In both cases a systematic approach to maintenance is required to ensure that structures remain safe and serviceable. Numerous management systems have been developed throughout Europe to assist engineers in deciding what maintenance is required and when it should be carried out. The simplest consists of a database that holds all the relevant information on each structure - for example structural details, records of inspections, previous maintenance history - that the engineer needs to reach a decision. More complex systems contain algorithms that manipulate the data to produce optimum maintenance strategies at both project level and network level, taking into account constraints such as inadequate funding.

Most systems have been developed either for a particular stock of bridges, or to meet the requirements of a particular bridge owner and then developed further to meet the needs of a wider market. The objective of the Bridge Management in Europe (Brime) project was to review the requirements for a bridge management system for the European Road Network and then develop an outline framework that would operate at both project level and network level.

The research was undertaken in seven work packages, six of which focused on the modules required to create a bridge management system. Each of these six work packages was split into two stages, firstly reviewing the state of the art and identifying the requirements for a BMS. The second stage involved developing guidelines for the various modules for the system. Under the seventh work package, existing systems were reviewed and the findings were used to develop the framework for a BMS.

The first work package reviewed current methods used in Europe and North America for inspecting and assessing bridge condition. Three basic types of bridge inspection were identified: superficial, general, and major. A fourth type of inspection - an in-depth or special inspection - is carried out on structures where there is a particular problem or cause for concern. These inspections are also carried out for a variety of other reasons, for example: on bridge foundations after flooding, and on structures after earthquakes. They involve extensive measurements on site and may include laboratory testing. Other types of inspection such as an 'acceptance inspection', which is carried out before a structure is opened to traffic and a 'guarantee inspection' are used in some countries.

The results of an inspection are used to provide as a measure of the structure's condition. Two approaches have been used; the first is based on a cumulative condition rating obtained from a weighted sum of all the assessments of the condition of each element. The second gives the assessed condition of the bridge as the highest condition rating of the bridge elements.

Artificial intelligence methods were investigated as a means of improving condition assessment and a review was undertaken of neural network, fuzzy logic and genetic algorithms. A neural network model was then developed for categorising the condition of corroded areas on reinforced concrete bridges. Whilst this gave promising results it could only give the condition at the time the measurement was made:, further work was required to evaluate the change in condition with time.

The second work package developed recommendations for methods to assess the load-carrying capacity of highway bridge structures. These methods were based on a review of current assessment procedures used in the countries participating into Brime. This included details of the characteristics of existing structures, the standards used in theirdesign and assessment, and experimental methods used in the assessment of bridge structures. The purpose of this work was to illustrate how assumptions for material and structural properties, and traffic loads can be obtained and used in structural assessment.

To assess whether structural elements are capable of carrying modern day traffic loads,requires models for both element resistance and applied loads are required. Load models thatthat tooktake account of the extreme traffic loads applied to structures were developed. Material strengths were obtained from statistical data for reinforced and prestressed concrete, steel, masonry and timber structures.

Bridge assessment in the partner countries is based either on a deterministic or a semi-probabilistic (ie with the use of partial safety factors ) approach in which the load effects are determined by structural analysis, using design standards which can be amended to take account of information from measurements on the structure. But these methods are sometimes considered to be conservative, and a new approach taking into account uncertainties in variables is emerging. Reliability calculations are beginning to be introduced, with the target reliability index becoming the governing factor for assessment.

The assessment procedure that was recommended is based on that used in the UK. It consists of several levels of assessment, starting with inspections and structural assessments using simple analysis and codified requirements and work up to the most sophisticated assessment using a full probabilistic reliability analysis.

The objective of the third work package was to quantify the structural effects of material deterioration. Results showed that corrosion of steel due to carbonation and chloride contamination was the most frequently occurring problem, although deterioration due to alkali-silica reaction, sulphate attack and freeze-thaw action were also common.

Existing methods of dealing with deterioration in assessment (reduced cross-sectional area, modified stress-strain relationship, modified bond properties and so on) were evaluated. Guidelines for taking account of deterioration were produced but these models are based on experiments using laboratory specimens, and calibration with site measurements is required. Such measurements need to be carried out over a long period of time to give realistic results. This is also complicated by the fact that the deterioration and its affect on load carrying capacity is not linear with time and the actual rate will depend on site specific conditions.

The fourth work package was concerned with predicting the rate of deterioration for the various processes, for which there are currently two approaches. The first uses historical data to predict future performance while the second attempts to model the various deterioration processes. This is an enormous subject, so the Brime project focussed on modelling the ingress of chlorides into concrete, which can be used to provide data for forecasting maintenance actions, but not for assessing deterioration and structural capacity.

Further research is needed to develop models to predict the initiation and rate of corrosion once the chloride ions reach the reinforcement. Similar models are also required for other forms of deterioration, so that the future condition of the structure can be predicted and input into work package three. The development of deterioration models and their use to determine load carrying capacity of concrete structures in general is being carried out under a separate European project - known as Contecvet - which will produce a validated users' manual for assessing the residual life of concrete structures.

The objective of the fifth work package was to develop a methodology for selecting the best maintenance option for a given bridge, considering safety, durability, functionality and socio-economic issues. A method was developed which was based on a global cost analysis which took account of all the costs involved in construction, inspection, maintenance, repair, failure, road usage and replacement. The method minimised the global cost while keeping the lifetime reliability of the bridge above a minimum allowable value.

This was taken further in work package six with the development of methods for determining an optimum maintenance strategy. It included a review of current methods for prioritisation and optimisation of bridge maintenance at both project and network level. Simple procedures were developed for selecting bridge structures for inclusion in the maintenance programme and for ranking bridges with respect to the impact of their location in the road network. Costs that had to be taken into account when examining different maintenance strategies were identified. The need to model deterioration rates, to enable future deterioration of structural elements to be predicted when the maintenance work is deferred, was identified.

Results from work packages 1 to 6 were brought together in work package 7 to produce a framework for a bridge management system. For example the assessment of bridge strength is required for the evaluation of maintenance strategies and for the decision making process. It is also a significant input for priority ranking, for the routing of abnormal vehicles and for the management of safety measures. The philosophy adopted in the development of the framework has been to identify the outputs required by the engineer and then determine the inputs required to produce those outputs.

This project will be of interest to organisations responsible for the management of bridges at both network and local level, national railway authorities, and owners of other infrastructure such as waterways. Other organisations such as consultants which are employed to assess the load carrying capacity of bridges and test houses responsible for determining structural condition will also benefit from the outputs of work packages 1, 2, &and 3. The project was partly funded by the European Commission Directorate General for Transport, with balancing funds provided by the authorities responsible for the national road networks in the participating countries.

Future developments are likely to include further application of the use of artificial intelligence methods for various aspects of bridge management and increased use of reliability techniques. Life cycle assessment is also likely to be used to minimise the environmental impacts of bridge management. Finally, the management of the highway network as a whole will mean that bridge management will become a part of a much larger asset management system that ensures that society gets maximum benefit from its investment in the highway infrastructure.

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