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Durability and Wood Protection for Historic Covered Bridges in the United States
2014 - IRG/WP 14-10829
A majority of the covered wooden bridges in United States were built in the mid -1800’s. These structures represent a unique cultural and technological heritage from that era. Over time, these bridges have been deteriorated by microorganisms and insects or damaged by acts of vandalism and arson. The National Historic Covered Bridge Preservation (NHCBP) Program sponsored by the Federal Highway Administration (FHWA) provides funds to support preservation and restoration efforts for historic covered bridges. The focus of the NHCBP Program is support and technology transfer efforts to preserve, restore and protect covered bridges in conjunction with providing educational resources to the general public. In this paper, an overview of NHCBP research on the durability and wood protection of covered bridges is provided. Research results assist the general public, field investigators and states in their efforts to restore, repair and preserve national historic bridges.
V W Yang, C A Clausen

Examining environmental conditions and the biodeterioration of historic waterlogged wood: the Kolding Cog
2002 - IRG/WP 02-10441
Survival of waterlogged wood from thousands and in rare cases millions of years presents scientists with a unique opportunity to examine wood specimens which, due to select properties of the wood itself and/or the depositional environment, have not been completely degraded. This paper discusses the biodeterioration of a submerged shipwreck buried in Kolding Fjord, Denmark for the past 1000 years. Sections taken from two waterlogged timbers within the wreck site were physically evaluated to determine the extent of degradation in the timber at various depths below the sediment-water interface. The condition of the wood specimens was then compared to environmental characteristics, such as oxygen, hydrogen-ion (pH), and sulfide concentrations. The baseline of information gained from the systematic study of these timbers provides valuable information for the future storage and conservation of the shipwreck.
B A Jordan, D J Gregory, E L Schmidt

Some experiences with attack of microorganisms on wooden constructions supporting foundations of houses and bridges
1997 - IRG/WP 97-10232
Reconstructions of bridges and public buildings or damage of houses during the construction of subway lines in Berlin have led to a number of inspections of wooden foundations, mostly pine or spruce piles, representing service lives of between ca. 70 and 140 years. In all cases bacterial attack was found both in wood submerged in ground water and in surface water. The extent of deterioration differs considerably in round wood and sawn wood and, furthermore, depends on the type of soil or water surrounding the wood. Within 140 years sawn scots pine sapwood can be completely destroyed by bacteria occurring below the level of the water table, whereas scots pine heartwood is remarkably durable. On sawn wood, only a small outer surface layer of the heartwood is damaged. In scots pine piles which had been installed about 110 years ago under the Reichstag building in Berlin bacterial attack produced bending strength losses of up to nearly 50% and crushing strength losses parallel to the grain of up to 55% in the outer sapwood as compared to the heartwood.
M Grinda

An Historical Roof Timber System in the Old Town of Berlin-Spandau
2019 - IRG/WP 19-10949
In Europe the “Charter of Venice” was enacted on the 31st of May 1964. It is the international directive for the preservation of historic buildings and monuments. All countries in Europe now involve professional wood scientists and engineers in maintaining and preserving historical buildings. Here we discuss a restoration project involving 17th century roof timbering. This project may be used as a model for the restoration of other wooden historical monuments.
M Luke, W Unger, D Nellessen

Severe decay damages of bridges made of ekki (Lophira alata) wood known as a durable species
2000 - IRG/WP 00-10383
Bridges made of ekki (azobe, bongossi, Lophira alata Banks et Gaertn.) timbers were severely decayed only 10 years after the construction possibly caused from no maintenance for the periods. The reason of no maintenance is due to the misunderstandings on wood durability against wood-decaying fungi. Some civil-engineers and architectures understand "durable species" means "absolutely decay-durable species." They recently like to use durable wood species imported from abroad instead of domestic wood treated with preservatives because Japanese policies and civic insistences avoid to use wood preservatives to maintain natural environment and human health. This paper deals with the details of the typical decay damages of wooden bridges.
S Doi, T Sasaki, Y Iijima

