TRAIL BRIDGE INSPECTION
101
1
Mission Statement
•This PowerPoint is intended to familiarize the
budding inspector with bridge terminology and
concepts so they are ready and able to
participate in a more in-depth discussions
during the classroom sessions.
2
Trail Bridges 101
•Why do we inspect trail bridges?
•Who can inspect trail bridges?
•What is a trail bridge?
•What does that bridge term
mean?
•What are checks, splits, etc?
•What tools do I need for
inspection?
•What should I wear for safety?
3
Why do we inspect trail bridges?
 Safety!!
 National
Bridge
Inspection
Standards
4
Bridge Inspection History
• During the bridge construction boom of the
1950’s and 1960’s, little emphasis was placed
on safety inspection and maintenance of
bridges. This changed when the 2,235 foot
Silver Bridge at Point Pleasant, WV,
collapsed into the Ohio River, on Dec. 15,
1967. 46 people were killed.
5
Bridge Inspection History
• The Federal Highway Act of 1968
required the Secretary of
Transportation to establish a national
bridge inspection standard and develop
a program to train bridge inspectors.
• National Bridge Inspection Standards
were developed for Road Bridges.
6
Forest Service Trail Bridge
Inspector Qualifications
• FSM 7736.33 - Qualifications of Personnel
Responsible for Trail Bridges Inspection
and Condition Assessment
• Qualification and certification requirements
shall be established by Regional guidance
(FSH 7709.56b, sec. 05).
7
What is a Trail Bridge?
General Definition of a Trail Bridge from
the
TRAIL BRIDGE MATRIX:
A trail structure, including supports,
erected over a depression or obstruction
such as water, roadway, trail, or railway
that provides a continuous pathway and has
a deck for carrying traffic or other loads.
8
Trail Bridge Matrix
9
Trail Bridge Matrix
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Classification of Trail Bridges
TRAIL BRIDGE MATRIX:
•
Complex
• Major
• Minor
* Inspection interval for all trail bridge
classifications is every 5 years
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Complex Trail Bridge
• Whose failure likely would put the
public at risk
• Made of wood, concrete, fiberglass,
steel, suspension, or trusses
• Usually greater than 20 ft long &
• Greater than 5 ft height
• Single or multiple span
• Any bridge that requires higher
inspection skills
• Requires a technical inspection by an
engineer or engineering technician
certified road bridge inspector
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COMPLEX TRAIL BRIDGE
Example: Steel Deck Truss
13
COMPLEX TRAIL BRIDGE
Example: Fiberglass
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COMPLEX TRAIL BRIDGE
Example: Steel Thru Truss
15
COMPLEX TRAIL BRIDGE
Example: Old Railroad Trestle
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COMPLEX TRAIL BRIDGE
Example: Suspension
17
COMPLEX TRAIL BRIDGE
Other Examples of
Complex Trail Bridges:
Concrete
Masonry
Arches
Multi-Span Structures
Complex Designs
18
Major Trail Bridge
• Whose failure likely would put the
public at risk
• Made of wood (log/timber/glulam)
• Greater than 20 ft long &
• Greater than 5 ft height
• Single span
• Requires a technical inspection by a
person:
1. Trained specifically for log and/or
timber trail bridge inspections; and
2. Deemed qualified, based on Regional
19
Guidance.
MAJOR TRAIL BRIDGE
Wood and >20 ft long and >5 ft high and single span
Example: Treated Log Stringer
20
MAJOR TRAIL BRIDGE
Wood and >20 ft long and >5 ft high and single span
Example: Untreated Log Stringer
21
MAJOR TRAIL BRIDGE
Wood and >20 ft long and >5 ft high and single span
Example: Glulam Beam
22
MAJOR TRAIL BRIDGE
Wood and >20 ft long and >5 ft high and single span
Example: Sawn Lumber
23
Minor Trail Bridge
– Whose failure poses no significant
risk to the public
– Made of wood (log/timber/glulam)
– Less than 20 ft long or
– Less than 5 ft height
– Requires a condition assessment
by a person trained and qualified,
based on Regional Guidance.
24
MINOR TRAIL BRIDGE
Wood and <20 ft long or <5 ft above stream
Example: Sawn Lumber
25
MINOR TRAIL BRIDGE
Wood and <20 ft long or <5 ft above stream
Example: Log Stringer
26
Quick Summary so Far
WHY WE INSPECT TRAIL BRIDGES
SAFETY!!!!
WHAT IS A BRIDGE?
A structure erected over a depression or obstruction
such as water that provides a continuous pathway and has
a deck for carrying traffic or other loads.
WHAT ARE THE THREE CLASSIFICATIONS OF TRAIL BRIDGES?
* Complex
*Major
*Minor
This class is only for Minor and Major trail bridges
27
Bridge Terminology
  
