RENAISSANCE OF TIMBER BRIDGES

Wood as a building materia/ of bridges has many advantages, especially considering the important ecological aspects. Wood is a renewable natural resource and the energy content of a finished structure is low. A timber bridge is an attractive and aesthetical alternative when adapting a bridge into a landscape. Finland, as a country of great forest resources and a high educational level of scientific and technical persons, has excellent possibilities to be in the van of development of timber bridges.

PRESENT STATUS OF TIMBER BRIDGES

The share of timber bridges is about 7% of the number of all the bridges owned by the Finnish National Road Administration. Two thirds of timber bridges were constructed in the sixties and seventies. At that time almost all wooden bridges were log bridges. In the middle of the seventies, the glued laminated timber bridges took the dominating role. In the eighties the investments on timber bridges drastically decreased: only a few new timber bridges were constructed annually.



A new timber arch footbridge with a span of 40 metres under construction in Lapland

RESEARCH PROJECTS

During 1992-94 a national research programme of timber bridges was executed in the Laboratory of Bridge Engineering at The Helsinki University of Technology. The programme was financed by the Finnish National Road Administration, Technology Development Centre TEKES and the timber industry. Literature research of timber bridges was executed, prospects of wood in various types of bridges were analysed and development of new structural solutions was commenced

The project was continued in 1994-96 as a Nordic joint project (Denmark, Finland, Norway and Sweden) as part of a more extensive research programme Nordic Wood In addition to the national financing sources, the Nordic Industry Foundation is financing the project.

The aim of the research project is:

• to clarify and analyse the markets of bridges suitable for wood structures-both in the Nordic countries and in potential export areas
• to study the general competitiveness of timber bridges
• to study and develop the guidelines of design of timber bridges especially considering the new structural Eurocodes
• to study and develop new structural solutions for timber bridges considering the possibilities of modern production technology
• to study and develop the protection methods of timber bridges
• to encourage the employers, designers and industry to consider wood as a serious alternative in bridge construction by means of an information campaign of the research results.

NEW INNOVATIONS

One of the main topics in the Finnish research projects has been a study of wood-concrete composite structures in bridge engineering. Practically all former applications of such structures have concerned buildings. Different connection types were studied both theoretically and experimentally. Three bridges based on this new type of structure were constructed in Finland during 1993-95. The concrete deck in timber bridges is one solution to avoid the problems caused by low abrasion resistance and decaying connected to wooden decks. Furthermore, it also serves as a protection against heat and UV-radiation.

A brand new Idea is a prestressea wooaconcrete composite bridge. Two test girders were loaded in the laboratory to clarify the behaviour of such structures. Ordinary timber girders are often considered to be too high, which can have a negative influence on the appearance of a bridge. By using this solution, timber girders can be made more slender and attractive

Arch is one of the most interesting structural elements used in bridges. Arch is both an aesthetical and economical structure and it is also suitable for prefabrication. Several innovative solutions, especially concerning the connections, were developed in the research projects mentioned above in order to improve the competitiveness of timber bridges in domestic and export markets.

Due to the goal-directed investments on the research activities of timber bridges and the increase of the general interest on the natural materials, timber bridges have become again a real alternative in bridge engineering.

AARNE JUTILA & PEKKA HAAKANA
Helsinki University of Technology

FINNISH BRIDGE EXPERTISE TO RUSSIA

More than 30% of the bridges on Russian federal highways are in poor or alarming condition. These bridges are or can soon become bottlenecks. More than 60% of the bridges require strengthening or widening in order to fulfill the present loading regulations and geometrical requirements. For improving the situation, Russia applied for a loan from the World Bank for bridge repair and reconstruction.

A bridge over the railway Bologoe-Polotsk on the road M10 Moscow - St Petersburg - Finnish border, assessed by the Finnish bridge experts.

