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THE REAL SERVICE LIFE OF ROAD BRIDGES IN SWEDEN – A CASE STUDY Road bridges in Sweden G. RACUTANU Department of Structural Engineering, The Royal Institute of Technology, Stockholm, Sweden Durability of Building Materials and Components 8. (1999) Edited by M.A. Lacasse and D.J. Vanier. Institute for Research in Construction, Ottawa ON, K1A 0R6, Canada, pp. 56-70. Ó National Research Council Canada 1999 Abstract To clarify the real condition of a country’s bridge stock and their structural members at a given time, reliable regular and systematic inspections are needed. Accurately documented, these inspections are essential for the road administration authority in the planning of the necessary maintenance and repair works on the existing bridge stock, thus contributing to an overall cost-effective bridge management. The Swedish Road Administration has, at the present, a relatively intact and well- organised bridge archive system. Most of the former bridge inspections performed on the public road network after the nationalisation of the Swedish roads in 1944, are documented and stored in different archives throughout the country. The information from these inspections has been fed into a Microsoft Access database called BEA (Bridge Element Analysis), with the purpose to explore the possibility to determine the damage occurrence, damage growth and the real service life for bridge structural members. In this case study, the database is used to examine, if certain information and factors like geographical location, traffic, and weather data at the time of casting, affect the service life of bridge structural members thus the service life of bridges. Based on the information stored in the database, the service life of bridge structural members in certain service life conditions may be estimated. For example, the real service life of bridge members as a function of the outside airs temperature at the time of the con- crete casting. The information stored in the database may also be used in the devel- opment of a damage growth model based on the assessed condition at the time of in- spection. Keywords: Bridges, service life, bridge structural member, bridge management, data- base, estimated service life, damage type, damage cause. 1 Introduction 1.1 General This paper is the result of a case study on the real service life of some 270 bridges located on the Swedish National road-network. However, the results from the extended study during 1998, comprising a total of 370 bridges are not presented in this paper. Bridges are an important part of a nations road system. Maintaining and repair- ing existing bridges is a major economic concern for many governments and local authorities around the world. Many bridges are built with outdated technical codes and demands. The service life of a bridge is often defined as the time from construc- tion to the time a critical limit state or property has been reached. It is generally ex- pected that during their service life, bridges can fulfil certain demands such as traffic safety, continuous traffic flow and a designed load bearing capacity. Regular and systematic inspection of the existing bridge stock should be performed in order to verify that such demands are met at all times. With the 1944 nationalisation of the public roads in Sweden, information about most of the regular bridge inspections have been carefully documented and filed by the Swedish National Road Administration in different archives. Damages are rated in condition grades on a scale between zero and three. 1.2 Background The research program ”The durability, management, repair and life cycle cost of concrete structures” conducted at the Royal Institute of Technology was initiated by the Swedish National Road Administration in 1991. As the program title suggests the program consist of a number of research projects. The project ”Actual durability and service life of Swedish concrete bridges” was started in late 1992. The aim of the project was, initially, to establish the research possibilities of the vast amount of in- formation in the archives and data in the bridge management system of the Swedish National Road Administration. The project resulted in the later part of 1997 in a Li- centiate Thesis, “The Real Service Life of Bridges”. 1.3 Aims and scope The second stage of the project was a further investigation in the use of the bridge information available with the aim of developing deterioration models. This has been achieved for bridge structural members in certain service conditions. In the future, bridge designers and inspectors would predict the performance of certain bridge structural members in certain service environments according to type and cause of the damage. Service life models in combination with a relational database containing actual durability information would result into a tool for assessing and predicting the actual service life. If such a model could be achieved, it would give researchers and owners a precious tool in the planning of maintenance works, design of the different struc- tural parts and component and feedback for future codes and regulations. The development in time of the condition grade can be a way of predicting the service life of bridge components, contributing to cost effective bridge management and improved bridge component design in the future. 2 Method Sweden has many different local climate conditions. In the north of Sweden there are few yearly frost-cycles, mainly because the temperature is always below zero degrees Celsius throughout the winter season while it can oscillate around zero degrees in central and southern Sweden leading to several frost-cycles. This implies better frost-resistance performance of the concrete in the central and southern parts of the country. De-icing salts are used on many roads during the cold season of the year. Be- cause of the various climate conditions in Sweden, bridges in the central and southern part of Sweden are especially exposed to de-icing salts. It became evident in the early part of the study that to minimise the service life variables, bridges should be studied on geographically close road sections. 15 different road and highways sections with 188 bridges were selected in the central part of Sweden. In order to be able to study how different climates affect the bridge structures, the geographical extent should be increased with road sections in different parts of the country. This resulted in the gathering of information on 82 bridges in the northern part of Sweden. The roads in that particular county are de-iced using very little salt or no salt at all which is an in- teresting factor to study. 2.1 The information gathering process 2.1.1 Extent In order to gather the information in an efficient way a strategy to find relevant information was prepared. During the first part of 1993, detailed checklists and rou- tines for the gathering process were produced. This was essential in order to minimise the risk for errors and loss of information. The gathered information was placed in project files for each road section in the investigation. This material is unique, and should be an important asset for many research projects. The limitation of the road sections, in both length and the amount of bridges were adjusted so that traffic flow and climate have similar conditions. This was made to make road sections comparable and thus enabling the study of certain factors im- posed by the surrounding environment that might affect the service life of structural members. In 1997, the investigation included 19 different road sections with a total of 270 bridges. The results and conclusions were presented in the Licentiate thesis “Konstbyggnaders reella livslängd”, the Royal Institute of Technology, Stockholm. The R&D project was continued and during 1998, 100 bridges on four road sections in the western and eastern parts of Sweden were added to the investigation, thus covering two new different parts of Sweden. 2.1.2 Selection of information The gathered information for each bridge can be divided into three different groups: · General information on the bridge · Inspections and repair works performed on the bridge · Information from the construction stage and the final inspection All performed inspections and repairs by the Swedish National Road Admini- stration were summarised in the inspection- and maintenance sheet of the bridge and archived. Even these have been copied, when available, for the bridges included in the investigation. Information given is notes the inspectors have taken during inspec- tion or the maintenance work and the date they were performed. The basis of the inspection- and maintenance sheet is ”the full inspection re- port”. That report gives information, in addition to that in the summarised inspection- and maintenance report, on for example suggestions of bridge maintenance measures or activities and who should carry them out. The full inspection reports were not always easy to find. Unfortunately, in many cases only the inspection- and maintenance report had been saved. The documentation from the performed special inspections is often in the form of tables and diagrams and have been found both at the central and regional archives of the Swedish National Road Administration. Values from the chloride profiles have been inputted the database BEA for analysis. Other gathered information, on bridges in the investigation found in the different archives, was copied and placed in the proj- ect files. Concrete castings are documented in concrete casting reports. The report includes facts about mixing conditions, quantity, concrete quality and meteorological conditions at the time of concreting. At many concrete castings, concrete tests are taken for analysis. The concrete samples are related to a testing record in the concrete casting reports. Some tested qualities are compressive strength, water tightness and frost resistance of the con- crete. Examples A lot of the gathered information is of historical value.

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