Proceedings of the
International Conference Timber Bridges
ICTB2010
Lillehammer, Norway
September 12 -15, 2010
Editors:
Professor Kjell A. Malo
Chief Engineer Otto Kleppe
Chief Engineer Tormod Dyken
Organizers:
Norwegian Public Road Administration
NTNU, Norwegian University of Science and Technology
NTI, Norsk Treteknisk Institutt
Innovation Norway
Secretariat:
Norwegian Public Road Administration
P.O Box 8142 Dep
NO-0033 Oslo, Norway
www.vegvesen.no
© ICTB 2010 & Tapir Academic Press, Trondheim 2010
ISBN 978-82-519-2680-5
This publication may not be reproduced, stored in a retrieval system or transmitted in any form or by any
means; electronic, electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise, without
permission.
Copyright remains with the authors.
Layout: The editors
Printed and binded by: Tapir Uttrykk, Trondheim, NORWAY
Tapir Academic Press publishes textbooks and academic literature for universities and university colleges, as
well as for vocational and professional education. We also publish high quality literature of a more general
nature. Our main product lines are:



Textbooks for higher education
Research and reference literature
Non-fiction
We only use environmentally certified suppliers.
Tapir Academic Press
NO–7005 Trondheim, Norway
Tel.:
+ 47 73 59 32 10
Email: forlag@tapir.no
www.tapirforlag.no
Publishing Editor: lasse.postmyr@tapir.no
Preface
Over the past twenty years, timber bridge construction has gathered headway in many
countries. Research in the area has produced significant results; new materials and
connections have been developed and various structural systems have been explored. New
developments have been presented in journals and at general timber construction conferences.
The time was now ripe for a specialized international conference on timber bridges to present
the state of the art.
In Norway, the ready availability of timber and the tradition of utilizing timber in houses and
other structures make it natural to consider timber an adequate construction material for
bridges with spans of up to 100 meters or even more. Today, there are many timber bridges in
Norway – both road and pedestrian bridges. Since 1995, the Norwegian Public Roads
Administration has built more than 100 timber bridges with spans up to 70 meters.
The main objective of the conference ICTB2010 at Lillehammer was to showcase and discuss
the state of the art in timber bridge technology. The conference topics were:
• Design aspects
• Environmental aspects
• Historical bridges
• Protection and durability
• Monitoring
• Timber bridge aesthetics
• Components, connections and detailing
• Pedestrian bridge projects
• Bridge decks
• Composite bridges
The primary emphasis of the conference was on the design of durable, environmentally
friendly and cost-efficient timber bridges.
Our hope is that ICTB 2010 can serve as a source of inspiration for designers, researchers,
architects and others, working within the field of timber bridges.
Lillehammer, September 2010.
On behalf of the facilitating organizations,
Børre Stensvold
Bridge Director, Norwegian Public Roads Administration
Conference Chair.
International Scientific Committee
Professor em. Heinrich Kreuzinger,
Technische Universität München, Germany
Professor Kurt Schwaner,
Biberach University of Applied Sciences, Germany
Professor Gerhard Schickhofer,
Graz University of Technology, Austria
Professor em. Aarne Jutila,
Helsinki University of Technology, Finland
Professor Robert Kliger,
Chalmers University of Technology, Sweden
Research Engineer James Wacker,
USDA Forest Products Laboratory, USA
Professor Kjell Arne Malo,
Norwegian University of Science and Technology, NTNU, Norway
Amanuensis Nils Ivar Bovim,
The Norwegian University of Life Sciences, Norway
Steering Committee
Bridge director Børre Stensvold - Conference Chair,
Norwegian Public Roads Administration
Mr Erik Aasheim, Conference Co-Chair,
Norsk Treteknisk Institutt (NTI)
Professor Kjell Arne Malo, Programme Co-Chair,
Norwegian University of Science and Technology, NTNU
Mr Otto Kleppe, Programme Chair,
Norwegian Public Roads Administration
Organising Committee
Mr Otto Kleppe, Chair
Norwegian Public Roads Administration
Mr Nils Ivar Bovim,
The Norwegian University of Life Sciences
Mr Rune B. Abrahamsen,
Sweco Norway
Mr Åge Holmestad,
Moelven Limtre AS
Professor Kjell Arne Malo,
Norwegian University of Science and Technology, NTNU
Mr Erik Aasheim,
Norsk Treteknisk Institutt (NTI)
Mr Trond Arne Stensby
Norwegian Public Roads Administration
Mr Tormod Dyken
Norwegian Public Roads Administration
Contents
Key note lecture
Kurt Schwaner, Germany: Timber Bridges - different countries, different approaches .....................
