To calibrate methods for condition assessment of prestressed concrete (PC) bridges, tests areplanned for a 50 year old five-span bridge with a length of 121 m in Kiruna in northern Sweden.Both non-destructive and destructive full-scale tests will be performed. This paper summarisesthe test programme, which comprises evaluation of the structural behaviour of the bridge, theresidual forces in the prestressed steel, methods for strengthening using carbon fibre reinforcedpolymers (CFRP) and the shear resistance of the bridge slab.

Tests have been carried out at service- and ultimate load levels of a 55 year-old prestressed concrete girder bridge. The bridge, located in Kiruna, Sweden, was continuous in five spans with a total length of 121.5 m. The overall aim of the study was to determinate the accuracy of assessment methods for existing structures and to provide procedures for optimized assessment. Before the tests a 2D finite element (FE) analysis was performed to predict the behavior and load-carrying capacity of the bridge. In order to more accurately assess the bridge response a 3D FE model has now been developed. The actual loading history and material properties has been considered in the model. A Life Cycle Cost Assessment of the bridge has also been performed

Three Swedish concrete bridges have been tested to failure and the results have been compared to assessment using standard code models and advanced numerical methods.

The three tested and assessed bridges were:

1. (1)

   Lautajokk, a 29 year old one span (7 m) concrete trough bridge tested in fatigue to check the concrete shear capacity.

    
2. (2)

   Ӧrnskldsvik, a 50 year old two span trough bridge (12 + 12 m) strengthened to avoid a bending failure.

    
3. (3)

   Kiruna Mine Bridge, a 55 year old five span prestressed concrete road bridge (18 + 21 + 23 + 24 + 20 m) tested in shear and bending of the beams and punching of the slab.

    

The main results in the paper are the experiences of the real failure types, the robustness/weakness of the bridges, and the accuracy of different codes and models. In all three cases the bridges had a considerable hidden capacity.

To calibrate methods for condition assessment of prestressed concrete (PC) bridges, tests were carried out on a 55 year old five-span bridge with a length of 121 m in Kiruna in northern Sweden. Both non-destructive and destructive full-scale tests were performed. This paper presents results regarding methods for assessment of the structural capacity of concrete bridges.

To calibrate methods for condition assessment of prestressed concrete (PC) bridges, tests were carried out on a 55 year old five-span bridge with a length of 121 m in Kiruna in northern Sweden. Both non-destructive and destructive full-scale tests were performed. This paper presents results regarding the residual forces in the prestressed reinforcement.

Twenty years ago, in 2003, a European project was started to increase the sustainability of existing railway bridges. This paper summarises what was achieved and looks ahead. Nine Working Packages were organized: (1) Background material; (2) Guidance by stakeholders; (3) Condition Assessment and Inspection Guidelines; (4) Loads, Capacity and Resistance Guidelines; (5) Monitoring Guidelines; (6) Repair and Strengthening Guidelines; (7) Demonstration with Field testing of Bridges; (8) Demonstration on Monitoring on Bridges; and (9) Training and Dissemination.

Some of the main results (from 4 Guidelines and 47 Background documents) are highlighted and some experiences, conclusions and thoughts about the future are given. Hidden strengths and weaknesses are discussed, analyses and codes for assessment can be improved, new monitoring and strengthening methods are available and life length can be prolonged. 

This study describes a series of experiments examining the behavior of seven beams prestressed with unbonded external carbon fiber-reinforced polymer (CFRP) tendons anchored using a newly developed anchorage and post-tensioning system. The effects of varying the initial tendon depth, prestressing force, and the presence of a deviator were investigated. The results were compared to those observed with analogous beams prestressed with steel tendons, common beam theory, and predictions made using an analytical model adapted from the literature. It was found that steel and CFRP tendons had very similar effects on the structural behavior of the strengthened beams; the minor differences that were observed are attributed to the difference between the modulus of elasticity of the CFRP and the steel used in the tests. The models predicted the beams’ load-bearing behavior accurately but were less effective at predicting the stress experienced by the tendons.

