PSI - Issue 29

Mario De Stefano et al. / Procedia Structural Integrity 29 (2020) 71–78 De Stefano and Cristofaro / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 2. Summary of the safety index for single structural units according to the churches model. Structural unit Soil Category T R,SLV Safety index Block I (Transept) B 505.28 0.710 Block I (Chapels) B 553.64 0.778 Block D+F B 285.54 0.401 Block D+E+F B 217.38 0.302

3.2. LV2: Evaluationof individual macro-elements (local collapse mechanism) The LV2 seismic vulnerability assessment was carried out according to loca l models, mechanisms referring to "single wa ll panels or larger portions of the buildingand favoured by the absence or insufficient effectiveness of the connections between wa lls and horizonta ls and between wa ll panels" (§ 8.7.1 NTC 2008). They are therefore structura lly autonomous portions of the construction (macroelements) characterized by a mechanica l response to the seismic action substantia lly independent from that of the rest of the building. Fig. 5 shows the results of the 10 kinematics analysed and the related safety factors derived from thecapacityon demand ra tio.

a 0st /a D = 0.32

a 0st /a D = 0.40

a 0st /a D = 0.92

a 0st /a D = 0.73

a 0st /a D = 0.99

a 0st /a D = > 2

a 0st /a D = 1.33

a 0st /a D = >2

a 0st /a D = 1.14

a 0st /a D = 1.49

a 0st /a D = capacity / demand ratio of the mechanism activation acceleration

Fig. 5. Kinematics analyzed

3.3. LV3:Overall evaluationof building’s seismic response A first eva luation of the complex was carried out using the subdivision into structura l units, on the basis of an accurate typologica l-constructive ana lysis, as defined in the level 1 ana lysis (LV1). This was performed through the static nonlinear ana lysis (pushover), carried out with the 3Muri (STADATA, 2012) software code, while a globa l model ana lysis was performed through the tools of the static and dynamic linear ana lysis, performed with the Straus7 (2010). The eva luation of the seismic action was carried out by assigning to the site the soil type B. Checks were carried out considering three limit states: Life Protection Limit State (SLV), Damage Limit State (SLD), Life Safety Limit State (SLV SITO ). The SLV SITO was considered with reference to a nomina l life V N equa l to 50 years in the hypothesis of a class of use III. In Fig. 6a the site spectrum and the elastic spectrum for soil type B (AA.VV., 2017) are reported with reference to the SLV. The structura l units ana lysed are: A, E, G, H, L, M. In Fig. 6b, we report the results of the risk index (RC/D) processed with the TreMuri code (non-linear static ana lysis) while in Fig. 6c the results, in terms of the rela tionship between capacity and demand, for SLV, they refer to type B soil and site spectrum. The results obta ined on the globa lmodel are shown in Fig. 7 as regards the ana lysis of vertica l loads. It should be underlined that the linear ana lysis carried out for the globa l moda l can be suitable only up to the onset of initia l masonry cracking due to tensile stresses exceeding masonry tensile strength. Nonetheless, it can give useful information up to initia l masonry cracking. The most tensile-stressed areas are located near some openings of the “ Sala dei Gessi ” , in the block conta ining the new offices and in the “ Sale Bizantine ” , in the wa lls of the sta irwell and at the head of the wa lls of the “ Sala II ” and “ Sala III ” . Fig. 7c shows the moda l deformation relating to the way