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Prefacricated modular wooden bridges
2017 - IRG/WP 17-40785
The bridge consists of simple, identical pre-fabricated triangular wooden panels joined top and bottom to make up trusses. These trusses are in turn joined together side by side in pairs and are braced to one another to create a girder construction. The deck is carried on top of the trusses, an arrangement which has several advantages for such an uncomplicated structure. It is built up on site, after the girders are launched, using a nailed laminated construction. The bridge has a slight built-in precamber. Longitudinal running boards direct the wheel loads of vehicles using the bridge. Handrails are normal in rural areas near villages where pedestrian safety is a consideration, although in remote countryside or forests these can be omitted for economy if desired. The design has proved most economical for spans between 9 meters and 24 meters, although design tables for up to 27 meters are provided.
L Jayanetti


Ekki heartwood - is “Durable”
2002 - IRG/WP 02-10444
Severe decay damages of bridges made of ekki (Lophira alata Banks) wood which is classified as a durable species in the EN 350:2 as already reported at the 31 IRG annual meeting. This paper deals with results of long-term decay tests of ekki heartwood specimens using 3 isolates (Loweporus tephroporus 2 strains and a fungus of other sp. from damaged ekki bridges) and Trametes versicolor as a reference. Sound ekki heartwood specimens, sized 20(T) x 20(R) x 5(L) mm were used. References were Japanese beech (Fagus crenata) specimens having the same dimensions. Oven dry weights of the specimens were measured at 60 oC for 48 h before and after the decay process. Nine replications of specimens were used per set. The procedure of decay test was about the same as that of the JIS Z 2101. All the test fungi including T versicolor decayed ekki heartwood in the case of long-term exposure (more than 6 months) using the appropriate nutritional condition under optimum temperatures. These facts suggest that the results of standardised decay test methods should be carefully interpreted.
S Doi, R Itoh, S Horisawa


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


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


Cost effective extension of service life of bridge tie (sleepers) - Effectively applying borate during Boulton conditioning and treatment with copper naphthenate
2014 - IRG/WP 14-30637
Current longevity of creosote treated wooden bridge ties in the South Eastern US is about 15 to 25 years, which is well below of the average service life of 33-50 years of railroad ties. Such short service life increases costs associated with maintenance of railroads including bridge down time for tie replacement as well as the cost for the new ties themselves. Because of this, many railroads are seeking non-wood alternative ties, even at vastly elevated initial cost. The objective of the study was to see if it is possible to apply borate as part of a dual treatment with copper naphthenate, in order to increase the service life of wooden bridge timbers at minimal additional cost. Green hardwood ties were ported, borate treated, and then Boulton treated with copper naphthenate at a commercial tie treatment plant in Pennsylvania. Diffusion of borate within the wood appeared to be significantly enhanced by the elevated temperature and steam generated during the Boulton cycle and subsequent pressure treatment with copper naphthenate. The achieved retention and penetration of borate and copper naphthenate met AWPA standard retentions and AREMA guidelines. The longevity of ties should be significantly increased by protecting the heartwood with disodium octaborate tetrahydrate (DOT) and the sapwood with copper naphthenate. The results suggested that hardwood ties can be successfully treated with borate during a Boulton cycle and should allow the continued effective use of sustainable wooden bridge timbers.
J D Lloyd, T Chambers, J-W Kim


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


Modelling of moisture content in timber bridge details
2017 - IRG/WP 17-20613
The design of details is an important aspect in durability design of timber bridges. Details are often considered the weakest points in bridges due to their tendency to trap and accumulate moisture and thus facilitate decay. When designing maintenance plans and inspection intervals, it is important to know how design choices will come to influence the service life. Moreover, service life and wood moisture content are closely related. Therefore, the aim of the present study was to develop a method that can be used to estimate the moisture content in typical timber bridge details. This was done by considering the moisture content in details as the sum of two components: a reference moisture content (ideal drying conditions) and an amplified moisture content response (due to actual drying conditions). The focus of the present paper was on the latter component. The proposed approach consists of a set of simple equations and a detail-specific parameter, kdry, which describes the detail-specific drying conditions. The detail-specific parameter was fitted to four time-series from two different data sets. In all cases, the estimated moisture content time-series exhibited the same behaviour as the measured data. In all three wood-to-wood details, the best fit was obtained for kdry=1/10 which indicates some level of consistency. Although the approach was only tested against a few time-series, it has so far shown some promising features. More data will be added in future work.
J Niklewski, C Brischke, E Frühwald Hansson, L Meyer-Veltrup


