Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives for Railway Bridges

Björn Paulsson1, Jan Olofsson2, Lennart Elfgren3, Göran Holm4 1Banverket/UIC, Borlänge/Paris, Sweden/France; 2SKANSKA, Gothenburg, Sweden;

3LTU, Luleå, Sweden; 4SGI, Linköping, Sweden In a sustainable society, the transportation work carried out by rail ought to increase and take a larger part than today of the transports. In order to enable such an increase, the capacity of existing railway bridges needs to be increased too. This is the objective of the project “Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives”. There are three specific goals: - Increase the transport capacity of existing bridges by allowing higher axle loads (up to 33 tons) for freight traffic with moderate speeds or by allowing higher speeds (up to 350 km/hour) for passenger traffic with low axle loads - Increase the residual service lives of existing bridges with up to 25 % - Enhance management, strengthening, and repair systems. A consortium consisting of 32 partners has carried out the project and the gross budget, which was more than 10 million €, has been spent. The partners have represented the whole supply chain from user to producer / designer / developer. They are drawn from bridge owners (25%), consultants (9%), contractors (9%), research institutes (19%) and universities (38%). Skanska, Sweden, has provided the overall co-ordination of the project, whilst Luleå University of Technology has undertook the scientific leadership. The consortium has brought together experience of the different types of challenges facing European railways. In central Europe, flooding from big rivers crossing a flat landscape is a major problem, whereas frost damage predominates in northern Europe. There are also different demands on railway lines; heavy iron ore traffic crossing the wilderness of northern Scandinavia and intense passenger traffic in the densely populated areas of central Europe and the UK. Some highlights of the work from the project are given in this paper. A group of railway owners mapped the existing stock of railway bridges and made an overview of relevant problems. The data from the survey covers over 220,000 bridges owned by 17 different railways and is considered to be representative of the well in excess of 300,000 railway bridges across Europe. Examples of some bridge types are given in below. The proportion of bridges is the following: - 41 % Arches of masonry, stone or concrete; - 23 % Concrete bridges; - 22 % Steel beam bridges; and - 14 % Steel/concrete composite bridges. More than 35% of the bridges are more than 100 years old, while only 11 % are less than 10 years old. Small span bridges are dominating, with 62% of the bridges spanning less than 10 m, while only 5% have spans larger than 40 m. The railway owners listed the following top ten priority research areas: - Better assessment tools - Non-disruptive maintenance methods - Verification of theoretical dynamic factors for both design and assessment - Use of new materials - System for diagnosis & maintenance needs selection - Ageing/deterioration of concrete bridges

- Indirect inspection and monitoring dynamics for evaluation/crack detection in metallic bridges

- Repair and waterproofing of concrete

- Better testing methods for existing bridges - Serviceability of arches Most of these priorities where addressed in Sustainable Bridges (SB). It became clear that a higher portion of old masonry bridges were existent than we were aware of. Consequently, the original plans were revised to reflect this. Results concerning masonry arch bridges where also exchanged with the Masonry Arch Project run by the International Union of Railways, UIC in Paris, France. The result from SB can be dealt up in deliverables and guidelines. The number of deliverables has been more than 120. Four of these have been transferred into guidelines. These four guidelines are the most important project results for the end-users. This paper will focus on these four guidelines. The four Guidelines developed within the Sustainable Bridges Project are:

- Guideline for Inspection and Condition Assessment of Existing Railway Bridges - SB-ICA (2007)

- Guideline for Load and Resistance Assessment of Existing European Railway Bridges - SB-LRA (2007)

- Monitoring Guidelines for Railway Bridges - SB-MON (2007) - Repair and Strengthening of Railway Bridges - Guideline - SB-STR

