A large number of the bridges in the European railway networks are metallic bridges. The increasing volume of traffic and axle weight of trains mean that for many structures the loads today are much higher than those envisaged when they were designed. This paper presents a summary of the different recommendations and advices proposed in "Guidelines for Load and Resistance Assessment of Existing European Railway Bridges" of the European Union founded project "Sustainable bridges" for assessing old metal railway bridges. The knowledge of the material properties of existing metal bridges is essential for the resistance assessment and the determination of the remaining lifetime of old metallic bridges. Furthermore, old bridges require more exact and efficient assessment methods that call for a precise description of the material. Among the problems met in metal bridges and material properties estimation, fatigue is the most common cause of failure. To be able to make accurate assessments of existing bridges, it is important to know the behaviour of bridges exposed to fatigue, and how the old materials behave due to cyclic exposure. The main question answered herein is how to make a safe estimation concerning the remaining life in service. The possible traffic load on steel rail bridges is usually limited by the fatigue resistance, but for certain situations the static resistance has also to be checked. Most design rules for steel structures, for instance those in Eurocode 3, are applicable also to riveted structures. However, some information is missing on how to deal with the special case that elements are intermittently connected in contrast welded structures that are connected continuously. As the traditional methods for assessing the resistance of steel bridges are based on elastic analysis, a method for utilizing a limited redistribution of bending moments based on beam theory is proposed.

EN 1993-1-5 provides harmonized European design rules for plated structures. It is a step forward in the harmonization process, but like all the Eurocodes it includes many options for national choices, in terms of parameters and also methods, which leads to quite different results. Actually, there are four different methods for dealing with buckling problems. One purpose of this paper is to illustrate differences by way of examples and also to suggest topics for studies intended to improve the design rules and bring them closer together. The revision of EN 1993-1-5 is due to take place around 2014 and there is ample time for performing research projects that can form the basis for the new version. Examples of such topics are the recalibration of buckling curves, reviewing the interaction checks and the verification format of the reduced stress method.

Cold formed sections can be optimized for different purposes and they are fairly inexpensive to produce in small series. They have an inherent weakness in their small torsional stiffness, which is unfavourable for columns. One solution presented here is to make a closed section by adding a thin cover plate connected discretely with self-tapping screws. It is here called a partially closed cross-section because it is not continuously and rigidly connected. The aim of this paper is to evaluate the efficiency of this solution by comparing the behaviour of partially closed and open cross-section. Four columns were tested within the project, two of them with centric axial load and two with eccentricities. Numerical analysis was performed using ABAQUS for establishing the influence of the cover plate on the critical load and the resistance. A good agreement between non-linear FEM and experiments were found. After this verification of the FE model a parametric study was carried out. Results of experiments and numerical analysis were compared with the predicted resistance by Eurocode 3, Part 1-3, and the Direct Strength Method. Both design methods give good predictions of the resistance.

Cold formed sections can be optimized for different purposes and they are fairly inexpensive to produce in small series. They have an inherent weakness in their small torsional stiffness, which is unfavourable for columns. One solution presented here is to make a closed section by adding a thin cover plate connected discretely with self-tapping screws. It is here called a partially closed cross-section because it is not continuously and rigidly connected. The aim of this paper is to evaluate the efficiency of this solution by comparing the behaviour of partially closed and open cross-section. Four columns were tested within the project, two of them with centric axial load and two with eccentricities. Numerical analysis was performed using ABAQUS for establishing the influence of the cover plate on the critical load and the resistance. A good agreement between non-linear FEM and experiments were found. After this verification of the FE model a parametric study was carried out. Results of experiments and numerical analysis were compared with the predicted resistance by Eurocode 3, Part 1-3, and the Direct Strength Method. Both design methods give good predictions of the resistance. Udgivelsesdato: July

During the incremental launching of steel and composite bridges high support reactions have to be introduced into the slender steel webs of the bridge girder. In the past, the specific characteristics of bridge launching such as long loading lengths and longitudinal stiffeners were not covered appropriately by existing design formulae for patch loading. In the frame of the research project “Competitive Steel and Composite Bridges by Improved Steel Plated Structures (COMBRI)” a clear improvement of the patch loading resistances for I-girders and box sections could be derived leading to more economic solutions for this type of loading. The paper introduces the basic concepts of the developed models for both unstiffened girders and girders with open-section and closed-section longitudinal stiffeners as well as a software tool for the advanced determination of elastic critical buckling loads and modes. A comparison of the main area of application and the resulting economic advantages concludes the survey.