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


In-service performance of treated plywood bridge decks in Australia
2017 - IRG/WP 17-40794
Engineered wood products have a long history of use in bridge construction in Australia. The first bridges incorporating chemically protected engineered wood components were installed in the 1850’s and some survive to this day. Preservative treated plywood bridge deck panels have been employed since the 1980’s as a replacement for the more traditional hardwood plank decks. This paper reports on the condition of engineered wood bridge deck panels through an examination of core samples cut from preservative treated plywood decks after up to 20 years’ in-service. The panels had been manufactured using either; copper chrome arsenic (CCA) preservative in an envelope treatment process or an alkaline copper quaternary (ACQ) preservative in a veneer treatment process. The in-service performance of both types of panels is discussed in relation to results from preservative penetration and retention testing together with a consideration of the severity of the termite and decay hazards to which they were exposed. All but one deck panel were found to be sound, unaffected by decay, the exception was a panel that had been adequately treated but came from a location where it appeared that poor design or detailing had increased the decay hazard. This proven long term satisfactory performance of both envelope and veneer treated plywood panels in what is a particularly hazardous above-ground end-use suggests that current penetration requirements are appropriate for this product category.
M A Powell


Borate and Copper Naphthenate Dual Treatment of Bridge Timbers-Borate movement over time
2017 - IRG/WP 17-40795
Preservative treated wooden bridge ties in the South Eastern USA have a service life of about 15 to 20 years, which falls well below the average service life of 40 years of railroad cross ties (sleepers). It has been shown that cross tie life is significantly extended using borate dual treatment and this is now commercialized in bridge timbers using borate inserts. In previous research, it was demonstrated that distribution of disodium octaborate tetrahydrate (DOT) within the wooden bridge ties was dramatically accelerated during Boulton treatment. The objective of this study was to determine how much diffusion of borate inside the bridge tie after initial treatment occurred over time. Green hardwood bridge ties were ported, borate treated, and then Boulton seasoned and treated with copper naphthenate at a commercial tie treatment plant in Pennsylvania, U.S.A. Retention and location of borate within the wood was tested at 3, 14 and 40 weeks after the treatment. It appeared that borate continued to diffuse inside of the tie and would likely treat and protect a significant volume of the heartwood over time and thus increase bridge tie life in a similar way to crossties.
J-W Kim, J D Lloyd


Performance of Norway spruce bridge in North-West Spain after 12 years exposure
2017 - IRG/WP 17-40796
Across Europe is very common to find bridges build in sawn and glue-laminated wood. Most of these bridges used softwood wood species such as: fir, spruce, larch and pine. In Spain wooden bridges, became more and more popular since nineties, when sawn and glue-laminated wood were utilized for building exterior wooden structures in overall Spain. This material, sawn and glue-laminated wood, are made in a lot of cases of fir (Abies alba) and spruce (Picea abies), generally from central and northern European origin and production without a correct treatment to improve their low natural durability because their use is previewed in use classes 1-2 according to the standard EN 335: 2013. The diversity of wood species, preservative treatments and designs, combined with the variability of environmental conditions (different climatic zones and exposure to weathering), has led to the emergence of pathological processes associated primarily with fungal decay (wood destroying fungi) and wood destroying insects in lesser extent. In some wooden bridges, the magnitude and extent of the damage due to early decay was such that it has reduced the cross section and strength of wooden components, directly affecting the safety of these structures. This paper, with a case situation of early decay in spruce bridge located in North-West Spain, tries to summarize the situation of these exterior structures built in the nineties. In some cases, damages had appeared before ten years of service life. As it will be shown, in this warm and wet area of Spain, wooden parts or joints that create water traps, including the structural elements, present such a destruction level that most of the times the substitution of the bridge is mandatory. So the aims of the study of this case are to understand the cause of early severe decay. It is important to remark that the definition of a proper approach to degradation of spruce bridges, need different competences such as architects, civil engineers, wood technologists, biologists, etc. The case of study has always been analyzed according to the occurrence of decay or failure, but this fact does not mean that all Spanish spruce bridges have this kind of problems, or that are not well designed.
D Lorenzo, J Fernández-Golfín, M Touza, M Guaita, A Lozano, J Benito