In the process of developing a new wedge anchorage to anchor prestressed CFRP rods, five different anchorage designs were manufactured. These designs have led to a constantly increased ultimate failure load of the prestressing system and an eventual load level above 95% of the ultimate failure load of the rod was achieved. If 100% efficiency is achieved the anchorage does not reduce the capacity of the system, but failure is then governed by the capacity of the rod itself, which is considered favourable and required by several guidelines. In the process seven different failure modes were identified: soft slip, power slip, cutting of fibres, crushing of rod, bending of fibres, frontal overload and intermediate rupture. In this paper the failure modes are discussed further. The failures are documented with explanatory figures and their backgrounds are found in the theory. Suggestions are given on how these failures can be avoided in theory and practice. From the experiences gained in the project, it is concluded that it is a challenging task to create a fully mechanical anchorage for CFRP tendons and that the failure margins are small between a successful and an unsuccesful anchorage system.

Föreliggande rapport är resultatet av laboratorieförsök vilka utförts på avdelningen för byggkonstruktion vid Luleå tekniska universitet. Försöken har genomförts under slutet av 2007 och är en direkt fortsättning av tidigare försök från 2004 och 2005. De tidigare rapporterna pekade på ett behov av fortsatt provning. Föreliggande rapport är således en fortsättning av tidigare arbete, dock med vidareutveckling av möjliga bulltyper för Vasaskeppet. De testade bulltyperna har konstruerats och tillverkats i Statens Maritima Museer regi av Anders Ahlgren. Försöken har genomförts vid Luleå tekniska universitet och Complab, av Civ. Ing. Georg Danielsson samt forskarstuderande Anders Bennitz.

This paper presents an upgrading and monitoring of a Swedish concrete railway bridge. The methods used for the upgrading as well as for the monitoring are innovative and new. Carbon fibre tubes are inserted in holes in the bridge deck, drilled in the transverse direction of the slab at a location ca. 40 mm from the top. Carbon fibre NSMR bars are bonded in transverse grooves in the soffit of the slab. Both methods are intended to increase the transverse bending moment capacity of the troughs' bottom slab in the ultimate limit state. Monitoring is performed to verify the effectiveness of the strengthening and to understand the behaviour of the bridge. However, for obvious reasons, monitoring is only carried out in the SLS (service limit state). Even though only marginal effects of strengthening could be recorded in the SLS, both the strengthening and monitoring were considered successful at a cost of approximately 8% of the total cost of a new bridge replacement.

Strengthening of structures with CFRP is considered today as an accepted method in the upgrading of concrete structures. This paper presents the use of two different CFRP strengthening systems combined to extend the service life of a Swedish double-trough-doubletrack railway bridge, constructed in concrete with a 10 meter span. One system is the reliable NSMR (Near Surface Mounted Reinforcement) while the other is new. They were used with the intention to strengthen the interior of a concrete structure using integrated CFRP tubes. Both systems were used to increase the tensile flexural strength of the slab transverse to the tracks. NSMR bars were positioned in the bottom concrete cover of the trough's bottom-slabs, while the new system was inserted in holes drilled through the bridge in the cross direction and located in the upper part of the slab. In connection with the strengthening monitoring was conducted in order to obtain an understanding of the bridge behaviour before and after strengthening, and to demonstrate any effects of the extra CFRP reinforcement. Results from these measurements are presented together with how the strengthening work was carried out. Sensors on bars and tubes show evidence of utilization of the CFRP while displacement sensors and strain gauges on the steel reinforcement show minor effect due to the small loads in the service limit state.

