Experiences from timber bridge inspections in Sweden – examples of influence of moisture

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Experiences from timber bridge inspections

in Sweden – examples of influence of moisture

Anna Pousette, Per-Anders Fjellström

SP Rapport 2016:45

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Experiences from timber bridge inspections

in Sweden – examples of influence of moisture

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Abstract

This report contains a compilation of experiences that SP Technical Research Institute of Sweden has obtained from inspections of timber bridges for bridge owners. The report has been prepared within the project DuraTB – Durable Timber Bridges.

Most damages recorded at the inspections of timber bridges are connected to high moisture levels, such as cupping of deck plates, problems with edge beams, anchor plates and asphalt surfaces and rot. In this report the values of moisture content are the values measured at the time of inspection.

Details of timber bridges are described, the focus is on timber railings and stress-laminated decks, because of the importance of good wood protection by design in these areas. Several examples are described with type of bridge and location, materials and dimensions, moisture contents and rot propagation and probable cause of the damage.

Key words: timber bridge, stress-laminated decks, moisture content, bridge inspection

SP Sveriges Tekniska Forskningsinstitut SP Technical Research Institute of Sweden SP Rapport 2016:45

ISBN 978-91-88349-49-1 ISSN 0284-5172

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3.5 Example 5 – Stressed laminated timber deck 23 3.6 Example 6 – Stressed laminated timber deck 25 3.7 Example 7 – Stressed laminated timber deck 27 3.8 Example 8 – Stressed laminated timber deck 30 3.9 Example 9 – Stressed laminated timber deck 33 3.10 Example 10 – Stressed laminated timber deck 36 3.11 Example 11 – Stressed laminated timber deck 39

4 References 41

Appendix A. Moisture measurements on timber truss bridges

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Preface

This report has been prepared within the project DuraTB – Durable Timber Bridges. The objectives of the project are to develop sustainable timber bridges by developing guidelines for moisture design methods and new and improved structural designs and bridge details with respect to durability and maintenance aspects.

The project DuraTB is a Wood Wisdom-net project with participants from Norway, Finland, Sweden and USA. Project manager is Kjell Arne Malo, NTNU, Norway. The project has been funded under the WW-net+ Research Programme by the ERA-NET Plus Scheme of the Seventh Framework Programme (FP7) of the European Commission. The Swedish participation has been funded by Vinnova and industry partners Martinsons Träbroar, Moelven Töreboda, Limträteknik and Trafikverket.

This report contains a compilation of experiences that SP Technical Research Institute of Sweden has obtained from inspections of timber bridges for bridge owners during several years. The report is part of WP2 “Performance based service life design of timber bridges”, managed by Sven Thelandersson, Lund University, and is a result from task 2.1 “Collection of field data from existing instrumented bridges” that Anna Pousette, SP Technical Research Institute of Sweden, is responsible for.

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1 Introduction

Improved guidelines to avoid the risk of moisture damages is one of the goals of the project Durable Timber Bridges. Data concerning actual service life performance of existing timber bridges can be used as a basis to evaluate today’s bridges and to develop new designs and new design tools.

Field data regarding moisture content and temperature in timber bridges together with information about the bridges and the climate of the sites can be used to calibrate calculation models of moisture distribution in timber.

To validate tools for service life design it is likewise useful to have field data regarding moisture content and temperature, but also information concerning actual service life performance from inspections. Any damages that has occurred in existing bridges are valuable. This report describes some results from timber bridge inspections in Sweden, carried out under the ordinary bridge management (1). It includes a compilation of bridge damages at the time of inspections. Some examples with measurements and assessments of damages are included. They show moisture content levels measured at different areas in bridges together with descriptions of where and in which extent a rot development has been observed.

Inspections of some Swedish timber bridges were also made in an earlier project in 2004 (2). The bridges were selected to include different bridge types, ages and geographical locations. No serious damages, which should affect the bearing capacity of the bridges over the next 10 years, were found. However, there were some details and moisture levels which in the longer term should be taken care of. The inspected bridges had several damages due to lack of detailed workmanship or unsuitable materials, which have then been improved in later bridges. Some comparisons with the earlier study are made in chapter 2.5.

Inspections and evaluations of timber bridges have of course also been carried out in other countries. There are many timber bridges built in Norway over the last 25 years (3). They have used somewhat different materials, treatments and constructions compared to Sweden but it may still be interesting to compare the experiences, see chapter 2.6.

The timber bridge manufacturer Martinsons has built many timber truss bridges for pedestrians/cyclists. They made a follow-up of some truss bridges in Sweden in 2009, when the bridges were 8-12 years old. Moisture was measured during one day, see Appendix A.

1.1 Timber bridge inspections in Sweden

During 2011 to 2015 SP Technical Research Institute of Sweden inspected about 145 timber bridges built after 1990. The inspections were made on behalf of the Swedish Transport Administration, local authorities or engineering consultants. The bridges were geographically spread all over Sweden, from Lund in the south to Kiruna in the north, but most were located in the northern parts of Sweden.

The bridges presented in this report is not a random selection from all timber bridges in Sweden. It contains only a minor part of the results from bridges that have been inspected by SP, mainly as part of the planned bridge management. In chapter 3 Details, the focus is on timber railings and stress-laminated decks, because of the importance of good wood protection by design in these areas.

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The inspected bridges were built during 1990-2015 and included 27 beam bridges (plus 12 older beam bridges); 66 stress-laminated deck bridges; 10 stress-laminated box-beam bridges; 9 stress-laminated T-beam bridges; 30 bridges of other types like trusses, suspended and cable-stayed bridges, etc. This report describes the type of damages at the time of inspection, but not the Condition Class. The Swedish Transport Administration has four classes 0-3 for the condition of a bridge, see table 1.1, and the requirement is a main inspection of bridges every six years.

Table 1.1. Condition classes of bridges in Sweden (4)

Condition class Definition

0 Malfunction beyond 10 years 1 Malfunction within 10 years 2 Malfunction within 3 years

3 Malfunction at the time of inspection

The documented deficiencies in this report required measures ranging from immediately to within ten years.

