CONDITION ASSESSMENT OF TIMBER BRIDGES IN SEVERE AND HIGH DECAY HAZARD ZONES

Transcription

1 CONDITION ASSESSMENT OF TIMBER BRIDGES IN SEVERE AND HIGH DECAY HAZARD ZONES By Vijaya (VJ) Gopu, Ph.D., P.E Associate Director External Programs, LTRC Endowed Professor of Civil Engineering, University of Louisiana Lafayette Formosa Plastics Distinguished Professor Emeritus, LSU LTC 2016, Baton Rouge, LA March 2, 2016

2 OUTLINE 1. Acknowledgements 2. Overview of timber bridge inventory statistics 3. Location of bridges inspected in Louisiana 4. Location within decay hazard zone(s) 5. Description of cluster bridges 6. Inspection methods 7. Bridge examples 8. Challenges 9. Summary

3 Timber bridge inspections in Louisiana were conducted with the support of the following agencies and DOT staff members: Louisiana Department of Transportation and Development (LADOTD) Louisiana Transportation Research Center (LTRC) Steven Sibley, State Bridge Inspection Engineer Haylye Brown, Bridge Maintenance Engineer Keith Antee, Bridge Inspector

4 Only 4% (24,267) of the nation s bridge (NBI) are timber bridges. However, nearly 8% (46,530) of the bridges have timber elements in the superstructure. Louisiana has the second largest number (2,068) of timber bridges in the nation, about one in twelve of are in Louisiana. Nearly two thirds of Louisiana timber bridges are either structurally deficient (47%) or functionally obsolete (16.5%).

5 States with 1,500+ Bridges with timber stringers 24,267 Timber Bridges National Bridge Inventory (Dec. 2010)

6 Location of Bridges in Decay Zone Location of a bridge cluster All Louisiana bridges are in Zone 5

7 Location of Bridges Selected for Study Location of a bridge cluster

8 Details of Bridges Inspected in District 08 Bridge No. Decking Runners / Overlay Stringers Piling Length Max Span Num. Spans Built 08-1 Timber Plank 7" Asphalt Sawn Lumber Timber Timber Plank 2" Gravel Sawn Lumber Timber Timber Plank 4" Asphalt Sawn Lumber Timber Timber Plank 4" Asphalt Sawn Lumber Timber

9 Details of Bridges Inspected in District 62 Bridge No. Decking Runners / Overlay Stringers Piling Length Max Span Num. Spans Built 62-1 Timber Plank 2" Gravel Sawn Lumber Timber Timber Plank 5" Gravel Sawn Lumber Timber Timber Plank 5" Asphalt Sawn Lumber Timber

10 Details of Bridges Inspected in District 02 Bridge No. Decking Runners / Overlay Stringers Piling Length Max Span Num. Spans Built 02-1 Timber Plank Runners Sawn Lumber Timber Timber Plank Runners Sawn Lumber Timber

11 Details of Bridges Inspected in District 61 Bridge No. Decking Runners / Overlay Stringers Piling Length Max Span Num. Spans Built 61-2 Concrete AC Ovrlay Sawn Lumber Timber Concrete AC Ovrlay Sawn Lumber Timber

12 A five step procedure was adopted to conduct the bridge inspections and it involved the following: Labeling abutments, piers, girders, etc. Conducting initial visual assessment with hammer sounding Obtaining moisture content measurement in suspect & decay-prone areas Establishing baseline NDE data by collecting stress-wave & resistance micro-drilling data from areas of suspected sound wood; Investigating marked areas to measure the extent of internal deterioration by utilizing stress wave timer and resistance micro-drilling tool as needed.

13 Bridge 08-4

14 Bridge 08-4

15 Bridge 08-4

16 NDE Inspection Tool Kit

17 PILE DECAY Air Part of pile alternating gets wet and dry Dry part of pile Decay comes from the bottom of the inside Ground level At ground level: perfect conditions for bacteria which destroy the wood Ground At lower level: bad conditions for bacteria

18 DRILLING PILE USING THE MICRO-DRILL TO DETERMINE DECAY 1. Drilling horizontally 1. Drill below 45 at ground level 2. Drill below 45 approx. 10 inches under the ground level

19 Drilling needle Drilling resistance measurement to150 drillings per needle (depending on application and correct use) - Drilling needle is made out of spring steel - Teflon coated surface - Reinforcment of front end on drilling needle 1,5 mm 3,0 mm Drilling needle

20 Measurement result The graph profile recording. The resistance against the drilling needle is measured and automatically recorded on the strip. Due to the different mechanical resistance within a tree the graph profile represents the difference between early wood and late wood. The graph profiles shows finer and thicker lines. Measurement curve

21 Measurement result Drilling resistance measurement Measuring curve

22 Drilling resistance measurement Drilling resistance measurement Drilling direction Grundlinie

23 Measurement 1 COMMENT NOT SOUND Drilling direction Drilling direction Ground level Decay Profile of an impregnated pole Decay