Kompletterande mätning på bron över Järpströmmen genomfördes då lasten vid föregående mätning ansågs för liten. Vid aktuell mätning bestod lasten av ett transportekipage med en totalvikt på cirka 400 ton fördelat på 20 hjulaxlar och en bit över 100 däck. Mycket låg påkänning i kolfibermaterial och stålarmering, i storleksordningen omkring 5 m/m. Den låga påkänningen härleds inte till en för låg last, då ekipagets tyngd är stor. Däremot kan mätresultaten förklaras i att tvärkraftsarmeringen och förstärkningen inte tar last förrän uppsprickning av brobetongen inträffar. Betongbrons spricklast förutsätts inte vara uppnådd vid aktuell lastnivå, vilket förklarar de små töjningarna på armering och kolfiber. Detta resonemang baseras på genomförda försök (Carolin, 2003). Erfarenhetsmässigt är tvärkraftsförstärkning med kolfiberlaminat en fungerande och effektiv metod för att uppgradera en konstruktion. Kolfiberförstärkningen har konsekvent en töjning omkring 5 με vid överfart, vilket visar att förstärkningen tar last och därmed fungerar. Ingen tendens av vidhäftningsproblem finns vid aktuell lastnivå, vilket stöds av att armeringen och kolfibermaterialet töjs lika mycket. Detta betyder att förstärkningen fortsätter ta mer last vid ökad belastning. Förstärkningen kan därför förutsättas bidra till en ökad kapacitet i brottgränstillstånd, då uppsprickning av betong inträffar, trots att effekterna är svåra att bestyrka i bruksgränstillstånd och utförd mätning.

Much effort has been put on investigating degradation of concrete structures, repair and upgrading separately, as can be read in numerous publications, i.e., Green et. al. (2003), Morgan (1995) and Täljsten (2004). However, an overall view has not been taken where the whole life cycle of a concrete structure is considered. In particular, no laboratory tests have been presented in the literature to the author's knowledge. A structure passes several stages during its life. Normally two major stages are discerned, the service limit state (SLS) and the ultimate limit state (ULS). Concrete structures are designed for both these stages. In the SLS normally the deformation and crack widths are controlled. Deformation due to comfort demands and crack widths due to durability demands. In the ULS the structure is designed for its ultimate capacity - which for civil and building structures almost never is reached. From a safety aspect the ULS is most important; however, for the client the SLS with regard to maintenance, repair and upgrading are most costly. If the SLS was better understood, in particular from a rehabilitation point of view, more robust and cost effective repair and upgrading system could be developed. (Figure Presented). This paper is also a part of "Sustainable bridges". "Sustainable bridges" is a European project which focus is to preserve bridges throughout Europe and create unanimous codes for all participating countries. The project presented in this paper, Degradation of Structural Performance (DOSP), will investigate the behaviour of concrete beams which will endure a simulated life cycle procedure. The test program will direct the beams from full strength of the intact beam through degradation, repair and upgrading with FRP plate bonding to its original strength again or near. The cross-sectional strain distribution will be monitored during the test using Fibre Bragg Grating (FBG) Strain Sensors as well as traditional strain gauges. This gives the possibility of comparing results in between the two monitoring techniques over proportionately long time span. An accelerated corrosion procedure is used to corrode the flexural tensile reinforcement. The cycle may be divided into seven stages, a to g, presented shortly in Figure 1, Horrigmoe (1998) and Sand 2001. This life cycle is possible in the real case scenario for bridges or other concrete structures which are subjected to chlorides, i.e. de-icing salt or sea water

Att utnyttja moderna metoder och material för att återställa befintliga och åldrande betongkonstruktioner till ett funktionellt skick är viktigt. Studier kring möjligheter att öka såväl den ekonomiska som fysiska livslängden är ett omfattande forskningsområde. Även de praktiska tillämpningarna ökar i antal. Trots att erfarenheten och kunskapen att bygga långsiktigt hållbara betongkonstruktioner hela tiden ökar finns det relativt nya konstruktioner som inte uppfyller ställda krav på säkerhet och funktion. Det finns dessutom otaliga betongkonstruktioner som har brukats under flera årtionden som börjar visa tecken på omfattande brister.

