Measuring Root Plate Movement Ken James ENSPEC. Dynamic Loading of Trees

Transcription

1 Measuring Root Plate Movement Ken James ENSPEC Dynamic Loading of Trees

2 Introduction 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 2

3 Structural Analysis An engineering approach Measure forces and strengths of structure Measure stability (movement at the base) 3

4 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 4

5 Structural failure Load exceeds strength 5

6 Trunk, branch failure 6

7 Root plate failure Inspections visual Can we measure something? 7

8 STATIC Current methods of structural analysis Tree pull (Germany) DYNAMIC Forestry modeling Urban trees very little. Wind loads need data 8

9 Static pull test KJ CUGE

10 Static Pull Germany 2010 Elastometer Trunk Inclinometer Root Plate

11 Inclinometer - tilt Two instruments 1. Inclinometer (Argus) Euro Tilt sensor (accelerometer) US$130 Both accurate to 1/100 th degree

12 Tree Quinetic system Wifi links to computer Elastometer

13 Munich Pull Test, 2010

14 Tree pull tests Ohio 2010

15 Ultimate test to failure

16 Success or failure?

17 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 17

18 Static Tree Pull - Brisbane 18

19 Load Cell 19

20 New Instrument Accelerometer Can use as a tilt sensor 20

21 New Instrument to measure Tilt Three axes X horizontal Y horizontal Z vertical Responds to ACCELERATION VIBRATION REMEMBER GRAVITY a force that causes acceleration vertically down towards the Earth Accelerometer 21

22 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 22

23 Tilt Sensor Accelerometer can be used as a tilt meter 23

24 Tilt Sensor 24

25 Exploded view 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 25

26 Tilt Sensor, holder and tree 26

27 Turn on sensor blue light flashes 27

28 Position on tree 28

29 Sample output BLACK N/S RED E/W 29

30 Case studies Tree stability after bush fires 30

31 Tree stability Victoria 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. 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 31

32 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 32

33 Sensor hidden 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 33

34 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. 34

35 Brisbane Trees Pull tests Monitoring root plate movement 35

36 36

37 Pull test, tilt sensor response 37

38 38

39 39

40 40

41 Ficus macrophylla, Davies Park, Bris. 41

42 Root Plate Tilt under wind (East) 42

43 Root Plate Tilt under wind (150 s) 43

44 Trunk and Root Flare (Flexibility) 44

45 Trunk and Root Flare (Flexibility) 45

46 Comparing Strain and tilt data Tilt data Red E/W Black N/S Strain data Red E/W White N/S 46

47 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 47

48 Dynamic tree response in wind gust Trunk response Root Plate response Eucalyptus viminalis Height DBH Manna Gum 42 m 1670 mm Slenderness 25 48

49 Dynamic tree response in wind gust Trunk response Root Plate response Eucalyptus viminalis Height DBH Manna Gum 42 m 1670 mm Slenderness 25 49

50 Dynamic tree response in wind gust Trunk response Root Plate response Eucalyptus viminalis Height DBH Manna Gum 42 m 1670 mm Slenderness 25 50

51 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 51

52 Dynamic tree response in wind gust Wind data Eucalyptus viminalis Height DBH Manna Gum 42 m 1670 mm Slenderness 25 52

53 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 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 Manna Gum 42 m 1670 mm Monitor again (6 months, 12 months?) Over time changes will be detected. Slenderness 25 53

54 Highest Tilt Data 54

55 Max Tilt Data 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 55

56 Summary 100 trees 56

57 Trees showing high tilt 57

58 Kinglake, Victoria Gordon s Bridge Rd 58

59 Tree #1 59

60 Tree#5 60

61 Compare root plate response 61

62 Marysville, Vic, Australia 62

63 Marysville, Victoria 63

64 Marysville Caravan Park 16 trees Manna gum, all 0ver 30 m Cabins directly under trees 64

65 Marysville Caravan Park 65

66 Wind Data 1 66

67 Wind Data 2 67

68 Wind Data 3 68

69 Wind Data 4 69

70 Wind Data 5 70

71 Wind Data 6 71

72 Castella Rd, Vic - Map 9 trees Tilt sensors monitor root plates 72

73 Castella Rd, Vic - Trees 73

74 Castella Rd, Vic Weather data 74

75 Castella Rd Tree6.1 75

76 Castella Rd Tree6.2 76

77 Castella Rd Tree6.3 77

78 Castella Rd Tree6.4 Gust from W 78

79 Castella Rd Tree6.5 79

80 Castella Rd Tree6.6 80

81 Castella Rd Tree7.1 81

82 Castella Rd Tree7.2 82

83 Castella Rd Tree7.3 83

84 Castella Rd Tree7.4 84

85 Castella Rd Tree7.5 85

86 Castella Rd Tree7.6 86

87 Gust from West Tree #4 and Tree #6 87

88 Castella Rd - Summary Tree# S 19/02/2011 Tree# S 19/02/2011 Tree# SW 18/02/2011 Tree# SW 19/02/2011 Tree# SW 19/02/2011 Tree# E/W 19/02/2011 Tree# SW 19/02/