damping is complex, not well understood

3. Branches provide balance,

influence energy flow from wind

into the tree, root plate

4. Multi-modal branch models are needed

5. Removal of branches (pruning),

GAP in the knowledge.

KJ 2014 KJ 53

Review

1. Topic - large open grown trees (above 10m) with many branches

2. Size of trees matter in winds (and dynamics)

3. Research – models of Trees (Simple to Complex multi-modal)

4. Role of branches – Dynamics of MASS(inertia) and Damping

5. Damping- not well understood (aerodynamic, mass damping, other?)

6. Wind loading on branches – upwards?

7. Form of tree is critical - effect of branch removal (pruning) ?

KJ 2014 KJ 54


10

Reference

KJ 2014 KJ 55 KJ 2014 KJ 56

The End

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Workshop 4




The Wind Environment

Dr Ken JamesENSPEC – Australia

2014

and the effects on trees

Introduction

• Wind environment - variability and never constant

• How wind is measured (speed)

• Wind SPEED and LOAD

• How wind LOADs are measured on BUILDINGS (Pressure)

• How wind LOADs are measured on TREES (Base Moments)

• Wind speed examples (around the world)

• Wind and TMS (Use official data)

2014 KJ

Wind gusts - Florida

2014 KJ

Large and small trees in wind

2014 KJ

Different Wind on two adjacent trees

Melbourne University

Is the leaning tree stable?

Stability testing

• Tree 1 leaning (Stable in winds?)

• Should it be left or removed?

• Tree 2 considered stable(used for reference)

• Two adjacent trees should experience the same wind loading

• Use tilt sensors to monitor in next wind storm.



Tilt Sensor – Put on tree base

• Put tilt sensor on base of each tree before a storm

• Use control sensor at 3m on one tree

• Wait for wind

• Remove tilt sensor, then upload data

• Results provide data on tilt in wind.

Reference Tree

Tilt sensor at Base

Monitor root plate movement in winds

Wind Gust through Melbourne

• Storm front at 3 am

• Wind gust Max 70 km/h

• Westerly direction

• Front moved across region

• Wind over short period

• Tilt data should resemble wind speeds

• Max tilt at 3 am.

Wind was considered high enough to adequately test for tree stability. Nearby, two trees blew down in a park during this brief storm.

Results

• Tree#1 0.14° SE

• Tree#2 0.20° NE

• Different directions of tilt

Tilt Sensor – Results

• Both trees tilt in LOW range• (0.14° - 0.20°) max tilt

• Wind environment seems affected by buildings• Decision – do not remove leaning tree• - monitor every 12 months

0.20°Reference Tree

0.14°Max tilt

Root plate movement in wind (70 km/h)

Wind Changes direction

Melbourne, AustraliaLooking South, typical front passes from SW to NE

TMS records Wind change (90 deg)

Direction Tilt

• Tilt records tilt magnitude and direction• At present only quoting tilt maximum value.



2014 KJ

North Wind

Force

Monash University, Wind Storm - 2 April 2008

2014 KJ

North WindForce

Monash University, Wind Storm - 2 April 2008

Wind speed - profile

2014 KJ

• Turbulence at tree height means no such thing as an average or

typical profile.

Wind speed – profile research

2014 KJ

Turbulence

How is wind measured?

2014 KJ

• Average speed – 10 min, 1 hour

• Gust – usually taken as a 3 sec average value (Holmes 2007)

• Wind speed is NOT the same as wind force on a tree! (Transfer function)

Cup anemometer Ultrasonic

speeddirection Gustiness, energy

Maximum Wind speeds

Perth124

Melb139

Buildings Code108 kphDESIGN

UK 1979Cornwall

USA 1992Andrew 265

How to manage trees? For what wind?



4.2 Wind speed and force!

2014 KJ

Wind Speed dataAverage or gust speed?