1-20
Design aspects Part I
Michael Flach, Austria: How to design timber bridges ......................................................................
Per Kr. Ekeberg, Norway: Technical concepts for long span timber bridges ....................................
Hauke Kepp, Norway: Thermal actions on timber bridges ................................................................
Kolbein Bell, Norway: Structural system for glulam arch bridges ....................................................
21-28
29-36
37-48
49-66
Design aspects Part II
João Nuno Amado Rodrigues, Portugal:
Use of composite timber-concrete bridges solutions in Portugal ........................................................ 67-78
Jarle Svanæs, Norway: Environmental timber bridges
– verification of material properties of Kebony modified wood ......................................................... 79-88
Hilde Rannem Isaksen, Norway: Construction cost of Timber Bridges in Norway
–A comparison with Steel and Concrete ............................................................................................. 89-98
Ove Solheim, Norway: New 4-lane Mjoesbridge in timber? ............................................................. 99-106
Environmental aspects
Johanne Hammervold, Norway: Environmental analysis of bridges in a life cycle perspective ........ 107-118
Jarle Svanæs, Norway: Environmental friendly timber bridges –
Environmental improvement through product development .............................................................. 119-122
Historical Bridges
Tsuneo Igarashi, Japan: The 62nd reconstruction of a traditional wood bridge ................................ 123-130
Guillermo Iñiguez-Gonzáles, Spain: Remarkable ancient timber bridges up to the 1850´s.
Part I: general review........................................................................................................................... 131-138
Miguel C. Fernández-Cabo, Spain: Remarkable ancient timber bridges up to the 1850´s.
Part II: case studies and breakthroughs................................................................................................ 139-156
Protection and Durability
Otto Kleppe, Norway: Durability of Norwegian timber bridges .......................................................
Anna Pousette, Sweden: Outdoor tests of timber beams and columns ..............................................
Masahiko Karube, Japan: Report of the collapsed wooden bridges in Japan ....................................
Elisabet Michelson, Norway: Polyurea based bridge membrane on wooden bridges .......................
157-168
169-178
179-194
195-204
Monitoring
Thomas Tannert: Structural health monitoring of timber bridges ...................................................... 205-212
Anders Gustavsson, Sweden: Health Monitoring of timber bridges .................................................. 213-222
Tormod Dyken, Norway: Monitoring the moisture content of timber bridges .................................. 223-236
Antti Karjalainen, Finland: Bridge Information Modelling (BIM) and Laser Scanning
In Renovation Design, Case Pyhäjoki Bridge ..................................................................................... 237-242
Jim Wacker, USA: Development of a Smart Timber Bridge Girder with Fiber Optic Sensors ......... 243-252
Timber Bridge Aesthetics
Richard J. Dietrich, Germany: Six timber bridges of special interest ................................................ 253-258
Yngve Aartun, Norway: Timber Bridge Aesthetics –Design and function (+ tradition) .................... 259-266
Bernt Jakobsen, Norway:
Spectacular Wooden Truss Bridges as Traffic Safety Enhancing Measures ....................................... 267-276
Components, Connections and Detailing
Lars Bergh, Norway: Construction of timber bridges by prestressing prefabricated segments ......... 277-280
Bjørn A. Lund and Matteo Pezzucchi, Norway:
Development of a new barrier system for stress laminated timber road bridge decks ........................ 281-296
Kjell Arne Malo, Norway: On Connections for Timber Bridges ........................................................ 297-312
Abdy Kermani, United Kingdom:
Developments in stress-laminated arch construction for footbridges ................................................. 313-320
Pedestrian Bridge Projects
Rolf Broennimann, Switzerland: Design, construction and monitoring of a bowstring
arch bridge made exclusively of timber, CFRP and GFRP ................................................................. 321-328
José L. Ferández-Cabo, Spain: Construction aspects of a 19.2 m Timber Truss
cantilevered view walkway in Vitoria, Spain ...................................................................................... 329-334
Anssi Laaksonen, Finland: Malminmaki Pedestrian Overpass .......................................................... 335-340
