PSI - Issue 62

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Alessandro Bellini et al. / Procedia Structural Integrity 62 (2024) 315–322 A. Bellini et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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(a) (b) Fig. 1. RC columns used during the experimental campaign: (a) detail of dimensions, steel bars and stirrups; (b) strain gauges position and order of the saw-cuts.

Table 1. Experimental program. Sample code Type of test

Number of tests

σ V (MPa)

Saw-cuts order P + O (BADC) O + P (DCBA) P + O (BADC)

Inclination

P10_1 P10_2 P10_3 P10_4 P10_5 P10_6 P15_1 P15_2 DS_1 DS_2 DS_3 DS_4 P5_1 P5_2

Prestress release test Prestress release test Prestress release test Prestress release test Prestress release test Prestress release test Prestress release test Prestress release test Prestress release test Prestress release test Shrinkage release Shrinkage release Shrinkage release Shrinkage release

2 5 3 2 1 2 3 2 3 2 3 1 1 8

10 10 10 10 10 10

45° (P) - 90° (O) 45° (O) - 45° (P) 45° (P) - 45° (O) 45° (O) - 45° (P) 45° (P) - 45° (O) 45° (P) - 45° (O) 45° (O) - 45° (P) 45° (P) - 45° (O) 45° (O) - 45° (P) 45° (P) - 90° (O) 90° (O) - 45° (P) 45° (O) - 45° (P) 45° (P) - 45° (O) 45° (O)

DBCA ADBC

O only (DC) P + O (BADC) O + P (DCBA) P + O (BADC) O + P (DCBA) P + O (BADC) O + P (DCBA) O + P (DCBA) P + O (BADC)

5 5

15

5 0 0 0 0

3. Experimental set-up and procedure Experimental tests were performed on the described RC columns by using a universal hydraulic machine, with a maximum axial capacity of 6000 kN and a set of strain gauges. Each column was placed vertically inside the machine, one strain gauge (with 30 mm gauge length) was applied, parallel to the direction of the applied stress, for each portion to be removed (Fig. 2a) and, finally, a preassigned and constant axial load was applied to the column. Five different areas, located at different heights on opposite faces of the column, were identified for the blocks extraction, with the purpose of reducing as much as possible alterations on the strain field caused by previous tests on the same column (see Fig. 1b). Particular attention was paid to the insulation and protection of the strain gauges (Fig. 2a), in order to make them as insensitive as possible to dust, vibrations and material residues produced during the extraction phase. In general, at least 2 strain gauges and 4 potentiometers were used during each prestress release test: in more detail, the potentiometers were placed vertically near the four corners of the column while the strain gauges on opposite sides of the same column; the formers were used to evaluate the elastic modulus of each column while the latter to identify and control possible load eccentricities (Fig. 2b). To reduce this possible issue, all the columns were prepared before the test with additional self-leveling concrete castings, in order to guarantee a perfect parallelism between the upper and bottom faces.