1.2 Measured moisture contents

In this report the values of moisture content are the values measured at the time of inspection. Moisture content values reported as high moisture values in this report are over 20% MC. Serious moisture levels in wood are above saturation point, which for spruce and pine is 25-30 %. Long periods with MC above the critical value of 25 % can cause problems with rot in the wood. Continuous measurements or measurements repeated often can give more accurate data, since measurements taken for example directly after a rainy day might not be representative if the wood has the possibility to later dry out. But data from the inspections can still provide valuable information if you also take into account the structure and location of the bridge. And MC from different depths in the wood can give information if the measured moisture is only temporary on the surface after rain or is spread into the whole wood element and probably will not dry out so quickly.

The moisture content in wood vary naturally with the seasonal variation of humidity of the air. The cause of the measured high moisture contents are typically condensation, rain or running water, and not high relative humidity of the air, but the reason for the high MC can sometimes be difficult to determine when bridge inspections are infrequent. To really understand the reasons for the high MC, measurements should be carried out more frequently. Also inspections on rainy days can provide more information and show how water spreads on the bridge. For bridges crossing over rivers the underside of decks can be influenced by evaporated water from river that can condensate. The distance from water can in these cases be an important factor for the MC at the bottom part of a bridge deck.

The measured high MC are usually connected to the details, but also sometimes to tear or cracks in the wood. The bridge details have been developed constantly since the first modern timber bridges were built in Sweden in the early 1990s. Today the knowledge about constructive wood protection is used more widely and also requirements and recommendations from the Swedish Transport Administration have are more rigorous. Examples are claddings on beams and arches and the use of spacers and treatment of end grain. Therefore some of the reported deficiencies and damages will probably not occur in newer bridges at all.

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Most commonly impregnated pine is used in unprotected bridge components like beams and railings. The stress-laminated bridge decks are on the other hand typically made of spruce. Impregnation affect moisture measurements and it can be difficult to know the exact moisture content in large beams, as there is a mix of impregnated sapwood and untreated heartwood in glulam.

2 Summary of inspection results

About 950 timber bridges have been built in Sweden since 1990. During 2011-2015 SP in Skellefteå have inspected about 145 of these bridges. The bridges are geographically spread all over Sweden. They are both road bridges and pedestrian bridges and built with different structures for example girder bridges, stress-laminated decks, stress-laminated box-beam and T-beam bridges, trusses, suspended and cable-stayed bridges.

General damages of many of the inspected timber bridges were in addition to those specified below for each bridge type:

• Damages from snow removal vehicles • Flaking of paint on painted members • Algae on the surfaces

• Cracks and sometimes blisters in asphalt paving • Bushes and other vegetation at or near the superstructure • Soil or gravel on bridge members or foundations

Most deficiencies were found on bridges built from 1990 to 2008. It can be expected that older bridges will get more damages due to aging, but from these inspections it is difficult to assess the time until maintenance or repair actions are needed, because during the same period the bridge designs have been improved a lot.

2.1 Beam bridges

Timber beam bridges are frequently used as pedestrian bridges, but also sometimes as road bridges especially on smaller roads. The beams are usually made of salt-impregnated pine. The bridges are often built with an open design with a wooden plank deck. Today the beams are normally covered on the outer sides, but earlier bridges had no weather protection and the outer beams often have many cracks on the outside. Recently some bridges have also been built with spruce beams covered with cladding on the outside to protect them from weather impact.

Inspected bridges were 10 road bridges (including also four bridges built 1737-1965) and 20 pedestrian bridges (including also six bridges built 1930-1989). At the inspections many bridges had cracks on unprotected and weather exposed beam surfaces, and the color of surface treatment had impact on the cracking. Not working joints/expansion joints at abutments in combination with no removal of soil and dirt from abutments for some bridges resulted in high moisture contents at the ends of main beams. Half of the beam bridges had cracks and the same amount of bridges had high moisture contents. Nearly half of the road bridges and one pedestrian bridge had rot.

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Table 2.1. Results from 27 inspected beam bridges, built 1990-2013.

Deficiencies in beams/girders Road bridges (6) Pedestrian bridges (21) Cracks 5 9

High moisture content 2 14*

Rot - 2

*At least three of these bridges are made of spruce

Figure 2.1. Beam with typical cracks. Figure 2.2. Beam end with high moisture content

2.2 Stress-laminated deck plates

The stress-laminated deck plates are made of spruce, and usually have an asphalt surface, but sometimes gravel or wood on the surface. Stress-laminated deck plates are common for both road bridges and pedestrian bridges, and sometimes in combination with other structural elements, for example various trusses or arches. The bridges were built with wooden railings, but steel railings are required today for road bridges.

Development of deck plates since the 1990´s has led to several important improvements such as better anchor plates and better coverage of the edges of deck plates. Timber bridge manufacturers have developed their own guidelines for the execution of waterproofing, and newer bridges have better quality.

Inspected bridges were 36 road bridges and 31 pedestrian bridges. At the inspections the sealing of the waterproofing layer at the edge was poor on several bridges, and this led to high moisture contents and sometimes rot on stress-laminated deck plates that were built from 1994 to about 2001. Bad sealing around railing posts results in drainage water running down the posts causing high moisture contents at the edges of the decks. Some problems with anchorage of the pre-stressed steel bars was observed. Aluminum plates had cracks; vertical hardwood anchor plates made of two separate pieces were too weak and bent. Newer bridges have larger horizontal hardwood anchor plates to spread the load in a better way.

Rhombic deck plates had potholes in asphalt paving where anchor plates of the pre-stressed steel bars were located. Leaking end joints/expansion joints resulting in water on the foundation. This led to high moisture content at the corners of some deck plates which can affect their durability. Cupping of some deck plates was observed.

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Table 2.2. Results from 67 inspected bridges with stress-laminated decks, built 1994-2015.

Figure 2.3. High moisture contents, indirect damages were rail posts inclined inwards and the asphalt coating started to crack along the edge. The leakage came from inadequate execution at the edge beam and the rail posts.

Figure 2.4. Two piece hardwood plates works poorly, they bend and due to that the aluminum plate cracks.

Figure 2.5. High moisture content and rot. Leakage from the attachement of rail posts and inadequate execution at the edge beam.

2.3 Stress-laminated box-beam and T-beam

bridges

Inspected bridges were 4 road bridges and 10 pedestrian bridges. There are few and quite new box-beam bridges and T-beam bridges, and not so many damages reported. Mostly the same problems occurred as for stress-laminated deck plates, with cupping, moisture, sealing at edges and with anchor plates. No decks had rot.