Recent development in North American industrial wood preservation plants
1988 - IRG/WP 3467
After remaining static for many years there have been a number of changes in plant design and treating cycles in recent years. This has been particularly true in the USA where few restrictions are placed on plant treating cycles by specifications; since only results type specifications are used. It is also important to realize that the AWPA Specifications for Southern Yellow Pine only call for treatment of the sapwood since the heartwood has a high natural resistance to termites and decay. This is evidenced by old plantation houses on Southern and West Indian sugar Plantation houses that have stood for several hundred years. This paper attempts to set out these changes and the reasons for them. Industry often appears to have jumped ahead of research or the results of research have not filtered down to the industry and these knowledge gaps are mentioned in the appropriate sections. These sections try to separate the many inter-related factors into simple headings covering plant components and other factors influencing treatment. Some of the criteria presented in this paper have only been recently recognized as of importance so that results from past research is often found to be inconclusive when studied under the light of present day knowledge (e.g. rate of pressure rise was not noted).
J F Bridges

Site characteristics impacting historic waterlogged wood: A review
2000 - IRG/WP 00-10344
Survival of waterlogged wood from hundreds and in rare cases millions of years presents scientists with a unique opportunity to examine wood specimens which, due to select properties of the wood itself and/or the depostional environment, have not been completely degraded. Although degradation patterns of various types of microbial wood decay have been studied in detail, the site parameters of the zone from which the wood was removed has not been systematically characterized and correlated to the specific types and cause of degradation. Studies have been conducted attempting to relate factors such as hydrogen-ion concentration (pH), redox potential (Eh), oxygen (O2) concentration, and chemical end-member concentration to specific environments, but there has been no unification of testing methodology. This paper proposes to review the literature concerning site characteristics that impact the biodegradation of historic submerged wood, and discuss the implication of such research to future needs for further advancement of the science.
B A Jordan, E L Schmidt

Monitoring a Timber Bridge in Norway
2004 - IRG/WP 04-40282
We have instrumented three different timber bridges in Norway for the Norwegian Public Roads Administration. The goal was to learn more about the properties of timber bridges. We have instrumented Evenstad Bridge, Daleråsen Bridge and the last year Flisa Bridge. All bridges are have creosoted glulam trusses and creosoted stress laminated deck. Evenstad and Flisa have an asphalt deck on top, while Daleråsen has wooden wear boards on top. This paper deals with Flisa Bridge only. In this bridge we monitoring the relative humidity (RH) and the temperature in the deck and the steel bar forces in the stress laminated deck since the construction in March/April 2003. The deck’s moisture content (MC) is calculated from the temperature and RH.. The results after 8 months shows that the steel bar forces are decreasing by time, but still within accepted tolerances. The calculated MC in the deck is in the start higher than in an untreated dummy but during time the deck have almost the same MC as the dummy.
F G Evans

PCP in aquatic environments arising from historic contamination at wood processing and preservation sites
1995 - IRG/WP 95-50040-14
Three different studies are reported that assess the impacts of Pentachlorophenol (PCP) in aquatic environments arising from its historic use at sawmilling and wood preservation sites. These studies involved New Zealand wood processing facilities, and collectively they aimed to measure the transport of PCP from sawmill sites into the aquatic environment, determine the background environmental concentration of PCP in isolated lakes of New Zealand, and assess the relative contribution of PCP from different potential sources, such as sawmills, urban areas and agricultural catchments. The PCP concentrations in water, sediment and biota from a lake catchment, near a major wood processing site, indicated that low level contamination had occurred. PCP levels in lake sediments and freshwater mussels were elevated compared to New Zealand remote lake sites but similar to comparable locations reported in the international literature. Water concentrations of PCP in the lake were less than the most stringent international water quality guidelines for the protection of aquatic life. Water and sediment PCP concentrations in streams within the catchment, isolated from point sources, were less than the detection limit. The PCP concentration found in sediments ( £ 1.3 ng.g-1 DW) from the remote lakes, reflects a New Zealand background concentration. The source of PCP in remote lake sites is unknown, though it is unlikely to be directly from the sawmilling industry. Although the historic use of PCP by the sawmilling industry appears to have caused localised contamination near areas of high use, the current evidence suggests that it has not lead to widespread contamination of New Zealand aquatic environments.
J S Gifford, P N McFarlane, M C Judd, S M Anderson

