Skovdiget Bridge Superstructure - Denmark

Transcription

1 Skovdiget Bridge Superstructure - Denmark Project Description: The Skovdiget bridge north of Copenhagen, Denmark opened in 1965 and is part of a main route for urban traffic, which is also used for heavy loads. The bridge carries the busiest highway in Denmark with app. 6 daily passengers over the S-train line with app. 6 daily passengers. The superstructure in the western bridge is severely deteriorated in critical positions, while at the same time facing an increased traffic load. The main girders are therefore under surveillance in order to follow the effect of the replacement of the water protection and drainage, while at the same time following the corrosion rates in the critical parts of the structure. The variations of the strains are at the same time logged, in order to generate a realistic statistic of the load variations and frequencies as well as provide a control of the FEM-modelling. Skovdiget Bridge, Copenhagen, Denmark. Quick Facts: Name and Location: Skovdiget Bridge, Copenhagen, Denmark Owner: Danish Road Directorate Structure category: medium span bridge Spans: 11 spans: 9.4/17.2/2.2/2.1x6/24.3/14.5 m Structural system: Prestessed concrete bridge, with hollow core girders and cross-beams, supported on concrete columns Start of SHM: 2, updated in 23. Number of sensors installed: 63 in superstructure. Instrumentation design by: RAMBØLL, Denmark. Page 1 of 5

2 Description of Structure: The superstructure comprises of two pre-stressed concrete girders with a hollow core, with a number of closed cells. The bridge deck is in each bridge supported by two main girders and by 111 pre-stressed cross-beams. The superstructures are supported by a number of columns, placed under each of the main girders. The bridge with a total length of 22 m consists of two separate, parallel bridges, of which the eastern received a major renovation in 1975, whereas the western bridge received only minor repairs and renovation of the water protection. The western bridge has therefore been under surveillance since cross-section of the bridge Purpose of Inspection: Initial inspection has shown severe damages in parts of the structure and the ingress of chloride and variations of humidity and corrosion potentials have been followed since 2. It has been found necessary to determine the condition of the reinforcement in the most deteriorated parts of the main girder as well as to determine the corrosion rate. This leads to the conclusion that the traffic loads must be logged in order to generate an overview of the actual variations of the traffic loadings in the bridge. Sensor Details*: Type of sensors Number Location Strain-sensors (based on fibre optics) Corrosion rate sensors (CorroEye) 1 Humidity sensors (HUM) on the two main girders plus 2 on two cross-beams The cell over the railway and another, equally deteriorated cell over the parking area Corrosion risk sensors (ERS) 1 Corrosion risk sensors (CorroRisk) 12 Humidity sensors (HUM) 7 Humidity sensors (MRE) 7 The edge beams, main girders and some of the cross-beams. Temperature sensors (PT 1) 4 Chloride sensors (CHL) 5 Page 2 of 5

3 Measurement Equipment and Data Management: Type of system Data Management CMS PC- based measurement system for strains. Manual system for reading CorroEye. Datalogger(s) for additional sensors. data pre-analysis (evaluating, averaging and identification of extreme load, leading to storage of data) on site main analysis, graphical presentation and documentation in office data transfer via modem long term data base in SMART light y Data Analysis Procedures: Type of analysis Software Additional features Transformation of strains into loading, speed and position on bridge. Transformation of corrosion current into corrosion rates. SMART Light and Excel SMART Light has a number of traditional Bridge Management facilities built-in. Examples of Outcomes: The corrosion rates have been determined several times by means of NDTmethods, using the Galvapulse equipment. This verified, that the apparent corrosion rate would limit the service-life of the structure, despite the recent renovation of the water-proofing august Average corrosion rate (microa/cm2) Aug 21 Dec 21 Apr 21 Aug 21 Dec Corrosion rate Temperature (Celcius) Temperature NDT-Mapping of corrosion rates in a cell during August 27 th 23 and corresponding logging of average corrosion rates by CorroEye sensors Page 3 of 5

4 The NDT-mapping requires, however, regulation of the traffic on the electrically powered railway line and was therefore combined with installation of corrosion rate sensors, which enable monitoring of corrosion rates without traffic regulations. The inspection, the FEM-calculations and the monitored corrosion rates indicate, that the structure within 1 years will have a insufficient load-carrying capacity and will require strengthening, replacement or a more detailed assessment of the traffic loadings. The deformations has since 2 been monitored continuously with sensors based on fiber optics, which allow measurements to be carried out app. 25 times pr. second. These deformations are averaged over each hour. Passage of a heavy vehicle will be detected by the system and the variations of the strains from app. 1 s before to 1 s after the passage will be kept in the records. This allows essentially a logging of the number of heavy vehicles, their loads, position on the road and their speed. DEFROMATION (MM OVER 5 M) EASTERN GIRDER WESTERN GIRDER CROSS BEAM 2 CROSS BEAM TIME (SEC) logging of strain variations during passage of a heavy truck Benefits of Using SHM Technologies in the Project: The monitoring of deterioration parameters (chloride, humidity, temperature and corrosion potentials) as well as the visual inspection have identified the need for monitoring. The use of corrosion rate monitoring provides a record of the actual corrosion rates in the critical structural parts without traffic regulations. The combination of NDT-mapping and monitoring with sensors provides both a general mapping of large areas of the structures and a recording of the variation in time. The logging of the passages of the heavy trucks generates an improved load model, which will be useful in the next probalistic assessment of the structures safety and will add some years to the structures service life. Page 4 of 5

5 References: P. Goltermann: Managing large bridge structures in Scandinavia, SAMCO Summer School, July , Cambridge, UK. Klinghoffer, O.; Goltermann, P. and Bässler, R.: Smart Structures: Embeddable sensors for use in the integrated monitoring systems of concrete structures, Proc. IABMAS 2, July 22, Barcelona, Spain. Goltermann, P. et al: SMART STRUCTURES Integrated Monitoring Systems for Durability Assessment of Concrete Structures. Project Report, February 22, available for downloading at Elsener, B. et al: Assessment of reinforcement corrosion by means of galvanostatic pulse technique, Proc. Int. Conf. Repair of Concrete Structures, Svolvær, Norway, Frølund, T. and Klinghoffer, O.: Comparison of half-cell potentials and corrosion rate measurements A field experience with evaluation of reinforcement corrosion, Proc EUROCORR 24, Nice, France, 24. Goltermann, P. et al.: SMART STRUCTURES. Integrated Monitoring Systems for Durability Assessment of Concrete Structures, Subtask 3.2 On-site Testing of Portable Systems. Extensive Testing of Portable Systems, February 22. Luping, T. Calibration of the Electrochemical Methods for the Corrosion Rate Measurement of Steel in Concrete. NORDTEST Project No , SP REPORT 22:25. Suppliers information on the CorroEye-sensor available at Bjerrum, J.; F. Jensen, J. and Enevoldsen, I.: "The owners perspective in probability-based bridge management", Proc. IABMAS2, Barcelona, Spain, July 22. Jensen, F.; Knudsen, A. and Enevoldsen, I.: "Probalistic-based Bridge Management Implemented at Skovdiget West Bridge" in Fourth International Conference on Bridge Management, April, 2, University of Surrey, UK. Mondrup, A. J.; Frederiksen, J. O. and Christensen, H. H.: "Load Testing as an Assessment Method", IABSE symposium "Durability of Structures", Submitted by: RAMBØLL Bridge Maintenance and Material Technology Bredevej 2 D-283 Virum Denmark Phone: Fax: peg@ramboll.dk Page 5 of 5