Force on CanopyForce on leaves in canopyAlmost impossible to find but we can measure response at tree base

Tree responseeg TMS dataAccurate data from TMSBecause all force must transfer down through the trunk

How wind energy transfers to the tree is known as the TRANSFER FUNCTIONVery useful to measure energy transfer and estimate DAMPING

Could be used to evaluate pruning of real trees.

Max wind speed, not same as max force

James 2008

2014 KJ

Wind gust

No peak force

Maximum wind does not necessarily mean biggest tree response.

James 2010

Results from field measurements of wind speed and tree response (at base)

4.3 Wind Loads on BuildingsCalculated from pressure

KJ 2014 KJ 21

Wind PRESSURE on flat surfaces

Positive PRESSURENegative PRESSURE

upwards

Force calculated from Pressure

KJ 2014 KJ 22

(at a Design Wind Speed)

Calculate FORCE - (PRESSURE x AREA)

Cannot determine pressure

Base moment Better measure of wind load on trees

4.4 How to determine wind loads on treesusing equation from structures

KJ 2014 KJ 23

Cullen 2005.Journal of Arboriculture 31(3): May

Force on solid objects

Drag Coefficient CD

Drag CoefficientUsually determined in a wind tunnel

2014 KJ

Drag Coefficient CD

Compares drag of different shapesA “fudge factor”

CD = 2.0

CD = 1.2

CD = 0.12

CD = 0.6



Drag Coefficientsof trees

2014 KJ

Mayhead 1973

2014 KJ

• 24 ft wind tunnel – 28 ft high tree.

Mayhead’s comments

Results - Mayhead 1973

2014 KJ

Wind Loads on Poles

KJ 2014 KJ 28

• Overturning at Base

Wind Load on Trees

• Measure Tilt Angle (degrees)

2014 KJ 29

Overturning at Base

Implications for managing trees



2014 KJ

Tree management – fear of failure?

Are trees managed based on fear of failure?

Tree Managers questions

• When will a tree break?

• How safe is this tree?

Liability issues?

Engineering manages buildings up to a design wind speed (not for the extreme)

Sometimes buildings fail and trees do not. Where is the liability boundary?

Can trees be managed for EXTREME events?

Can trees be managed to a design wind speed using and Engineering approach?

Manage to Design Load or Failure?• Buildings are strong enough to withstand a DESIGN WIND SPEED

in Australia 30 m/s (110 km/h, 70 mph)

• Not built for EXTREME WIND SPEEDS

• Sometimes buildings fail and trees survive (not always though).

2014 KJ

Manage for extremes?• Extreme winds will cause failure in buildings and trees

• Should trees be managed to the same level as buildings up to some “design wind speed” and not for extremes.

• What is the liability for tree managers in extreme wind events?

2014 KJ

Buildings - Design Wind SpeedAustralia

mph kph m/s knots

67.1 108.0 30.0 58.3Design Wind Speed AS/NZS1170.2:2011

2014 KJ

Is the bridge strong enough?(strength criterion)

• Is the structure strong enough to withstand expected loads? (Design Loads)

• Sydney Harbour Bridge loaded with railway engines to 1.5 times design load

• Proof test then bridge assessed as safe to carry a design load

• No idea of when it will fail!

Sydney Harbour Bridge, Australia

The End

Thanks for listening

[email protected]

2014 KJ



2014 KJ

Wind Speeds

Windthrow &

Breakage

Cullen (2002)

Spatz (2000)

Sanderson et al (1999)

Hurricane

Hedden(1995)

Dennis(2005) 185 kph

Hurricane max gust

Hedden(1995)

Australian Wind Code

Drag – Bluff body

2014 KJ

Vortex shedding

2014 KJ

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Workshop 5


18/11/2014

1

Tree Stability - Case Studies

Tree Stability Assessment2014

Dr K James, ENSPEC Pty Ltd

Tree stability case studies1. How a City uses stability data.

o 80 trees monitored in a Storm - Brisbane January 2013. (1 failed)

o Norfolk Island Pines, root damage - Burnie Tasmania, Australia

2. Roots Illegally cuto Norfolk Island Pines (30m high) – Frankston, Victoria, Australia

o Eucalyptus (25m) - Berwick , Victoria, Australia

o Eucalyptus (15m) – Preston, Victoria, Australia

3. Examples of wind loadingo Two eucalyptus – Melbourne University

o Eucalyptus, Monash University

4. Tree Failureo Jacaranda, Brisbane, January 2013

o NASA pull tests

o Fatigue Failure Concept

o Failure in Sandy Soil, Yarra Yarra, Melbourne, Australia.