Deficiencies found in stress-laminated decks. Road bridges (36) Pedestrian bridges (31) Cupping, 1994-2014 16 15

High moisture content, 1994-2015 8 13

Rot, 1994-2000 2 6

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Table 2.3. Results from 19 inspected bridges with stress-laminated box and T-beam decks, built 1993-2015.

2.4 Trusses, arch bridges, suspended bridges and

cable styed bridges

Most of these types of bridges have been in quite good condition at inspections. They are often built with a bridge deck of beams or a deck plate. Inspected bridges were 5 road bridges (including 3 suspended bridges built 1920-1981 and 1 arch bridge from 1889) and 21 pedestrian bridges (including 1 bridge from 1920). Many damages were the same as occurred for beam bridges and stress-laminated deck plates. Cracks, cupping and high moisture content were the most common damages. Rot was found in two bridges and asphalt damages in three bridges.

Table 2.4. Number of trusses, arch bridges, suspended bridges and cable styed bridges with reported damages

2.5 Comparison with earlier inspection project in

Sweden

Some Swedish timber bridges were inspected in an earlier inspection project in 2004. The 13 timber bridges were chosen based on different bridge types, ages and geographical locations. The bridges were built 1994-2001. Timber bridge structures were developed very much during 1994-2001, and much improvement work was done to find good design solutions. The inspected bridges had some damages due to lack of detailed workmanship or unsuitable materials, which has been improved in later bridges.

No serious damages were found, which should affect the bearing capacity over the next 10 years from inspection, however, there were details and moisture levels which in the longer term should be taken care of. The highest moisture contents were measured in unprotected cross beams, main beams, arches and pillar supports, in railings especially at the bottom of the railing posts, and at the end or edge of deck plates.

At abutments was a lot of soil, dirt and leaves, and sometimes a lot of vegetation around them. Expansion joints between road and bridge had some damages resulting in leakage Deficiencies found in stress laminated box

and T-beam decks.

Road bridges (9)

Pedestrian bridges (10)

Cupping, 1994-2008 - 3 (T-beam)

High moisture content, 1993-1997 2 (T-beam) 3 (T-beam)

Rot - -

Cracks in stress-bar anchor plates, 2003 2 -

Damage Road bridges Pedestrian bridges

Cracks 1 4

Cupping - 3

High moisture content 1 9

Edge beam 1 3

Anchor plate/ aluminum plate - -

Plywood anchor plate - 2

Rot 1 1

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of water, gravel and dirt onto the abutments, which affected the deck plates or beams at the ends. There were also some bridges with bad contact with the abutments, loosened or damaged bolts or bracings.

Several beams, arches and other structural elements had delamination and/or cracks on painted surfaces, especially on south sides. Some steel covers were damaged and the surface treatment was often eroded and with some cracks on the outer weathered sides of structural parts. No repainting had been made, just small touch up on small areas. High moisture contents occurred at some unprotected and exposed parts.

Several stress-laminated deck plates had anchor plates pressed into the wood and the wood was deformed and crushed around the anchor plates. Forces in pre-stressing rods were reduced since the bridges were built, but this is normal and they were still at acceptable levels. There was a lot of vegetation around some deck plates, and some gutters were not cleaned.

Some railings had broken railing boards, loosened nails and gaps in the railings. The surface treatment of wooden railings was often quite worn, with flaking, cracking and with algae, and there were some rusty screws. Mechanical damages of plowing were found on several railings.

Commonly some loosened or insufficiently tightened bolts were observed on several bridges. Some joints were made with too small washers, which had been pressed into the wood and damaged the wood grain. Especially wood screws and the ends of threaded rods were corroded and also nuts and washers that were not galvanized were found. A comparison of the quantity of damages reported at inspections in 2013-2014 and 2004 shows that damages with cracks, high moisture contents, edge beams and asphalt surfaces have been reduced since the earlier inspections. This can be a result of improved bridge design during later years. But also of course the different selection of the bridges and the different number of inspected bridges may influence the comparison. High moisture contents are still found in many bridges at the later inspections and sometimes also rot have been detected which was not the case in 2004.

2.6 Comparison with bridges in Norway

In Norway The Norwegian Public Roads Administration has gathered information from inspections, operation and maintenance and plan to use this to improve future timber bridges and to be a basis for preparation of standardized bridge details.

Most of the details where problems have occurred in Norwegian bridges are similar to reported damages from the Swedish inspections, but some damages do not occur in Swedish timber bridges because of different construction techniques and materials. The main difference is the use of creosote impregnation in Norway.

Table 2.6. Risk/damage of details in Sweden and Norway

Risk/damage of detail Norway Sweden

Deck encased in the abutment X -

Deck surrounded by concrete strings at the abutment X (X)

Water at end grain at abutment X X

Accumulation of water and wetting on bearing X X

Inclined ends of deck plate (rhombic deck) X X

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Constructive protection of end grain at deck ends X X

Plants and bushes at abutments X X

Railing posts attached to deck side X X

Water runoff from edge to underlying parts - failure in edge

fitting and missing drip at deck edge X X

Connection through steel fittings – penetration of

constructive protection X X

Accumulation of dirt and snow etc. on cross beams X X

Encasement of water at arch and pillar ends X X

Standing water in lower joints with slotted-in plates X ?

Water runoff along pillars into connections X X

Water on deck due to missing transverse or longitudinal

incline X ?

Crushing of wood under anchor plate X X

Failure to protect whole surface treatment with splints X ?

Cracking X X

Sealing with sealant that shrinks X ?

External steel plates on the outside of the wooden parts X ? Runoff of copper ions on to e.g. galvanized steel X -

Leakage of water at elevated curb X ?

Creosote spills X -

Wetting due to attached cables along outside of bridge X ?

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3 Details – influence of moisture

Most damages recorded at the inspections of timber bridges are connected to high moisture levels, such as cupping of deck plates, problems with edge beams, anchor plates and asphalt surfaces and of course rot. Depending on the moisture level, increased moisture content in the wood can provide dimensional changes when the wood swells and long periods with high moisture contents above 25% provide suitable environment for decay fungi to grow. A reduction in moisture content may on the other hand mean that the wood shrinks and probably cracks. In outdoor climate in Sweden the moisture content in wood is normally between 14 and 20 %.

