PSI - Issue 64

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

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hoop stresses generated by the wedging pressure of the inner LTM bonded to the 37 CFRP wires composing the cable. Curing of the filament wound CFRP part lasted 10 hours at 140°C. After demolding and milling, a steel sleeve was glued on the CFRP sleeve front face to compensate for slight angular errors in the bridge construction and to prevent micro-buckling of the carbon fibers in the compression load introduction area of the anchor. The finally produced cable anchor sleeve is depicted in Figure 3.

Fig. 3: Filament wound CFRP sleeve no. SN04 with front abutment strengthened with a bonded steel ring (courtesy of Carbo-Link AG)

2.5. Production of the cable tensile specimens and of the bridge cables The 37 CFRP wires at each cable termination were thoroughly cleaned with acetone, subsequently roughened with an 100 medium grit sandpaper and finally cleaned again with acetone. A polyethylene positioning organizer at the end and the beginning of the CFRP sleeve was used to keep the wires parallel in the anchor and at a distance of 4 mm to each other. The inner surface of the conical CFRP anchor sleeve was then treated with release agent. This was followed by the mixing of the anchor's potting resin (the as called load transfer media, LTM) which consisted of the hot curing epoxy resin Araldite LY564/AD2954 (Ciba-Geigy 1998) and 20% in volume of a hard alumina powder. This LTM is monolithic as opposite to the gradient anchorage concept patented by Empa in 1995 (Meier et al. 1995). The LTM is finally injected in the 50°C heated sleeve from the lower end of the vertically aligned CFRP cable termination as shown in Figure 4, left. Curing of the LTM takes 12 hours at 100°C. After adding the counter part of the spherical bearing on to the cable, the same process is repeated for the other side of the cable. A finished LTM-cone cast around the 37 wire cable ends is shown in Figure 4, right.

Fig. 4: Left : Injection of the LTM in the CFRP anchor sleeve after positioning the 37 reused CFRP-wires, and Right : Hardened LTM-cone made of ceramic powder strengthened epoxy at each end of the 37 CFRP wire cable (courtesy of Carbo-Link AG)

2.6. Tensile tests on full scale cable specimens In order to validate the newly developed Carbo-Link anchor system for the 37 CFRP parallel wire cables, the authors performed two quasi-static tensile tests to failure in winter 2022-23. Each of these two experiments were preceded by a several days long sustained tensile load creep test. In the creep test the 5.2 m long cable samples were initially loaded to a tensile force of 1400 kN. Thereafter the cable load was reduced to 1300 kN and kept constant during 133 hours (sample 1) and 66 hours (sample 2) in order to monitor the creep behaviour under continuous load. The creep strength of the novel cable system should be proved at a 30% higher sustained tensile load than the foreseen