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

A deformation criterion is proposed for the fatigue failure of concrete in tension. According to the criterion, a fatigue failure is imminent when the total deformation approaches the deformation at maximum stress in a corresponding static test. This criterion was originally proposed for bond slip by Balázs in 1991. It is tested on two series of new and old concrete cylinders loaded in cyclic tension. How the criterion may be used to predict the number of load cycles to failure for existing structures under cyclic tensile loading is also shown

A pullout test using post-installed inserts has been examined as an alternative to drilled cores to determine the in-place concrete compressive strength. Tests have been carried out on eight railway bridges from 1965 to 1980 and on a one year old concrete slab. An empirical strength relationship is proposed between the compressive strength of a drilled core with the diameter and height of 100 mm and the pullout force from the pullout test. It is a power function and the relationship is valid for concrete compressive strengths up to 105 MPa; it gives higher concrete strengths than earlier proposed functions.

Background - In the project Sustainable Bridges (www.sustainblebridges.net) important objectives are to increase the transport capacity and service life of existing bridges. In order to demonstrate new and refined methods developed in the program, field tests of existing bridges were carried out in Work Package 7. One of the bridges which have been tested is a 50 year old two-span concrete bridge located in Örnsköldsvik in northern Sweden.Due to time, legal and cost restraints, concrete bridges are seldom tested to failure. It was therefore deemed vital to carry out such a test here, as it is the only way to check if applied analytical and numerical models do catch the essential behaviour at failure of a structure.Objective - The Örnsköldsvik reinforced concrete bridge was loaded to failure to test new and refined methods developed in the project regarding procedures for inspection and condition assessment (WP 3), load carrying capacity in combined shear, torsion and bending (WP 4), monitoring (WP5), and strengthening (WP 6).To achieve a shear failure and to avoid an uninteresting bending failure, the bottom slab was strengthened before the final test. Near Surface Mounted Reinforcement (NSMR) was used consisting of Carbon Fibre Reinforced Polymers (CFRP).Results – The Bridge has two spans of 12 m. A loading beam made of steel was placed in the centre of one of the spans. The loading beam was then pulled down with cables injected to the bedrock beneath the bridge.The methods developed in the Sustainable Bridges program showed to be reliable. The inspection and condition assessment indicated that bridge was in good condition with almost no reinforcement corrosion. This was shown to be true. Material tests gave important contributions to steel and concrete properties. The load carrying capacity was underestimated with Swedish and European Codes, BBK04 and EN1992-2. combined with linear elastic finite element calculations. Better results were obtained with non-linear methods as the Modified Compression Field Theory (MCFT) and the non-linear finite element program Atena, recommended by the Guideline SB-LRA (2007) produced in the project. The monitoring methods used for concrete and steel strains, crack initiation, deflections and damage detection worked well. The strengthening method also worked very well. The bridge could carry a load of 11,7MN which was 20 to 50 % more than predictions based on BBK04 and EN 1992-2.The failure test showed that the bridge without strengthening managed to carry not only one train, as it was designed to do, but eight trains on top of each other with an axle load of 250 kN. With strengthening it could carry 11 trains. This shows that concrete railway bridges might have a considerable reserve of extra load-bearing capacity.

A reinforced concrete railway trough bridge has been strengthened and loaded to failure. The aim was to test and calibrate methods developed in the European Research Project "Sustainable Bridges" regarding: (a) condition appraisal and inspection, (b) load carrying capacity analysis, (c) monitoring and (d) strengthening of existing bridges. The tested methods proved to be useful and to give accurate predictions. A failure in combined shear, bending and torsion was reached for an applied mid span load of 11,7 MN. This was well predicted by enhanced methods but 20 to 50 % higher than ultimate load evaluated according to predictions based on common codes and models.

The load carrying capacity of damaged prestressed concrete railway sleepers has been investigated in order get information about how the cracking influences the remaining load carrying capacity compared to an un-cracked sleeper. The following tests have been performed: bending capacity of the midsection, the rail section, horizontal load capacity of the fastener, control of the concrete properties and fatigue capacity in bending of the rail section. A visual inspection and classification of the damages are also presented. The test results have been compared with calculations according to the Swedish railway code for sleepers and show that railway sleepers are quite robust. Small cracks do not seem to influence the load carrying capacity and it is first when the cracking is very severe that the load carrying capacity is reduced significantly.

The load carrying capacity of damaged prestressed concrete railway sleepers has been investigated in order to obtain information about how the cracking influences the remaining load carrying capacity compared with an uncracked sleeper. The following tests have been performed: bending capacity of the midsection, the rail section, horizontal load capacity of the fastener, control of the concrete properties and fatigue capacity in bending of the rail section. A visual inspection and classfication of the damages are also presented. The test results have been compared with calculations according to the Swedish railway code for sleepers and show that railway sleepers are quite robust. Small cracks do not seem to influence the load carrying capacity and it is first when the cracking is very severe that the load carrying capacity is reduced significantly. Udgivelsesdato: september

Results and analyses are presented from cyclic uniaxial tensile tests on plain cylindrical concrete cores. The influence of the load amplitude and the mean load level were studied with so called factorial design. It was found that both factors were important but that neither of them could be established to be more important than the other. Further, the deformation rate was studied. It appears that a certain fatigue limit exists below which a clearly greater number of load cycles is required for failure. From this research the exact limit cannot be predicted, but for tests with a mean load level of 40% of fpeak and an amplitude of 40% of fpeak, a very low deformation rate has been obtained. Finally, the test results have been compared with other Wöhler curves proposed for cyclic load in tension.