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TRAIL BRIDGE INSPECTION TRAIL BRIDGE INSPECTION 101101

TRAIL BRIDGE INSPECTION TRAIL BRIDGE INSPECTION 101101

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Mission Mission StatementStatement

•This PowerPoint is intended to familiarize This PowerPoint is intended to familiarize the budding inspector with bridge the budding inspector with bridge terminology and concepts so they are terminology and concepts so they are ready and able to participate in a more in-ready and able to participate in a more in-depth discussions during the classroom depth discussions during the classroom sessions.sessions.

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Trail Bridges 101Trail Bridges 101•Why do we inspect trail Why do we inspect trail bridges?bridges?

•Who can inspect trail bridges?Who can inspect trail bridges?•What is a trail bridge?What is a trail bridge?•What does that bridge term What does that bridge term mean?mean?

•What are checks, splits, etc? What are checks, splits, etc? •What tools do I need for What tools do I need for inspection?inspection?

•What should I wear for safety?What should I wear for safety?

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It’s just water over the bridge…☺

Safety!! National

Bridge Inspection Standards

Why do we inspect trail bridges?

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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.

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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.

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Forest Service Trail BridgeInspector 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).

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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.

What is a Trail Bridge?

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Trail Bridge Matrix

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Trail Bridge Matrix

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TRAIL BRIDGE MATRIX:• Complex

• Major • Minor

* Inspection interval for all trail bridge classifications is every 5 years

Classification of Trail Bridges

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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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Example: Steel Deck Truss

COMPLEX TRAIL BRIDGE

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Example: Fiberglass

COMPLEX TRAIL BRIDGE

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Example: Steel Thru Truss

COMPLEX TRAIL BRIDGE

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Example: Old Railroad Trestle

COMPLEX TRAIL BRIDGE

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Example: Suspension

COMPLEX TRAIL BRIDGE

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Other Examples of

Complex Trail Bridges:

Concrete

Masonry

Arches

Multi-Span Structures

Complex Designs

COMPLEX TRAIL BRIDGE

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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 Guidance.

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MAJOR TRAIL BRIDGEWood and >20 ft long and >5 ft high and single

spanExample: Treated Log

Stringer

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MAJOR TRAIL BRIDGEWood and >20 ft long and >5 ft high and single

spanExample: Untreated Log Stringer

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MAJOR TRAIL BRIDGEWood and >20 ft long and >5 ft high and single

spanExample: Glulam Beam

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MAJOR TRAIL BRIDGEWood and >20 ft long and >5 ft high and single

spanExample: Sawn Lumber

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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.

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MINOR TRAIL BRIDGE

Example: Sawn Lumber

Wood and <20 ft long or <5 ft above stream

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MINOR TRAIL BRIDGEWood and <20 ft long or <5 ft above stream

Example: Log Stringer

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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

Quick Summary so Far

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Bridge Terminology

Clear Span – Distance between face of support.

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LEFT

RIGHT

UPSTREAM

DOWNSTREAM

Bridge Orientation Terminology

APPROACH

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Span Arrangements

• SINGLE or SIMPLE SPAN

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• MULTIPLE SIMPLE SPANSimple Span – many spans, but each acts independently

Span Arrangements

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• MULTIPLE CONTINUOUS SPANContinuous Spans – 1 girder spans across 2 or more supports

Span Arrangements

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Approach Types

Gravel and Steps Gravel

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Rail System

Curbs, rails, posts, and bracing provided for user Safety

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Deck

The Deck supports loads applied to the bridge

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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.

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Superstructure Components

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.

GLULAM GIRDER

LOG STRINGER

SAWN BEAM

Is it a girder or a stringer?

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Superstructure

Diaphragms (*), Bridging, Cross Bracing

*

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Superstructure

Log Stringer, aka Footlog

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Substructure

The Substructure carries loads to the ground

42Sills or Ledgers

Substructure Types

43Cribs and Gabions

Substructure Types

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Columns, piers, piles, bents

Substructure Types

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Stream Channel

But stream channels may have problem with aggradation, degradation and floating debris.