Rot decay includes many rot fungi, brown rot, white rot and soft rot. In these inspections usually the type of fungi was not determined. The rot propagation was determined by piercing with a knife and in some cases with drills.

The resistance to rot of heartwood of spruce and pine is better than of sapwood. Heartwood of pine has the best resistance, but sapwood of pine has the lowest resistance. Both sapwood and heartwood can normally be included in construction timber and glulam. Salt impregnation of timber with fungicides that give good resistance to rot is only made in sapwood of pine, as impregnation agents do not penetrate into heartwood of pine or into spruce. Salt impregnated sapwood has considerably better resistance than heartwood of pine.

3.1 Example 1 – Railing post

3.1.1 Type of bridge and location

Built: 2006

Construction no: BatMan no: 40-4015-1, Martinsons

no: 5922-B.

Type: Road bridge over water on a gravel

road.

Construction: Stress-laminated glulam deck and

timber abutments.

Age at inspection: Six years.

Maintenance or reconstruction: No.

Location/coordinates RT90: Bjurholm, X7096290, Y1647560

Local climate Open forest

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Figure 3.1. Bridge

3.1.2 Materials and dimensions

Railing posts: Glulam L40, Spruce (Pica Abies).

Dimension: 115 x 180mm

Surface treatment: Primer with fungicide, two layers of

non-transparent glazing paint.

Connections: M16 washers Ø18 x 75 x 6mm.

Distances: Polythene washers Ø18 x 90 x 20mm.

Figure 3.2. Detail of abutment and railing post connection.

3.1.3 Moisture contents and rot propagation

M.C: Lower part of posts, over FSP.

3.2 Example 2 – Railing post

Built: 2007.

Construction no: Moelven no: 07-BR-176A. There are

two identical bridges at the same site, one short with several deficiencies and one longer in good condition.

Type: Pedestrian bridge over water.

Construction: Glulam girder bridge with glulam

deck.

Age at inspection: 7 years

Maintenance or reconstruction: No

Location/coordinates RT90: Ekerö, 6573703, Y1612203

Local climate: Water front.

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Figure 3.4. The short bridge with several deficiencies.

Railing posts: Glulam L40, Spruce (Pica Abies).

Dimension: 90 x 135mm.

Surface treatment: Primer with fungicide, two layers of

non-transparent glazing paint.

Connections: M16, washers Ø18 x 75 x 6mm.

Distances: Wood and sheet metal cladding.

Figure 3.5. Section of the bridge superstructure.

M.C: Lower part of posts, over FSP.

3.3 Example 3 – Railing panel

Built: 1996.

Type: Pedestrian bridge over road.

Construction: Arch bridge with stress-laminated

glulam deck.

Age at inspection: 19 years.

Location/coordinates RT90: Vaxholm, X6590565, Y1642588

Local climate: Shaded north slope.

Weather data: No

Figure 3.8. Bridge

Railing panel: Treated pine (Pinus Silvestris), NTR

class A.

Dimension: Shown in figure 3.9.

Surface treatment: Two layers of primer with fungicide,

two layers of non-transparent glazing paint.

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Figure 3.9. Section of railing.

M.C: Lower part of panel, over FSP, top

17-24%, measured in the heart-wood

Area with decay: None

Figure 3.10. East side of railing panel, paint erosion on all parts but no visible signs of decay.

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3.4 Example 4 – Railing panel

Built: 2004.

Construction no: BatMan no: 1490-215-1, Svenska

Träbroar (Martinsons) no: 5637/D.

Type: Pedestrian bridge, over road.

Construction: Stress-laminated glulam deck.

Age at inspection: 11 years.

Location/coordinates RT90: Borås, X6400427, Y375340.

Local climate: South slope.

Weather data: No

Figure 3.11.Several panels have been replaced with plywood boards due to decay in the original railing panels.

Railing panel: Spruce (Pica Abies).

Dimension: Shown in figure 3.12.

Surface treatment: One layer of primer with fungicide,

one or two layers of non-transparent glazing paint.

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Figure 3.12. Section of railing.

M.C: Bottom, over FSP, top 15-19%

Area with decay: Decay in lower rails and in the lower

part of most of the pickets.

Figure 3.13. Severe decay in the lower part of the railing panels.

Material: Spruce is used instead of a more

durable material like treated pine.

Wood protection by design: Water trap between pickets and lover

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3.5 Example 5 – Stressed laminated timber deck

Built: 1993.

Träbroar (Martinsons) no: 4003/B.

Type: Road bridge, over small stream.

Construction: Stress-laminated glulam T-section

deck.

Location/coordinates RT90: Stöverfors, close to Skellefteå,

X7194352, Y764797

Local climate: Forest

Weather data: No

Figure 3.14. Stress-laminated glulam T-section deck. 3.5.2 Materials and dimensions

Glulam: L40, treated pine (Pinus Silvestris),

NTR class A.

Dimension: Deck 225mm.

Girders 190.x.585mm.

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Figure 3.15.Section of superstructure.

M.C: Over FSP. Along the top edges of the

deck.

Girders15- 17%, measured in the heart wood.

Area with decay: None.

Figure 3.16.The edges of the deck are exposed to drainage water at both sides of the deck, resulting in plant growth and high moisture content. Crushing damage in the wood by the pre-stressing anchor plates. The girders are dry, protected by the deck.

Wood protection by design: None

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3.6 Example 6 – Stressed laminated timber deck

Built: 2000.

Träbroar (Martinsons) no: 5308/B

Type: Pedestrian bridge, over small stream.

Construction: Stress-laminated plank deck.

Location/coordinates RT90: Lumnäs, X6836882, Y1561020

Local climate: Water front, forest

Weather data: No

Figure 3.17. Bridge elevation.

Deck planks: Spruce K30 (Pica Abies).

Dimension: 72x285mm.

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Figure 3.18. Detail of railing post connection to bridge deck.

Figure 3.19. Section of railing post connection to bridge deck.

M.C: Over FSP. in outer plank along both

sides of the deck,

Area with decay: Visible in outer plank along west side

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Figure 3.20. Decay in bridge deck, south-west corner.

Wood protection by design: Poor design with water leakage at the

railing posts and several water traps.

Maintenance: None

Material: Spruce is used in the outer planks

instead of a more durable material like treated pine.