(2007) The purpose is to give bridge engineers, bridge owners and operators guidance 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. Performance assessment The performance assessment of a bridge is the heart of the "investigation and performance assessment" activity and the main focus area of the Sustainable Bridges project. Both special inspections (supported if necessary by testing) and focused monitoring are the main activities that have to provide information for the completion of a performance assessment. Due to its importance in informing decisions about any actions necessary to ensure safety and continuity of the traffic, performance assessment (safety, durability, serviceability, etc.), using the most advanced methods and tools that are presently available, is necessary. This may show that a major intervention is unnecessary. The guidance on the most appropriate procedures, methods and tools for the assessment of concrete, metal and masonry arch bridges is given in the SB-LRA (2007). This Guideline also gives advice regarding how and where to search for the data that is required to perform advanced bridge assessment and refers to SB-ICA (2007) and SB-MON (2007) when a more detailed description of the specific testing or monitoring method is necessary. Appendices attached to this Guideline contain practical applications of the procedures and methods proposed for higher-level assessment that might be unfamiliar to assessing engineers.

Figure 1: The figure shows in read the area where the four guidelines are assessing. In figure 1 the four guidelines are shown how they fit into the assessment process. The idea is that they should complement regular operation of maintenance if there are concerns regarding performance. In most cases only assessment is probably necessary. General procedure It is generally accepted that the assessment of the performance of a bridge, irrespective of whether it is a safety, serviceability or durability assessment, and whether it aims to permit increased loads, higher speeds or to extend bridge service life, should be performed in phases with increasing level of accuracy and complexity. Figure 2 shows the general procedure adopted in the Guideline SB-LRA (2007) for the reassessment of existing bridges, where the expression “Doubts” really means “Decision to assess” based on the considerations outlined above. A simple assessment using basic calculation checks based on readily accessible data (drawings, design calculations, earlier assessment calculations, inspection records, etc.) should first be used to initially assess the performance of a bridge. If this shows that the bridge is adequate, no further action is required, but if the doubts remain then an intermediate level assessment is required. In this process, more advanced analysis (e.g. elastic but giving better idealization, plastic, etc.) and data that are more accurate on the material properties, the loads, the current state and the behavior of the bridge (e.g. material properties obtained from simple measurement, loads defined by measurements, etc.) assist the evaluation of the performance of the bridge. If doubts continue after the intermediate assessment then an enhanced assessment will be necessary. Here the most advanced assessment methods (e.g. reliability-based assessment methods, etc.) and tools available (e.g. non-linear FEM analysis, testing, monitoring, etc) to evaluate the performance of the bridge.

Regular operation and maintenance

BRIDGE MANAGEMENT (Administration)

Regular inspections followed by condition

assessment (qualitative information)

Optional Structural Health

Monitoring (qualitative information)

Regular, minor maintenance

(preventive, corrective)

Bridge Management System (more/less advanced)

Political and economical requirements (higher loads and speeds, increased traffic volume,

extended service life, etc. )

Special stage

Investigation and assessment

BRIDGE ASSESSMENT (Carried out in

phases)

Special inspections supported by more/less

advanced tests (quantitative information)

Focused monitoring through limited time period

(quantitative information)

Required performance confirmed?

Decision making and action taken

Redefine use Intensify monitoring

Replacement Strengthening and/or repair

Concern regarding bridge/s performance (safety, serviceability, durability)

yes

no

Regular operation and maintenance

Special stage

No

DOUBTS

INITIAL Site visit, study of documents, simple calculation checks.

INTERMEDIATE Further inspections, detailed

calculations/analysis, material investigations.

ENHANCED Refined calculations,

laboratory examinations, statistical modelling,

reliability-based assessment, economical decision analysis,

monitoring.

Compliance with codes and

regulations?

Strengthening or repair of the bridge

Simple repair or strengthening

solve the problem?

Update maintenance

Sufficient capacity?

Redefine use of the bridge

Demolition of the bridge

Continuous monitoring

Continued use of bridge

Doubts confirmed?