 
 







   



 








 




 






 












 







Clear Span – Distance between face of support.
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Bridge Orientation Terminology
DOWNSTREAM
APPROACH
RIGHT
UPSTREAM
LEFT
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Span Arrangements
• SINGLE or SIMPLE SPAN
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Span Arrangements
• MULTIPLE SIMPLE SPAN
Simple Span – many spans, but each acts independently
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Span Arrangements
• MULTIPLE CONTINUOUS SPAN
Continuous Spans – 1 girder spans across 2 or more supports
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Approach Types
Gravel and Steps
Gravel
33
Rail System
Curbs, rails, posts, and bracing provided
for user Safety
34
Deck
The Deck supports loads applied to the bridge
35
Decking Types & Terms
•
•
•
•
Planks
Glulam panels
Split logs
Puncheon
•Wearing Surface
•Running plank
•Non-skid
•Gravel
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Superstructure
The Superstructure carries loads from the deck to
the substructure.
37
Superstructure Components
Is it a girder or a
stringer?
GLULAM GIRDER
LOG STRINGER
SAWN BEAM
 Girders or stringers or beams – main load carrying
members
 Diaphragms or bridging or cross bracing – provide
lateral support to girders (help stabilize the girders)
 Backwalls – attached to the ends of the girders or
stringers.
38
Superstructure
*
Diaphragms (*), Bridging, Cross Bracing
39
Superstructure
Log Stringer, aka Footlog
40
Substructure
The Substructure carries loads to the ground
41
Substructure Types
Sills or Ledgers
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Substructure Types
Cribs and Gabions
43
Substructure Types
Columns, piers, piles, bents
44
Stream Channel
This
stream
channel is
fairly
stable
But stream channels may have problem with
aggradation, degradation and floating debris.
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Stream Channel
Bank and bank protection, debris in the
waterway, streambed movement
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Stream Channel
Aggradation is the accumulation of sediment in rivers
47
Stream Channel
Degradation is erosion of the streambed
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Stream Channel
Floating Debris can be trees and/or vegetation
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Scour
SCOUR is loss of ground support
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Scour
“Undermining”
is localized
scour under a
Substructure
51
Scour
Scour failure is
most common in
bridges that are
too short
52
Scour
Scour failure is also common in areas
where the banks are weak and
unprotected by vegetation or riprap
53
Scour
Is this substructure fully supported?
54
Reviewing Bridge Terminology
Isn’t this fun?
• Railing
• Deck
• Approach
• Substructure
(Sill)
• Superstructure
(Log Stringer)
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HOW A BRIDGE WORKS
Live Loads are applied to the DECK.
The DECK transmits live loads and
deck dead load to the SUPERSTRUCTURE.
The SUPERSTRUCTURE transmits these loads and
the superstructure dead load to the SUBSTRUCTURE.
Deck
Superstructure
Substructure
Earth 56
HOW A BRIDGE WORKS
The SUBSTRUCTURE transmits all these
loads and the substructure dead load to
the EARTH.
The EARTH supports the bridge and all its
loads
It’s all about LOAD PATHS.
Deck
Superstructure
Substructure
Earth 57
Loads and Forces Acting on the Bridge
• Dead Load – weight of bridge and its components
• Live Load – temporary loads
• Soil Reaction – support from the earth
58
Dead Loads
are determined by bridge materials and design
59
Dead Loads
include weight of stringers, decking, and railing
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Live Loads
are loads placed on the bridge
People, pack animals, ATV’s, groomers…
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Live Loads
… also include snow, wind, and earthquakes…
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Soil Reaction
is the ground supporting the structure
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How does a bridge react to loads?
Is there going to be math?
64
SHEAR and MOMENT
• SHEAR forces are
• MOMENT, or BENDING,
greatest at the ends of
forces are greatest in the
the bridge. They are
middle of the bridge. They
critical in the design of
are critical in the design of
SHORT bridges.
LONG bridges.
compression
tension
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Shear
• SHEAR FORCES are highest at the ends of a
bridge. Shear failure is common in short spans
66
Moment
• MOMENT FORCES are highest at the middle of the
bridge.
Bending failure is common in long spans
67
Wood Terminology
• We can break the terminology for
wood into three groups:
– Basic Wood Definitions
– Natural Defect of Wood
– Evaluation or Inspection Terms
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Basic Wood Definitions
• Different timber shapes are used for different
applications.
• Beams can either be rectangular for sawn or glulam
beam bridges or round for log stringer bridges.
69
Basic Wood Definitions
• Dimension Lumber. Lumber with a nominal
thickness of from 2 inches up to, but not including,
5 inches and having a nominal width of 2 inches or
greater.
• Rough Lumber. Lumber that has not been dressed
but that has been sawn, edged, and trimmed.
• Sawn Lumber. The product of a sawmill not
further manufactured other than by sawing, resawing and cross-cutting to length.
70
Basic Wood Definitions
• Glued Laminated Timber (glulam). An engineered,
stress-rated product of a timber laminating plant
comprised of assemblies of specially selected and
prepared wood laminations securely bonded together
with adhesives.
• Log Stringer. Round logs that are used as beams or
stringers that have been debarked.
• Timbers. Lumber that is nominally 5 inches or more
in least dimension.
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Basic Wood Definitions
• Dressed Size. The dimensions of lumber after being
surfaced with a planing machine. The dressed size is
usually 1/2 to 3/4 in. less than the nominal or rough
size. A 2- by 4-in. stud, for example, actually
measures about 1-1/2 by 3-1/2 in.
• Nominal Size. As applied to timber or lumber, the
size by which it is known and sold in the market i.e,
2x4, 2x6,4x4,etc. (often differs from the actual
size).
72
Wood Related Definitions
• Fastener. Generic term for individual mechanical
devices such as bolts, nails, etc., used in a connection.
• Oil-Borne Preservative. A preservative that is
introduced into wood in the form of an oil-based
solution.
• Waterborne Preservative. A preservative that is
introduced into wood in the form of a water-based
solution.
73
Natural Defects of Wood
• 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.
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Natural Defect of Wood
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Checks
Seasoning checks may occur in the wide side of a
member at or near the neutral axis.
The cracks form because the wood near the surface
dries and shrinks first.
In larger pieces of lumber, the inner core of the
member loses moisture and shrinks much slower.
Checking relieves the stresses caused by nonuniform drying.
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Checks

