Page 218 - Handbook of Materials Failure Analysis

214 CHAPTER 8 Seismic risk of RC water storage elevated tanks

Table 8.22 Characterization Scale of Cracking
Value of Crack Index Importance of Cracking
0-0.5 Negligible
0.5-1 Low
1-2 Moderate
2-5 Strong
5-10 Very strong
>10 Considerable

Table 8.23 The Vulnerability Index “I V ” Calculated for the Tank Investigated
No Parameter Class K i W i K i W i
1 Seismic behavior C 15.00 1.75 26.25
2 The clashing A – 1.75 -
3 The bracing system C 15.00 1.50 22.50
4 Regularity in plan B 5.00 1.50 7.50
5 Regularity in elevation B 5.00 1.50 7.50
6 Soil type B 5.00 1.00 5.00
7 Site effect A – 1.00 -
8 Seismic zone B 5.00 1.00 5.00
9 Quality of the nodes A – 0.75 -
10 Qualities of the bracing system B 5.00 0.75 3.75
11 Maintenance B 5.00 0.25 1.25
12 Details C 15.00 0.25 3.75
I V 82.50

6 CONCLUSION
The method developed is used to establish a hierarchy of tanks with risks from pre-
defined safety criteria. The decision on the choice of maintenance, accrued to the
manager of the tanks, consists in fact to estimate the limit vulnerability, which leads
them to choose preventive maintenance (short-term repairs in order to prevent further
deterioration to come) or consider a deferral of intervention if the tank does not rep-
resent high risk in terms of safety or cost, or without repairs.
According to the principles used for the vulnerability index evolution in the life-
cycle of the tank for the establishment of maintenance schemes, two terminals of
vulnerability will be defined (I V1 and I V2 ) segmenting all of the scale in three cate-
gories maintenance:

• Tanks whose vulnerability index is less than 33 (I V1 ): no maintenance is planned;
only a regular monitoring (visual inspection, auscultation) is considered.