Analysis of the boron content of preservative treated oak and pitch pine heartwood before and after leaching
1992 - IRG/WP 92-3697
Studies to determine the effects, if any, of a variety of boron formulations on heartwood of English oak and American Pitch pine have been previously reported (King et al (1991)). Small wood blocks were treated, at 10°C or 45°C, with borax, polybor or Boracol 20 for periods of 1 month or 4 months then analysed or continuously leached with tap water for a period of 1 month. Reported results showed minor dimensional changes coupled with some weight loss in most test blocks. The boron contents of all blocks have been analysed by the spectrophotometric method of (Williams (1968)). Although an average of 92% boron was lost many of the treated blocks still retained a protective level of boron (>0.04% B). Boron concentrations left in the leached/treated blocks relate to wood species, block orientation, overall weight loss and type of formulation. The results presented in this paper provide further evidence for the applicability of boron formulations to historic timbers and indicate that even in situations of some moisture movement protection may still be afforded by boron treatments.
S McCutcheon, G M Smith, J W Palfreyman, B King

Effects of boron formulation on specific timber types used in ships of historical importance
1991 - IRG/WP 3676
This paper reports results of preservative treatment and leaching experiments, using borax, polybor and boracol 20, on small wood blocks of English oak and American pitch pine heartwood. Earlier experiments on the performance of various biocides as possible additives to bilgewater to prevent fungal decay of shipping timbers had suggested that some formulations of boron might be associated with physical changes to specific types of timber. Since samples of oak and pitch pine were to be supplied for remedial work on the historic ship RRS Discovery it became important to investigate more critically the effects of boron on such timbers. Variable factors investigated in this study included temperature, sample type, soaking time in preservative and time of leaching. Weight changes and dimensional changes were measured. Preliminary results indicate that there was little effect, at 10°C, on block weight or dimension. Some changes were found at 45°C indicating that the results obtained in earlier experiments may be unrepresentative of those which might be obtained when the biocide is used under service conditions.
B King, G M Smith, J W Palfreyman, S McCutcheon

An Important Wood Destroying Beetle: Anobium punctatum (De Geer) (Coleoptera: Anobiidae) and Distribution of Western Black Sea region
2008 - IRG/WP 08-10666
Anobium punctatum (De Geer) is an economically important insect species regarding damage to wooden structures. The damage mostly occurs in historic wooden buildings, wooden chairs, tables and seats. It has been determined in the Istanbul, Ankara, Ayancik, Bartin, Rize, Trabzon, Gumushane and Gole regions of Turkey. There is no detailed study in terms of the distribution of this insect and the degree of its damage in the Western Black Sea region of Turkey. In this study, it was determined that furniture beetle is intensively widespread in the region.
A Toper Kaygin, Y Yildiz, Ü C Yildiz, S Yildiz, S M Onat, N K Özkazanç, B Kaygin, S Çelíkyay

Penetration Depth of Borates in Historic Wooden Structures in Virginia City Montana
2008 - IRG/WP 08-30475
Virginia City, Montana contains some of the best preserved examples of gold boom construction in the United States. Unfortunately, even the dry climate and fortuitous lack of fire have not prevented decay from claiming parts of the historic fabric. This project aims to determine if borates should be integrated into the preservation plan of the Montana Heritage Commission. Solutions of disodium octaborate tetrahydrate (DOT) were tested in both new and historic lodgepole pine (Pinus contorta) in a fashion that mimics remedial treatments likely carried out in the field. DOT (available commercially as Tim-Bor Professional from Rio Tinto Mineral or Nisus Corporation) and glycol borate (DOT in a proprietary mixture of glycols including polyethylene glycol, available commercially as Bora-Care® from Nisus Corporation) solutions were tested.
A A Turner

The amazing wooden churches from Northern Romania - learning from the past, restoring for the future, preserving the present valuable heritage of forgotten wood building tradition
2009 - IRG/WP 09-10683
The beauty and the uniqueness of the north-western region of Romania called “Maramureş” are well known in Europe. Surrounded by mountains, the region remained to some extend isolated from modern influences, preserving the local village architecture and craftsman traditions learnt and passed on from generation to generation. Local folklore and past heritage sets you back centuries ago when the manual work and wood in particular was the only way to build. Wood construction with specific architecture has developed in this region. Houses and churches were erected in a way in which even today some of these building are still standing and integrate nicely with the landscape. As always good time and bad time are cycles in the human history and time have its impact on the any wooden construction. Restoring and preserving these unique wooden churches from Maramureş is not only a necessity for the local people but an honour and duty in order to preserve their heritage and traditions. In this study, a biological evaluation of the aged and destroyed wood from an historical wooden church from Maramureş, Romania, recently restored, is being investigated and discussed. The aged oak material used in the initial construction is compared with today’s oak wood material available on the market. The option of using VPT treated wood as a material of choice for restoring these monuments are being suggested and eventually considered as a recommendation. The knowledge, the talent and the traditional craftsman type of work used in building these churches are slowly disappearing and somehow needs to be preserved by maintaining this knowledge through restoration work. The question which remains to be answered is whether this material will last centuries like the original one used for construction?
R Craciun, R Möller