Julio Vivas, Spain: Design and installation of a covered timber footbridge over the A8
motorway in Bilbao, Spain .................................................................................................................. 341-350
Bridge decks
Mats Ekevad, Sweden:
Prestressed Timber Bridges - Simulations and experiments of slip .................................................... 351-358
Roberto Crocetti, Sweden:
Anchorage systems to reduce the loss of pre-stress in stress-laminated timber bridges ..................... 359-370
Rune B. Abrahamsen, Norway:
Bridge deck rehabilitation using cross-laminated timber .................................................................... 371-382
Composite bridges
Aarne Jutila, Finland:
Wood Concrete Composite Bridges – Finnish Speciality in the Nordic Countries ............................. 383-392
Jeno Balogh, USA:
Testing of Wood-Concrete Composite Beams with Shear Key Detail ................................................ 393-398
Leander A. Bathon, Germany:
Performance of single span wood concrete - composite bridges under dynamic loading .................. 399-402
International Conference on Timber Bridges (ITCB 2010)
KEY NOTE LECTURE
Timber Bridges - different countries, different approaches
1968: University of Stuttgart,
Civil Engineering
1974: Engineering Office in
Stuttgart
1981: Self Employed Engineer,
Mainly Timber Constructions
1987: German Timber Council,
Düsseldorf
Since 1996: Institute of Timber
Engineering, University Biberach
- R+D- Projects
- Member of DIN (Timber
constructions, Bridges, Building
physics)
- Expertise
Kurt SCHWANER
Prof. Dipl.-Ing.
Chair Institute of Timber
Engineering
University of Applied
Sciences
D 88400 Biberach
Germany
schwaner@fh-biberach.de
Summary
A brief overview shows important steps in the development of timber bridges from the early simple
timber logs for pedestrians in the past to modern bridges of today. Three different means for
developments in wooden bridges are: new structures, new materials or new connections. Using
these new concepts in addition with constructive protection durable and economic bridges for
extreme wide spans or high loadings can be built.
Timber buildings in general and bridges in particular require careful design and execution. The
design properties and the low energy consumption, increasing energy costs and disposal problem of
other building material lead to increasing importance for timber in bridge constructions.
A bridge is like a living organism. It requires frequent health check-ups and maintenance, and its
lifespan is 50 years on the average. With limited resources and an ageing bridge population, bridge
owners need reliable information on bridge health in order to manage their bridge inventory
efficiently and economically.
1. Introduction
Bridges connect people, regions, countries or continents. They inspire poets, travellers, and also
engineers. No other structure has such a close relationship of function and form. The location alone
often puts a bridge directly into the spotlight which means a high burden of responsibility on
landscape or town planners. In order to create a successful, durable and aesthetic structure it is
important for architects, planners and construction companies to work together from the very
beginning.
Simple timber logs were the early steps to surpass barriers. The first timber bridge mentioned in
documents 3000 BC is the bridge of Pharaoh Menses crossing the Nile. Up to now in Asia similar
simple beam or cantilever bridges are used
The most important criteria for a decision to build a timber bridge are durability and long lifespan
with low maintenance needs.
Damages to construction components of wooden bridges only happen when planning or
construction is carried out improperly and wrong material is used. The reasons for damage lie
almost exclusively in the lack of protection. It is of outmost importance for the planning and
construction of bridges to consider an extensive protection concept, which includes design, material
choice and detail of construction.
Construction components of timber bridges have been classified in Germany according to DIN
1074:2006-09 Timber Bridges into “protected” and “unprotected” classes in order to measure or test
1
International Conference on Timber Bridges (ITCB 2010)
their durability as well as the effectiveness of certain construction modes. This is the only way to
compare the various types of wooden constructions among each other and with constructions of
other materials. Protected elements do not need any chemical treatment.
T. Dyken: Most modern timber bridges in Norway have exposed frame structures, as cladding is
less desirable. Therefore other methods of timber protection have to be used. In Norway chemical
timber preservatives are restricted but not forbidden. However, CCA-impregnated timber has to be
disposed of as hazardous waste.
