Crossings : newsletter of the Wood in Transportation Program

8 Pages·2000·0.67 MB·English

by  National Timber Bridge Initiative (U.S.)

Historic, Archive Document
Do assume
not content reflects current
scientific knowledge, policies, or practices.
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i
Issue 38 Winter 2000
Assessment of the Environmental
In This Issue Effects Associated With Wooden
Bridges Preserved With Creosote,
Pentachlorophenol, or Chromated
Assessment ofthe Environmental Effects
Associated with Wooden Bridges Preserved Copper Arsenate
with Creosote, Pentachlorophenol, or
Cromated Copper Arsentate
1
USDA
In 1997, the Forest Service's Forest Products Laboratory
8th National Timber Bridge Design in conjunction with the Federal Highway Administration
Competition Results Announced 2 contracted with Oregon State University and Aquatic
Environmental Sciencestoconductathree-phasestudy(contract
Second Internatinal Conference on
AdvancedEngineered Wood Composites 4 RJVA-2828).
....
New Publications: The purposes ofthis study were to:
Assessmentofthe EnvironmentalEffects 1. assesstheenvironmentalresponseassociatedwithexisting
Associatedwith Wooden Bridges Preserved timberbridges,
with Creosote. Pentachlorophenol, or
Cromated CopperArsentate
1 2. determinethe lossofvarioustypesofpreservativesfrom
Role ofConstruction Debris in Release of overhead bridge structures, and
Copper, Chromium, andArsenic From Treated
Wood Structures 4 3. develop acomputermodel to assist in the understanding
Field Performance ofTimber Bridges of site-specific environmental risks associated with
18. Byron Stress-Laminated Truss proposed timber bridge construction.
Bridge 5
The author of the report is Kenneth M. Brooks, Owner and
Distribution ofBorates Around Pointsource
Principal Scientist, Aquatic Environmental Sciences, Port
Injections in Wood Members Exposed
Townsend, Washington.
Outside 5
GuidelinesforDesign. Installation, and Following is the abstract from the 100-page report that resulted
Maintenance ofa WaterproofWearing Surface from this study.
forTimber Bridge Decks 6
Field Performance ofTimber Bridges Timberbridgesprovideaneconomicalalternativetoconcreteand
20. Gray Stress-Laminated DeckBridge ... 6 steel structures, particularly in rural areas with lightto moderate
Insert:
Continued on page 2
New Publications Since 1998
Visit our website at www.fs.fed.us/na/wit
Assessment of the Environment . . . continued Regulatory benchmarks used in risk assessments of
frompage 1 this type need to be indexed to local environmental
conditions. The robust invertebrate communities
vehicletraffic. Woodencomponentsofthesebridges
are treated with chromated copper arsenate type C associatedwith slow-movingstreamsoversoftbottoms
were not susceptible to the concentrations of PAHs
(CCA), pentachlorophenol, or creosote to prolong
the life ofthe structure from a few years to many that would be expected to affect more sensitive taxa,
which typically are located in faster moving water
decades. This results in reduced transportation
overhardbottoms. Contaminantsreleasedfromtimber
infrastructure costs and increased public safety.
bridges intothesefastersystems(wheremoresensitive
However, the preservative used to treatthe wooden
taxa are located) are significantly diluted and not
components in timber bridges is lost to the
found at biologically significant levels.
environment in small amounts over time. This
report describes the concentration of wood
To obtain a copy of this report, please contact the
preservatives lost to adjacent environments and the
National Wood In Transportation Information Center
biological response to these preservatives as
at304-285-1 591 andrequestpublication number WIT-
environmental contaminants. Six bridges from
05-0023 or visit the Wood In Transportation website
various states were examined for risk assessment:
at www.fs.fed.us/wit; click on "New Publications
two creosote-treated bridges, two
Available".
pentachlorophenol-treated bridges, and two CCA-
treated bridges. In all cases, the largest bridges
located in biologically active environments
associated with slow-flowing water were selected
to represent worst-case analyses.
