Structural Condition Assessment of In-Service Wood · • Ultrasound •Moisture content is...

10/13/2015

Copyright © 2015 American Wood Council1

Structural Condition Assessment of In-Service Wood

Bob Ross, USDA Forest Service, Forest Products Laboratory

This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without

written permission of AWC is prohibited.

© American Wood Council 2015

Copyright Materials

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• The American Wood Council is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider # 50111237.

• Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request.

• This course is registered with AIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner ofhandling, using, distributing, or dealing in any material or product.

• Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

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Course Description

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• This webinar will present state-of-the-art assessment methods for wood and timber structures. Results from several interesting projects will be presented—including those from evaluation of USS Constitution.

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• Provide background information on the unique characteristics of wood as a structural material

• Provide information on assessment methods for in-service wood, including state-of-the-art nondestructive evaluation methods and equipment

• Present example evaluations

• Provide state-of-the art sources for information on assessment of in-service wood

Objectives

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Sources of Information

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Polling Question1. What is your profession?

a) Architect

b) Engineer

c) Code Official

d) Building Designer

e) Other

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Polling Question2.Have you done existing wood condition assessment?

a) Yes

b) No

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Thinking Wood

S-diagram – U of Canterbury

CelluloseHemi-celluloseLigninExtractives

Property Variation: High

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• Advantages:• High strength to weight ratio• Good record for durability and

performance• Good insulation against heat,

sound, and electricity• Absorb and dissipate vibration• Easy repair

• Disadvantage:• Moisture problem

Keep It Dry!

Species• Species ID

Quality/Property• Grade stamp• Visual characteristics• Properties

Condition• Mechanical and biological damage• Fire and chemical damage

Assessment

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• Visual examination (low magnification)• Microscopic examination

• Small Sample• Consultants, universities, USDA Forest Products Laboratory

Species Identification

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• Grading Rules• Visual grading rules• Machine grade or product stamps

• Visual Characteristics• Knots• Slope of grain• Warp• Check/split• Decay

Quality/Property Assessment

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• External Deterioration• Visual• Probing

• Internal Deterioration• Sounding• Drilling and Coring• Stress Wave Timing• Moisture Meters

Condition Assessment

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• Look for the obvious• Foundation failure (sloping floor, cracks in walls, other evidence of

settlement)• Signs of distress (collapsed, failed members, excessive deflections)• Missing members• Fruiting bodies• Sunken faces or localized surface depressions• Staining or discoloration• Plant or moss growth in splits, cracks• Insect damage• Fire damage

Visual Inspection

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Corrosion of metal fastener■ Fasteners lose thickness or cross-section■ Chemical by-product attacks the wood

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Polling Question3. Corrosion of metal fasteners can create chemical

by‐products which attack wood. T/F

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Polling Question4.Visual inspection and condition assessments

should take into account items including:

a.Plant/moss growth in splits or cracks

b.Missing members

c.Staining or discoloration

d.All of the above

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Inspection Equipment

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• Old and commonly used technique• Requires some skill • Provides only a partial picture

of the extent of decay• Will not detect decay in early

stages

• Verify using additional techniques

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• Use a forestry increment borer

• Determine voids• Allows for analysis of

the core sample for presence of decay

• Potential species ID• Determine preservative

penetration• Replug with treated

wood dowel

• Locate decay and termite damage

• Concept: • Drill resistance is well

correlated to wood density• Measure the relative resistance

as a rotating drill bit is driven into the wood.

• Display relative density profile

Drilling depth [cm]

Amplitude[%]

0246810121416182022242628300

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50

75

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• Stress wave is induced into wood perpendicular to grain.• Impact

• Accelerometer monitors waves and starts timer

• Backside accelerometer monitors the waves arrival and stops the clock

• Timer displays transit time or velocity

• Ultrasound

• Moisture content is indicative of the potential for decay

• Recommended as an initial check• Sound wood

• Interior moisture content 6-12%

• Exterior moisture content 10-20%

• Potentially decayed wood• Moisture content (20-30%)

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Polling Question5. An increment borer can be used to determine the

following:

a. Voids

b. Presence of decay

c. Species identification

d. Preservative penetration

e. All of the above

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• USS Constitution (Old Ironsides)• School Gymnasium• Trestle• Timber Bridges

Example Evaluations

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Questions???

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USS Constitution

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Interesting Facts

• Construction started in 1794• Cost: $302,718.84• 200 ft long• Crew of 400• Never defeated in battle• Oldest commissioned ship in Navy• 1,000,000+ visitors/year

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Preparing to Sail Again

• Minimize keel “hogging”• Preservation of original materials

• National Geographic – July 1996

• Inspection Techniques• Visual (photographic)• Stress wave/ultrasound• Radiography• Chemical analysis• Mechanical tests

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Connection Performance

• Copper Pins• Ultrasonic/x-ray/mechanical tests• Estimated 50.4 tons of copper pins used below waterline in

ship; equal amount above waterline

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School Gymnasium

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Rathdrum School Gymnasium

• Main support structure:• Laminated barrel arches

• Problem area: • Arch end was exposed to the weather and rest on concrete foundation• Heavy non-breathing paint

• Decay indication:• Cracking and peeling of paint

• Inspection:• Locate decay

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Inspection diagram showing stress wave travel time (s)

Trestle

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Construction: 1976-1979Test stand for aircraft (550,000 lbs)Largest known glue laminated structureAccess ramp: 50 by 394 ftPlatform: 200 by 200 ftHeight: 118 ft

484 glulammembers tested

(5% of the total structural members)

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Decisions

• NDE and structural testing showed only slight decrease in rated strength

• Replacement of some decking material• OK to increase loads to accommodate alternate aircraft

Timber Bridges

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Timber bridge-Gaithersburg, Maryland

• Constructed in 1946• Nail-laminated deck sitting on

steel girders in a 3-span configuration

• Deck replaced in 2000• Recent concerns

• Significant checking in the timber substructure

• Uncertainty about their significance within the load rate analysis

Mapping deep checks & splits

Metal feeler gauge

Determine the extent of checks and splits

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Sources of Information

55FAQ: Where can I find information on evaluation, maintenance

and repair of existing structures?

• This concludes The American Institute of Architects Continuing Education Systems Course

Questions?

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[email protected]

http://awc.org/faqs/general/where-can-i-find-information-on-evaluation-maintenance-and-repair-of-existing-structures

Structural Condition Assessment of In-Service Wood · • Ultrasound •Moisture content is...

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