These circumstances have led to a practise of double impregnating as the preferred method for
protecting load-bearing structures of timber bridges. This is done by first making BS timber out of
CCA treated laminate and then pressure-treating the finished component with all its holes and cuts
with Kreosot. Additionally, in order to protect the top of beams and arches against the weather and
to keep moisture from entering vertical cracks, in recent years metal sheet coverings are used more
often. While sheet copper might seem an expensive choice, it is less work intensive and more
pleasing to the eye than for example zinc.
The road directorate’s bridge division – the central authority – has also taken an active part in the
development of modern timber bridge construction, both financially and practically through
research and development programmes. Especially the comprehensive research programme “timber
bridges” which is sponsored under the name “Nordic Wood” by all Scandinavian national road
authorities as well as industrial partners needs mentioning here. Figure 1
Figure 1 Vihantasalmi Bridge, Mäntyharju FIN, 1999, SLW60, l = 150 m,
span = 42 m, width = 14 m
2.
New Concepts for load bearing Structures and Constructions
The trend in recent years to more use of timber in the construction of bridges is probably due to the
development of appropriate structural systems.
One of the biggest demands is still a solution to problems with durability of timber which is
constantly under the influence of moisture. Constructive timber protection is of the utmost
importance. On the other hand, examinations of timber bridges often also show damages through
corrosion of the steel components or other metal connection devices.
2
International Conference on Timber Bridges (ITCB 2010)
2.1
Round Wood
Burbach Niederdresselndorf Roundwood Bridge of, D, 2008
Here is a successful example of a standardised procedure which enabled the low-cost construction
of a timber bridge suitable for heavy load vehicles. This standardised bridge is now available for
other communities.
For the bridge „Zum Markt“ regional sourced timber was used, mainly spruce and larch. Seven
roundwood beams of approximately 70 cm diameter bear the load. Squared timber mounted
crosswise on top of the beams spread the load evenly. The carriageway surfacing is made from two
layers of 33 mm pressure treated laminated veneer lumber with an intermediate weather seal of
welded asphalt sheeting. A diagonal banister protects the timber structure from moisture. Span is up
to 20 m, Load bearing up to 60 tons. Figure 2, Figure 3.
Figure 2 Burbach Bridge of Roundwood, D, heavy load, prototype
Figure 3 Seven roundwood poles, diameter 70 cm, 2 layers LVL
Kerto, pressure impregnated
Usability: Heavy load vehicles up to 60t (DIN report 101). Span: Structural calculations and
construction procedures exist for spans of 6,00 m, 9,00 m and 12,00 m. Load-bearing structure: for
the length usually untreated spruce, larch, fir or douglas fir with a diameter of 40 to 75 cm,
crosswise untreated squared timbers of larch or Douglas fir Surface: 30 mm impregnated laminated
veneer LVL, bituminous mastic asphalt sheet,
This bridge provides an attractive alternative to reinforced concrete bridges on agricultural or
forestry roads.
3
International Conference on Timber Bridges (ITCB 2010)
2.2
Box-Beam
Box-Beam, Bridge Weikersheim, 2000
Construction: the glulam main beam is glued together to make a hollow box, which is protected by
bituminous mastic concrete. Inside the box pipes are integrated. Lighting is incorporated in the
banister.
The bridge uses the single cell box beam in order to reduce the material needed by about 30%
compared to a glued block cross section. Therefore the bridge with a span of 22,50 m and 5,00 m
width costs only Euro 760/m² Figure 4, Figure 5.
Figure 4
Pedestrian bridge Weikersheim, 2000, span = 22,50 m,
width = 2,50 m, bituminous mastic as water protection
Figure 5
Box-type construction, single glulam girders glued
together
4
International Conference on Timber Bridges (ITCB 2010)
2.3
Wildlife Bridge
Wildlife Bridge Wilmshagen D, 2004
Roads block the natural pathways of animals. Every year accidents involving wildlife cause around
325 Mio Euro in damages and end often deadly for the animal. In Germany up to now there are
only about 30 wildlife crossing bridges for 11800 km of motorway. Each bridge costs between 2.5
and 3 Mio Euro. Figure 6
Figure 6
Wildlife Bridge Wilmshagen D, 2004
A comparison of timber versus concrete structures leads to building the bridge in timber. The truss
height of 90 cm is comparable with that of concrete. Due to the lower weight the foundations are
slimmer. The construction time is lower but cost and maintenance are comparable to concrete.
