Results of the Cyclic Loading

Figure 6 shows the hysteretic stress-strain diagram for about 200 cycles.

Figure 7 shows the load-displacement cyclic diagram but limited to the first 10 cycles; analogous cycles, corresponding to the carbon “Tempcore” rebar, are inserted, for comparison purposes, in the same figure.

It is interesting to point out: AISI304 presents higher values of the force for a given elongation than the carbon steel; this is because of the higher yield point and of the higher strain hardening of the AISI304 with respect the “Tempcore”. The decrease of the maximum resistance, especially

Table 1. Resistances and ductility values.

Re [MPa]

Rm [MPa]

RmlRe

Agt [%]

Inox (016) test 1

558.01

788.89

1.41

29.00

Inox (016) test 1

554.66

785.10

1.42

26.75

Tempcore (014)

472.78

584.95

1.24

14.39

Tempcore (014)

478.36

599.03

1.25

12.89

Low cycle fatigue – AL/L = 1%

hoxd=16mm-test2 nox d=16mm – test 3

Tempcore C d=14mm

•800

AL/L

Fig. 7. Load-elongation hysteretic curves for the first 10 cycles.

in compression (i. e. in the negative side of the horizontal axis) is due to: (i) the crack initiation in the plastic hinge of the middle section and (ii) to the geometric effect, which is due to the fact that the pure compression mode becomes a bending-compression deformation mode. Figure 8 shows the decrease of the tension (greater values) and of the compression (smaller values) force along the cycles; it is evident how the carbon steel curve lies always below the lines of the AISI304. Low cycle fatigue resistance of AISI304 is almost twice (200^250 cycles) as much as the carbon steel (100^120 cycles).

Figure 9 gives total energy dissipation with the number of cycles, while Figure 10 gives the energy dissipated inside each cycle for all cycles.

n° cycles

Fig. 8. Resistance decrease along the cycles.

Energy dissipation – AL/L = 1 %

— Inox d=16mm (test 2) — Inox d=16mm (test 3)

Tempcore C d=14mm

100 150

n° cycles

Fig. 9. Energy dissipation along the cycles.

2. Tests on R. C. Frames under Cyclic Loading

2.1. The Prototype Design

Figure 11 shows the steel reinforcement of the column and of the foundation. The steel reinforcement of the column consists of 4 016 and stirrups 08 at 70 mm distance, inside the plastic hinge, made of AISI304.