Repair and Strengthening
Any To keep a structure at the same performance level it needs to be maintained at predestined time intervals. If lack of maintenance has lowered the performance level of the structure, need for repair up to the original performance level can be required, see Figure 6.2. In cases when higher performance levels are needed upgrading needs to take place. Upgrading is here defined as increased durability or load bearing capacity, aesthetics and functionality.
Need of assessment of the state of a structure in order to plan maintenance, repair and upgrading over the life cycle of the structure.
There are urgent requirements from the European societies and industries to increase the axle loads and the train speed on the existing railway lines for both economic and environmental reasons. This new situation will create problems with 1) safety 2) deformations/settlements, and 3) vibrations. These problems have to be solved without reduced track availability. Exiting methods do not fulfill this requirement. Both users of road and rail transport experience the .jump and bump. as the vehicle they are traveling in approaches or leaves a fixed structure such as a bridge. The depression in the road or railway that causes the .jump and bump. is where the transition from the rigid structure to the approach has deformed excessively. In fact such transitions exist where the road or rail foundation has a significant change in stiffness. Problems with the transition zones are causing reduced track speed to avoid derailments followed by disruption of schedules and increased maintenance. Existing construction and rehabilitation techniques for the transition zones implies too high maintenance costs, traffic limitations and interruptions as well as high life cycle cost in the transition zone for new infrastructure.
The main objectives in WP6 are to find technical, environmentally stable and for the traffic non-disturbing methods, that are financially justified, to repair and strengthen existing railway structures. Here a .toolbox. with different repair and strengthening methods will be put together which will cover specific needs for railway bridges, embankments and transition zones.
For repair and strengthening of bridges carbon fibre, reinforced polymers can be used. For the efficient application of these systems a good bond has to be guarantied between the CFRP (Carbon Fibre Reinforced Polymer) material and the bridge structure. Here both non pre-stressed and pre-stressed systems will be developed and tested, for railway bridges in concrete as well as in steel. For controlling the final result of the repair or strengthening measures a quality system, assuring excellent results will be developed, here the use of transient infrared thermography will be evaluated and implemented. Use of monitoring systems, such as fibre optic sensors, together with advanced composites may give systems that will be able to follow a repair or strengthening measure over time. In these cases, an optical fibre may be imbedded into the composite.
The project also deals with the foundation/geotechnical aspects of railways including the subsoil below railway structures (embankments) and transition zones between an embankment and a bridge (in fact between sections with a difference in stiffness). The projects comprise assessment of subsoil properties below existing embankments and the long-term properties/behaviour of soils and improved soils and related design models and also strengthening methods of the subsoil. All methods shall have no or a minimum of influence on the track availability and the environment. This will then be used to improve long-term subsoil behaviour models for deformation prediction for both natural soils and improved soils (by ground improvement methods). As a consequence cost-effective durable assessment and strengthening methods of the subsoil causing no or minimum influence on the traffic (track availability for railway lines) and with a minimized environmental impact will be developed.
Ongoing research has shown that traditional mechanical (patch) repair on bridges subjected to marine environment (ingress of chlorides) can result in accelerated degradation following the repair. The main problem is the formation of so-called macro-cell or incipient anode corrosion. As a result, other repair methods are usually recommended for marine structures. In the case of railway bridges it is reasonable to expect that corrosion induced by carbonation is often a dominating deterioration process. Hence, a detailed survey is needed for comparison to marine structures. In order to evaluate deterioration subsequent to mechanical repairs for railway bridges, field surveys will be conducted and evaluation of deterioration subsequent to repairs will be carried out. The scope is to reduce costs of cathodic protection systems for reinforced concrete structures. Such systems are, in case of extensive damages caused by chloride ingress, the only reliable alternative to prevent further deterioration. The need for the method itself is therefore obvious, but simpler and less expensive systems are required. It is essential to develop calculation models for different types of repaired or strengthened structural elements for different types of loadings. Existing models often do not take into consideration the behaviour of a structure after repair or strengthening. Furthermore, within WP6 a guideline for repair and strengthening of railway bridges, embankments and the transition zones will be produced. The all-embracing aim with WP6 is to develop repair and strengthening systems that will extend the service life and/or increase the service capacities (load capacities) of existing infrastructures. The objectives may be summarised in the following tasks:
- specification of strengthening needs
- mapping of existing repair and strengthening methods for railway bridges
- design methods and calculation models for repair and strengthening of railway bridges.
Integrated with WP4
- evaluation, testing and implementation of traditional repair and strengthening techniques
- validation and optimisation of different cathodic protection techniques, as a repair method
- modelling and testing of repair and strengthening technologies based on advanced
composites. Integrated with WP3
- assessment of subsoil properties below existing embankments and related design models and
also strengthening methods of the subsoil
- evaluation, testing and implementation of physical quality assurance methods to meet
satisfactory results from repair and strengthening measures
- evaluation, testing and implementation of monitoring systems integrated into composite repair and strengthening systems, integrated with WP5
- implementation of suitable repair and strengthening methods on existing railway bridges.
Integrated with WP7 and WP8.
Fed Inst f Materials Res. and Testing (BAM)
Rheinisch-Westfälische Tech Hochschule
BPE Systems AB
Chalmers University of Technology
Luleå University of Technology
Lund University of Technology
Royal Institute of Technology
Swedish Geotechnical Institute
The Swedish Rail Administration
Swiss Federal Institute for Materials Testing and Research (EMPA)