PSI - Issue 64

Giovanni Pietro Terrasi et al. / Procedia Structural Integrity 64 (2024) 1347–1359 Giovanni Pietro Terrasi et al/ Structural Integrity Procedia 00 (2019) 000 – 000

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The draw-in displacements of the passive anchor's LTM during prestressing to 1 MN were 11.2 mm on average for cable north and 10.4 mm for cable south. These draw-ins increased by 0.7 mm for cable north and by 0.4 mm in the case of cable south during the first 7.5 monitoring months indicating thus a negligible setting (creep) of the polymeric LTM in the CFRP sleeves. The longitudinal and transverse strains on the CFRP sleeves showed nearly constant values over 7.5 months and were at -0.21% (cable north) and -0.27% (cable south) and 0.13% (cable north) and 0.21% (cable south) respectively. The long-term measurements of strains on the CFRP sleeves and the LTM draw-in will be particularly important in order to obtain information about whether an anchorage component tends to creep (viscoplastic, time-dependent deformation under permanent load). The strains and LTM shifts should eventually reach a constant value. The decrease in wire elongation shown in Figure 11 is explained by the time dependent creep and draw-in of the LTM in the sleeve of the cables, which results from the respective average slippage of the LTM and by the bridge compression due to a decrease in temperature from summer to autumn and to winter (since the old concrete hardly creeps). E.g. with a 25° temperature reduction between the strengthening day August 23 rd and end of January this results in approx. 250 µm/m due to thermal concrete contraction. After 7.5 months of monitoring, a total decrease of approximately 85 µm/m was measured (corresponding to the -1% in Figure 11). (Assumptions CTE = approx. 10 x 10 -6 for concrete, CTE // of CFRP wire in the longitudinal direction = approx. 0). 5. Discussion and Conclusions This papers describes the successful re-use of 25 years old and serviced pultruded CFRP wires to assemble two post-tensioning cables used to reinforce a 1988 built prestressed concrete bridge (Ilfis Bridge) in the central Swiss Alps. A novel resin-cast CFRP anchorage system was developed successfully for CFRP parallel-wire cables by the authors and its effectiveness was initially proven in full scale sustained tension creep tests and in quasi static tensile tests to failure (achieving a 95% utilization ratio). This gave the team confidence to use the novel CFRP anchor system for post-tensioning Ilfis Bridge in Summer 2023. Finally the strengthening of the bridge box girder is described and first monitoring data gathered during the initial 7.5 bridge service months are presented and discussed. The strain gauge sensors used on the 25 years old CFRP wires and on the novel CFRP anchor sleeves were effective in measuring the tensile, hoop and compressive strains during post tensioning and allow a reliable monitoring of the prestress force. The wire and anchor sleeve strains are nearly constant and are only influenced by seasonal temperature variations. In addition only a negligible resin load transfer media draw-in could be assessed. Hence the performance of the newly developed CFRP parallel-wire cable anchorage system based on filament wound CFRP sleeves and a monolithic resin grout was successfully validated. Future monitoring data shall prove the effectiveness and reliability of the novel CFRP cables built using reclaimed CFRP wires, of their anchorages and of the strain gauge based CFRP We would like to thank Mr V. Bemetz and A. Guelzow ( Carbo-Link AG ) for their contribution to develop the anchorage and for the production of the prototypes, and we thank Valentin Ott ( Empa MSE) for elaborating the strain measurements. We acknowledge the valuable inputs and fruitful discussions with Mr. Andreas Rösli ( vif , Canton of Lucerne), B. Leu, T. Glauser ( Deuring+Öhninger AG ), M. Kaufmann, and S. Jedelhauser ( Basler & Hofmann AG ). References Fib 2019. ‘Externally applied FRP reinforcement for concrete structures’, International Federation for Structural Concrete. Bulletin 90, July 2019. Fib 2013. fib Model Code for Concrete Structures 2010. International Federation for Structural Concrete, October 2013 American Concrete Institute 2015, Guide for the design and construction of structural concrete reinforced with fiber-reinforced polymer (FRP) bars, 1st printing. in ACI report, no. 440.1R – 15. Farmington Hills, MI: American Concrete Institute, 2015 Yamaguchi T., Y. Kato, T. Nishimura, and T. Uomoto 1997 ‘Creep rupture of FRP rods made of aramid, carbon and glass fibers’, Proceedings of the Third International Symposium on Non-Metallic (FRP) Reinforcement for Concrete Structures (FRPRCS-3), Japan Concrete Institute, Tokyo, Japan, pp. 179-186. Terrasi, G.P. 2013. Prefabricated Thin-walled Structural Elements Made from High Performance Concrete Prestressed with CFRP Wires, Journal of Materials Science Research; Vol. 2, No. 1; 1-10. monitoring system. Acknowledgements