Detection and Assessment Healthy Situation of Poulus Euphratica Oliv. with Stress Wave
2009 - IRG/WP 09-20415
The defects of tree trunk of Poulus euphratica Oliv were inspected by stress wave method and diagnosed with transmission time and velocity. The reference values of transmission time of unit length and velocity from stress wave were used to assess the healthy situation of tree trunk. The goal is provide fast inspecting technology and assessment method for the historic trees in China. The results shown: 1) Single-path method of stress wave is effective nondestructive method to diagnoses the defect of wood, but it can not effective assess wetwood in standing trees using the reference value of unit length transmission time (670 m/s )and average velocity (942 m/s), there would have more accurate assessment results if reference value be summarized from sound wood and used to diagnoses healthy situation of tree trunk; 2) Two directions testing of stress wave can not accurate diagnose the edge crack and small area decay in stem, multitude point test should be used to get more useful information of wood ; 3) the multitude point test from single-path stress wave shown that the trend of velocity of healthy tree trunk was increasing firstly with the angle increase and decreasing when the transmission angle more than 180o. There has a binomial formula relationship between velocity and transmission angle and the correlation coefficient arrived at 0.9942. This velocity trend of cross-section in healthy tree trunk and binomial formula can be used to diagnoses the defects of tree trunk.
Shanqing Liang, Nana Hu, Lanying Lin, Feng Fu

Use of Internal Remedial Treatment to Extend Wood Life at the Fort Vancouver National Historic Site
2010 - IRG/WP 10-30525
The condition of wood in a reconstructed fur trading fort was assessed over a 30 year period. Poor initial treatment had resulted in the development of extensive early decay. While supplemental treatment with chloropicrin and methylisothiocyanate had arrested the attack, the results suggested that remedial treatments were unable to completely overcome the initial problems associated with treatment. The results show both the value and limitations of using remedial treatments in these applications.
C S Love, C Freitag, J J Morrell

Chemical protection of historic timber structures: Results and future needs
2010 - IRG/WP 10-40487
The paper concentrates on the analysis of the effectiveness of chemical protection for timber structures in the Russian State Museums “Kizhi” (Karelia) and “Vitoslavlitsy” (Novgorod). The condition of historic timber was tested at the monuments treated with PCP, borax, potassium carbonate, boric acid, Pinotex chemicals in the 1970-80. Long-term analysis revealed that in many cases the deep-treatment with PCP and borax chemicals proved to be efficient only for a short period of time. Profound activity of wood-borers was noted in the structures deep-treated with preservative chemicals. Deep treatment caused emergence of new cracks of timber and enlargement of existed ones. Changes in absorption and desorption processes are occurred. Changes in color are easily seen in a majority of the treated monuments. The treatment also deteriorated the ecological situation. Modern chemicals (Rocima-243, Rocima-293, ULTAN (CCA-type), Ventti, etc.) were tested on pilot structures established in the “Kizhi” museum in 2005. The results of the microscopical investigation of the samples after 3-year - long exposure are given. The chemicals appropriate for restoration and conservation of wooden architectural monuments are presented. The need of environmentally save approaches to preserve an essential part of our cultural heritage – historical wooden structures is emphasized.
M Kisternaya, V Kozlov

Cobblestone Church in Gross Gievietz: Historic Wooden Construction and Potential for Conservation and Use
2011 - IRG/WP 11-10760
A majority of cobblestone churches situated in the German Federal State Mecklenburg-Vorpommern demonstrates immense construction deficiencies and are threatened by decay. The historic cobblestone church located in Groß Gievitz, built in the 13th century, is one such church in which the roof beam constructions have degraded considerably due to deficiencies in reconstruction measures. This paper documents the current state and deficiencies of the roof constructions. Investigations concerning the history of building were carried out in order to classify the periods of additions and repairs to the building (SCHULZE 2006). Dendrochronological techniques were used to determine the age of the beams and as part of the beam characterization process. Existing beam defects and deficiencies were determined by a wood conservation survey. The causes for deterioration have been identified, and suggestions for remediation made. Mapping and analyses were based on regulations and bulletins of German associations for conservation of monuments and various specialized literature. The results of our research will support the implementation and performance of remediation measures to conserve the roof beam construction and to maintain durability as long as possible.
A Schulze, W Unger

