METHOD FOR PRE-STRESSING A STEEL STRUCTURE, AND STEEL STRUCTURE PRE-STRESSED USING SAID METHOD
According to the method, at least one carbon fibre-reinforced polymer band is joined to the steel structure at the end regions thereof, capable of transferring tensile forces. Subsequently, at least one lifting element (7) disposed between the carbon fibre-reinforced polymer band (4) and the steel girder (3) to be reinforced in a region between these end anchorages (5), is extended substantially perpendicular to the carbon fibre-reinforced polymer band (4). So, a tensile force stress is generated between the end regions of the carbon fibre-reinforced polymer band (4). Then, a steel girder treated in such a manner includes at least one carbon fibre-reinforced polymer band, which is each joined to the steel structure (1) at the end regions thereof, capable of transferring tensile forces. In the region between these end regions, a lifting element (7) is disposed between the carbon fibre-reinforced polymer band (4) and the steel girder (3) to be reinforced, by means of which the carbon fibre-reinforced polymer band (4) is subjected to tensile stress by lifting away from the steel girder (3). The tensile force is transferred to the steel girder (3) via the anchoring elements (5).
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- METHOD FOR PRE-STRESSING A STEEL STRUCTURE, AND STEEL STRUCTURE PRE-STRESSED USING SAID METHOD
This invention relates to a method for pre-stressing a steel structure, and the steel structure existing both on a new construction and preferably on an existing one, especially on bridge constructions. According to a study by Bien J. Elfgren L. and Olofsson J. entitled Sustainable Bridges, Assessment for Future Traffic Demands and Longer Lives, Wroclaw, Dolnoslaskie Wydawnictwo Edukacyjne, 2007, the European Railway Authorities confirm that there are about 220,000 railway bridges in Europe alone, and these are located in different climatic regions. Approximately 22% of which are metal or steel constructions, which are also often referred to as steel bridges. 3% are cast iron bridges, 25% are welded steel constructions, and 53% are made of steel, and about 20% are made of a material, not clearly identified. 28% of these metal constructions are more than 100 years old and almost 70% of the bridges are more than 50 years old. Since today trains are becoming longer, heavier and faster, the loading of these bridges is increasing very much. Each axle load generates vibrations, and thus, small cracks and gaps develop with time in the structures, and the fatigue of the carrier is progressing ever more quickly.
Tests at EMPA in CH-Dübendorf demonstrated that the steel girders can be strengthened in principle by the application of carbon fibre-reinforced polymers (CFRP=Carbon Fiber Reinforced Polymers). These CFRP are attached to the steel girders by means of adhesives and are capable to absorb a tensile stress, which slows down or even stops the crack formation. Nevertheless, adhesives are only partially suitable in many places, because steel is heated to high temperatures by the sunlight and this can bring the adhesive to the glass transformation limit thereof. The publications Engineering Structures 45 (2012) 270-283 and the international Journal of Fatigue 44 (2012) 303-315 in Elsevier Journal (www.elsevier.com) should be followed in this respect.
Another issue is the galvanic corrosion. Although, CFRP are not corrosive, they form galvanic cells in combination with steel. Then, there are many riveted steel bridges. In these, the problem is how best to attach the flat CFRP bands to the steel girders. And finally, the protection of monuments should often be taken into account, in which for instance it is required that historically important structures must again be restored into their original state where appropriate, which could hardly be achieved with glued on CFRP bands. And finally, it would be desirable, not only to strengthen the structures, but also to pre-stress, thus in order to completely close the already existing cracks and gaps and to continuously prevent further growth of these cracks and gaps. Therefore, one of the most important objects of a reinforcement system is the appropriate selection of the mechanical anchoring system, so that this develops sufficient clamping force, is subjected to minimal corrosion, if possible, requires no direct contact of the CFRP bands with the steel, and the stress-initiation in the anchoring system takes place gradually.
It is the object of the present invention to specify a method for pre-stressing a steel structure, and also a steel structure prestressed thereby. Therefore, the crack formation on a new or existing steel structure should be prevented by means of this pre-stressing, or already existing cracks should be closed or their further growth should be stopped or at least slowed down.
The object is accomplished by a method for pre-stressing a steel structure, in which at least one carbon fibre-reinforced polymer band each is joined to a steel girder to be reinforced at the end regions thereof, capable of transferring tensile forces, and subsequently at least one lifting element disposed between the respective carbon fibre-reinforced polymer band and the steel girder to be reinforced, is extended in a region between these end anchorages, substantially perpendicular to the carbon fibre-reinforced polymer band, for causing a tensile stress between the end regions of the respective carbon fibre-reinforced polymer band.