Yes

Yes Yes

Yes

No No

No

No

Strengtheningof the bridge

Figure 2: Flow diagram for reassessment of existing bridges (SB-LRA, 2007) A sensitivity analysis, performed during the assessment, may help to identify where a refinement of knowledge about the bridge may be most beneficial for the particular situation. Generally, such refinements will depend on the assessment methodology (deterministic, probabilistic, etc.) and analysis method (linear, non-linear, etc.) chosen, and may include further collection of data about generalized loads (traffic load, environmental actions, etc.) and/or generalized resistance (member strength, fatigue resistance, serviceability condition, etc.). Measurement and testing methods The guideline SB-ICA Inspection and Condition Assessment presets new and enhanced tools, equipment and procedures for railway bridge inspection and condition assessment to achieve the objectives of the project. The guideline SB-ICA Inspection and Condition Assessment with three annexes summarizes and completes the technical research work described in technical deliverables, available as background documents. The guideline also refers to UIC-documents, national standards and results of research done so far in international research. The guideline is prepared to transfer the latest research results to the end-users, the Infrastructure Managers (IM). The technical deliverables, attached as background document to SB-ICA, describe the research, which focused on the following topics:

- Basic research for appropriate non-destructive testing methods to be used by the IMs in refined inspection and condition assessment of

reinforced concrete, steel and masonry arch bridges as well as for the investigation of foundations and subsoil,

- Development of procedures for effective condition assessment and

defect appraisal,

- Enhancing the applicability of non-destructive inspection tools to railway bridges with focus on the compatibility with the railway infrastructure,

- The application for railways bridges includes both, the reviews of

techniques and methods (state of the art) and the latest research, e.g. automation of acoustic imaging techniques, advanced image data processing for result obtained from different non-destructive testing (NDT) measurement.

- Development of automated equipment for faster operating onsite

measurements with high geometrical accuracy, which is a precondition for super positioning of data obtained from different methods and different measurements,

- A proposal for classification of defects, description of deterioration, defect

location,

- Finite element modeling of reinforced concrete deterioration processes and degradation by corrosion.

Based on refined information from inspections about the current condition of the bridge elements, an entire bridge and the capability of the bridge stock along a railway line has to be assessed in a fast and unique way, e.g. in order to allow new train types, increase of train frequency, transfer of higher loads or higher speed. The guideline on inspection and condition assessment presents tools to update bridge documentation, which is some times insufficient, inaccurate or incomplete. Systematic application of repeatable procedures are presented, which are using new tools with high degree of geometrical accuracy. Advanced technologies also help to follow time dependant processes and to alleviate the effects of the loss of operational experience of retiring workers. Research for better inspection and condition assessment tools for the IMs, e.g. using NDT methods was concentrated on gaps, identified in the first face of the project. The analysis of the bridge stock by the partner railways in SB revealed that masonry arch bridges need to be more focused on in SB. Following this advice the guideline now covers inspection of reinforced concrete, steel and masonry arch bridges as well as testing of subsoil and foundation. The guideline proposes inspection and condition assessment tools to get comparable description of the railway infrastructure condition in different countries of the European Community. The work also revealed the need of common terminology, a database for defects and a database with applicable NDT methods in single page information. The guidelines present the result of the work in a three level structure.

Figure 3: Structure of the guideline on Inspection and Condition Assessment In Annex 1, terminology and definitions focus on NDT, inspection and condition assessment. The defect catalogue with typical defects for all types of bridge defects in Annex 2. The NDT-toolbox provides information about NDT procedures to railway bridge inspectors in a consistent and comprehensive one-page information in Annex 3. Many bridge defects are incapable of full visual evaluation. If a visual inspection suggests the existence of a hidden defect, advanced testing to check real performance and, if necessary, determine the extent, severity and significance of the defect becomes necessary. Testing can determine actual material properties for inclusion in performance assessment calculations where the available data is of poor quality.

