TRAIL BRIDGE INSPECTION TIMBER DETERIORATION & DECAY

1. TRAIL BRIDGE INSPECTION TIMBER DETERIORATION & DECAY

2. OBJECTIVES: Recognize the Types and Causes of Timber Deterioration Recognize Natural Defects In Timber Elements Understand What Causes Decay Identify Where Decay Is Likely To Occur Identify Methods Used to Detect Deterioration TIMBER DETEROIRATION & DECAY

3. Types and Causes of Timber Deterioration • Natural Defects In Timber Elements • Fungi (Brown and White Rot) • Insects • Termites • Carpenter Ants • Powder-post Beetles • Caddis Flies • Marine Borers

4. Types and Causes of Timber Deterioration • Delamination of Glulam Beams • Fire • Impact or Collisions • Abrasion or Wear • Overstress • Weathering or Warping • Animals

5. NATURAL DEFECTS OF TIMBER

6. Fungi

7. Mold and Stain

8. Brown and White Rot Fungi types that weaken the wood include: Brown rot - degrades the cellulose and hemi-cellulose leaving the lignin as a framework which makes the wood dark brown and crumbly White rot - feeds upon the cellulose, hemi-cellulose, and the lignin and makes the wood white and stringy

9. Brown and White Rot

10. Insects • Insects tunnel in and hollow out the insides of timber members for food and shelter. Some common types of insects include: • Termites • Carpenter ants • Powder-post beetles or lyctus beetles • Caddis flies

11. Termites

12. Carpenter Ants

13. Powder-post Beetles or Lyctus Beetles

14. Caddis flies

15. Marine Borers

16. Marine Borers

17. Marine Borers

18. Types and Sources of Deterioration • Delaminations • Delaminations occur in glued-laminated members when the layers separate due to failure within the adhesive or at the bond between the adhesive and the laminate. • They provide openings for decay to begin and may cause a reduction in strength.

19. Other Types and Sources of Deterioration • Delaminations

20. Types and Sources of Deterioration • Loose connections • Loose connections may be due to shrinkage of the wood, crushing of the wood around the fastener, or from repetitive impact loading (working) of the connection. • Loose connections can reduce the bridge’s load-carrying capacity.

21. Types and Sources of Deterioration • Loose connections

22. Types and Sources of Deterioration • Surface depressions • Surface depressions indicate internal collapse, which could be caused by decay.

23. Types and Sources of Deterioration • Fire

24. Types and Sources of Deterioration • Impact or Collisions • Severe damage can occur to truss members, railings, and columns from floating debris or ice.

25. Types and Sources of Deterioration • Abrasion or Wear

26. Types and Sources of Deterioration • Excessive Wear • Usually indicated by knots that are above the surrounding wood. • Nails protruding above the surface and bent over. • Rounding on the edges of the planks at the bridge end. • Dished and polished Planks.

27. Types and Sources of Deterioration • Overstress

28. Types and Sources of Deterioration • Overstress

29. Types and Sources of Deterioration • Weathering or Warping

30. Other Types and Sources of Damage Animal Wood swell

31. NATURAL DEFECTS OF TIMBER

32. Check – A separation of the wood normally occurring across or through the rings of annual growth and usually as a result of seasoning. Split – A separation of the wood through the piece to the opposite surface or to an adjoining surface due to the tearing apart of wood cells. Shake – A lengthwise separation of the wood which occurs between or through the rings of annual growth. NATURAL DEFECT DEFINITIONS

33. Defect - Check

34. Defects - Split

35. Defect - Shake

36. Review of Natural Defects

37. WHAT CAUSES DECAY? • Decay detection is a significant part of the timber bridge inspection. • Basic understanding of the decay is essential. • The source of the decay is a plant – a fungus that has tiny microscopic, thread-like roots called “hyphae” that penetrate throughout the wood in search of food. • The hyphae penetrate the wood secreting powerful enzymes that reduce the wood into food for the plant. • This chemical alteration of the wood cell is what we call decay.

38. Life Cycle of Fungus

40. Fungus

41. DECAY MECHANICS • The wood is initially infected when the fungus spores land on the surface or in the checks and splits of wood and geminate. • The following four conditions must exist for germination: • A sufficient supply of oxygen. • A favorable temperature range. (32° - 90° F) • An adequate food supply. • Available water. (Wood must be above the fiber saturation point of the wood. Moisture content of approximately 25%).

42. Controlling Decay • Depriving the spores of any one of these requirements will effectively slow, stop or prevent decay. For example: (1) If wood is underwater, there is no usable oxygen present and the wood will not decay; HOWEVER DECAY WILL FLOURISH AT THE WATERLINE (2) If the wood is treated, there is no palatable food for the fungi; HOWEVER, IF THE TREATMENT ENVELOPE IS BREACHED AS IN A CHECK - -DECAY MAY BE PRESENT. (3) If the wood is always dry there is no moisture for germination.

43. Where do I look for decay?

44. Common Areas Where Decay Occur • Locations to look for decay: • Around Checks • Around Splits • Around Shakes • Around Cracks • Around Fasteners • Areas in contact with soil • Areas where debris and water collect

45. Where do I look for decay? • Conditions and locations conducive to decay can be readily identified: • Members that are in contact with soil such as posts, piling, abutments, wing walls, etc. • Sawn timber members that have large checks open to the weather or stream flow (water entry). • Wood penetrating fasteners and wood to wood contact. • End grained surfaces.

46. Decay Detection Methods • Method for Detecting Exterior Deterioration • Visual Inspection • Probing • Method for Detecting Interior Deterioration • Sounding • Moisture Meter • Drilling and Coring

47. Method for Detecting Exterior Deterioration -Visual Inspection • The simplest and most common method for locating deterioration and decay • The inspector observes the structure for signs of actual or potential deterioration and decay • Visual inspection requires a strong light and is useful for detecting intermediate or advanced surface decay • Visual inspection cannot detect decay in the early stages, cannot detect internal decay, and should never be the sole method used.

48. Method for Detecting Exterior Deterioration -Visual Inspection What to Look for: • Fruiting bodies almost always indicate a severe decay problem. • Staining and discoloration indicate areas of potential decay. • Sunken faces and localized surface depressions can indicate decay. • Horizontal checks that can entrap water. • Interfaces between different wood members, wood and concrete, etc. • Where dirt and debris has been placed against the wood. • At fastener locations • Insect activity – Most insects prefer the softer decayed wood to the hard dry wood.

49. Visual Signs of External Decay • Fungi or fruiting bodies (conks) • Under the bridge, on girders and sills, anywhere the wood is subject to wet/dry cycles.

50. Visual Signs of External Decay • Spongy and Rotted areas. • Look at wood/soil interfaces and anywhere water collects. Stains may be rot indicators.