Together with Imidis from Russia, the Company Finnroad Ltd has carried out the inspection and condition survey, the assessment of the reconstruction options and detailed design of the reconstruction of two bridges in Highway M-10 from Moscow to St. Petersburg. These are typical precast concrete bridges which are common in Russia. This was the first project commissioned by the Russian Federal Highway Department (FHD) within the framework of the Bridge Rehabilitation Project of the Word Bank.

Finnroad Ltd was responsible for the preparation of the contract documents for national competitive bidding and for the standard specifications of the bridge repair and reconstruction. Russian material, construction and acceptance requirements (SNIP, GOST, etc.) were improved by using Finnish know-how.

Concrete investigations included strength testing, carbonation tests, chloride determination and electropotential measurements. The target standards for bridge reconstruction conform to Russian Bridge Feasibility Study decisions. Bridges shall be widened by strengthening the structural elements to required load capacity All and NK-80. After reconstruction they shall have a service life not less than 25 years. Reconstruction will include the removal of all damaged concrete from the bridge deck and supports, casting a new concrete slab, constructing of a new waterproofing and pavement, repair of the ends of the element beams, replacement of bearings, repair of the support crossbeams, replacement of the transition slabs and the improvement of the bridge approaches, re placement of the railings and guard rails as well as the widening of the abutments. Drainage pipes, perforated drain pipes and impregnation of the concrete surfaces were used as new solutions for Russian bridges. The contract documentation was delivered to FHD in February 1996.

In 1994, Finnish Consulting Engineers Ltd. (SITO) carried out the feasibility study of the rehabilitation of the federal highway M-10 (E18) on section St. Petersburg - Vyborg Finnish border. This project included bridge inspection and rehabilitation proposals for 33 bridges. The employer of the study was Leningrad Area Road Committee from Russia and the Finnish Ministry of Communication.

In 1995, within the World Bank financed Highway Rehabilitation and Maintenance Project, SITO carried out the assessment of 92 bridges on the federal highway M-10 Moscow - St. Petersburg between section km 62 and km 673. Based on this assessment, associated cost estimates for the rehabilitation project were made.

TONIS TAGGER
Finnish Consulting Engineers (SITO)

Top

R&D Projects of Finnra s Bridge Engineering Unit

(ARCH. CODE
PROJECT NAME
RESULTS OR CONTENTS OF THE STUDY)

TIEL 2230095... TIEL 2230098
Bridge repair manual
Manual is an efficient tool for designers, owners, contractors and suppliers of materials involved in repair.

TIEL 2230001
Maintenance of bridges
Instructions for yearly inspections, routine maintenance and smaller repair works.

TIEL 2232219
Bridge inspection guidelines
Inspection system, inspection methods, characteristic damages of materials, damages of structural components, reports and files are presented.

TIEL 2230003
Bridge inspection manual
Manual is used when inspection data is classified and entered into the bridge register.

TIEL 2170004
The aesthetics of flyover bridges
Factors affecting the aesthetic appreciation of flyover bridges and underpasses, and the ways of design and finish.

TIEL 3200085
The Lumberjack's Candle Bridge. Regional development and road planning.
The planning and construction of the Lumberjack's Candle Bridge.

TIEL 703451
How to plan the surroundings of a bridge
Model plans for different finishes of bridge sites.

TIEL Letter no. S 518/23.1 0.1992
Bridge site classification
Evaluation of the significance of the bridge sites, and their division into four categories. The impact of each category on the design and the construction.

TVH 723443
A bridge and its environment
Factors influencing the appearance of a bridge and its environment. The goal is to help designers in creating bridges that look good and suit the environment.

TVH 732220...TVH 732223
SILKO directives
(continuosly updated) Rehabilitation directives, also to be applied in planning the finishing touches for bridges and bridge sites.

Contents of FinnContact 1/1996:

• Editorial
• Fitting bridges to their surroundings
• Renaissance of timber bridges
• Finnish bridge expertise to Russia