Ola Enochsson

Assessment of the Strengthening of an RC Railway Bridge with CFRP Utilizing a Full-Scale Failure Test and Finite-Element Analysis

A finite element (FE) model was calibrated using the data obtained from a full-scale test to failure of a 50 year old reinforced concrete (RC) railway bridge. The model was then used to assess the ...

Photographic strain monitoring during full-scale failure testing of Örnsköldsvik bridge

Full-scale failure tests are rarely performed on structures, primarily due to their high costs and the lack of suitable test objects. This article reports the results of a ‘test-to-failure’ performed using a real bridge. The results obtained in such tests are valuable for assessing analytical models, updating finite element models and investigating the real behaviour of structures. The specific intention in these experiments was to study the shear failure of the bridge, which is a less well-understood mode of failure than is bending. To this end, it was necessary to strengthen the bridge using near-surface-mounted reinforcements made of carbon fibre–reinforced polymer bars in order to prevent bending failure. The bridge was heavily monitored during the test, using both traditional sensors such as electrical strain gauges and linear variable differential transducers alongside new monitoring systems such as fibre-optic sensors, strain rosette linear variable differential transducers and a novel photographic monitoring system. This article presents the photographic strain measurements and describes the use of the photographic tools in monitoring and characterizing the behaviour of the failure zone during the full-scale test. The strains measured using the photographic method were found to agree well with those measured using classical strain gauges. In addition, the strain contour plots generated using the photographic method provided crucial insights into the strains within the bridge’s failure zone. This study was conducted under the remit of the EU ‘Sustainable Bridges’ Project.

Loading to failure and 3D nonlinear FE modelling of a strengthened RC bridge

A reinforced concrete railway trough bridge in Örnsköldsvik, Sweden, was strengthened in bending with rods of carbon-fibre-reinforced polymer and loaded to failure. The aim was to test and calibrate methods developed in the European Research Project ‘Sustainable Bridges’ regarding assessment and strengthening of existing bridges. A steel beam was placed in the middle of one of the two spans and was pulled downwards. Failure was reached at an applied load of 11.7 MN. It was initiated by a bond failure caused by a combined action of shear, torsion as well as bending after yielding in the longitudinal steel reinforcement and the stirrups. The bond failure led to a redistribution of the internal forces from the tensile reinforcement to the stirrups, causing the final failure. The computer models developed to simulate the loading process were improved step by step from linear shell models to more detailed models. The most developed model, a three-dimensional nonlinear finite element model with discrete reinforcement, gave accurate accounts of the response of the bridge.

Protecting a five span prestressed bridge against ground deformations

A 50 year-old, 121.5 m long, five span prestressed bridge was situated in the deformation zone close to a mine in Kiruna in northern Sweden. There was a risk for uneven ground deformations so the bridge was analyzed and monitored. Results and measures taken to ascertain the robustness of the bridge are presented. The analysis resulted in an estimate that the bridge could sustain 24 mm in uneven horizontal and 83 mm in uneven vertical displacement of the two supports of a span. To be able to sustain larger deformations, the columns of the bridge were provided with joints, where shims could be inserted to counteract the settlements. To accomplish this, each one of the 18 columns of the bridge was unloaded by help of provisional steel supports. The column was then cut and a new foot was mounted to it. This made it possible to lift each individual column with two jacks, when needed, and to adjust its height by inserting or taking away shim plates. The deformations of the bridge and the surrounding ground were monitored. The eigenmodes of the bridge were studied with accelerometers and by analysis with finite elements (FE) models. Comparison indicated good agreement between the model and the actual bridge, with calculated eigenfrequencies of 2.17, 4.15 and 4.67 Hz, for the first transversal, vertical and torsional modes, respectively. Measurements during winter resulted in higher values due to increased stiffness caused by frozen materials.

Finite Element Analysis of Small Span Reinforced Concrete Trough Railway Bridge

The static behavior of a reinforced concrete trough railway bridge is analyzed by finite element method. The influences of load distribution fashion, supporting width of the bearings and the additional support beneath the girder are investigated; and the spatial effect of the stress distribution is studied as well. To confirm the analysis accuracy, the results are calibrated with the field load test results. It is found that the influence of load distribution fashion is minor and negligible, while those of supporting width and additional support are not negligible; and the spatial effect is significant.

Assessment and condition monitoring of a concrete railway bridge in Kiruna,Sweden

A two-span railway concrete trough bridge over Luossajokk in Kiruna in northern Sweden has been studied. The owner wanted to increase the axle loads from 250 to 300 kN in order to reduce freight co ...