This stream channel is fairly stable

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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

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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 is loss of ground support

Scour

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Scour

“Undermining”

is localized scour under a Substructure

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Scour failure is most common in bridges that are too short

Scour

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Scour

Scour failure is also common in areas where the banks are weak and unprotected by vegetation or riprap

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Scour

Is this substructure fully supported?

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• Railing

• Deck

• Approach

• Substructure (Sill)

• Superstructure(Log Stringer)

Reviewing Bridge Terminology Isn’t this fun?

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HOW A BRIDGE WORKSLive 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

SuperstructureSubstructure

Earth

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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

SuperstructureSubstructure

Earth

HOW A BRIDGE WORKS

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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

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are determined by bridge materials and design

Dead Loads

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Dead Loadsinclude weight of stringers, decking, and railing

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Live Loadsare loads placed on the bridge

People, pack animals, ATV’s, groomers…

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… also include snow, wind, and earthquakes…

Live Loads

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is the ground supporting the structure

Soil Reaction

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How does a bridge react to loads?

Is there going to be math?

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• MOMENT, or BENDING, forces are greatest in the middle of the bridge. They are critical in the design of LONG bridges.

SHEAR and MOMENT• SHEAR forces are

greatest at the ends of the bridge. They are critical in the design of SHORT 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

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• MOMENT FORCES are highest at the middle of

the bridge. Bending failure is common in long spans

Moment

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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.

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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, re-sawing and cross-cutting to length.

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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).

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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.

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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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ChecksSeasoning 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 non-uniform 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

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Backpack

A good backpack is needed to store and carry your tools to the bridge site.

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Boots or WadersA 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.

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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.

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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 not lock should not be used.

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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.

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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.

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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.

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Essential Items

Don’t forget the essentials!!!

Duck tape for fixing everything and toilet paper for when nature calls.

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Record KeepingBasic record keeping tools are:

• Clipboard

• Inspection Forms

• Write-in-rain notebook

• Pencils

• Camera

• Maps

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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

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Bridge Inspection Forms & Tools

Make sure you have enough pencils, write-in-the-rain paper, forms and a clipboard to write on before going into the field.

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Camera

Take a camera along and take lots of pictures and document any deficiencies or problems.

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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.

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Surveying Equipment

Surveying equipment will be used for taking measurements of the bridge. The basics are a 6-foot rule, 25-foot tape, 100-foot cloth tape, a level and a GPS unit.

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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.

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Levels

Levels or a pocket level & ruler are not required, but maybe useful for checking slope of the bridge and settlement of the structure.

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Measuring Devices

Tapes and rulers should be used to take measurements of the bridge and problems. At minimum, the inspector should carry a 6-foot rule and a 100-foot cloth tape.

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Safety Equipment

Basic Safety Equipment consists of:• Hard Hat• Safety Glasses• Orange Vest• Gloves• Cell Phone• Hiking Boots

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Hard Hat

Hard Hats protect your head from sharp or protruding objects under the bridge.

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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 insects and poisonous plants.

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BootsBoots should provide ankle support to prevent sprains and twisted ankles

The treads should provide good traction

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Safety Vests

Safety vests are needed to provide visibility from traffic using the trail

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CommunicationsA proper communication device should be carried at all times in case of emergency

Examples are Forest Service Radios, cell and satellite phones

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First Aid Kit

A first aid kit should be carried into the field for emergency use.

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Optional Safety Equipment

Optional safety equipment can include:

• Snake Chaps

• Bear Spray

• Insect Repellent

• Sun Screen

• Rain Gear

• Coveralls

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Snake Chaps (optional)

Snake chaps should be worn in areas where poisonous snakes are known to live.

Do not provoke or handle snakes.

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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 needed.

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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.

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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.

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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