Issue 41

S. K. Kourkoulis et alii, Frattura ed Integrità Strutturale, 41 (2017) 536-551; DOI: 10.3221/IGF-ESIS.41.64 541 0 150 300 450 0.0 1.5 3.0 4.5 Load, P [kN] Opening of the fault, ζ [mm] P ζ Α ΄ Β ΄ C ΄ D ΄ E ΄ 0 150 300 450 0 1 2 3 Load, P [kN] Deflection, δ [mm] Α Β C D E P δ (a) (b) Figure 3 : The overall load imposed versus the (a) deflection, δ, of the epistyle’s central section and (b) the opening of the fault, ζ , at the lowest edge of the epistyle. (a) (b) Figure 4 : (a) First macroscopically visible cracking of the upper corner of the left fragment at time instant t~1140s. (b) The epistyle after the final failure (fracture of all reinforcing titanium bars). titanium) under tension indicating, perhaps, some kind of yield and flow of the lowest level of reinforcing bars. The abrupt load drop following (portion CD of the graph) is difficult to be explained, however it could be attributed to either a local fracture of the upper corner of one of the two fragments (which is clearly seen in Fig.4) or to fracture of the titanium bars of the lowest layer or even to both of them. After this sudden drop the load starts increasing again, indicating that the ad- ditional load imposed is undertaken by the bars of the upper level, for which the stress level is below the respective yield limit. The maximum deflection recorded (at the maximum load imposed) was equal to about 2.7 mm. The second mechanical parameter, of crucial importance, from the engineering point of view, is the opening, ζ , of the fault, i.e. the increase of the distance between the two fragments, which was measured with the aid of traditional clip- gauges attached at the lowest edge of the epistyle and also at the level of the lowest layer of restoring bars. The variation of ζ versus the overall load imposed is plotted in Fig.3b. It exhibits a behaviour quite similar (from a qualitative point of view) with that of the deflection (Fig.3a). Again the dependence is initially linear, followed by a regime of non-linear response. However, instead of a “plateau” (as it was the case of the P - δ graph) the non-linear portion is terminated by a sudden drop and the characteristic “plateau” appears afterwards. Then the opening of the fault starts increasing again slowly until a value equal to about ζ =3.2 mm. From this point on, the increase becomes steeper attaining a