Roots cut illegally - Eucalyptus (25m)

Brisbane St, Berwick, Vic

Should the tree be kept or removed?

TMS monitors tilt in next wind Storm 19 Feb 2014 – wind 50 km/h

Airport located 15 km from tree site

18/11/2014

2

Max tilt 0.14°

Tree within limits of stability (under conditions of the monitoring)Tree not removedAnnual monitoring recommendedCompare tilt values (in winds) from one year to the nextData provided to assist decision to keep tree.

Case Study 2Roots cut illegally

104 Loongana Avenue, Glenroy, Vic

Should the tree be kept or removed? TMS monitors tilt in next wind

Community values Trees Storm 19 Feb 2014 – wind 80 km/h

Airport located 2 km from tree site

18/11/2014

3

Max tilt 0.14°

Tree within limits of stability (under conditions of the monitoring)Tree not removedAnnual monitoring recommendedCompare tilt values (in winds) from one year to the nextData provided to assist decision to keep tree.

Roots cut illegallyNorfolk Island Pines (30m high)

Roots cut illegallyNorfolk Island Pines (30m high) – Frankston, Victoria, Australia

Frankston

Roots cut illegally – will the trees be weakened by the excavation?

Frankston

30 m trees – high profile area along busy road, with pedestrian traffic.

Results – wind 70 km/h

Tilt of 6 trees – in 70 km/h wind1. 0.14°2. 0.12°3. 0.11°4. 0.12°5. 0.25° Tree 5 moves more than the others

6. 0.14°

Data used to advise contractor of future liability and to record illegal excavation.

Future – unknown?Tree may re-establish roots.Regular monitoring of tilt.Compare future results with current.

If tree fails, data may be used to seek compensation.

Burnie, Tasmania, Australia

5 trees along foreshore (Norfolk Island Pines)• Tree5 roots damaged in 2010 landscape project

• Tree5 moving in soil, (2 arborists reports suggest removal)

• keep or remove all 5 trees?

2014 KJ

1 2 3 4 5

18/11/2014

4

Landscape constructionDamage to roots

• Roots damaged in 2010 landscape project

• Tree5 moving in soil (2 arborists reports suggest removal)

• Keep trees or remove all(one goes all go)

Burnie, Tasmania, Australia

• Burnie trees & storm.mp4

2014 KJ

Results from monitoring trees in stormsRoot plate tilt

Max tilt - 0.40°

Max gust - 63 km/h

Heavy rain and

Wind change at 2100.

Note: Max tilt does not occur

at same time as max. gust.

2014 KJ

Summary of 5 Trees – tilt data

Tree#1Max tilt

Tree#2Max tilt

Tree#3Max tilt

Tree#4Max tilt

Tree#5Max tilt

0.14° 0.15° 0.16° 0.14° 0.40°

All trees show similar trend in tilt data in response to wind loading during this storm.Max wind 63 km/h at beginning of graph (1300 hr) 20 June 2012Max tilt occurs when rain and wind occur at (2100 hr) 20 June 2012 -wind 55 km/h

2014 KJ

Summary

• All trees recorded tilt in the LOW range of values

• Wind gust max speed 63 km/h at 1300 hrs.(BOM – Wynyard)

• Maximum load when heavy rain was falling and wind 55 km/h.

OUTCOME

• Tree 5 tilt similar to 4 other trees

• Decision made to retain all trees

• Cables to be removed in the next 12 months

• Regular monitoring with tilt sensors (annual)

2014 KJ

Reference: James, K.R. and Hallam, C. 2014. Stability of urban trees in high winds. Arboriculture Journal. UK. 35 (1), 28-35.