 
   
  
 



   
 
  
  
   
  
 

  

  

   
 
  
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Checks
  
   



  
 

  

  

   
 
  
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Split
 

 
 


  


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Shake
  
 
 


  

 

 


   
  
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Inspection Terms
• Crack – Complete separation of wood fibers across
short axis of wood cells
• Decay*** - Decomposition of wood substance by
fungi. Some people refer to it as “rot”
• Delamination. The separation of layers in laminated
wood or plywood because of failure of the adhesive,
either within the adhesive itself or at the interface
between the adhesive and the adhered.
*** Will be covered in the classroom in more detail.
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Crack
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Other Inspection Terms
• Moisture Content (MC). The amount of water
contained in the wood, usually expressed as a
percentage of the weight of the oven dry wood.
• Twist. A distortion caused by the turning or winding
of the edges of a board so that the four corners of
any face are no longer in the same plane.
• Warp. Any variation from a true or plane surface.
Warp includes bow, crook, cup, and twist, or any
combination thereof.
• Weathering. The mechanical or chemical
disintegration and discoloration of the surface of
wood caused by exposure to light, the action of dust
and sand carried by winds. Weathering does not
include decay.
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Inspection
Tools & Equipment
Basic inspection
tools & equipment
consists of:
• Backpack
• Light
• Boots
• Pick
• Awl
84
Backpack
A good backpack
is needed to
store and carry
your tools to the
bridge site.
85
Boots or Waders
A set of waders or
boots are required
for walking in the
water to inspect
the underside of
bridges.
Boots with felt
soles work well
walking in areas
with slippery rocks.
86
Prospector’s Pick
A prospector’s pick works well for sounding
logs and beams with the hammer side and
checking for decay with the pick side.
87
Probes
Narrow screw drivers and
awls work best for checking
for decay in wood members.
Locking knives may be used, but are
strongly discouraged. Knives that do
88
not lock should not be used.
Lights
A good light for
use under bridges
is highly
recommended.
Both for safety
and to perform a
good bridge
inspection.
Shining the light under a bridge before entering is a
good safety practice, while it helps the inspector see
animals and other obstacles that may cause problems.89
Optional Tools
A pair of binoculars
is good for looking at
the underside of a
bridge when you can
not get right up on
the member you need
to look at.
A telescoping pole can
be used to look for
scour holes and help
to steady the
inspector while
walking in the stream.
90
Optional Tools
A mirror can be used for inspecting hard to reach
locations or around corners.
A plumb bob will help to check if things are perpendicular
to the ground.
A wrench can be used for checking bolt tightness.
91
Essential Items
Don’t forget the essentials!!!
Duck tape for fixing everything and toilet paper for
when nature calls.
92
Record Keeping
Basic record keeping
tools are:
• Clipboard
• Inspection Forms
• Write-in-rain notebook
• Pencils
• Camera
• Maps
93
Maps
Maps are a
necessity for
working for
the Forest
Service.
Getting lost
is not fun.
Taking the time to mark the location of the trail
bridges on the map makes them easier to find in
the field
94