Figure 4 shows an example from the SB-ICA (2007) and the "NDT toolbox". As NDT-methods have their specific capabilities and limitation in use, knowledge of the physics (described in the toolbox) behind the various methods assists the understanding of their applicability and helps the establishment of realistic limitations

Guideline for Inspection and

Condition Assessment

Annex 1: Terminology and Definitions

Annex 3: NDT Toolbox

Annex 2: Defect Catalogues

Background Documents

Technical

Deliverables

on the application of the methods to different materials. As mentioned above an electronic version of the toolbox is available for use on site to assist decision-making. Monitoring techniques The guideline concerning Monitoring techniques (sensors, data communication and data processing) provides recommendations how to specify, design, implement and operate systems in a systematic and coherent way. It defines the actors and their roles within the monitoring activity. The guideline introduces the concept of model monitoring systems 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 different actors and to clearly define the interface between structural engineer (the bridge expert) and monitoring experts. The guideline requires that the design of the model monitoring system have to be based on a bridge model. This approach automatically provides an interpretation scheme for the data generated by the physical monitoring system without it this data is meaningless. 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. Since monitoring technology evolves rapidly, this guideline does not address in detail the technological oriented components of the monitoring process. Nevertheless, a monitoring toolbox is included, which provides briefly the most relevant information of different methods, algorithms and sensors being used in monitoring. The goal of the toolbox is to provide condensed technological background information for the structural engineer. This information allows him to influence the design of the physical monitoring system. In appendices there are guidelines for novel monitoring techniques developed in SB. The scoop of these guidelines is to promote the use of these novel techniques in practical monitoring activities. A guide for assessment of loads, capacity and resistance 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 rating the bridge as deficient. Therefore, the design codes (e.g. EC codes) are not 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. 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 European Railway Bridges - advices on the use of advanced methods" is the research work carried out in this work package of the SB project combined with the best practical experience and know-how of all the partners involved. The research activities have been carried out in the following five subgroups:

− Loads and dynamic effects, with focus on train loads and dynamics

− Safety and probabilistic modeling

− Concrete bridges, with focus on non-linear analysis

− Metal bridges, with focus on riveted bridges

− Masonry arch bridges including soil/structure interaction.

The results of these activities are reported in corresponding Background Documents (the 120 deliverables) The main results from the research activities performed and the most relevant know-how of all the partners in the specific areas of bridge assessment are presented in this 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 SB 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. 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 subgroups of this work package. Regarding the loads and dynamic aspects, the innovative elements suggested in the Guideline are:

− Train load models for assessment of railway bridges based on the UIC 71 load model and calibrated α-values;

− Original methods for quantifying dynamic effects that may lead to reduced dynamic amplification factors.

Regarding the requirements, safety formats and limit states, the main innovative elements implemented in this Guideline are:

− Overview of target reliability indices recommended for bridges and structures, which makes a bridge owner able to specify a required safety level for a bridge in cause;

− Systematized methodology of applying several safety formats and reliability methods (characterized by different degree of accuracy and complexity) in the assessment process;

− Methodology for considering the durability and fatigue aspects in the assessment of existing bridges including requirements regarding the remaining service life.

Regarding the concrete bridges, the main innovative elements in the Guideline are: − Recommendations for performing non-linear finite element analysis of railway

bridges (deterministic and probabilistic); − Comprehensive models (i.e. fully probabilistic) of material properties of

concretes and reinforcing and prestressing steels used in the construction of existing bridges;

− Models for bonding of the reinforcement affected by corrosion; − Methodology for assessing concrete bridge elements subjected to

combination of shear and torsion.

