Jonny Nilimaa

Reinforced Concrete T-Beams Externally Prestressed with Unbonded Carbon Fiber-Reinforced Polymer Tendons

Unbonded carbon fiber-reinforced polymer (CFRP) offers promise for use in prestressing applications due to its minimal creep and relaxation, low weight and high resistance to degradation. This study highlights the potential of CFRP rods in external and unbonded prestressing applications. A series of experiments were conducted on seven beams prestressed with unbonded external CFRP tendons anchored using a newly developed anchorage and post-tensioning system. The experiments investigated the effects of varying the initial tendon depth, prestressing force, and the presence of a deviator. The experimental results were compared to those observed with analogous beams prestressed with steel tendons, predictions made using an analytical model adapted from the literature and common beam theory. Results showed that steel and CFRP tendons had very similar effects on the structural behavior of the strengthened beams. Minor differences were observed that could be attributed to the difference between the modulus of elasticity of the CFRP and the steel used in the tests. Reinforced concrete beams prestressed with external bonded CFRP tendons exhibited the expected increase in strength, stiffness, and failure load, as well as decreased ductility, relative to unstrengthened beams. Under the loads examined in this study, the bending of CFRP tendons due to beam deflection did not significantly affect the tendon’s performance. Although the models predicted the beams’ load-bearing behavior accurately, they were less effective at predicting the stress experienced by the tendons. The findings from this study contribute to a better understanding of structural behavior of reinforced concrete beams post tensioned with external unbonded CFRP tendons throughout the load scheme.

Loading to failure of a 55 year old prestressed concrete bridge

In order to provide relevant data for calibration and development of methods for assessment ofexisting bridges, a 55 year old posttensioned concrete bridge has been subjected to non-destructiveand ...

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.

Tested versus code capacity of existing bridges : Three examples

This paper presents the results from three tests to failure of different types of bridges: a two span reinforced concrete railway trough bridge; a five-span prestessed concrete beam bridge; and a o ...

Unbonded Transverse Posttensioning of a Railway Bridge in Haparanda, Sweden

The majority of railway lines in Sweden are designed to support axle loads of up to 250 kN. Because of increased transport needs on some lines, an axle load limit of at least 300 kN would be beneficial. To upgrade the Haparanda line in northern Sweden to 300 kN, the slabs in existing concrete trough bridges require a higher transverse shear resistance. Methods for in situ strengthening of bridge slabs in this way have not been fully developed, and this paper discusses the possibility of increasing the load capacity by horizontal prestressing. Internal, unbonded posttensioning was performed on one bridge on the Haparanda line, and the strengthening effects were investigated. The strengthening was designed according to the European Eurocode design regulations, and testing was conducted before and after the implementation. Strains in the main transverse reinforcement, caused by a train with an axle load of 215 kN, were completely counteracted by eight prestressing bars, stressed with 430 kN/bar. The results indicate that the actual strengthening effect is larger than what is predicted by the design equations. The Haparanda project showed that unbonded posttensioning can be implemented relatively fast and does not obstruct the ongoing railway traffic during installation.

Full-Scale Tests to Failure Compared to Assessments – Three Concrete Bridges

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.

Assessment and failure test of a prestressed concrete bridge

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 tota ...

Extend the life of existing railway bridges – Results from EU FP7 project MAINLINE

There is a need to extend the life and capacity of many existing bridges. One of the objects of the EU FP7 Project MAINLINE, 2011-2014, was to facilitate this. Guidelines for assessment and strengt ...

Extended Life of Railway Bridges. Results from EC-FP7-project MAINLINE

There is a need to extend the life of many existing railway bridges. To facilitate this is one of the objects of the EC-FP7-Project MAINLINE, covering a period from 2011 to 2014. Three case studies ...