Sediment and water column concentrations of
8th National Timber Bridge Design
preservative were analyzed upstream from, under,
Competition Results Announced
and downstream from each bridge. The observed
levelsofcontaminantwere comparedwith available
regulatory standards or benchmarks and with the Eleven teams ofstudents from ten universities across
quantitative description ofthe aquatic invertebrate the United States matched wits to devise a better way
community sampled from vegetation and sediments. to “cross the creek” during the 8th National Timber
Pentachlorophenol- andcreosote-derivedpolycyclic BridgeDesign Competition. Open to studentchapters
aromatic hydrocarbons (PAHs) were not observed ofAmerican Society ofCivil Engineers (ASCE) and
in the water near any of the selected bridges. Forest Products Society (FPS), the competition was
However, low levels ofPAHs were observed in the made possible by a grant from the USDA Forest
sediments underand immediatelydownstream from Service, Wood In Transportation Program. The
these bridges. Pentachlorophenol concentrations Southern PineCouncil ofthe Southern ForestProducts
did not approach toxicological benchmarks. Association, Unit Structures LLC, and Willamette
Sediment concentrations of naphthalene, Industries provided additional financial support.
acenaphthylene, and phenanthrene exceeded the Southwest Mississippi Resource Conservation and
probable effect level. Metal levels at the bridges Development (RC&D), Inc., coordinated the
treated with CCA were less than predicted effect competition,andtheCivi EngineeringDepartmentat
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levels, in spiteofquestionableconstructionpractices. Mississippi State University provided technical
Adverse biological effects were not observed in the assistance.
aquatic invertebrate community or laboratory
bioassaysconductedon waterand sedimentssampled Each team designed, constructed, and tested their
at each ofthe bridges. Results ofthis study reveal bridges on their home campus, then submitted
the need to follow the construction information documentationoftheiractivitiesand resultstoapanel
found in Best Management Practices for the Use of ofjudges forreview. The competition was conducted
Treated Wood In Aquatic Environments published online via the Internet. Each team was required to
by Western Wood Preservers Institute.
Continued on page 3
2
.
Timber Bridge Design Competition Results • UniversityofNorth Carolina at Charlotte ASCE
Announced . . . continuedfrompage2 Team 2—
2nd Most Innovative
post design drawings, test results, and project • Oregon—State University ASCE
highlights on the Internet at www.msrcd.org. To 2nd—Most Aesthetic
view details ofcompetition results and to access each 3rd Best Design.
entry in its entirety, go to www.msrcd.org; when the
map of Mississippi appears, click on "SW", choose Also competing were University of Louisiana at
the "National Timber Design Competition," and click Lafayette ASCE and University of North Carolina
on “2000 Competition Results/' ASCE Team
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WinneroftheBestOverallDesignAward sponsored Rules for the 2001 competition are posted at
by Willamette Industries was Virginia Tech Forest www.msrcd.org (follow links as previously
Products Society. Their design featured a pair of instructed). For additional information, contact
longitudinal glulam beams supporting a transverse Southwest Mississippi RC&D, Inc., competition
deckof3/4-inch CCA-treated southern pine (SP), each coordinators at [email protected].
centered over transverse floor beams of 2-inch by
4-inch SP. essentially forming acontinuous series of Thecompetition's objectives areto promote interest
transverse T-beams. In turn, two tapering, glued- in the use ofwood as a bridge construction material,
laminated, yellow poplar arches supported the entire to generate innovative and cost-effective timber
structure. Both the arches and the longitudinal bridge design techniques, and to develop an
stringers incorporated carbon fiber strips between appreciation ofthe engineering capabilities ofwood
laminations in regions ofhighesttension forces. The among future transportation and forest products
bridgeused nometal fasteners, onlyresorcinol/phenol engineers. Following the competition, most ofthe
formaldehyde adhesive, carbon fiberandwood. This bridges were placed into actual use on campus
entry also placed first in Best Support Structure, walkways, golf courses, cross-country tracks, park
Best Deck, and Most Innovative Design. trails, etc.