Much effort has been invested separately on degradation, repair and upgrading of concrete structures. However, few holistic studies including laboratory testing have been performed on the entire cycle during a structures life. Reinforced concrete is the most widely used building material in the world. Normally the life of concrete structures is very long. However, concrete structures possess one drawback; at least in severe environments, the steel reinforcement may corrode. The effects can clearly be seen when the steel reinforcement is attacked by chlorides. The reduced steel cross-section area and loss of bond strength between steel and concrete will lead to increased deformations, cracking and premature ultimate load, thus affecting both the serviceability limit state (SLS) and the ultimate limit state (ULS). Procedures to repair and upgrade the damaged structure are used to increase the structural performance. They follow the structural member of time, a SHM (Structural Health Monitoring) approach is adapted to this project. By applying SHM to a degrading structure it assures that it will keep up to current standards by continuous monitoring, analysing, evaluation and eventually also retrofitting.

The results obtained when performing a load test to failure of an existing structure are valuable when assessing calculation models, updating finite element models, and investigating the true structural behavior. In this paper a destructive testing and monitoring of a railway bridge in Örnsköldsvik, Sweden is presented. In this particular test the shear capacity of the concrete girders was of primary interest. However, for any reasonable placement of the load (a line load placed transverse to the track direction) a bending failure would occur. This problem was solved by strengthening for flexure using carbon fiber reinforced polymer (CFRP) rectangular rods epoxy bonded in sawed up slots, e.g., near surface mounted reinforcement. The strengthening was very successful and resulted in a desired shear failure when the bridge was loaded to failure. The load-carrying capacity in bending for the unstrengthened and strengthened bridge as well as the shear capacity was predicted with Monte Carlo simulations. The particular calculation presented showed that there was a 25% probability of a bending failure instead of a shear failure. Monitoring showed that the strengthening reduced the strain in the tensile steel reinforcement by approximately 10%, and increased the height of the compressed zone by 100 mm. When the shear failure occurred, the utilization of the compression concrete and CFRP rods were 100 and 87.5%, respectively. This indicates that a bending failure indeed was about to occur, even though the final failure was in shear.

Strengthening of concrete structures with epoxy bonded carbon fiber reinforced polymers (CFRP) has been proved to be a good strengthening technique. However, this strengthening technique with epoxy adhesives do contain some disadvantages such as diffusion closeness, thermal incompatibility to the base concrete, working environment and minimum application temperature. Some of these drawbacks can be overcome by substituting the epoxy to a polymer reinforced mortar as the bonding agent. This work presents a pilot study with CFRP strengthened concrete beams. In this case the epoxy bonded CFRP has been replaced with a mineral based composite (MBC). The results from the pilot study indicates that the MBC strengthening system do achieve very good composite action and strengthening effects. These results warrant for further research and improvement of the MBC strengthening system

The steel truss railway bridge at Åby River was built in 1957 with a span of 32 m (105 feet). In 2012 it was replaced by a new steel beam bridge and the old bridge was placed beside the river. It was tested to failure to study its remaining load-carrying capacity in September 2013. The test was carried out by Luleå University of Technology by commission from Trafikverket as a part of the European Research Project MAINLINE (www.mainline-project.eu). In this paper some preliminary results are given. Two hydraulic jacks, anchored by cables to the bedrock, pulled the bridge downwards. The bridge remained elastic up to about three times the original design load and the load could then be almost doubled with substantial yielding deformations before a buckling failure appeared in the top girders for a load of ca. 11 MN (1000 short tons) for a midpoint deflection of ca. 0, 2 m (8 inches). No brittle or fatigue failure in any of the joints appeared and the bridge proved to behave in a ductile way with a substantial hidden capacity.

