10/13/2015
Structural Condition Assessment of
In-Service Wood
Bob Ross, USDA Forest Service, Forest Products Laboratory
Copyright Materials
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
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Copyright © 2015 American Wood Council
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10/13/2015
•
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 of
handling, 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
• 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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Objectives
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Provide background information on the unique characteristics of wood as
a structural material
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Provide information on assessment methods for in-service wood,
including state-of-the-art nondestructive evaluation methods and
equipment
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Present example evaluations
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Provide state-of-the art sources for information on assessment of inservice wood
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Sources of Information
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Polling Question
1. What is your profession?
a) Architect
b) Engineer
c) Code Official
d) Building Designer
e) Other
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Polling Question
2.Have you done existing wood condition assessment?
a) Yes
b) No 8
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Thinking
Wood
Property Variation: High
Cellulose
Hemi-cellulose
Lignin
Extractives
S-diagram – U of Canterbury
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• Advantages:
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High strength to weight ratio
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Good record for durability and
performance
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Good insulation against heat,
sound, and electricity
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Absorb and dissipate vibration
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Easy repair
• Disadvantage:
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Moisture problem
Keep It Dry!
Assessment
Species
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Species ID
Quality/Property
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Grade stamp
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Visual characteristics
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Properties
Condition
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Mechanical and biological damage
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Fire and chemical damage
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Species Identification
• Visual examination (low magnification)
• Microscopic examination
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Small Sample
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Consultants, universities, USDA Forest Products Laboratory
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Quality/Property Assessment
• Grading Rules
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Visual grading rules
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Machine grade or product stamps
• Visual Characteristics
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Knots
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Slope of grain
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Warp
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Check/split
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Decay
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Condition Assessment
• External Deterioration
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Visual
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Probing
• Internal Deterioration
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Sounding
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Drilling and Coring
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Stress Wave Timing
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Moisture Meters
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Visual Inspection
• Look for the obvious
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Foundation failure (sloping floor, cracks in walls, other evidence of
settlement)
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Signs of distress (collapsed, failed members, excessive deflections)
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Missing members
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Fruiting bodies
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Sunken faces or localized surface depressions
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Staining or discoloration
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Plant or moss growth in splits, cracks
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Insect damage
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Fire damage
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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 Question
3.
Corrosion of metal fasteners can create chemical by‐products which attack wood. T/F
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Polling Question
4. 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
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Requires some skill
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Provides only a partial picture
of the extent of decay
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Will not detect decay in early
stages
• Verify using additional
techniques
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• Use a forestry
increment borer
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Determine voids
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Allows for analysis of
the core sample for
presence of decay
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Potential species ID
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Determine preservative
penetration
• Replug with treated
wood dowel
• Locate decay and termite
damage
• Concept:
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Drill resistance is well
correlated to wood density
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Measure the relative resistance
as a rotating drill bit is driven
into the wood.
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Display relative density profile
Amplitude
[%]
100
75
50
25
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
0
Drilling depth [cm]
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• Stress wave is
induced into wood
perpendicular to
grain.
Impact
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•
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Accelerometer monitors
waves and starts timer
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Backside accelerometer
monitors the waves arrival
and stops the clock
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Timer displays transit time or
velocity
Ultrasound
• Moisture content is indicative of
the potential for decay
• Recommended as an initial check
• Sound wood
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Interior moisture content
6-12%
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Exterior moisture content
10-20%
• Potentially decayed wood
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Moisture content (20-30%)
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Polling Question
5. 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 31
Example Evaluations
• USS Constitution (Old Ironsides)
• School Gymnasium
• Trestle
• Timber Bridges
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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
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National Geographic – July 1996
• Inspection Techniques
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Visual (photographic)
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Stress wave/ultrasound
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Radiography
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Chemical analysis
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Mechanical tests
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Connection Performance
• Copper Pins
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Ultrasonic/x-ray/mechanical tests
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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:
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Laminated barrel arches
• Problem area:
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Arch end was exposed to the
weather and rest on concrete
foundation
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Heavy non-breathing paint
• Decay indication:
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Cracking and peeling of paint
• Inspection:
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Locate decay
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Inspection diagram showing stress wave travel
time (s)
Trestle
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Construction: 1976-1979
Test stand for aircraft (550,000 lbs)
Largest known glue laminated structure
Access ramp: 50 by 394 ft
Platform: 200 by 200 ft
Height: 118 ft
484 glulam
members 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
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Nail-laminated deck sitting on
steel girders in a 3-span
configuration
• Deck replaced in 2000
• Recent concerns
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Significant checking in the
timber substructure
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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
FAQ: Where can I find information on evaluation, maintenance
and repair of existing structures?
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Questions?
• This concludes The American Institute of Architects
Continuing Education Systems Course
www.awc.org
info@awc.org
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