San Francisco State University’s ASCE chapter The test bridges w^ere 10.8 feet long and 4.6 feet
was the second highest prize winner, capturing wide and were loaded with a test weight of
second place in Best Overall Design and Best approximately4,500pounds. Average weightofthe
Support Structure and third in Most Aesthetic bridge models was 548 pounds. At full loading,
Design and MostInnovativeDesignwiththeirbuilt- maximum bridge deflection ranged from .055 inch
up laminated arch structure. to .191 inch. Maximum allowable deflection was
.31 inch. Net deck deflection for the nine bridges
Other award winning teams w^ere that met the maximum allowable deflection ofdeck
:
span divided by400averaged45 percentofmaximum
• Clarkson University ASCE allowable. Percentnon-woodmaterials inthebridges
Practical Design
— averaged 9 percent; maximum percent non-wood
3rd Best Deck materials allowed was 25 percent by weight. A total
• Califo—rnia State-Fresno of98 students spent4,930 hours on the competition,
1st Most Aesthetic Design competing for $1 0.000 in prizes. Judges were Greg
• Lawren—ce Technological University ASCE Jones, Willamette Industries; Dr. Ralph Sinno,
Mississippi State University; and Marshall
3rd Best Support Structure
McLaughlin,USDANatural ResourcesConservation
• Washin—gton University of St. Louis ASCE Service.
3rd Most Practical
• Merrim—ack College ASCE Bennie Hutchins
2nd Best Deck Competition Coordinator
RC&D
Southwest Mississippi
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Second International Conference
on Advanced Engineered Wood
Composites
Role of Construction Debris in
The Second International Conference on Advanced Release of Copper, Chromium,
Engineered Wood Composites (AEWCs) will be and Arsenic From Treated Wood
held from August 14-16, 2001, atthe Grand Summit
Structures
&
Resort Hotel Conference Center-Sunday River,
near Bethel, Maine. The First International
Conference, held in Bar Harbor, Maine, in 1999, was Recentresearch on the release ofwood preservatives
attended by over 150 people from seven countries. from treated wood used in sensitive environments
has not considered the potential contribution from
The upcoming conference will provide a focused
construction residues. This study sought to develop
venue forpresentingand discussingthe commercial,
scientific, and engineeringaspectsofAEWCs. These leaching rate data for small construction debris and
compare those to the release rate from treated wood
composites, which combine wood with fiber-
itself. Western hemlockboards werepressuretreated
reinforced polymers (FRPs), represent an important
with chromated copper arsenate-Type C (CCA-C),
industrial segment with a unique set of issues. A
and then common construction tools were used to
combination of industrial researchers, business-
generate sawdust or shavings from those boards.
development specialists, structural engineers, and
These wood particles werethen leached in deionized
materials researcherswill gatherin asettingdesigned
water, and the leaching rate was compared with that
to create valuable and necessary interactions among
ofsolid wood samples cut form the same specimen.
all interested parties.
Releasedratedatafrom thisstudywerealsocompared
Papers and posterpresentationsare beingsolicited in with those from end-matched samples that were
the following areas: leached in artificial rain in an earlier study. The
• market-development case studies, release rates ofcopper, chromium, and arsenic from 4
• durability, CCA-C treated chainsaw sawdust, circular saw
• structural performance, sawdust, and spade bit shavings were many times
higher than from solid wood when samples were
• processing,
immersed in water. There was little difference in the
• extruded composites,
release rates among the three types ofshavings and
• reinforced composites (both laminated
sawdust, despite differences in their particle sizes.
and integral reinforcements),
The rates ofrelease from decking exposed to rainfall
• code implementation, were many times lower than that of construction
• alternative technologies, debris or solid wood continually immersed in water.