3.7 Example 7 – Stressed laminated timber deck

Built: 1998.

Träbroar (Martinsons) no: 5308/B

Type: Pedestrian bridge, over road E4.

Construction: Cable stayed with stress-laminated

glulam deck.

Location/coordinates RT90: Södertälje, Pershagen, X6560835,

Y651361

Local climate: Over high way.

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Figure 3.21.View from south.

Deck planks: Spruce K30 (Pica Abies).

Dimension: 45-72 x 395mm.

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Figure 3.23.Detail of deck with connections for cross beam

M.C: Over FSP. in outer planks along both

sides of the deck.

Over FSP. in the deck at crossbeams and drainage holes.

Area with decay: Visible decay in outer planks along

both sides of the deck.

Figure 3.24. High moisture content and decay in the area of the drain system in bridge deck.

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Figure 3.25. Decay in the connecting area for a cross beam.

Wood protection by design: Poor design with water leakage at the

railing posts and along both sides of the deck. Many water traps.

Maintenance: None

Material: Spruce is used in critical parts instead

of a more durable material like treated pine.

3.8 Example 8 – Stressed laminated timber deck

Built: 2007.

Träbroar (Martinsons) no: 6020/A.

Type: Road bridge over water, gravel road.

Location/coordinates RT90: Hädanberg, X7051859, Y657350

Local climate: Forest.

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Figure 3.26. Bridge over Hädanbergån.

Deck: Glulam L40, Spruce (Pica Abies).

Figure 3.27. Section of stress-laminated glulam deck with two levels of stressing rods.

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Table 3.1. Moisture content measured under the deck

Measuring point Depth 5mm Depth 30mm

North West corner 23 22

South West corner 23 20

North East corner 23 23

North East corner +0,5m 1a lamella 23 22

South East corner 23 22

Area with decay: None.

Figure 3.28.Uplift in every corner of the deck.

Moisture gradient in the deck: The moisture content in the glulam

was about 12% when the bridge was constructed. The M.C. under the waterproof membrane is still around 12% but the M.C. in the underside of the deck is 23%. This gradient causes a cup/deformation of the deck

Uplift: 5-10mm in all corners of the bridge

deck, caused by the moisture gradient driven deformation,( cup) of the deck.

Local climate: Condensation on the underside of the

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3.9 Example 9 – Stressed laminated timber deck

Built: 2010.

Träbroar AB no: 7196/D.

Type: Pedestrian bridge over water.

Location/coordinates RT90: Umeå, X7091361, Y755429

Local climate: Open field.

Weather data: No

Figure 3.29. Pedestrian bridge with a relatively thin stress-laminated deck and only one level of stressing rods.

Dimension: 94,5 x 360mm.

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Figure 3.30. Section of stress-laminated glulam deck with one level of stressing rods.

Figure 3.31.Measuring points.

Table 3.2. Moisture content measured at the underside of the deck

Measuring point Depth 0-45mm

1. 20

2. 21

3. 19

4. 20

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Figure 3.32. Uplift in every corner of the deck.

was about 12% when the bridge was constructed. The M.C. under the waterproof membrane is still around 12% but the underside of the deck has a M.C of 20%. This gradient causes a cup/deformation of the deck

Uplift: 15-30mm in all corners of the bridge

deck.

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3.10 Example 10 – Stressed laminated timber deck

Built: 2009.

Construction no: BaTMan no: 2480-129-1, Martinsons

Träbroar AB no: 7129/A.

Type: Road bridge over water.

Location/coordinates RT90: Umeå, X7076671, Y766043

Local climate: Open, over water.

Weather data: No

Figure 3.34. Road bridge with a stress-laminated deck with three levels of stressing rods.

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Figure 3.35. Section of stress-laminated glulam.

Figure 3.36. View of stress-laminated glulam deck with three levels of stressing rods.

North West corner 18 17

South West corner 18,5 17

North East corner 18 17

South East corner 17,5 17

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Figure 3.37. Slight uplift in two corners of the deck.

was about 12% when the bridge was constructed. The M.C. under the waterproof membrane is still around 12% but the underside of the deck has a M.C of 17%. This gradient causes a cup/deformation of the deck

Uplift: 5-20mm in two corners of the bridge

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Figure 3.38. Small amounts of water follows the railing posts but it does not effect the M.C in the deck.

3.11 Example 11 – Stressed laminated timber deck

Built: 1994.

Construction no: BaTMan no: 40-280-2, Svenska

Träbroar AB no: 4254/A.

Type: Road bridge over water.

Construction: Stress-laminated deck.

Location/coordinates RT90: Avan, X7147880, Y806204

Local climate: Shaded, over water.

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Figure 3.39. Road bridge with a stress-laminated deck covered with a rubber membrane and deck planks.

Deck planks: Treated pine (Pinus Silvestris), NTR

class A.

Stress-laminated deck: Spruce K30 (Pica Abies).

Surface treatment: None

North West corner 17,8 17

South West corner 18,2 17

North East corner 18,6 17

South East corner 17,7 17

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Figure 3.40. No visible damages.

4 References

(1) Fjellström, Per-Anders, 2013-2015, selections from inspections for Swedish Transport Administration, municipalities and other bridge owners.

(2) Pousette, Anna, Fjellström, Per-Anders, Broinspektion – träbroar, SP Rapport 2004:41.

(3) Hauke Burkart, Statens Vegvesen, Trebrudetaljer, Erfaring fra inspeksjoner, drift og vedlikehold, Draft version 0.5, 9/6‐2014 (4) BaTMan, Bro och tunnel Management, Koder för inspektion av

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Appendix A

Appendix A. Moisture measurements on timber

truss bridges from Martinsons

A1. Timber truss bridges

Moisture measurements were made by Martinsons during a few days in May 2009, so all the bridges were not measured on the same day. The measured moisture values represent the value of one day, and no trends of the moisture levels are shown. However the measurements may provide some information about where to expect the highest/lowest moisture contents in this type of bridges.

Martinsons Träbroar AB has built many timber truss bridges for pedestrians/cyclists. A follow-up of six truss bridges in middle and southern Sweden was made when the bridges were 8-12 years old; see location and description of bridges in Table A1 and Figure A1. Today this type of bridge is designed with more protection against rain. In the studied bridges the bottom parts were unprotected and that was the reason for high moisture contents. Water runs down along the diagonals to the bottom chord. The measurements showed that the moisture levels could be too high and it meant that several parts of the bridge should protect in a better way. Today there are usually metal fittings on connection points on new truss bridges.

