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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Fig. 7: Load vs machine displacement diagrams measured in the quasi-static tensile failure tests of cables 1 and 2

Table 3 summarizes the maximum loads and wire stresses achieved. The average tensile stress σ in one CFRP wire assuming that n wires are carrying load is calculated according to: = = ∙ 24∙ (1) with the cable load F and the diameter of the reused Kleine Emme Bridge CFRP wires being d=5.08 mm. The tensile strength evaluation of the regained wires is presented in Table 1. The 99% quantile derived from these 12 quasi-static tensile tests to failure was 2'647MPa. There out a CFRP material utilization factor is calculated as the ratio between the average wire stress  at first wire or cable failure and the 99% quantile of the wire strength. It should be noted that only 35 load-bearing wires were taken into account for the stress calculation at maximum force for cable number 2. Two wires have previously failed as described above.

Table 3. Evaluation of tensile tests to failure of the two 37-wire CFRP cables: loads, average stresses and material utilizations factors

Cable number

Load F 1 at first wire failure

Maximum load of cable

σ at first wire failure

Material utilization at first-wire failure

σ at maximum load

Material utilization at maximum load

1

1'889 kN

1'889 kN

2'519 MPa (n=37) 2'200MPa (n=37)

95.2% (n=37) 83.2% (n=37)

2'519MPa (n=37) 2'505MPa (n=35)

95.2% (n=37) 94.6% (n=35)

2

1'650 kN

1'777 kN

A material utilization of 95.2% was achieved with cable 1, while cable 2 reached a material utilization of only 83.2% at the first wire failure (Table 3). In general, the cables' failure pattern is good-natured because the 37-wire bundles fail due to tensile or tensile/shear wire failure and not through delamination of the CFRP wires from the LTM. This indicates a high contact pressure in the LTM cone inside the CFRP anchor sleeve and the use of effective lubricants. In cable 1, the failure is "fibrous" (characterized by a fanning out of fiber bundles of the pultruded wires in the free length), which indicates a high tensile failure stress in the wires and is normally the case with these wires at tensile stresses greater than 2500 MPa. A first hypothesis of the initial wire failure in cable 2 is due to combined tension and shear (caused by transverse overcompression). This usually happens at lower fracture stresses and results in cross-sections that are sheared off at fairly right angles without a “fibrous” structure. Typically, this failure occurs when the wires are under high lateral (contact) pressure, which is corroborated by the higher draw-in observed for cable 2 when using the highly