PSI - Issue 13

Mihaela Iordachescu et al. / Procedia Structural Integrity 13 (2018) 584–589 M. Iordachescu, M. de Abreu, A. Valiente / Structural Integrity Procedia 00 (2018) 000 – 000

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during its tensile tensioning up to failure. One of the effects that the test sought to reproduce was the local compression that may occur in service between the wires of a loaded prestressing strand. Fig. 1 shows the test arrangement used in the experiments. Commercial wedge grips for prestressing wires were used to fix the specimens, of 350 mm length, in the vertical loading frame of the 200 kN servo-hydraulic machine which provided the tensile loading. The transverse compression was applied and held constant by the actuator and the support plate of a small loading frame, which remained attached to the wire through the compression load, without sliding or axial force transmission. This was assured by a pulley counterweight system by maintaining the horizontality of the frame and balancing its weight (Fig 1a). The actuator of the small loading frame is a hydraulically driven piston connected to an air-oil pressure converter that assures controlled thrust through the air-pressure regulator mounted to the outlet of a compressed air cylinder. Thus, on the piston side, the compression load was applied perpendicularly to the tested wire axis by using a small wire-sample of same type (Fig 1b); the other side of the tested wire was longitudinally supported on a V-shape die, of 30 mm length. The die shape and the counterweight system of the horizontal frame prevented the lateral displacement of tested wire, once fixed in wedges (Fig. 1c). Details capturing the main testing sequences, namely the wire fixing, bi-axial loading and failure are given in Fig. 1c, Fig. 1d-1 and Fig. 1d-2. These were acquired with an optical acquisition system VIC-2D, and allowed obtaining the elongation data corresponding to the longitudinal tensioning of the wire.

Table 1. Mechanical properties of studied wires Elastic modulus, [GPa] Yield strength, R p0.2 [MPa]

Tensile strength, R m [MPa]

Maximum uniform elongation, A gt [%]

Reduction of area, RA [%]

LDS (1.4482) DSS (1.4462) ES (1.4482)

180 160 205

1350 1429 1640

1820 1660 1740

2.3 2.2 3.2

51 70 50

Fig. 1. Tensile testing of wire specimens under transverse loading: a) general view of the test arrangement; b) loading mode; c) frame and actuator for transverse loading; d-1) transversely compressed zone before tensioning; d-2) wire´s failure