• engineered wood composites, These results showthe importance ofminimizingthe
• building systems, amountofconstruction debristhat is allowed to enter
• bridge systems, the aquatic environment. However, example
• automotive applications. calculationsalsodemonstratethat ifreasonableefforts
are made to minimize release ofconstruction debris,
Proceedings of the papers will be available at the
the contribution of these particles to the overall
conference. In addition, a workshop covering
release of preservative from the structure well be
processing and design fundamentals of wood/FRP
minimal.
hybrid composites will be offeredto assist interested
parties in becomingmorefamiliarwiththis important
To obtain a copy, please contact the National Wood
and expanding materials area.
In Transportation Information Center at 304-285-
Forfurtherinformation, contact: Ms. Doreen Parent, 1591 and request publication number WIT-05-0024
AEWC ME
793 Bldg.,University of Maine, Orono, or visit the Wood In Transportation website at
04469-5793; Telephone: [phone]; Fax: (207) www.fs.fed.us/wit; click on "New Publications
581-2074; E-mail: [email protected];
Available".
AEWC
Website Address: http://www.aewc.umaine.
edu.
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NEW
PUBLICATIONS
Distribution of Borates Around Point Field Performance of
Source Injections in Wood Members Timber Bridges 18.
Exposed Outside Byron Stress-Laminated
Truss Bridge
In bridge timbers, wood decay is usually found where
water has accessed the end-grain surfaces. In The Bryon bridge was constructed in the fal of 993
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preservative-treated members, end-grain surfaces are in Bryon, Maine. The bridge is a single-span, two-
most likely to be those resulting from on-site framing lane, stress-laminated truss structure that is
cutsorborings. Becausetheseat-risk surfacesareeasy approximately 46 feet long and 32 feet wide. The
to see, it seems feasible to establish a program where truss laminations were produced using chromated
diffusible preservatives are repetitively inserted into copper arsenate (CCA) treated southern pine
thosecritical areas spatiallydistributed in agrid andon connected with metal plate connectors. This report
aschedulethatwiIIensureprotection,therebyextending includes information on the design, construction,
the life ofthe entire structure. The objective ofthis and field performance of the bridge. Field
study was to determine the vertical and lateral performance was monitored for approximately five
distributionandthepost-treatmentbehaviorofinjected years, beginning shortly after bridge construction.
and inserted borate preservatives in wood exposed to Performance monitoring involved collecting and
natural wetting in field exposure. Duringthis 1- and 2- evaluating data relative to wood moisture content,
yearexposure,rainwettingelevatedthemoisturecontent force level of stressing bars, behavior under static
ofthewoodenoughtosupportgrowthofdecayfungi in truck loading, and overall structural condition. The
wood notprotected byborates. Pointsourcetreatments field evaluations showed that the Byron bridge is
consistedofeitherboratesolutionsorfusedboraterods performingwell, with no structural orserviceability
that were injected or inserted, respectively, into deficiencies.
predri ledholes.Thelongitudinal movementofborates
1
applied as either glycol or aqueous solutions was To obtain a copy, please contact the National Wood
generally greaterthan that occurring with treatment of In Transportation Information Center at 304-285-
borate rods only. Lateral distribution of borates was 1591 and request publication number WIT-06-0038
similaramongtreatments. Insouthernpine,differences or visit the Wood In Transportation website at
in both vertical and longitudinal movement of borate www.fs.fed.us/wit; click on "New Publications
from the insertion holes were associated with the type Available".
of closure used. Results indicate that borates can be
included in amaintenance program consistingoftime-
sequencedtreatmentofcritical regionsofwoodbridges
that are at risk for internal decay. Grids for placement
of point sources of diffusible borates in engineered
wood structurescouldbedevelopedonawood-species-
specific basis. Such treatments would Complementthe
exterior shell of protection provided by the original
pressure treatment and enhance long-term durability.
To obtain a copy, please contacttheNational Wood In
Transportation Information Center at 304-285-1591
and request publication number WIT-06-0021 or visit
the Wood InTransportationwebsiteatwww.fs.fed.us/
wit; click on "New Publications Available".