Regarding the metal bridges, the original elements implemented in the Guideline are: − Comprehensive database for material properties of old metal bridges; − Assessment tools for riveted steel bridges (also considering fatigue

problems). Regarding the masonry arch bridges the innovative elements applied in the Guideline are:

− Recommendations for using several fundamental methods of assessment, specific for arch bridges, with which assessing engineer are usually not familiar;

− Concepts for taking into account the effect of cyclic loading and determining the influence of abutment fixity on masonry arch behaviour;

− Recommendations regarding consideration of the effect of train traffic on the load distribution and deflections in the bridge transition zone;

− Recommendations regarding modelling damages in arch bridges and the selection of the most suitable analytical method for the assessment of masonry arch bridges with damages.

Geotechnical issues in SB Geotechnical issues in SB has focused on the transition zone between the bridge and the approach embankment and specifically on the subsoil conditions/properties and behaviour including long-term behaviour and also appropriate strengthening methods for the subsoil with minimum influence on the terrain traffic. The cross hole tomography method to determine the properties of the subsoil below existing railway embankments has been developed and tested at two sites. The method implies no influence on the train traffic. The other advantage of the cross hole tomography method is that the properties of the soil is obtained in the whole cross section and not point-wise as with traditional methods. An example of results is shown in the Figure 5.

Figure 5 shows cross hole tomography method in Norrköping, Sweden. An inventory of possible strengthening methods for the subsoil have been performed presenting

• Strengthening effect possible to achieve • Influence on existing railway and train traffic • Applicability for different European railway and soil conditions • Availability in Europe

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Dep

th (m

)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36Distance (m)

EMBANKMENT

2030405060708090100110120130140150160170180190200

Vs (m/s)

In SB-SRT (2007) page 54 you can see a table of this. One method, anchored sheet pile walls, has been tested at a railway line in Sweden with good results. Numerical analyses of load distribution and deformations in transition zones due to passing trains have been performed for a typical concrete bridge and for a typical masonry arch bridge. The results are important input when assessing bridges. A simplified prediction method of settlements with a probabilistic approach regarding the long-term behaviour of subsoil below railway embankments in the transition zones has been developed. The method is applicable to soft subsoil conditions. The method is to be used as a first step in the assessment to calculate the magnitude of the future settlements to get a basis for evaluating if the future settlements are acceptable or not. If the predicted settlements are acceptable, monitoring of the settlements is recommended and a comparison shall be made with the calculated settlements. If the measured settlements follow the predicted settlements no strengthening measures are needed. If the calculated settlements are too large to be acceptable or the monitoring shows large settlements then strengthening measures shall be performed. When using the presented method it is important to have high quality data on the subsoil properties representative for the actual conditions in the transition zones. Possible records of maintenance, including settlements and related additional fill material is of great value at the assessment and the evaluation of the long-term behavior. Many innovative elements presented in the guideline together with the state-of-the-art information regarding methods, models and tool for bridge assessment should be very helpful for bridge engineers evaluating load carrying capacity of existing railway bridges. Strengthening methods Not all bridges need to be strengthened. More refined calculation models or following up through monitoring may show that strengthening is obsolete. Nevertheless, if it is found that strengthening is necessary then it would be advantageous if the owner, designer and contractor are given guidance. The guideline presents a structured way to address strengthening needs and suitable strengthening systems connected to that need. The purpose with the guideline is to give the railway owners (and also the designer and contractors) guidance for repair and strengthening of railway bridges. The proposed method of working with the guideline is new and innovative, taking the standpoint in the bridge component that needs to be strengthened, i.e. flexure, shear etc. and from that level suggesting a strengthening method. The method itself is connected to what here has been denoted a graphical index. For each bridge type and/or structural element a sketch is presented and locations for different common strengthening problems are highlighted. To the problem, a method description and a case study are then connected which clearly explain how the strengthening problem can be solved. In the guideline focus has foremost been placed on new repair and strengthening methods that have been investigated in the work within the SB project. However, an extended summary of commonly used strengthening methods for concrete, metallic and masonry arch bridges is also presented – but not to the same extend as for fibre-reinforced polymer (FRP) bonding and external prestressing. It is suggested that the report is used as a living document and has also been written as such. That means that it should be easy and possible to upgrade the method of working with new strengthening methods and systems, it should also be possible to