Three-hinged arch, span 27 m, length = 55 m, 1675 m² bridge deck, 600 m³ timber, 66 tons steel,
780 m³ concrete for foundations, construction time all together 3 month, timber work 2 weeks.
Figure 7
Figure 7 Arrangement of glulam arches, roof covering
5
International Conference on Timber Bridges (ITCB 2010)
Because of the optimal waterproofing on the top and the effective ventilation in longitudinal
direction the total construction does not need any biocide treatment. To prevent dirt and dust inside
the bridge a protective coat without chemical treatment is used.
Even in the worst case when underneath a vehicle is burning the timber construction performs
better than a concrete shell. Concrete looses its compression strength with 650° C. The surface of
timber will be covered with a coal layer. Within one hour the coal thickness is only 40 mm. The
inner part of the timber shows no loss of its resistance.
3.
New Concepts for Materials
3.1
Glued-Blocks
Glued laminated timber (glulam) is the most important material for bigger constructions and
complies with all the requirements. Curvatures even multi-axle shapes are possible almost without
any problems.
As a general rule 33 mm thick boards were layered and glued together. The maximum height of the
elements is up to 3,00 m. With solid timber finger jointing almost any length of the lamellas is
feasible. Transport and the maximum length of the press bed limit the length of glulam from 30 to
60 m. Due to fabrication and property of material e. g. width of boards the width of a lamella is
limited from 22 to 26 cm.
Glued-blocks are a further development of glued laminated timber. The technology of gluing is to
take finished glulam-beams and glue them over the width together to a block. The width of a block
is according to the restrictions of transport limited to 4,00 till 4.50 m. The glue line is either
horizontal or vertical range. Figure 8, Figure 9
Figure 8
Glued-block with vertical joints
Which location of the two glue-lines is to be used depends on the curvature of the block. In plan
view you choose horizontal joints. In elevation view you use vertical joints. For a two axial curved
member it is crucial to have the glue-lines in the plane of less curvature in order to reduce the
pressure in the bigger radius.
When using large-size glulam elements conditions of production affect unevenness of the surface.
For gluing these elements it is necessary to use special adhesives. They must be joint filling. DIN
1052 require a maximal thickness of the glue-line of 2 mm. Figure 10.
6
International Conference on Timber Bridges (ITCB 2010)
Figure 9 Glued-block with horizontal joints
When using large-size glulam elements conditions of production affect unevenness of the surface.
For gluing these elements it is necessary to use special adhesives. They must be joint filling. DIN
1052 require a maximal thickness of the glue-line of 2 mm. Figure 10
Figure 10 Manufacturing glued block, press of biaxial curved glulam
Bridge „Akkerwinde“ Sneek NL, 2008
In Sneek NL there is bridge designed and constructed as a monument for the Region. The bridge
incorporates several innovations. Especially the new method of timber modification seems to point
to new possibilities for timber construction.
The span is 32,00 m, the width is 12,00 m (double line) and the height is 15,00 m. The bridge is
designed for 60 tons. The components were twisted and glued en bloc, a novelty in timber
technology. Figure 11
The structural system is a spatial curved lattice framework of glued-bloc members with a suspended
steel deck. Figure 12, Figure 13
Here for the first time the big glued-bloc members of the latticed framework are specially treated.
Modified timber was applied. Pine wood from New Zealand was acetylized and after strength
testing was laminated as glulam.
7
International Conference on Timber Bridges (ITCB 2010)
Figure 11 Bridge „Akkerwinde“ Sneek NL 2008 SLW 60
Figure 12 Glued-block, Brücke „Akkerwinde“ Sneek, twisted and 3
dimentional curved
Figure 13 Assembly of crown steel connection with glued in rods
8
International Conference on Timber Bridges (ITCB 2010)
3.2
Cross Laminated Timber CLT
The massive-timber-construction technique, defined by the building product cross laminated timber
(CLT), was invented in the 90's of the 20th century and is characterized by consistent development
and international increasing establishment in numerous areas of construction. The first time we
have a material which is effective in two directions (e.g. load bearing). It consists of at least three
layers of softwood board which are glued together at rectangular angles. Figure 14, Figure 15
Figure 14 Cross-laminated-timber CLT
Figure 15 Production CLT
Bridge in Mühlhausen near Affing, 1996, footbridge
This bridge was a pilot project. It is built from a single board cross-laminated –timber CLT of
spruce (Lenotec). The thickness of the boards is 17 and 27 mm. The CLT consists of crosswise
glued boards. The span is 7,30 m and the width is 1,72 m. The necessary jacking pressure for the
gluing generated with vacuum. The different layers of the boards were adjusted and evacuated.
