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 current prestressing force was approx. 46 MN which should be raised by 5%, i.e. with 2 parallel wire bundles (PWB) cables made of 37 tendons and a prestress of 1'000 kN each. Final decision by the involved parties (building authorities, general contractor, engineering companies and Empa) was the post-strengthening with 2 PWB cables, as this fulfilled load model 3 of SIA 269 2011, leading to a utilization coefficient of 0.93 at midspan (previously 1.06). The strengthening of the bridge with 2 supplementary post-tensioning cables should be placed inside the narrow and congested box section (Figure 8 and 9), as the belated installation of the CFRP-cables is much simpler than with steel strands due to their low bending stiffness and very low weight. A special challenge was the anchoring of the cables and the load introduction into the bridge box section, as the available space was very limited (also due to utility lines and water pipes inside the box section). Figure 9 shows a cross section of the bridge with the planned cable position. Large welded steel jokes had to be built and installed to bear the cable loads and transmit them to the bridge structure. The box-shaped structures lead the prestress into the bridge via several shear dowels, see Errore. L'origine riferimento non è stata trovata. 9. They had to be designed in a way that the prestressing of the cables could be performed with mobile hydraulic presses (and small auxiliaries). Figure 10 shows the final installation.

Fig. 9: Welded steel construction to support the cable sleeves, and to transfer the loads via shear dowels into the bridge

Fig. 10: Installed cable after prestressing, with both supports (left with the monitoring system) and the framework for deflecting the PWB cable

The installation of the CFRP cables and the prestressing was performed in 1 day on 23 August 2023, and the monitoring system was started to record the strains on selected tendons and the draw-in of the grouted cones in the CFRP sleeves. First results of this long-term measurement are presented in chapter 4. 4. Installation and Monitoring After cable production took place at Carbo-Link AG, the two CFRP parallel wire cables were equipped with resistive strain gauges (RSG) on four wires 1 meter before the passive anchor end (denominated no. 1-4 and arranged as shown in Figure 11) and with one longitudinal and one transverse strain gauge on one of the two CFRP sleeves