The object is further accomplished by a steel structure, which is characterized by that at least one carbon fibre-reinforced polymer band each is joined to a steel girder of the steel structure to be reinforced at end regions thereof, capable of transferring tensile forces, wherein at least one lifting element disposed between the respective carbon fibre-reinforced polymer band and the steel girder to be reinforced, is disposed in the region between these end regions, by means of which, the respective carbon fibre-reinforced polymer band is subjected to tensile stress from the steel girder by substantially perpendicular lifting of the carbon fibre-reinforced polymer band.
The invention is schematically represented in the figures and described in the following with the help of these exemplary figures and the function of the method as well as the steel structure reinforced thereby is described.
It shows:
In
The bridge according to
In
By means of such reinforcements, cracks or gaps in steel structures, i.e. in the elements which are tensioned, are closed in some cases. In other cases, a further growth of these cracks and gaps can be prevented, or at least the weakening process can be substantially slowed down, and overall the structures can be definitely reinforced and stabilized, so that the service life thereof is extended, or optionally, the load bearing capacity is enhanced.
Claims
1. Method for pre-stressing a steel structure, in which at least one carbon fiber-reinforced polymer band (4) each is loosely joined to a steel girder of the steel structure (1) to be reinforced at the end regions thereof with end anchorages (5) in the form of clamping shoes purely based on friction forces and without gluing, capable of transferring tensile forces, and subsequently, in a region between these end anchorages (5), at least one hydraulically, pneumatically, electrically or mechanically operated lifting element (7) disposed between the respectively carbon fibre-reinforced polymer band (4) and the steel girder to be reinforced (3,8), is extended substantially perpendicular to the carbon fibre-reinforced polymer band (4) above the tensile stress to be finally achieved for generating several 10 kN lifting force and the lifting of the polymer band (4) by means of a mechanical latch is secured, then supports are placed between the polymer band (4) and the steel structure and subsequently the lifting element (7) is relieved again, so that the target stress is achieved and the supporting force is absorbed by the supports for providing a permanent tensile force stress between the end regions of the respective carbon fibre-reinforced polymer band (4).
2. Method for pre-stressing a steel structure according to claim 1, characterized in that several carbon fibre-reinforced polymer bands (4) are laid on the same over the length of the steel girders (3,8) to be reinforced.
3. Method for pre-stressing a steel structure according to claim 1, characterized in that several carbon fibre-reinforced polymer bands (4) are aligned parallel to each other over the length of the steel girder (3,8) to be reinforced and each is laid on the same over the entire length of the steel beam (3,8).
4. Method for pre-stressing a steel structure according to claim 1, characterized in that several carbon fibre-reinforced polymer bands (4) are laid over partial sections of the lengths of the steel girders (3,8) aligned parallel to each other, over the length of the steel girders (3,8) to be reinforced.
5. Method for pre-stressing a steel structure according to claim 1, characterized in that several carbon fibre-reinforced polymer bands (4) are laid over partial sections of the lengths of the steel girder (3,8) aligned parallel to each other, over the length of the steel girder (3,8) to be reinforced, so that these are adjacent to each other and overlap in partial sections with reference to the lengths thereof.
6. Method for pre-stressing a steel structure according to claim 1, characterized in that several carbon fibre-reinforced polymer bands (4) are mislaid over the lengths of the steel beam (3,8) to be reinforced, which are disposed extending in a direction deviating from the longitudinal direction of the steel girder (3,8) and are intersected.
7. Steel structure, characterized in that at least one carbon fibre-reinforced polymer strip (4) each is joined to a steel girder of the steel structure (1) to be reinforced at the end regions thereof, capable of transferring tensile forces, wherein at least one lifting element (7) disposed between the respective carbon fibre-reinforced polymer band (4) and the steel girder (3,8) to be reinforced in the region between these end regions, by means of which the respective carbon fibre-reinforced polymer band (4) is subjected to tensile stress from the steel girder (3,8) by substantially perpendicular lifting of the carbon fibre-reinforced polymer band (4) and supports are inserted between the polymer band (4) and the steel structure on both the sides of the lifting element (7).
8. Steel structure according to claim 7, characterized in that the lifting elements (7) are the hydraulically, pneumatically, electrically or mechanically operated lifting elements (7) with such a translation that only fractions thereof are generated by their paths as the reaction paths of the lifting element.
9. Steel structure according to claim 7, characterized in that in addition to the lifting elements (7), mechanical supports are installed between the band (4) and the steel girder (3,8) to be reinforced, for relieving the lifting elements (7) after completion of the working stroke of the same.
10. Steel structure according to claim 8, characterized in that in addition to the lifting elements (7), mechanical supports are installed between the band (4) and the steel girder (3,8) to be reinforced, for relieving the lifting elements (7) after completion of the working stroke of the same.
Type: Application
Filed: Apr 16, 2014
Publication Date: May 26, 2016
Applicant: S&P CLEVER REINFORCEMENT COMPANY AG (Seewen)
Inventors: Masoud Motavalli (Forch), Elyas Ghafoori (Dübendorf)
Application Number: 14/898,452