During the last two decades, strengthening concrete structures with epoxy bonded carbon fiber reinforced polymers (CFRP) has shown excellent results in increasing bearing capacity. However, there are some limitations with epoxy coated concrete surfaces, e.g.; low permeability which may provoke freeze/thaw problems, poor thermal compatibility to the concrete substrate which makes epoxy coating more sensitive to the surrounding temperature and regulations when it comes to the security and health (allergic reactions) of applicators and third party users. In this respect, using mineral based composites (MBC) may overcome some of these challenges associated with epoxy bonded strengthening systems. MBC, in this context, refers to high strength fibers bonded to the surface using a mineral based bonding agent. This study examines the cracking behavior and strain development of shear MBC strengthened RC beams. The results show that using MBC as shear strengthening postpones the formation of macro-cracks and that a considerable strengthening effect is achieved by using MBC.

During the last two decades, strengthening concrete structures with epoxy bonded carbon fiber reinforced polymers (CFRP) has shown excellent results in increasing bearing capacity. However, there are some limitations with epoxy coated concrete surfaces, e.g., low permeability which may provoke freeze/thaw problems, poor thermal compatibility to the concrete substrate which makes epoxy coating more sensitive to the surrounding temperature and regulations when it comes to the security and health (allergic reactions) of applicators and third party users. In this respect, using mineral based composites (MBC) may overcome some of these challenges associated with epoxy bonded strengthening systems. MBC, in this context, refers to high strength fibers bonded to the surface using a mineral based bonding agent. This study examines the cracking behavior and strain development of shear MBC strengthened RC beams. The results show that using MBC as shear strengthening postpones the formation of macro-cracks and that a considerable strengthening effect is achieved by using MBC

Rehabilitation and strengthening of concrete structures have become more common during the last 10-15 years, partly due to a large stock of old structures and partly due to concrete deterioration. Also factors such as lack of understanding and the consequences of chloride attack affect the need for rehabilitation. In addition, more traffic and heavier loads lead to the need for upgrading. Existing externally bonded strengthening systems using fiber-reinforced polymers (FRP) and epoxy as bonding agents have been proven to be a good approach to repair and strengthen concrete structures. However, the use of epoxy bonding agents has some disadvantages in the form of incompatibilities with the base concrete. It is, therefore, of interest to substitute epoxy with systems that have better compatibility properties with the base concrete, for example, cementitious bonding agents. This paper presents a study on reinforced concrete beams strengthened in shear with the use of cementitious bonding agents and carbon fiber grids, denoted as mineral-based composites (MBC). In this study it is shown that the MBC system has a strengthening effect corresponding to that of strengthening systems using epoxy bonding agents and carbon fiber sheets. Different designs and material properties of the MBC system have been tested. An extensive monitoring setup has been carried out using traditional strain gauges and photometric strain measurements to obtain strains in steel reinforcement, in FRP, and strain fields on the strengthened surface. It has been shown that the use of MBC reduces strains in the steel stirrups and surface cracks even for low load steps as compared to a nonstrengthened concrete beam.

During the last two decades, strengthening concrete structures with epoxy bonded carbon fibre reinforced polymers (CFRP) have shown excellent results in increasing bearing capacity. However, there are some limitations with epoxy coated concrete surfaces, e.g.; low permeability which may provoke freeze/thaw problems, poor thermal compatibility to the concrete substrate which makes epoxy coating more sensitive to the surrounding temperature and regulations when it comes to the safety and health (allergic reactions) of applicators and third party users. In this respect, using mineral based composites (MBC) may overcome some of these challenges associated with epoxy bonded strengthening systems. MBC, in this context, refers to high strength fibres bonded to the surface using a mineral based bonding agent. This study is examining the cracking behaviour and strain development of shear MBC strengthened RC beams. The results show that using MBC as shear strengthening postpones the formation of macro-cracks and that a considerable strengthening effect is achieved by using MBC.