5
NEW
PUBLICATIONS continued
Guidelines for Design, Installation, Field Performance of
and Maintenance of a Waterproof Timber Bridges 20.
Wearing Surface for Timber Bridge Gray Stress-Laminated
Decks Deck Bridge
To enhance long-term timber bridge performance, The Gray bridge was constructed in the fall of 1991 in
timber material must be protected from moisture. Gray, Maine. The bridge is a single-span, two-lane,
Wearing surfaces made of asphalt pavement with stress-laminated deck structure that is approximately
and withoutawaterproofmembrane have been used 24 feet long and 23 feet wide. It was constructed from
to provide protection from moistureontimberdecks. chromatedcopperarsenate (CCA)treatedeastern hem-
This type ofwearing surface also protects the deck lockgrown in Maine. This reportpresents information
from other damage while providing a smooth, skid- on the design, construction, and field performance of
resistant surface. However, the long-term thisbridge. Field performance ofthe bridge was moni-
performance of timber bridges has often not been tored for6-1/2 years, beginning shortlyafterconstruc-
satisfactory as a result of cracking of the wearing tion. During the field monitoring program, data were
surface or separation of the asphalt or membrane collectedrelativetowood moisturecontent, force level
from the deck. Cracking or separation allows of stressing bars, behavior under static truck loading,
moisture migrationtothetimberdeckand decreases and overall structural condition. With the exception of
ride quality. To improve the performance of a having to be retensioned approximately every 3 years,
wearing surface, it must be designed, installed, and the bridge is performing well, with no structural or
maintained properly. This document provides serviceability deficiencies.
guidelines for the proper design, installation, and
maintenance of a waterproof wearing surface for To obtain a copy, please contacttheNational Wood In
timber bridge decks. The design section includes Transportation Information Center at 304-285-1591
material descriptions and asphalt mixture and request publication number WIT-06-0040 or visit
reccommendations. The installatin section presents theWood InTransportationwebsiteatwww.fs.fed.us/
material testing, field inspection, detaileddrawings, wit; click on "New Publications Available".
anderrorstoavoid. Themaintenancesectionexplains
the typical signs of distress and corrective
procedures.
To obtain a copy, please contacttheNational Wood
In Transportation Information Center at 304-285-
1591 and requestpublication number WIT-12-0002.
Article contributions questions or comments may be sent to Ed Cesa. Program Coordinator. National Wood In Transportation Information
Center or Mr. Chris,Grant. Program Assistant. USDA Forest Service, 180 CanfieldStreet. Morgantown. WV26505; Phone: [phone]:
FAX [phone]~: E-mail to [email protected] or website at www.fs.fed.us/na/wit.
Crossings is a service of the USDA Forest Service, Northeastern Area, State and Private Forestry, and is distributed quarterly to
individuals and organizations without fee. Products, designs, and treatments mentioned by contributors from outside the USDA are not
necessarily endorsed by the USDA, nor do statements made herein reflect the policy ofthe USDA. In all cases, consult with appropriate
professional and state or local regulatory agencies for conformance to applicable laws and regulations.
The U.S. DepartmentofAgriculture(USDA)prohibitsdiscriminationinall itsprogramsandactivitiesonthebasisofrace, color,national origin,sex,religion,
age.disability,politicalbeliefs,sexualorientation,ormaritalorfamilystatus. (Notallprohibitedbasesapplytoallprograms.) Personswithdisabilitieswhorequire
alternativemeans forcommunicationofprogram information(Braille, largeprint,audiotape,etc.)shouldcontactUSDA'sTARGETCenterat(202) 720-2600
(voice andTDD).
To file a complaint of discrimination, write USDA, Director, Office ofCivil Rights, Room 326-W, Whitten Building, 1400 Independence Avenue, SW.
Washington, D.C. 20250-9410orcall [phone] (voice andTDD). USDA is an equal opportunity providerandemployer.
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