Figure A1. Map of Sweden with locations of bridges (5, 11, 14, 15, 16, 18)

5

11

16 15 18

14

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Appendix A

Table A1. Description of bridges

POS No. Name Built year Location Surface treatment.

5 5289 Södra länken 2001 Stockholm Oil

11 5165 Valabäcken Dösjebro 1999 Helsingborg OIl

14 5405 Högsby 2000 Högsby Oil

15 5013 Ronneby 1997 Ronneby Red paint

16 5305 Dösjebro 2000 Landskrona Red paint

18 5404 Kallinge 2000 Ronneby Red paint

Design life

The design life of this type of bridge is usually 40 years in Sweden.

A2. Moisture measurements

Measurements

Electric moisture meters measure the electric resistance in wood which varies with the moisture when the moisture content is less than 30 %. Moisture contents over this value up to 60 % were registered in some bridges, but these values are not actual moisture levels but mean the moisture contents are high and above fiber saturation point of the wood.

Measurement protocol

Measurement points (1-12 as shown in Figure A2) were the same on all six bridges, to allow for comparisons.

The positions a, b, c and d refers to the various occurrences of the detail described, e.g. for measurement point 1 "Angle block bottom chord" all the angle blocks on the corresponding position at both bridge ends and both sides are separated with the above indexes as shown in the table below.

The orientation of the measuring points was registered, south, east, north, etc.

Moisture contents were measured at two levels from the wood surface, 10 mm and 40 mm.

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Appendix A

Figure A2. Measuring points

Table A2. Protocol with measuring points

Measuring

point Position Location

1a Angle block, bottom chord Outside angle block

1b _-”- _-”-

1c _-”- _-”-

1d _-”- _-”-

2a Compression diagonal Outside diagonal

2b _-”- _-”-

2c _-”- _-”-

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Appendix A

3a Bottom chord Under angle block, Outside chord, High location

-”- -”- -” - , Middle location -”- -”- -” - , Low location

3b Bottom chord Under angle block, Outside chord, High location

-”- -”- -” - , Middle location -”- -”- -” - , Low location

4a Bottom chord At washer of tension rod

4b -”- -”-

4c -”- -”-

4d -”- -”-

5a Angle block, top chord Outside angle block

5b -”- -”-

5c -”- -”-

5d -”- -”-

6a Side strut Above cross beam

6b -”- -”-

6c -”- -”-

6d -”- -”-

7a Bracing Outside, Low location

7b -”- -”-

7c -”- -”-

7d -”- -”-

8a Cross beam At side strut, Top of beam

-”- -”- -”- , Bottom of beam

8b Cross beam At side strut, Top of beam

8c Cross beam At side strut, Top of beam

8d Cross beam At side strut, Top of beam

9a Cross beam At vertical member, Top of beam

9b Cross beam At vertical member, Top of beam

9c Cross beam At vertical member, Top of beam

9d Cross beam At vertical member, Top of beam

10a Cross beam At middle of beam, Top of beam, End of bridge

10a Cross beam At middle of beam, Bottom of beam, End of bridge

10b Cross beam At middle of beam, Top of beam, End of bridge

-”- -”- At middle of beam, Bottom of beam, End of bridge

11a Support In bottom chord, At support

11b -”- -”-

11c -”- -”-

11d -”- -”-

12a Angle block of wind

bracing

At support

12b -”- -”-

12c -”- -”-

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46

Appendix A

A3. Results

Dörsjebro 5305-D

Figure A3. Description of bridge

Dörsjebro 5305-D (Built year: 2000) Surface treatment: Red paint

Average moisture content: 24.8% (10mm: 24.3% 40mm: 25.2%) Wearing surface: Wood deck

Surroundings: Somewhat leafy around the bridge (trees and bushes) Passage: Over river, high clearance

Comment:Very high moisture contents in the angle block on bottom chord and in bottom chord around it. Very high moisture contents around the lower washers of tension rod.

Table A3. Average moisture content (%) in different directions

South-East South-West North-East North-West

23.8 25.5 24.2 26.7

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Appendix A

Table A4. Measured moisture contents (%) at depths 10 mm and 40 mm

Angle block, bottom chord

1a NE 1b SE 1c SW 1d NW 10 60.0 60.0 60.0 60.0 40 60.0 60.0 60.0 60.0 Compression diagonal 2a NE 2b SE 2c SW 2d NW 10 16.2 13.8 16.3 17.8 40 18.0 15.4 17.4 18.9

Bottom chord, under angle block, high

3a NE 3b SE 3c SW 3d NW

10 27.7 30.4 53.5 25.6

40 25.9 29.5 53.3 25.8

Bottom chord, under angle block, middle

10 26.7 27.5 28.5 26.9

40 28.5 29.1 30.3 27.0

Bottom chord, under angle block, low

10 25.0 25.5 25.8 22.0

40 26.8 25.8 26.5 23.9

Bottom chord, at 2nd washer of tension rod

10 26.8 24.8 23.7 60.0

40 29.8 33.8 25.7 60.0

Angle block, top chord

5a NE 5b SE 5c SW 5d NW 10 12.4 16.0 14.8 14.7 40 14.1 16.0 16.2 16.0 Side strut 6a NE 6b SE 6c SW 6d NW 10 18.4 16.2 18.8 20.2 40 18.3 16.8 19.0 21.6 Bracing 7a NE 7b SE 7c SW 7d NW 10 17.4 20.5 15.6 22.7 40 18.2 23.8 16.7 22.9

Cross beam at side strut, high

10 19.3 16.8 18.3 18.2

40 20.6 20.2 18.5 20.4

Cross beam at side strut, low

10 19.1 16.9 20.5 18.9

40 20.0 18.1 22.4 17.2

Cross beam at vertical member, high

10 21.7 15.2 16.0 18.3

40 22.4 16.2 16.7 19.0

Cross beam at vertical member, low

10 18.4 16.9 17.3 21.5

40 18.9 18.0 19.6 22.8

Cross beam at middle of bridge, high 10a E 10b W

10 23.3 22.2

40 22.0 22.1

Cross beam at middle of bridge, low 10a E 10b W

10 19.0 18.6

40 17.7 18.5

Angle block of wind bracing

10 24.7 21.5 21.0 23.0

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Appendix A

Dörsjebro 5165-D

Välabäcken 5165-D (Built year: 1999) Surface treatment: OIl

Average moisture content: 26.7% (10mm: 26.7% 40mm: 27.2%) Wearing surface: Wood deck, with dense mat on deck

Surroundings: Very leafy around the bridge (trees and bushes) Passage: Over river, high clearance

Comment:Very high moisture contents in the angle block on bottom chord. Very high moisture contents around the lower washers of tension rod.