Dual Borate and Copper Naphthenate Treatment of Bridge Timbers:- Potential Performance Enhancements and Cost Savings
2017 - IRG/WP 17-40797
Dual treatment technology combining diffusible preservatives with oil borne preservatives, widely used for crossties in the USA, has now also been commercialized with bridge ties/timbers. In order to understand the implications of these changes, the historic service life of creosote treated bridge timbers in northern and southeastern USA were considered as well as field test data for both creosote and copper naphthenate. These were used to estimate potential future service life. Estimates on life expectancy with added borates were also made from published data on performance. Cost benefit analysis based on creosote and copper naphthenate costs as well as assumptions made from field test efficacy data suggest cost savings of up to $20 per timber per year of additional service. Service life extension and the resulting cost savings could be achieved in a number of ways: change preservative from creosote to copper naphthenate; increase active ingredient retention; and/or add dual treatment protection. A preservative change from creosote to copper napthenate would be the simplest and lowest cost way of increasing service life of bridge timbers, with potential savings to both treater and railroad. An increase in copper retention could also give significant life extension, could be carried out at little additional cost and without increasing bleeding. The addition of borate to protect the heartwood also provides significant assumed increase bridge tie life, and can be used with either creosote or copper naphthenate treatments.
J Lloyd, C Brischke, R Bennett, A Taylor


Review on protection of timber bridges in Norway and other countries
2017 - IRG/WP 17-40809
Wood plays a major role in design and construction of modern bridges in Norway. Typical elements of those bridges are double impregnated glued laminated members, stress laminated timber decks, slotted-in steel plates, metal cladding of the surfaces of loadbearing members, and cross girders made of steel. Selected examples of timber bridges in Norway are presented. This review paper gives an overview of the importance of timber bridges in Norway, Sweden, Finland, Germany, Switzerland and the USA. The literature in the fields of protection by design, preservative treatment, monitoring and inspection of timber bridges is summarized. In the light of the potential ban of creosote as wood preservative, protection by design is crucial for modern timber bridges in Europe. The basic principles of protection by design are outlined, and an overview of approaches to find alternatives for creosote and the application of modified wood as material for timber bridges is given. Monitoring and inspection are essential to investigate the performance of a timber bridge and to gather data for life cycle estimation. The importance of monitoring the moisture content in bridge structures is pointed out, and an overview of techniques and tools for destructive and non-destructive inspection of timber bridges is presented.
K-C Mahnert, U Hundhausen


Performance of wood exterior structures above ground in Spain built with softwood species. The situation case of a shelter bridge
2018 - IRG/WP 18-40844
Across Europe is very common to find wood exterior structures build in sawn and glue-laminated wood. Most of these exterior wood structures use softwood wood species such as: fir, spruce, larch and pine. In Spain exterior wood structures, became more and more popular since nineties, when sawn and glue-laminated wood were utilized for building exterior wood structures in overall Spain. This paper shows the situation of several exterior wood structures in sawn and glue-laminated wood, built in the nineties in Spain mainly in softwood species as: fir, spruce, larch and pine. In most cases, damages due to early decays appear before ten years of service life and the magnitude and extent of the damages is very important. In some wood exterior structures, the magnitude and extent of the damage due to early decay is such that it has reduced the cross section and strength of wood components, affecting the safety of these structures, with a destruction level that most of the times the substitution of the structure is mandatory. The aim of this study is to understand the causes of early decays, showing the case study of an wood exterior structure located in the city of Pontevedra, in the Northwest of Spain, analyzing the influence of the diversity wood species, preservative treatments and protection by design (detail designs); combined with the variability of environmental conditions (different climatic zones and exposure to weathering), use classes and position and thickness of wood elements in the emergence of early pathological processes associated primarily with fungal decay (wood destroying fungi) and wood destroying insects in lesser extent. It is important to remark that a proper approach to performance of wood exterior structures, need different competences such as architects, civil engineers, wood technologists, biologists, etc.
D Lorenzo, M Touza, J Fernández-Golfín, A Lozano, J Benito