add for example design suggestions and more detailed work descriptions if needed. The method of working is very suitable to incorporate in a database which then easily could be upgraded over time. However, this has not been possible to accomplish within the current project. The guideline contains a main report showing the structure to follow. In the appendices are the method descriptions and cases studies appended. The studies concerning repair and strengthening methods have among other things resulted in a guideline using carbon fibre reinforced polymers (CFRP) and methods for strengthening of subsoil in transition zones without interrupting the traffic. Demonstration and field testing Demonstration and field testing of existing bridges have also been carried out. An old riveted steel bridge in France, a reinforced concrete bridge in Sweden and a masonry arch bridge in Poland have been tested and evaluated. Behind these results there are approximately 120 scientific reports. All these reports have been successively reviewed by the bridge owners partly to give railway input but also to avoid duplication of work. Special efforts have been allocated to give the four guidelines a layout that makes them easier to implement for the end-users.

Figure 6 shows the test bridge in Örnsköldsvik, Sweden What’s new? Historically very little research has been carried out concerning existing structures and especially on railway structures. Therefore this work is especially important considering that the railway bridge stock often is old.

Today we often treat the existing bridges in the same way as newly built bridges. This means that many bridges are replaced unnecessarily. This is often the case when new demands like heavier axle loads and higher train speeds are being introduced. With the tools and methods presented in SB many bridges will be proven possible to keep in service instead of being replaced. However, sometimes it may require some strengthening of identified weaker parts of the bridge, which is also treated in the project. Author’s Biography Björn Paulsson today works for UIC in Paris leading an EU-project called INNOTRACK. He has a MSc in Civil Engineering from University of Lund 1974. He worked for Skanska, Sweden for 17 years very much focusing on civil engineering structured. In 1991 he joined Banverket, Sweden and has been head of Track and Civil Engineering Department until 2007. In this position he has been responsible for R&D in the area of Track and Civil Engineering in Sweden. Jan Olofsson, Department Manager – Bridge and Civil Engineering, Skanska Sweden, is also coordinating this EC project “Sustainable Bridges”. He got his MSc in civil engineering at the Chalmers University of Technology in Göteborg in 1984 and have since then been working with different bridge and civil engineering projects at Skanska. During 1997 to 2001 he was a task leader in the Brite/EuRam project IPACS (Improved Production of Advanced Concrete Structures). Lennart Elfgren is a professor of Structural Engineering at Luleå University of Technology in Sweden. He is currently Scientific Leader of the EC integrated project “Sustainable Bridges”. He got his PhD from Chalmers University of Technology in Göteborg in 1971. He has earlier also worked at the University of California in Berkeley, at SP – the Swedish Research Institute in Borås, and with the consultant firm J&W (now WSP) in Göteborg. He is the author of more than 100 scientific papers mostly dealing with the load-bearing capacity of concrete structures. Göran Holm is Director of Research and Development at Swedish Geotechnical Institute (SGI). He got his MSc in civil engineering at the Royal Institute of Technology in Stockholm in 1970. He has been chairman of the Swedish Commission on Pile Research, project manager for the Swedish Deep Stabilization Centre. He has been heavily involved in the EC-funded research projects “EuroSoilStab” (scientific co-ordinator), “RuFUS” (WP-leader and co-author of handbook) and the integrated project “Sustainable Bridges” (taking care of the geotechnical issues). He is the author of more than 70 papers/ publications. ----------------------------------------------------------------------------------------------------------------- * Agreement In submitting an abstract, you certify that the paper is an original contribution that has not been presented or published elsewhere and give permission for the Conference organizers to publish it, if accepted, in the Book of Abstracts. You further agree that if your abstract is accepted, you promise to appear and present your paper or arrange for its poster presentation.