24 Measurement 2 Drilling direction below 45 COMMENT SOUND Drilling direction below 45 Ground level Crack Profile of an impregnated pole Crack

25 Measurement 3 Drilling direction below 45 COMMENT Differneces in quality: Differences in quality of the poles Ground level - Impregnation of the poles - Age of the poles - Woodqualitiy caused by growth and source area Curve 1 Curve 2

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27 IML Micro Hammer Sound velocity measurement

28 IML Micro Hammer Early detection thanks to sound velocity measurement

29 Bridge 62-2, Side View

30 Bridge 62-2, View of Abutment

31 Bridge 62-2, View of Concrete Deck and Stringer Bracking

32 Bridge 62-2, Pile Damage

33 Bridge 62-1, Decayed Pile

34 Bridge 62-2, Pile Damage

35 Begin Bridge 62-2, Pile Damage

36 Bridge 62-1, Pile Damage

37 2 Bridge 62-1, Pile Damage

38 Bridge 62-2, Pile Damage

39 END Bridge 62-2, Pile Damage

40 Bridge 62-2, Damaged Pile

41 Bridge 62-1

42 Bridge 62-1

43 BEGIN Bridge 62-1

44 Bridge 62-1

45 Bridge 62-1

46 Bridge 62-1

47 Location of a bridge cluster All Louisiana bridges are in Zone 5 Bridge 08-4

48 Location of a bridge cluster All Louisiana bridges are in Zone 5 Bridge 08-4

49 Location of a bridge cluster All Louisiana bridges are in Zone 5 Bridge 08-4

50 Bridge 08-4

51 Bridge 08-4

52 Bridge 08-4

53 Bridge 08-4

54 Bridge 08-4

55 Bridge 08-4

56 Bridge 08-4

57 Bridge 08-4

58 Bridge 08-4

59 Bridge 08-4

60 Begin Bridge 08-4

61 Bridge 08-4

62 Notching of stringers at Bent #2

63 Pile bent replacement

64 Girder decay

65 Crushing of girder at pile cap

66 Deterioration at bottom of pile

67 Piles out of alignment

68 Some of the timber bridges originally selected for inspection could not evaluated because of the high water level, currents and inadequate headroom to conduct an inspection from a boat. Substitutions were made to ensure the desired number of bridges were inspected. In long-span bridges it was extremely difficult, if not next to impossible, to use the resistance microdrill to assess the condition of the stringers and deck due to height of the pile bent. Climbing the braces provide access only to the pile cap and the stringers at the supports.

69 Operating the microdrill at the top of the bent with one hand is nearly impossible without mobilizing Considerable equipment to gain access to the underside of long-span bridges with tall bents. Bridges with low clearance under the stringers offered a challenge also since it was difficult to operate the micro-drill in such small clearances. It was critical to have a three member team to conduct the investigation in order to manage the equipment and carry out the necessary documentation of the bridge inspection and assessment.

70 In long-span bridges it is extremely difficult, if not next to impossible, to use the resistance microdrill to assess the condition of the stringers and deck due to height of the pile bent. Climbing the braces provide access only to the pile cap and the stringers at the supports.

71 The absence of a durable vapour barrier between the wood deck and the asphalt overlay allowed moisture to be trapped at the interface of the deck and the overlay and contribute to the decay and deterioration of the deck. Once the asphalt cracks -- which it does due to the flexibility of the timber deck -- moisture travels to the wood deck and gets trapped above the deck if there is no provision for the moisture to escape. It is critical that a flexible and reliable vapour barrier be placed between the timber deck and the asphalt paving to improve the service life of the deck.

72 The use of a water shedding groove in the timber deck board is important to avoid trapping of moisture. Timber abutments/wing walls must be constructed with a durable vapour barrier between the boards and the soil material. Mechanisms weep holes -- to drain moisture behind the wall must be in place. Inexpensive continuous flashing on timber stringers will prevent moisture accumulation on stringers. End grain of pile caps, decking boards, guard rail posts must be sealed to inhibit decay.

73 Timber pile deterioration in the wet-dry zone can be inhibited by relatively inexpensive treatment of piles sections in this zone. Several methods are available to retard pile deterioration and improve the service life of bridges. These methods include: External Treatment Paste applied at ground level External Treatment Pre-made bandages with preservative External Treatment Paper after treatment with external paste Internal Fumigant Treatment Boron rods

74 The stringers in most of the bridges inspected were performing satisfactorily even after five decades and only occasional upgrading or strengthing was performed to repair damaged stringers or accommodate change in wheel loads. The key to performance and durability of the timber bridge superstructure is the design and detail to keep it dry or protected by treatment. Effort is underway to develop cost effective solutions for repairing and rehabilitating deteriorated timber piles.

75 Performance of fluoride paste and cooper borate paste treatment after 42 months in Hazard Zone 4 Performance of fluoride rods and cooper borate paste rod treatment after 42 months in Hazard Zone 4

76 Questions?

77 QUESTIONS???