Innovative Intelligent Railways, In2Rail, is a European Horizon 2020 Project with the objective to enhance capacity, increase reliability and reduce Life Cycle Costs of European Railways. Bridges and Tunnels is the main focus in Work Package 4. The aim is to study, benchmark and further develop new Inspection Technologies in order to create more proactive maintenance procedures. In this paper some preliminary results are presented.

The size of loads wearing on the railroad and highway systems have increased in recent years. For concrete structures with a very long life and also under difficult conditions, it is not uncommon that measures must be taken to improve the structure's durability or its load bearing capacity. Recently, the use of advanced composites in external bonding of extra reinforcement has become an accepted method. However, there are some drawbacks to this method, including that the pretreatment of the concrete surface is highly work intensive and time consuming, as well as quality concerns. With the improved plate bonding presented in this paper, the aforementioned problems are less troublesome. The technique has also been tested with a cementitious bonding agent.

The need for structural rehabilitation of concrete structures all over the world is well known, and a great amount of research is going on in this field. The use of carbon fiber-reinforced polymer (CFRP) plate bonding has been shown to be a competitive method with regard to both structural performance and economic factors. This method consists of bonding a thin carbon-fiber laminate or sheet to the surface of the structure to act as an outer reinforcement layer. However, most research in this area has been undertaken to study flexural behavior. This paper deals with shear strengthening of reinforced concrete members by use of CFRP. Tests on rectangular beams 3.5 to 4.5 m long have been undertaken to study different parameters, such as fatigue, anchorage, and others. The strain field in shear spans of beams simultaneously subjected to shear and bending is also studied. The tests presented also contribute to the existing literature on tests of concrete members strengthened for increased shear capacity.

For a long period of time CFRP plate bonding has been shown to be a competitive method for shear strengthening, both in regards to structural performance and economical aspects. A handful of models for design that include different strengthening aspects exist. Most proposals are derived from assumptions made for the design of new structures and are also based on a deterministic approach where in the best cases a safety factor is added. The use of probabilistic methods is extending and reliability of a designed structure is sometimes calculated. This paper presents how the reliability should be used in the design for strengthening an existing structure, which issues should be considered and also what safety one can expect from a structure strengthened in shear. Partial coefficients on material properties and loads are used to give a uniform treatment of the risk of failure. When partial coefficients are chosen, the reason for strengthening and the strengthening method may be considered to achieve an optimal strengthening with respect to structural safety and economy. The results from the analysis indicate design models for shear strengthening should be analytically determined with a transparent strategy for the uniform treatment of reliability aspects.

In recent years, the use of carbon fiber reinforced polymer (CFRP) has been shown to be a competitive method for strengthening both the structural and economic performance of concrete. The method has been used for almost a decade, yet – most research undertaken has studied the flexural behavior of strengthened structures, while research on shear strengthening has been limited. The work presented in this paper focuses on CFRP shear strengthening of concrete beams. The theory presented addresses the limitations of the widely used truss model, and a refinement is suggested. A reduction factor to consider the nonuniform strain distribution over the cross section is proposed and strain limitations are prescribed for the principal strain in the concrete instead of the fiber strain, as in previous studies. The derived analytical model is compared to experimental data from tests. Fairly good agreement is found between results from tests and calculated values from theory with regard to both shear-bearing capacity and average fiber utilization.

Vasaskeppet bärgades 1961 och är unik i storlek och skick. Av flera anledningar önskas befintliga stålbultar, vilka utgör en del av befintligt förband i skeppet, ersättas. En möjlighet är att ersätta befintliga bultar med bultar av kolfiberkomposit. I denna rapport redovisas resultat från försök där möjligheten till att använda kolfiberbultar för Vasas sammanfogning studerats. Två olika bultsystem har undersökts utifrån lämplighet med avseende på bärförmåga, handhavande samt flexibilitet. Försöksuppställning har utformats utifrån tänkt verkningssätt i skeppet. Ett av bultsystemet har bedömts lämpligare varför utökad provning genomförts på detta system. Laboratorieförsöken visar på att det är fullt möjligt att ersätta stålbultarna i Vasaskeppet med bultar av kolfiberkomposit.