On top of the CLT a 33 mm thick LVL Kerto Q is glued. The LVL is impregnated and forms both
protection and wear-and-tear layer for the bridge. A 50 mm edge of the Kerto board over the bridge
9
International Conference on Timber Bridges (ITCB 2010)
lengthwise also covers the protection boards on the site. Figure 16.
Figure 16 Bridge Mühlhausen, cross-laminated-timber CLT, prototype
Bridge over B 85 Ruderting D, 1998
As part of the bypass road of Ruderting 1998 a rural road bridge for 30 tons was built. Figure 17.
Figure 17 Ü. d. B 85, Ruderting D, 1998, SLW 30/30
The load-bearing structure consists of a truss with inclined tresles out of glulam of larch and with
four T-beams of glulam of spruce. The width is 40 cm, the height 55 to 75 cm the total length 30 m
and the span 11,70 m. The slab consists of seven layers cross-laminated-timber with 22 cm
thickness. Figure 18, Figure 19.
To reduce the rolling shear stress at the bottom layer of the CTL board a 27 mm intermediate layer
of Kerto was glued on. To transmit the shear forces the bridge deck is connected to the web girder
with glued in steel rods of 30 mm diameter as well as threaded bars. CLT board is especially suited
for surface boards in road bridges with their high single loads.
10
International Conference on Timber Bridges (ITCB 2010)
Figure 18 Bottom view, glulam girders, LVL underside, inclinated
column
Figure 19 Detail cross section
11
International Conference on Timber Bridges (ITCB 2010)
Ganderbach-Bridge Barbian Kollmann Südtirol I 2009
The Ganderbach Bridge (Barbian South Tyrol) curved in the plane and built with CLT. Eleven
layers of CLT each 84 mm thick staying on edge and glued together form the main beam. Figure 20
to Figure 22. The cross section is a one-piece triangle. The bridge is 19,35 m long in the middle of
the radian measure. Width changing from 2,34 m to
3,06 m. Wide enough to allow an emergency
2
vehicle to cross. The life load is limited to 5 kN/m .
Figure 20 Ganderbach-Brücke Kollmann Südtirol I
Due to the bending capabilities of the 11 layers CTL, each 3-layered thick, in the plan view the
radius of curvature of minimal 25,50 m was achieved.
Figure 21 Detail deck and railing
Figure 22 Cross section midspan, x = l/2
The longitudinal girder of larch timber consists of 80 x 80 mm, with 40 mm thick planks attached
with concealed connectors. A double layer of split larch shingles effectively protects the timber.
4.
Developements of Connectors
4.1
Stress Laminated Deck (Pre-stressing perpendicular to the Grain)
This construction method was originally developed in Canada 40 years ago to repair the rotten
decks of timber or steel bridges.
The simplest form of QS-slabs are vertically placed boards, planks or squared timber which have
been combined by pre-stressing steel rods. This leads to the load being distributed to parts of the
slab not directly under pressure. The pre-stressing prevents movement of the single boards against
each other and therefore friction forces cause the static function of the whole deck. Figure 23.
12
International Conference on Timber Bridges (ITCB 2010)
Figure 23 Stress-laminated-deck (Prestressing perpendicular to the
grain), distribution of a single load to the support
The load bearing behaviour of the slab leads to transversal bending. However, the pre-tension
pressure can easily balance the possible flexural tensile stress.
As the pre-stressing forces at the edge of the slab would be too high for the soft wood of the main
slab material, often hard wood of steel profiles are used as end beams to induce the pre-stressing.
The forces are taken from the pre-stressing rods into the timber by nuts and metal plates.
If the pre-stressing forces diminish over time due to shrinkage or creeping, it is always possible to
re-adjust them. This cross-dimensional stressing leads to a high dimensional stability and to a very
stiff deck which is suitable for very high wheel loads.
