Exploitable results
There is a great demand for European railway bridges to carry increased loads and allow higher speeds, increasing infrastructure capacity for passenger and freight traffic. In many cases these demands can be met through proper structural assessment, determination of the true behaviour of the structure, strengthening of certain sections or by monitoring critical properties. Research has shown that there is a great potential for a big step forward in all these areas. Using a probabilistic approach for loads and resistance is one example of a new generation of methods that can be developed and applied.
Codes for bridge design has been developed gradually and have been designed to consider all the uncertainties that are present in the construction phase of a structure. These codes are also often used for the evaluation of existing bridges. However, far better information on material and structural properties is available for an existing structure than for one not yet built. Nevertheless the same factors of safety are often applied to existing structures as to the ones being constructed. Many bridges can be allowed to carry greater loads and faster trains if better codes and methods for assessment are used.
The Sustainable Bridges project showed that it is possible to save about 2 % of the capital value of the bridges by allowing increased loads and extending residual service life.
The outcome of the project are four documents which contain useful information and guidelines for bridge engineers, bridge owners and operators on the state-of-the-art knowledge and tools to help operation, maintenance and management activities and ensure the most efficient use of existing railway infrastructure.
These documents are:
1.'Guideline for inspection and condition assessment of railway'. It provides inspection and condition assessment tools to get comparable description of the railway infrastructure condition in different countries of the European Community. Furthermore, it presents tools helping to update bridge documentation that might be insufficient, inaccurate or incomplete.
2. 'Guideline for load and resistance assessment of existing European railway bridges - advices on the use of advanced methods'. It provides guidance and recommendations for applying the most advanced and beneficial methods, models and tools for assessing the load carrying capacity of existing railway bridges. This includes a systematised step-level assessment methodology, advanced safety formats (e.g. probabilistic or simplified probabilistic) refined structural analysis (e.g. non-linear or plastic, dynamic considering train-bridge interaction), better models of loads and resistance parameters (e.g. probabilistic and/or based on the results of measurements) and methods for incorporation of the results form monitoring and on-site testing (e.g. Bayesian updating). In most of the topics this guideline uses the current state-of-the-art knowledge and the presently best practice. Nevertheless, in many subjects it proposes the use of new and innovative methods and models that have been developed, obtained or systematized due to research performed.
3. 'Monitoring guidelines for railway bridges'. It provides a procedure for specifying, designing, implementing and operating monitoring systems in a systematic and coherent way. It defines the actors and their roles within the monitoring activity. This guideline introduces the concept of a model monitoring system as the fundamental planning tool for specifying the physical monitoring system. This tool allows bridge owners and structural engineers to specify their requirements on a monitoring system by using concepts that are familiar to them. The concept of model monitoring system permits to separate the roles and responsibilities of the different actors and to clearly define the interface between a structural engineer and monitoring experts. The task of the monitoring expert is to implement and operate a monitoring system that conforms to model monitoring system specified by the structural engineer.
4. 'Repair and strengthening of railway bridges - guideline'. This guideline supports the railway owners in deciding necessary strengthening measures for concrete, steel or masonry railway bridges. In addition possible strengthening measures for the bridge subsoil are presented. Strengthening of bridges is usually performed to fulfil the safety requirements regarding the ultimate limit state (ULS). Therefore, the principal focus in this guideline is on the methods suitable for this purpose. However, many of the strengthening methods that are described in this document will also be applicable when measures ar needed to fulfil the serviceability limit state (SLS), for example increased stiffness of the structural elements or decrease crack sizes in concrete members. The scope of this guideline has been limited to modern methods and strengthening systems known to the authors or developed within the project. Methods that can be considered traditional or methods that can be considered well known to the railway owners have not been presented. The guideline tries to highlight strengthening methods that are environmental friendly, not disturbing the ongoing traffic and at the same time are economically competitive.
The project has also produced the 'Overall project guide' which provides support to the railway engineer, operator or manager in using the technical guidelines and reports developed within the project, and it shows where to find relevant technical information for the specific operational or maintenance activity. Furthermore, it gives some guidance on the number of possible approaches and methods presented in the project guidelines and reports that might be helpful in upgrading existing railway bridges for higher speeds and loads or that might help to extend their service life.
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