The need for structural rehabilitation of concrete structures all over the world is well known. Extensive amounts of research have been carried out and are ongoing in this field. Most of the laboratory research has been undertaken on structural elements without live load during the strengthening process. Normally owners of structures want to continue their activity or service during strengthening. Full-scale applications have shown that this is possible, but there is a lack of understanding as to how cyclic loads are distributed during strengthening; for example, traffic loads affect the final strengthening result. This paper presents laboratory tests on concrete beams strengthened with carbon fiber-reinforced polymer laminates and near-surface mounted reinforcement. The beams were subjected to a cyclic load during setting of the adhesive, and after additional hardening were then loaded by deformation control up to failure.

I rapporten visas på möjligheterna med att använda tillförlitlighetsanalys på byggnadskonstruktioner som förstärks. I det stora fokuseras på betongkonstruktioner och särskilt diskuteras förstärkning av betongkonstruktioner med hjälp av utanpåliggande kolfiberkompositmaterial. Förstudien visar att tillförlitlighetsanalys i generella termer kan vara mycket användbart när det gäller att studera bärförmågan samt vilken konsekvens detta har för den befintliga konstruktionen, speciellt tydligt blir detta när det kopplas till verkliga objekt. Utöver detta visar studien på möjligheter att på ett mer nyanserat sätt förstärka konstruktioner där tillförlitlighetsanalys är ett viktigt verktyg. Studien visar också på behov av fortsatt forskning, speciellt tydligt är detta när det gäller vilka värden samt vilka partialkoefficienter man ska välja för de nya materialen som börjar användas, dvs. för kompositmaterial. I tillägg till detta behöver en nyanserad studie göras gällande de beräkningsmodeller som används i samband med förstärkning och även avseende på de brottmoder som kan uppstå.

Under 2002 och 2003 genomfördes vid Luleå tekniska universitet, Avdelningen för Konstruktionsteknik en studie av stålrör uppstyvade med kol-, aramid- respektive glasfiberkomposit för att på så sätt öka knäcklasten. De metoder som användes var handuppläggning samt montage av förtillverkade skal tillverkade genom vakuuminjicering. Totalt provades nio stålrör vardera med längden 3.800 mm och diameter 88,9 mm. Ett rör lämnades oförstärkt och användes som referens. Resultatet från provningen visade att det var möjligt att öka knäcklasten genom att använda metoden med utanpåliggande fiberkomposit. I samband med undersökningen har även en analytisk och numerisk modellering av försöken gjorts. Denna stämmer bra överens med försöken. Förutom försök i laboratorium och teoretiska analyser utfördes en praktisk studie om gällande möjligheten att förstärka stålrör i fält. Denna undersökning gjordes hos Spännarmering AB i Upplands Väsby. Det visade sig att metoden med förtillverkade rör var att föredra framför handuppläggning. Dock bör speciella verktyg tas fram för att applicera lim på en mast i fält.

The Iron Ore Railway Line was built around 1900 and has more than 100 bridges. It has a length of ca 500 km and runs from Kiruna and Malmberget in northern Sweden to the ice-free harbour in Narvik in Norway on the Atlantic and to Luleå in Sweden on the Baltic. The original axle load was 14 ton. The axle load has gradually been increased to 25 ton in 1955, to 30 ton in 1998 and to 32,5 ton in 2017.

The increases in axle loads have been preceded by monitoring and assessment studies of the bridges. The capacity and need for strengthening or replacement of the bridges have been evaluated. Many of the bridges could carry a higher load than what it was designed for. Experiences from studies before the axle load was increased in 1998 and 2017 are presented and discussed.