Brisbane Storm

27 January 2013

18/11/2014

5

Sites in BrisbaneSites represent areas where known tree failures due to wind have been recorded.

Approximately 80 trees have been monitored, 2012-2014

1. Davies Park, West End

2. New Farm Park, New Farm

3. City Botanic Gardens

4. Roma St Park

5. Sherwood Park

6. Nadine St, Chelmer

7. Sanananda St Park, Wacol

8. Markham St, Wacol

9. Bowen Park

10. Victoria Park

2014

Tree status after stormSites in Brisbane

1. Davies Park, West End

2. New Farm Park, New Farm

3. City Botanic Gardens

4. Roma St Park

5. Sherwood Park

6. Nadine St, Chelmer

7. Sanananda St Park, Wacol

8. Markham St, Wacol

9. Bowen Park

10. Victoria Park

2014

Within limits

High tilt

Send tree crews here

GPS Mapping of Trees

• Trees mapped using GPS

• numbered for this project

• Data ready to go into BCC data base.

2014

Davies Park, West End

2014

Davies Park, West End

2014

Within limits

High tilt

No work needed here

New Farm Park, New Farm

2014

18/11/2014

6

New Farm Park, New Farm

2014

Within limitsHigh tiltFailed Send tree

crews here

Tree failed in stormTree 11 New Farm Park

2014

Stable tree Tilt = 0.66Tree 25 New Farm Park

2014

Stable tree Tilt = 0.34Tree 26 New Farm Park

2014

Compare Tree 25 and 26 – Two Leopard Trees

Summary - New Farm Park

2014

Within limits

High tilt

City Botanic Gardens

2014

18/11/2014

7

City Botanic Gardens

2014

Within limits

High tilt

Roma St Park

2014

Roma St Park

2014

Within limits

High tilt

Sherwood Park

2014

Sherwood Park

2014

Within limits

High tilt

WacolSanananda St Park

Markham St,

2014

18/11/2014

8

Tilt data – Jan 2014

2014

DAILYWINDSPEED

TILTTree51CONTROLID884a

TILTTree59CONTROLID886

Example of tilt data from 2 trees monitored for 20 daysNOTE: daily cycle of tilt from winds, and storm period 27 Jan 2014, Brisbane

1000 FILES of continuous data

Tree64 • Sanananda St Park, Wacol, Brisbane – Max tilt=0.97°

2014

Tree 64

2014

Tilt values in storm – 27Jan2014

2014

Tilt values in storm – 27Jan2014

2014

Tree 53

• Eucalyptus, Sherwood Arboretum, Sherwood, Brisbane - ID584

Note; Left graph tilt from wind gust looks like a spike in the data

Right graph shows 20 seconds of the graph, with clear tilt data due to wind and not vibrations

2014

18/11/2014

9

Wind data - Brisbane

Major storm Brisbane, 27 January 2013,

• severe tree damage across Brisbane region.

Maximum wind gust 70 km/h

2014

Although maximum gust speed was below max January record (145 km/h), the winds were sustained and were accompanied with heavy rain.

Storm 27 January 2013

Strong winds AND heavy rain on 25,26,27 and 28 Jan

2014

Maximum wind gust 70 km/h

Summary• Tilt data useful to measure tree root plate movement in winds

• This can be used as a measure of stability

• Data assists managers, it does not make the decision

• Can identify a tree in a row that is moving more than its neighbours

• Can identify stable trees, useful after roots are cut

• Cannot predict failure

• No guarantees in future storms because– Do not know strength of future winds.

– Trees are biological organisms and may have future fungal/disease problemsthat affect stability.

KJ 2014 KJ 52

The End

THE END

[email protected]

Major limb failure

• Moreton Bay fig with major limb failure, 25 Feb 2014, Davies Park, West End, Brisbane.

2014

boominfodag 2014: presentaties ken james

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