PSI - Issue 11

Siro Casolo et al. / Procedia Structural Integrity 11 (2018) 20–27 Siro Casolo & Giuseppina Uva / Structural Integrity Procedia 00 (2018) 000–000

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Figure 6. A direct graphical comparison between pushover and full ND analyses in terms of displacements (for the pushover analysis, a load profile proportional to the 1 st mode is considered). (Casolo & Uva, 2013)

Instead, when the failure condition is determined by the partial collapse of the tympanum (like in the case of the texture (2), that has a better quality), the pushover is not capable to catch it, and over-estimates the capacity. The pushover analysis, in specific situations, fails in predicting the ultimate capacity related to partial failures, consistently with the limitations related to the standard formulation in describing the damage induced by higher vibration modes. In conclusion, considering that historical and monumental buildings often have peculiar and unrepeatable characteristics, a full nonlinear dynamic analysis would be recommended when the objective is to perform a detailed vulnerability assessment. This research work can be considered, in this sense, a preliminary step and many crucial points should be specifically investigated. 4. Natural accelerograms, repeated Earthquake and Cumulative Seismic Damage In many Italian seismic Areas, seismic shocks can occur as a sequence, close in space and time, of destructive events of comparable intensity. In these cases, a significant portion of the damage to historical buildings can be related with the cumulated damage. The recent examples of the Earthquakes in Central Italy are an evident example of this, and this situation is related to the peculiar tectonic configuration of the Apennine and sub-Apennine area. The survey of data collected from recent major earthquakes in Italy shows that strong ground motions often occurred in sequences of 2 or 3 main shocks of comparable intensity during a short period of time. There is a further step forward to be done, at this point, with respect to the previously issues: we have adopted an efficient computational model able to heuristically describe the peculiar masonry features and the effects of the texture; we have been able to perform several dynamic analyses and to appraise their relevance. We need now to introduce real natural records into the analyses and to consider them in sequence of repeated events, and to appraise how the specific increase of damage can be determined, and – possibly – which are some threshold-parameters (Casolo, 2017). Again, as case studies, the façades of Rosario and Trasfigurazione are analysed, considering for each of them the 2 types of masonry textures (see Section 2), and applying the specific RBSM with various sequences of recorded accelerograms. For the analyses, 24 strong ground motions recorded during 2 sequences of Italian seismic events characterized by a close succession of seismic shocks whose intensity was comparable to the main shock have been selected (Friuli, 11 and 15 September 1976, stations of Gemona and Forgaria-Cornino; Umbria-Marche 1997;