Load testing is a way to control the capacity and function of a bridge. Methods and recommendations for load testing are described and examples are given form tests carried out in Croatia and Sweden. In order not to damage the bridge being tested, the load must be limited, often to be within the serviceability limit state (SLS). Numerical models can be calibrated by load tests and then be used to check the carrying capacity for higher loads than what has been tested. Need for further work and recommendations are discussed. By effective planning, costs can be saved and a more sustainable use of bridges can be obtained.

En 55 år gammal spännbetongbro med fem spann med längden 121,5 m har provats till brott för att studera och kalibrera metoder för tillståndsbedömning av befintliga broar. Projektet harbidragit till att ge svar på flera av de frågor som ställs beträffande hållbart byggande och uppföljning av befintliga konstruktioner inom BBT - Branschprogram för forskning och innovation avseende byggnadsverk inom transportsektorn. Framför allt adresseras följande områden:A.2.1 Säkerhet, robusthet och sårbarhet – En betydande robusthet finns i den studerade typen av broar och säkerheten mot brott är större än den som erhålls med modellerna i de europeiska betongnormerna.A.2.4 Metodik för individuell bärighetsklassning av broar – En kombination av FE-modellering och analytiska studier baserade på verklig geometri och aktuella materialdata har goda förutsättningar att kunna ge betydligt mer kvalificerade bedömningar av kvarvarande bärförmåga än nu tillämpade metoder.A.2.5 Beständighet och livslängd hos nya byggnadsverk – Projektet ger underlag för förbättrade metoder att bestämma beständighet och livslängd hos spännbetongbroar.A.3.1 Mätmetoder – I projektet har en ny metod för fotografisk töjningsmätning provats. Resultaten har ännu inte hunnit helt utvärderas men de ser lovande ut.A.3.2 Bedömning av tillstånd och livslängd – Projektet ger underlag för förbättrade metoder för bedömning av tillstånd och livslängd.Projektet har hittills redovisats i en doktors- och en licentiatavhandling och i tio tidskrifts- och konferensartiklar.

- Apply new technologies to extend the life of elderly infrastructure - Improve degradation and structural models to develop more realistic life cycle cost and safety models - Investigate new construction methods for the replacement of obsolete infrastructure- Investigate monitoring techniques to complement or replace existing examination techniques -Develop management tools to assess whole life environmental and economic impact.

There are many traditional technologies available to extend the life of elderly rail infrastructure, some of which are being improved or developed, whilst new technologiescontinue to emerge. In this guideline some of the most promising new or updated technologies are presented forbridges, track and earthwork regarding: - Assessment methods- Repair and Strengthening methodsIn an Appendix strengthening methods are presented in more detail with examples of designcalculations and work carried out.The guideline is based on work presented in earlier reports in MAINLINE: ML-D1.1 (2013):Benchmark of new technologies to extend the life of elderly rail infrastructure, ML-D1.2(2013): Assessment methods for elderly rail infrastructure and ML-D1.3 (2014): Newtechnologies to extend the life of elderly infrastructure; In these reports, backgroundinformation and more references can also be found.

Monitoring of several railway bridges has been carried out in northern Sweden in order to increase the allowable axle load. The work is part of a European Integrated Project "Sustainable Bridges - Assessment for Future Traffic Demands and Longer Lives". The paper describes the project and gives some examples of applications.

Ett EU-projekt med avsikt att förlänga livlängden för befinmtliga järnvägsbroar

In co-operation with a Finnish Group of researchers a pre-feasibility study was undertaken regarding potential development of the Infrastructure in NW Russia. Special emphasis was given: Winter Transportation and Reinforcement of Load Bearing Ice Covers; Concrete Construction and Strengthening of Concrete Structures; Timber Construction and Mechanical Wood Industry Development; and Energy Conservation and Industrial Energy Development.

Based on the study three Russian-Swedish co-operation projects have started:

- Load Bearing Ice Covers (Literature Survey)

- Forces caused by Ice Crushing against Off-Shore Structures (EC funded Research Project)

- Strengthening of a Bridge. Co-operation Stabilator/Skanska - Arkhangelsk Road