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STRENGTHENING CONCRETE BEAMS FOR SHEAR WITH CFRP SHEETS

The method of strengthening concrete structures with FRP composites has existed for over a decade; the most common way to strengthen structures is in bending, but also wrapping of columns is quite ...

Concrete Structures Strengthened with Near Surface Mounted Reinforcement of CFRP

The need of maintenance, repair and upgrading of concrete structures has increased considerably over the last decade and will most likely continue to do so. There can be several reasons for this, but it can often be attributed to normal change of use, increased demands on the structure, errors in the design and/or construction phase or in the worst case, accidents. Different methods have been developed over the years for solving different rehabilitation problems. Recently, advanced composites used for external bonding in the form of fabrics or laminates have become an accepted method. Several thousands of objects around the world have been upgraded with advanced composites bonded to its surface. In most cases, this method is very competitive regarding both structural behaviour and economy, but there are also some drawbacks. The surface bonded composite material is relatively sensitive to fire, accidents or vandalism. In addition, the pre-treatment is relatively intensive and time consuming. However, if the composite material is placed in slots in the concrete cover some of these drawbacks can be overcome. This paper presents work carried out on near surface mounted reinforcement (NSMR) at Luleå University of Technology in Sweden.

Strengthening concrete beams for shear using CFRP-materials : evaluation of different application methods

This paper presents different methods and tests for the application of carbon fibre reinforced plastic (CFRP) fabrics and tapes to concrete beams. The purpose of the tests were twofold; first to study the shear force capacity of the beams both before and after strengthening; and second, to examine three different ways of applying the fabrics. These were: two hand lay-up systems, one vacuum injection system and one pre-preg system. The total number of beams tested was eight. The test results proved that a very good strengthening effect in shear could be achieved by bonding fabrics to the face of concrete beams. However, a lot of energy was released at failure, which led to brittle failures. The tests also showed that the techniques which used hand lay-up were preferable as compared to other systems, even though the fibre weight fraction was considerably less. However, the vacuum injection system was the most environmentally friendly method.

Advanced Composite Bridge Decking System—Project ASSET

Throughout the world, a significant percentage of reinforced concrete bridges are in a deteriorated state. The main reasons are inadequate cover, cracking of the concrete, leading to corrosion of the steel reinforcement and spalling of the surface concrete (worsened by the use of de-icing salts), inadequate initial detailing and the increase in traffic loads over time. The cost of reinstating or reconstruction of these bridge decks is economically prohibitive using conventional means, and would be equally prone to deterioration. Fibre-reinforced polymer (FRP) bridge decks provide the possibility of a more durable, lightweight and easily installed alternative. To this end, project ASSET (a four-year EC-funded research programme) was initiated to develop an optimised FRP bridge deck system for deck replacement and new-build, culminating with the replacement of the West Mill bridge in Oxfordshire, UK. The ASSET system forms a complete deck system with associated parapet and street furniture fixing concepts for all situations. The detailed analysis and optimisation of the ASSET profile together with the design and practical issues for West Mill Bridge are described.

Assessment of European railway bridges for future traffic demands and longer lives – EC project “Sustainable Bridges”

A European Integrated Research Project has recently been started within the 6th Framework Program of the European Commission. The project aims at improved methods for the upgrading of existing railway bridges within the European railway network. The main objectives of the project are to increase the transport capacity by allowing higher axle loads and by increasing the maximum speeds. Other objectives are to increase the residual lifetime of existing bridges and to enhance management, strengthening and repair systems. The overall goal is to enable the delivery of improved capacity without compromising the safety and economy of the working railway. A consortium consisting of railway bridge owners, consultants, contractors, research institutes and universities will carry out the project, having a gross budget of more than 10 million Euros. Funding from the European Commission covers a major portion of the four-year project costs.

Are Available Models Reliable for Predicting the FRP Contribution to the Shear Resistance of RC Beams

In this paper the trustworthiness of the existing theory for predicting the fiber-reinforced plastic contribution to the shear resistance of reinforced concrete beams is discussed. The most well-known shear models for external bonded reinforcement are presented, commented on, and compared with an extensive experimental database. The database contains the results from more than 200 tests performed in different research institutions across the world. The results of the comparison are not very promising and the use of the additional principle in the actual shear design equations should be questioned. The large scatter between the predicted values of different models and experimental results is of real concern bearing in mind that some of the models are used in present design codes.

Failure Load Test of a CFRP Strengthened Railway Bridge in Örnsköldsvik, Sweden

The results obtained when performing a load test to failure of an existing structure are valuable when assessing calculation models, updating finite element models, and investigating the true structural behavior. In this paper a destructive testing and monitoring of a railway bridge in Ornskoldsvik, Sweden is presented. In this particular test the shear capacity of the concrete girders was of primary interest. However, for any reasonable placement of the load (a line load placed transverse to the track direction) a bending failure would occur. This problem was solved by strengthening for flexure using carbon fiber reinforced polymer (CFRP) rectangular rods epoxy bonded in sawed up slots, e.g., near surface mounted reinforcement. The strengthening was very successful and resulted in a desired shear failure when the bridge was loaded to failure. The load-carrying capacity in bending for the unstrengthened and strengthened bridge as well as the shear capacity was predicted with Monte Carlo simulations. The particular calculation presented showed that there was a 25% probability of a bending failure instead of a shear failure. Monitoring showed that the strengthening reduced the strain in the tensile steel reinforcement by approximately 10%, and increased the height of the compressed zone by 100 mm. When the shear failure occurred, the utilization of the compression concrete and CFRP rods were 100 and 87.5%, respectively. This indicates that a bending failure indeed was about to occur, even though the final failure was in shear.

Strain Measurement Using Embedded Fiber Bragg Grating Sensors Inside an Anchored Carbon Fiber Polymer Reinforcement Prestressing Rod for Structural Monitoring

Results are reported from a study carried out using a series of Bragg grating-based optical fiber sensors written into a very short length (60 mm) optical fiber network and integrated into carbon fiber polymer reinforcement (CFPR) rod. Such rods are used as reinforcements in concrete structures and in tests were subjected to strain through a series of cycles of pulling tests, with applied forces of up to 30 kN. The results show that effective strain measurements can be obtained from the different sensors mounted along the rod. Additionally, the tests show that close agreement with the results obtained from the calibrated force applied by the pulling machine and from a conventional resistive strain gauge mounted on the rod itself is obtained. Calculations from strain to shear stress show a relatively uniform stress distribution along the bar anchor used. The results give confidence to results from various methods of in situ monitoring of strains on such CFRP rods when used in different engineering structures.

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.