The deck forms a stable, immobile base on which a permanent seal can be placed. This leads to a
reduction of minimal height of the structure compared with a structure of main and subsidiary
beams.
Span widths of 6,00 to 12,00 m can be achieved economically, while almost any width is possible in
these constructions. Loads of up to 60 tons are achieved. The load bearing ability is restricted by the
Figure 24 Tynset Bridge N, 2001, SLW 60, l = 124 m, span = 70 m,
width = 10 m, prestressed laminated deck
13
International Conference on Timber Bridges (ITCB 2010)
available width of the planks (and therefore the thickness of the deck).
Tynset-Bridge N 2001
The support structure consists of three circular arches, two small ones of solide glulam with a span
of about 26,50 m and one large arch with a span of 70 m. The main arch, which is a two parallel
glulam truss arch, supports 12 vertical steel hangers, each of which carries a secondary steel beam
supporting a stress laminated timber deck. The bridge has two lanes for ordinary road traffic and
one lane for light (pedestrian/cycle) traffic. The total width (between the parallel arches) is 11,70 m.
Figure 24, Figure 25.
Figure 25 Detail unfinished slab
Forest-Road-Bridge Wila CH
The one lane forest road bridge in Wila has no load limit. The bridge is a special case because the
deck slab is stress laminated and curved in plan view. The 3 glulam beams of spruce are 18,00 m
long 1,17 m wide and 30 cm thick. The beams were glued together on the building site. The
boundary element of the slab is plywood of beech to ensure the load distribution of the prestressing. The waterproofing on top is a foil and asphalt. Figure 26, Figure 27.
Figure 26 Forest road bridge in Wila CH, curved stress laminated
deck (prestressing perpendicular to the grain)
14
International Conference on Timber Bridges (ITCB 2010)
Figure 27 Detail, 3 prefabricated curved glulam girders
4.2
Glued in Rods
Limiting factor in a timber structure is usually the low performance of the joints or connections.
Joints using glued-in rods have shown high performance.
The adjustment of the stiffness of the timber and the glued-in rod minimises the loss of stiffness of
the complete connection. The higher but only local deformations have no significant influence on
the stiffness element. Global measurements cover the influence of the glued connection because of
variance of the modulus of elasticity. Figure 28.
Figure 28 GSA-components: threaded bars; GSA-resin and glulam
Larger structures must be transported in sections. Therefore a jointing technique is required which
uses the higher performance of factory gluing and the simple and reliable mechanical joint by use
e.g. of steel pins or bolts at the erection place.
High performance can only be achieved if any of the influencing parameters are near to the
optimum. This requires a reliable control of the design and of the production process. This is the
main reason for a factory made connection, where the production is made under better controlled
climatic and working conditions.
Bridge „Akkerwinde“ Sneek NL, 2008 (s. 3.1)
The kind of connectors turned out to be of high importance. In this case glued-in rods were chosen.
The requirements of the connectors are high capacity and low visibility. Glued-in rods are proofed
15
International Conference on Timber Bridges (ITCB 2010)
Figure 29 Bridge „Akkerwinde“ Sneek NL 2008 SLW 60
in Germany up to diameter 30 mm. To get a rigid connection the use of diameter 48 mm was
necessary. Figure 29. The length of the rods exceed 2,00 m. They are drilled trough the chords into
the diagonals. There was no experience with this kind of connection. It was necessary to execute
various full-size tests. As bonding agent epoxy resin was used. The total amount of resin was 2,5
tons to glue in the rods. Figure 30.
Because of edge distances and the big diameters the net cross section has to be taken into
Figure 30 Connection with glued in rods before pressure grouting.
Bridge „Akkerwinde“ Sneek“ NL 2008 SLW 60
16
International Conference on Timber Bridges (ITCB 2010)
calculation. Some of the construction elements had only 50% remaining of the cross section.
4.3
Timber-Concrete-Composites TCC
The idea of timber-concrete composites is to combine the high tensile strength of timber with the
high compression resistance of concrete. The application started with building constructions in new
buildings and in renovation. Figure 31.
In Germany hybrid bridges with block-glued timber as load-bearing element of bridges is only used
for the construction of pedestrian-and bicycle use. Main beams with high stiffness and stability of
dimension can be produced by block-glued timber. For road bridges these hybrid cross sections can
be used alternatively to conventional methods of construction.