Bridge Inspection
Forms & Tools
Make sure you have enough pencils, write-in-therain paper, forms and a clipboard to write on
before going into the field.
95
Camera
Take a camera along and take lots of pictures
and document any deficiencies or problems. 96
Optional Recording Tools
Other optional
tools maybe a
straight edge,
triangles,
compass and
scale for
drawing up
sketches of
the bridge.
Who knows, a calculator may even be handy to have.
97
Surveying Equipment
Surveying equipment will be used for taking measurements
of the bridge. The basics are a 6-foot rule, 25-foot tape,
98
100-foot cloth tape, a level and a GPS unit.
GPS or Compass
A GPS unit will help you from getting lost and to get
the coordinates of the site.
Some people still like to use a compass in the woods.
99
Levels
Levels or a pocket level & ruler are not
required, but maybe useful for checking
slope of the bridge and settlement of the
structure.
100
Measuring Devices
Tapes and rulers should be used to take
measurements of the bridge and problems.
At minimum, the inspector should carry a 6foot rule and a 100-foot cloth tape.
101
Safety Equipment
Basic Safety
Equipment
consists of:
• Hard Hat
• Safety Glasses
• Orange Vest
• Gloves
• Cell Phone
• Hiking Boots
102
Hard Hat
Hard Hats protect your head from
sharp or protruding objects under the
bridge.
103
Safety Glasses & Gloves
Glasses
protects eyes
from flying
debris when
sounding
timbers and
sharp objects
when walking
under bridge
Gloves protect hands from blisters, slivers
and cuts. They also protect against biting
104
insects and poisonous plants.
Boots
Boots should
provide ankle
support to
prevent sprains
and twisted
ankles
The treads
should provide
good traction
105
Safety Vests
Safety vests are needed to provide
visibility from traffic using the trail
106
Communications
A proper
communication
device should
be carried at
all times in
case of
emergency
Examples are Forest Service
Radios, cell and satellite phones107
First Aid Kit
A first aid kit
should be carried
into the field for
emergency use.
108
Optional Safety Equipment
Optional safety
equipment can include:
• Snake Chaps
• Bear Spray
• Insect Repellent
• Sun Screen
• Rain Gear
• Coveralls
109
Snake Chaps (optional)
Snake chaps
should be
worn in areas
where
poisonous
snakes are
known to live.
Do not provoke or handle snakes. 110
Insect Repellent &
Sunscreen (optional)
Insect repellent should
be used when
mosquitoes, flies and
other biting bugs are
present.
In addition, long sleeve
shirts and pants should
be worn. Gloves and
head nets may also be
a good idea.
The same holds true for sun screen. Prevent sunburn by
wearing long sleeves and hard hat. Use sun screen if 111
needed.
Rain Gear (optional)
A light weight
packable rain
coat is a great
way to go.
You need to wear
clothing suited
to the weather.
A layering approach works best for working in
unpredictable weather conditions.
112
Acknowledgments
• Thanks to R6 & R10 bridge engineers for
their past training presentations and
information to help develop this training.
• Thanks to Michael Knutson and John
Kattell for reviewing the training.
113
References
• FHWA Bridge Inspection Reference Manual
• FHWA Field Manual for Timber Bridge Inspection,
Draft
• FPL Timber Bridges Design, Construction, Inspection
and Maintenance
• FSM 7736
• FSH 7709.56b, Chapter 8
• R1 Major Trail Bridge Inspection Form & Minor Trail
Bridge Condition Assessment Form
• R2 Trail Bridge Inspection Guidelines
• R4 Trail Bridge Inspection Guidelines
• R6 Trail Bridge Inspection
• R10 Training PowerPoints
114