25.3 32.8 24.1 23.1

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Appendix A

1a NW 1b NE 1c SW 1d SE 10 23.0 29.4 60.0 29.3 40 25.0 30.6 60.0 31.5 Compression diagonal 2a NW 2b NE 2c SW 2d SE 10 14.7 30.5 19.3 17.9 40 15.6 30.0 19.5 19.0

3a NW 3b NE 3c SW 3d SE

10 22.4 25.1 60.0 30.3

40 24.1 25.5 43.5 30.3

10 21.2 24.5 60.0 22.6

40 21.7 24.8 60.0 21.0

10 27.7 25.2 34.7 23.6

40 26.6 23.4 29.7 22.3

10 60.0 42.4 47.2 40.7

40 60.0 60.0 60.0 60.0

5a NW 5b NE 5c SW 5d SE 10 14.1 14.7 14.3 15.8 40 14.2 14.3 14.6 15.4 Side strut 6a NW 6b NE 6c SW 6d SE 10 17.3 16.0 18.4 17.7 40 17.7 15.9 18.3 18.1 Bracing 7a NW 7b NE 7c SW 7d SE 10 14.2 18.6 19.2 17.1 40 17.6 19.5 21.7 20.1

10 14.1 24.5 17.8 17.3

40 15.0 21.0 17.7 17.3

10 13.6 14.8 17.4 16.7

40 14.5 15.1 18.4 16.7

average 14.1 15.0 17.9 16.7

10 15.7 16.9 24.0 21.1

40 16.1 16.5 23.5 20.4

10 16.4 21.1 20.0 28.0

40 16.9 22.7 18.7 28.5

Cross beam at middle of beam, high

10a N 10b N

10 37.0 49.0

40 31.0 45.0

Cross beam at middle of beam, low

10a S 10b S

10 23.4 23.8

40 21.4 19.0

10 36.0 25.6 41.7 41.5

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Appendix A

Ronneby 5013-D

Ronneby 5013-D (Built year: 1997) Surface treatment: Red

Average moisture content:: 24.6% (10mm: 23.6% 40mm: 25.5%) Wearing surface: Wood deck

Surroundings: Open country Passage: Over river, low clearance

Comment:Very high moisture contents in the angle block on bottom chord. Very high moisture contents around the lower washers of tension rod. Gravel on bottom chord and angle block.

23.8 23.2 24.2 28.0

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Appendix A

1a SW 1b NW 1c SE 1d NE 10 30.2 50.0 35.0 29.0 40 30.2 60.0 46.0 32.5 Compression diagonal 2a SW 2b NW 2c SE 2d NE 10 20.7 22.4 17.3 24.1 40 21.7 22.0 20.0 25.2

3a SW 3b NW 3c SE 3d NE

10 22.0 21.9 21.7 21.8

40 23.6 23.8 22.6 23.7

10 29.6 24.8 25.7 22.2

40 31.4 26.8 27.6 24.0

10 19.3 20.5 21.6 18.8

40 20.8 23.0 22.5 18.8

10 35.7 60.0 49.6 60.0

40 60.0 60.0 60.0 60.0

5a SW 5b NW 5c SE 5d NE 10 17.4 13.8 16.4 16.2 40 18.0 14.0 16.0 17.2 Side strut 6a SW 6b NW 6c SE 6d NE 10 20.7 22.9 16.8 17.9 40 22.0 24.3 17.6 19.2 Bracing 7a SW 7b NW 7c SE 7d NE 10 16.8 21.0 18.6 19.3 40 18.9 22.3 19.0 19.5

10 17.2 22.3 16.8 18.2

40 18.4 24.0 17.6 19.1

10 18.7 23.7 16.9 17.2

40 20.7 25.2 17.7 18.3

10 15.8 23.6 18.2 18.3

40 17.6 23.7 18.9 18.7

10 18.2 25.5 17.3 19.9

40 20.0 26.0 18.8 20.5

Cross beam at middle of bridge, high

10a W 10b W

10 24.8 21.1

40 25.5 20.4

Cross beam at middle of bridge, low

10a E 10b E

10 21.8 17.8

40 21.3 17.8

10 22.2 28.4 24.0 29.3

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Appendix A

Kallinge 5404-D

Kallinge 5404-D (Built year: 2000) Surface treatment: Red

Surroundings: Somewhat leafy around the bridge (trees and bushes) Passage: Over river, high clearance

Comment:Very high moisture contents in the angle block on bottom chord. Very high moisture contents around the lower washers of tension rod

South West North East

21.5 21.4 21.2 25.3

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Appendix A

1a E 1b S 1c W 1d N 10 60.0 27.5 28.1 31.0 40 60.0 31.4 31.2 36.7 Compression diagonal 2a E 2b S 2c W 2d N 10 20.0 16.6 17.9 16.7 40 20.7 17.4 17.9 16.8

3a E 3b S 3c W 3d N

10 20.0 16.6 17.9 16.7

40 20.7 17.4 17.9 16.8

3a E 3b S 3c W 3d N

10 23.8 26.3 23.1 25.1

40 25.0 28.2 24.0 26.5

3a E 3b S 3c W 3d N

10 25.8 24.3 23.1 34.9

40 27.4 25.2 23.1 35.7

4a E 4b S 4c W 4d N

10 40.0 27.0 39.0 22.0

40 57.9 30.9 45.0 28.0

5a E 5b S 5c W 5d N 10 16.7 16.0 17.0 15.0 40 18.0 17.4 18.0 17.0 Side strut 6a E 6b S 6c W 6d N 10 21.6 21.0 17.9 15.9 40 22.3 22.7 19.8 18.0 Bracing 7a E 7b S 7c W 7d N 10 15.7 16.7 15.8 40 17.8 17.3 15.6