The shear forces were transmitted by yielding mechanical connectors or by direct contact between
timber and concrete. The stress distribution depends on the rigidity of the connectors.
Figure 31 Deformation of shear connector
Crestawald-Bridge Sufers CH
The structure of the Crestawaldbridge in Sufers CH. Figure 32 is a combination of 4 glulam girders
Figure 32 Crestawald-Brücke Sufers CH, spandrel-braced arch
bridge
17
International Conference on Timber Bridges (ITCB 2010)
of larch and concrete composite-plate. The plate with 32,50 m length and 3,50 m width works
together with the main girders as T-beam. The shear forces between concrete slab and the glulam
webs are transferred by headed stud connectors with 16 mm diameter welded to a ground plate of
20 mm thickness. Figure 33, Figure 34. The ground plate is fixed on the glulam beams by screws.
First used for renovations of timber decks, the applications for this method increases.
Figure 33 Construction detail, shear connector Figure 34 Construction detail, steel-plate with
with concrete reinforcement
stud and indented tapered steel bar
4.4
Timber-Concrete-Composites glued
The Berner Fachhochschule CH succeeded in a project on connecting timber and concrete without
any mechanical fastener only with adhesives. A competitive method was developed to substitute the
classical connections witch does not cut the timber fibres. It achieves higher stiffness and no slip.
The shear forces are uniformly distributed by the use of adhesives. The joint between timber and
glue is waterproof. Figure 35, Figure 36.
Figure 35 Timber and concrete adhesion, shear Figure 36 Detail Timber and concrete
connection
adhesion-gluing (red)
5.
Composites
Composite materials are engineered materials made from two or more constituent materials with
significantly different physical or chemical properties which remain separate and distinct on a
macroscopic level within the finished structure.
5.1
Timber-Plexi-glass-Bridge Darmstadt THD D, 2007
The worldwide first Bridge out of composite glulam and plexi-glass was completely prefabricated.
The span is 26 m, the weight is 28 tons. The filigree construction was developed at university
18
International Conference on Timber Bridges (ITCB 2010)
Darmstadt and Evonik a subsidiary of Röhm GmbH.
The cross section of both main girders is like a double T-shape. The upper and lower chords are
taking the compression and tension forces. The plexi-glass pane acts as a diaphragm against shear
forces. Both chords are screwed to the plexi-glass. Figure 38, Figure 37.
Figure 38 Composite: timber-plexiglass-bridge, Darmstadt D
Length: 26 m, span: 15,20 m, width: 4,10 m, width of walkway: 1,60 m, weight: 28 tons, traffic
load: 5 kN/m2.
Cross section of the timber chords 2 x 15/20 cm
Dimensions of the plexi-glass pane: thickness: 70 mm, size: 8 x 3 m
Deck: timber plank larch
Figure 37 Detail bearing
19
International Conference on Timber Bridges (ITCB 2010)
5.2
Composite Balsa USA, 2009
Core materials are manufactured into very light and yet rigid sandwich panels in combination with
two outer skins. The core material distinguishes itself as an easy-to-process material which
demonstrates specific attributes such as high strength and stiffness, fire and temperature resistance,
temperature and acoustic insulation, resin absorption and many others. Figure 39, Figure 40.
A new balsa-cored composite bridge deck recently opened to traffic over the Pierre Part Bayou in
Assumption Parish, La. The latter company says this installation is believed to be the very first
balsa-cored composite deck project containing Single-Walled-Carbon-Nanotubes (SWCNTs).
Figure 39 Alcan balsa-cored composite bridge Figure 40 Testing with 60 to.
deck containing single-walled
carbon nanotubes (SWCNTs). Pierre
Part Bayou in Assumption Parish
Louisiana USA
The bridge is intended to replace traditional steel structures. Half of the six 6-feet by 25-feet plates
are additionally comprised of SWCNTs. This along with installed fibre optic strain gauges in the
bridge panels is intended to monitor the performance of the material over several years. The
location was chosen because it is heavily travelled by sugar cane trucks heading south to New
Orleans
6. References
See www.fh-biberach/forschung/holzbau/downloads:
- List of photographs
- Literature
- Brochures
20