PSI - Issue 64

Alba Hyseni et al. / Procedia Structural Integrity 64 (2024) 246–253 Alba Hyseni / Structural Integrity Procedia 00 (2019) 000 – 000

252

7

The CASA-method ended after the third try since the seismic vulnerability check was not satisfied anymore being the demand lateral displacement capacity equal to 40 mm and so higher than the capacity at the 323-year found equal to 34.5 mm. Thus, the safety index (capacity/demand) was < 1 and = 0.86. It can be concluded that, even if the studied tank-tower was on the safety side (index > 3) due to the poor seismic risk assumed in the site-location; this level of safety is gradually thinning over the time due to the creep effect influencing the lateral displacement capacity in case of horizontal loading.

Fig. 7. Acceleration Displacement Response Spectrum (ADRS) seismic vulnerability check.

Table 2. Main results.

Creep Point

Age

Young's Modulus E

Stiffness

Max base shear/total weight*

Capacity displacement CD

Demand displacement DD

Safety index CD/DD

Seismic vulnerability check

[-]

[years]

[MPa]

kN/cm

[-]

[mm]

[mm]

[mm]

[-]

A B C D

12

3360 2950 2520 2100

1103

0.08 0.07 0.06 0.04

75.7 62.1 46.9 34.5

25 33 36 40

3.03 1.88 1.30 0.86

Satisfied Satisfied Satisfied

119 240 323

930 836 649

NOT satisfied

* total weight=41505 kN

Conclusions and final remarks Masonry constructions are, in some cases, valuable for the cultural relevance in a human society. For this reason, preservation in a long-term may became the main goal. This means that, when dealing with seismic vulnerability, the structural safety check should deal also with time-dependent effects related to the decay of the material and micro damaging due to creep effect typically devoted in masonry. To provide preliminary evidence of this potential lack in the historical masonry building ’s conservation, a case-study is herein reported and discussed concerning a creep-prone structure: a masonry tank-tower. The choice was guided by two several factors. First, the tower is in a poor seismic prone zone in the south of Italy to make the study on the conservative side. Second, the historical tower was axially overloaded for many years during its service as a water-tank (i.e. creep activated). Therefore, a novel CASA-method was proposed consisting in the multi-analysis of the structures by varying the elastic parameters of the masonry obtaining a different lateral displacement capacity accordingly to the age of the building, as well as its creep level. A three-stages formulation of a viscoelastic creep model with damage was implemented according to existing literature by Verstrynge et al. (2011). The analysis did not consider additional few factors, such as weathering, deterioration, and fatigue. The findings evidenced that the lateral failure may occur after 323 years due to the dramatic creep