7a E 7b S 7c W 7d N

10 17.4 18.4 13.6 14.3

40 18.4 18.7 15.6 15.0

8a E 8b S 8c W 8d N

10 16.2 19.6 17.4 14.9

40 17.2 20.4 18.9 17.1

9a E 9b S 9c W 9d N

10 18.0 17.0 15.3 15.3

40 19.4 18.5 16.0 16.2

9a E 9b S 9c W 9d N

10 23.5 20.4 19.3 17.8

40 24.3 20.9 21.1 20.1

10a SE 10b SE

10 21.0 17.0

40 23.1 17.6

10a NW 10b NW

10 16.0 15.3

40 16.2 15.7

11a E 11b S 11c W 11d N

10 19.6 24.3 24.1 24.6

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Appendix A

Mönsterås A-002 (Södra Länken 5289)

Mönsterås A-002 (fd Södra Länken 5289) (Built year: 2000) Surface treatment: Oil

Surroundings: Open (no bushes etc.) Passage: Over river, low clearance

Comment:Very high moisture contents in the angle block on bottom chord. Very high moisture contents around the lower washers of tension rod

16.2 16.8 16.2 18.8

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Appendix A

1a SE 1b SW 1c NE 1d NW 10 17,0 21,5 15,5 22,2 40 18,0 21,3 16,5 25,8 Compression diagonal 2a SE 2b SW 2c NE 2d NW 10 15,6 15,5 14,7 14,3 40 16,9 17,0 17,3 15,5

3a SE 3b SW 3c NE 3d NW

10 14,7 17,9 17,1 24,8

40 20,1 17,0 18,6 24,8

10 18,5 18,2 18,1 18,6

40 20,0 19,3 18,9 19,3

10 16,8 16,5 16,1 21,0

40 18,5 18,0 16,9 22,7

10 19,3 19,0 19,7 18,0

40 23,2 22,3 22,0 23,4

5a SE 5b SW 5c NE 5d NW 10 13,0 12,8 11,6 13,2 40 14,4 13,6 13,6 14,1 Side strut 6a SE 6b SW 6c NE 6d NW 10 13,0 15,2 12,1 13,0 40 15,0 16,3 14,8 14,6 Bracing 7a SE 7b SW 7c NE 7d NW 10 12,0 14,0 14,2 40 13,2 15,2 15,6

10 13,5 14,1 13,8 18,1

40 17,5 14,6 15,5 19,9

10 13,8 15,0 13,7 14,0

40 14,0 15,3 14,0 15,1

10 14,6 14,5 15,2 21,2

40 15,8 16,2 16,6 21,5

10 13,8 16,3 17,3 16,9

40 15,1 17,4 19,1 18,2

10a S 10b S

10

40

10a N 10b N

10

40

10 17,6 17,4 17,2 18,8

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Appendix A

5405-D Högsby

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Appendix A

Högsby 5405-D (Built year: 2000) Surface treatment: Oil

Average moisture content: 16% (10mm: 15,12% 40mm: 17,0%) Wearing surface: Wood deck

Surroundings: Open country Passage: Over river, high clearance

Comment:Very low moisture contents. Cracks on inside of upper chord.

14.9 15.3 15.4 17.8

Figure A14. Moisture content (%) for all measuring points

1a SW 1b NW 1c SE 1d NE 10 14,1 20,5 15,8 17,6 40 21,0 25,5 20,2 20,8 Compression diagonal 2a SW 2b NW 2c SE 2d NE 10 11,3 15,0 11,7 13,8 40 14,1 16,8 13,7 15,7

10 14,0 15,4 14,9 14,8

40 14,0 15,8 15,4 15,8

10 17,5 16,2 17,4 16,0

40 18,8 16,9 18,9 17,8

10 17,8 16,7 16,8 16,8

40 18,6 18,0 17,8 19,2

10 16,9 22,5

40 23,7 47,0

5a SW 5b NW 5c SE 5d NE 10 13,2 10,6 12,2 12,0 40 13,9 13,4 13,8 12,7 Side strut 6a SW 6b NW 6c SE 6d NE 10 12,5 15,9 11,2 12,4 40 13,4 16,2 13,3 14,5

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58 Appendix A Bracing 7a SW 7b NW 7c SE 7d NE 10 11,5 14,7 40 13,4 16,2

10 12,5 15,8 12,6 12,8

40 13,7 16,7 13,2 13,8

10 12,8 14,4 12,5 13,7

40 13,9 15,3 14,4 15,2

10 12,3 15,4 13,3 13,2

40 14,2 16,0 14,4 14,2

10 13,0 15,0 14,9 15,2

40 14,8 16,7 15,1 17,5

10a W 10b W

10 20,4 18,4

40 19,3 18,9

10a E 10b E

10 18,7 15,3

40 17,1 15,4

10 19,2 18,5 17,5 17,3

Experiences from timber bridge inspections in Sweden – examples of influence of moisture

Experiences from timber bridge inspections

in Sweden – examples of influence of moisture

Anna Pousette, Per-Anders Fjellström

S

P

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es

T

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ni

sk

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Experiences from timber bridge inspections

in Sweden – examples of influence of moisture

Abstract

Contents

Preface

1

Introduction

1.1

Timber bridge inspections in Sweden

1.2

Measured moisture contents

2

Summary of inspection results

2.1

Beam bridges

2.2

Stress-laminated deck plates

2.3

Stress-laminated box-beam and T-beam

bridges

2.4

Trusses, arch bridges, suspended bridges and

cable styed bridges

2.5

Comparison with earlier inspection project in

Sweden

2.6

Comparison with bridges in Norway

3

Details – influence of moisture

3.1

Example 1 – Railing post

3.2

Example 2 – Railing post

3.3

Example 3 – Railing panel

3.4

Example 4 – Railing panel

3.5

Example 5 – Stressed laminated timber deck

3.6

Example 6 – Stressed laminated timber deck

3.7

Example 7 – Stressed laminated timber deck

3.8

Example 8 – Stressed laminated timber deck

3.9

Example 9 – Stressed laminated timber deck

3.10

Example 10 – Stressed laminated timber deck

3.11

Example 11 – Stressed laminated timber deck

4

References

Appendix A. Moisture measurements on timber

truss bridges from Martinsons