Effectiveness of Water Based Bentonite-Borate Slurry for In-situ Remedial Protection of Historic Wooden Piles: The Eurobor Protocol, Part 2
2011 - IRG/WP 11-30574
The study of the biocide product Eurobor®, water mixture of boric acid, borax and sodium bentonite, aimed to verify previous findings regarding borates penetration from a clay-water mixture of foundation timber. The product was applied on samples from 100 year old timber foundation from the city of Göteborg. Although in ground for this long the timber was in acceptable god condition due to ground water coverage of the foundation piles. The results show that borates diffuse readily into the sapwood and reach toxic concentrations (> 1 kg BAE/ m3 wood) for decay fungi in the decay front. Penetration of borates from the clay-mixture correlated with wood samples decay pattern and reached into sound heartwood. Concentrations reached 60000 mg BAE/kg in sapwood and 2500 mg BAE/kg inside the decay front towards heartwood. The technique with Eurobor® has been demonstrated both in field and laboratory to be effective by penetration and retention of the borates in toxic levels for decay fungi.
M. Theorin, K. Fimmerstad, K-M. Bandh

Quasi-in-situ durability tests on oak timber bridges
2013 - IRG/WP 13-20510
This study aims on developing a method for determination of wood durability on samples taken from real structures in service. Therefore quasi-in-situ durability tests have been conducted exemplarily on timber bridges made from English oak (Quercus robur L.). Drilling cores were found to be a feasible alternative to standard specimens for laboratory durability tests against pure cultures of Basidiomycetes and against soft rot and other soil-inhabiting micro-organisms in unsterile soil. Drilling cores were therefore taken from various components of six bridges, which were similar in design, but differed in previous service life. The determined mass losses due to fungal decay were compared with the level of damage of the studied bridge components. The results indicated that the material-inherent resistance was responsible for damages rather than poor details of the construction. The methodological approach should be seen as quasi-in-situ resistance tests providing further knowledge about the relationship of timber in service and under ideal laboratory test conditions.
C Brischke, C J Behnen, M-T Lenz, K Brandt, E Melcher

Laboratory investigation of fire protection coatings for creosote-treated timber railroad bridges
2014 - IRG/WP 14-30639
As the incidence of timber railroad bridge fires increases, so has the need to develop protective measures to reduce the risk from accidental ignitions primarily caused by hot metal objects. Of the six barrier treatments evaluated in the laboratory for their ability to protect timbers from fires sourced with ignition from hot metal objects only one intumescent coating provided adequate fire protection. The intumescent barrier treatment also met environmental, performance (e.g. bond durability) and application criteria set forth in this study. These criteria also dictated the development of a flammability test, called the hot metal test that is compatible with the fire scenario specific to this study. The hot metal test evaluates protective materials on creosote-treated timber against ignition of gases generated by an 1100ᴼC heat source.
C A Clausen, R H White, J P Wacker, S T Lebow, M A Dietenberger, S L Zelinka, N M Stark

CreoSub – New protection technology to substitute creosote in railway sleepers, timber bridges, and utility poles
2014 - IRG/WP 14-30644
Creosote oil is one of the oldest industrially used wood preservatives. Due to its toxic profile, the European Commission has restricted the use of creosote specific applications, but it is highly controversial within the European Commission. Its approval for use after 2018 is very questionable and may depend on derived research results until then, i.e., the viability of alternatives developed to replace creosote as a preservative of wood products in heavy-duty applications outdoors, like railway sleepers, timber bridges, utility poles, and piles in marine applications. The overall objective of the three year WoodWisdom research project CreSub is the development of a new protection technology to substitute creosote in railway sleepers, timber bridges, and utility poles. The technological objective is to develop production processes for railway sleepers, timber bridges, utility poles, and piles treated with new wood protection systems from laboratory to industrial scale and test the products under real conditions in the field. This implies to individually consider process-related, economic and environmental aspects for each of the three different product groups mentioned above. Alternative products to creosote have to be hydrophobic and biocidal effective, particularly with respect to soft rot and copper tolerant fungi. Last-mentioned are mainly responsible for that conventional impregnations with solely copper-based salts do not provide sufficient protection of products in heavy-duty applications outdoors. In addition, alternative protection technology must be economically viable. In this regard, one-step treatment processes, which preferably can be carried out in existing creosote plants, are desirable. Last but not least, new technologies should have better human toxicological as well as environmental toxicological profiles than creosote technology.
U Hundhausen, K-C Mahnert, A Gellerich, H Militz