The bridge assessment in many aspects is very similar to the bridge design. The same basic principles lie at the heart of the process. Nevertheless, an important difference lies in the fact that when a bridge is being designed, an element of conservatism is generally a good thing that can be achieved with very little additional costs. When a bridge is being assessed, it is important to avoid unnecessarily conservative measures because of the financial implications that may follow the decision of ratingthe bridge as deficient. Therefore, the design codes (e.g. EC codes) may not always be appropriate for assessment of existing bridges and some additional recommendations or guidelines are required that will lead to less conservative assessment of theirs load carrying capacity. Such guidelines have been already proposed for assessment of highway bridges in Europe. However, there is a lack of this type of documents that can be applied for the assessment of railway bridges.

The present "Guideline for Load and Resistance Assessment of Existing European Railway Bridges - advices on the use of advanced methods" is providing 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 systematized 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).

Basis for the "Guideline for Load and Resistance Assessment of Existing EuropeanRailway Bridges - advices on the use of advanced methods" is the research work carried out in the work package WP4 of the Sustainable Bridges project combined with the best practical experience and know-how of all the partners involved.

The research activities within the work package WP4 have been carried out in the following five groups:

• − Loads and dynamic effects, with focus on train loads and dynamics (Deliverables D4.3, also referred as SB 4.3 Dynamic (2007), or just SB4.3 (2007));
• − Safety and probabilistic modelling (Deliverables D4.4, also referred as SB4.4Safety (2007), or just SB4.4 (2007));
• − Concrete bridges, with focus on non-linear analysis (Deliverables D4.5, also referred as SB4.5 Concrete (2007), or just SB4.5 (2007));
• − Metal bridges, with focus on riveted bridges (Deliverables D4.6, also referredas SB4.6 Metal (2007), or just SB4.6 (2007));
• − Masonry arch bridges including soil/structure interaction (Deliverables D4.7,also referred as SB4.7 Masonry (2007), or just SB4.7 (2007)).

The results of these activities are reported in corresponding Background Documents (Deliverables) listed above within parenthesis.

The main results from the research activities performed and the know-how of all the partners in the specific areas of bridge assessment are tried to be presented in this Sustainable Bridges SB-LRA 2007-11-30 6 (428) Guideline in such a way that the target reader of the Guideline, a structural engineer experienced in assessment of railway bridges, is able to apply them in the everyday practice, without necessity of searching for several specific scientific publications. Nevertheless, in some cases it has been necessary to refer to public available literature and Background Documents prepared in the Sustainable Bridges project.

The present Guideline has been prepared aiming to follow somehow the structure of the EC codes and it is divided into 10 chapters and 12 Annexes concerning:

• − Assessment procedure (Chapter 2);
• − Requirements, safety formats and limit states (Chapter 3, Annexes 3.1-3.7);
• − Basic information for bridge assessment (Chapter 4);
• − Load and dynamic effects (Chapter 5, Annex 5.1);
• − Concrete bridges (Chapter 6);
• − Metal bridges (Chapter 7, Annex 7.1);
• − Masonry arch bridges (Chapter 8, Annexes 8.1 and 8.2);
• − Foundations and transition zones (Chapter 9);
• − Improvement of assessment using information from testing and monitoring (Chapter 10, Annex 10.1).

In most of the topics related to railway bridges assessment the Guideline uses the current state-of-the-art knowledge and the presently best practice. Nevertheless, in many subjects it propose the use of original methods and models that have been developed, obtained or systematized due to research performed within one of the five groups of work package WP4.

The present section of Deliverable D.4.3 is dedicated to the static and fatigue assess-ment of old metal bridges. It forms the basis of the Chapter 7 guideline developed in work package 4 (WP4) “Guideline for Load and Resistance Assessment of Existing European Railway Bridges”. This section is divided into four parts related to the four research activities of the WP4 metal subgroup:

– Analysis of material properties of existing metal railway bridges, – Fatigue of riveted structure,

– Updated assessment methods for riveted structures,

– Enhanced non destructive techniques for inspecting riveted structures.

Integral abutment bridges are bridges without any expansion joints, and their largest benefits are the lower construction- and maintenance costs. In order to build longer integral bridges it might be necessary to allow plastic hinges to be developed in the piles. Lateral thermal movements are the major reason to plastic deformations, and since temperature variations are cyclic it has to be proved that low-cycle fatigue will not occur. A simulation of the pile strain spectra should be able to take into account the strains caused by temperature variations and traffic loads. Such a model has been created from real temperature data and traffic loads measured by Bridge-Weigh-In-Motion technology. Monte Carlo simulations have been performed in order to simulate daily and annual temperature changes as well as the varying traffic loads. Piles strains have been calculated, and their fatigue effect has been evaluated.