Cultural heritage – research into innovative solutions and methods for historic wood conservation
2016 - IRG/WP 16-10874
Nowadays, interdisciplinary knowledge, tools and techniques are increasingly used to protect and conserve monuments representing our cultural heritage. This is of great importance especially in case of conservation and restoration of wooden historic artefacts which, as a result of physical, chemical and biological corrosion, have lost their technical, aesthetic and decorative properties. If those processes are not consciously stopped by appropriate conservation works, with the elapse of time they will start to threaten the existence of valuable relics leading to their irreversible destruction. Our generation is responsible for evolving modern, improved techniques and methods ensuring adequate, professional protection for historic artefacts. What is necessary to achieve this goal is close and smooth cooperation between conservators and museum workers, strongly supported by specialised knowledge of scientists representing diverse research disciplines, including biology, microbiology, chemistry, and physics. The aim of the new “Cultural heritage – research into innovative solutions and methods for historic wood conservation” project, supported by the Polish Ministry of Science and Higher Education ( “Dziedzictwo kulturowe – poszukiwanie nowoczesnych środków i metod konserwacji drewna zabytkowego”, No. 2bH 15 0037 83), is to develop new materials and techniques for conservation of wooden artefacts. Many different types of wood are planned to be studied, including dry wood (e.g. sculptures, paintings on wooden panels as well as various wooden constructions: churches, cottages, sheds, etc.) and wet wood (archaeological wood), individually selected for research in accordance to the level of wood degradation. The main idea behind the innovative solutions is based on technology using organosilicon compounds, particularly polysiloxanes and silsesquioxanes, and nanocellulose. Taking into consideration unique opportunities offered by the mentioned substances, it is highly probable that a new method for strength restoration of destroyed wood will be developed, which will therefore enable wooden historic objects to keep their shape and spatial form. Successful realisation of the project’s assumptions will open new horizons in research on conservation and preservation of wooden cultural heritage.
M Broda, B Mazela

Creosote leaching from timber bridges in Norway – a practical classification approach
2016 - IRG/WP 16-40744
Creosote is widely used as a wood preservative for highway timber bridges in Norway. However, excessive creosote leaching at various highway timber bridge sites leads to a bad reputation for the use of creosote treated timber constructions and the use of wood in general. Macro- and micro anatomical factors such as amount of heartwood, annual ring width, annual ring orientation, ray- height and composition and resin canal area were investigated in order to classify seven timber bridges in Norway into leaching- and non-leaching bridges. With three anatomical factors a classification into leaching and non-leaching was possible for two discriminant categories based on observations on wood core samples and on entire bridges. The amount of heartwood content dominated the influencing factors, even obscuring the significance of other factors.
A Treu, K Zimmer

Comparative Durability of Timber Bridges in the USA
2017 - IRG/WP 17-20615
As engineers begin to utilize life-cycle-cost design approaches for timber bridges, there is a necessity for more reliable data about their durability and expected service life. This paper summarizes a comprehensive effort to assess the current condition of more than one hundred timber highway bridge superstructures throughout the United States. This national study was jointly administered by the Forest Products Laboratory and the Federal Highway Administration and relied on data from the National Bridge Inventory database. In-depth inspections were conducted using visual and non-destructive evaluation techniques to characterize the condition of the primary bridge components and detect any structural deficiencies. The most popular superstructure system studied in this project was the multiple sawn stringer and plank deck system. This system was evaluated in a number of wood hazard (climate) zones with numerous examples of 60 or 70 year service records. The durability of the timber bridges studied was predicated on use of pressure treated materials for the primary structural members as required by the national bridge design code.
J P Wacker, B K Brashaw

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