PSI - Issue 78

Somayeh Gholami et al. / Procedia Structural Integrity 78 (2026) 1459–1465

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4.2. Results and discussion

The seismic safety index I a , LSLS was computed for each case-study building by comparing the estimated spectral capacity a LSLS with the design demand a g defined by NTC2018 for a return period of 475 years (Table 2). All buildings exhibit safety indices below the threshold of 1.0, with values ranging from 0.34 to 0.59, indicating insufficient capacity to withstand the expected seismic action at the Limit State of Life Safety. These results reflect a combination of factors. The observed capacity variations can be attributed to several key factors. First, moderate to high plan irregularity ( β x|yi ≥ 1.01) indicates non -uniform stiffness distribution, which adversely affects seismic response. Second, the dynamic reduction coefficients suggest diminished energy dissipation in certain cases. Third, the limited wall surface areas in the weaker direction reduce lateral resistance, and finally, end-restraint coefficients ( μx|yi, ζ ) approaching their penalizing bounds further constrain performance. These aspects collectively highlight the critical role of wall layout, plan regularity, and construction detailing in shaping the capacity predictions made by the EL1 model.

Table 2. Summary of seismic capacity, demand, and safety index for case-study buildings

I a , LSLS

Building ID

Height(m) T 1 (s)

M(ton)

F LSLS (kN)

a LSLS (m/s

2 )

a

g

213sub 4

7.95

0.24 0.19 0.24 0.21 0.13

800.2

453.03 1048.5 1077.23 516.07

0.45 0.53 0.39 0.58 0.33

1.005 1.005 1.005 1.005 1.005

0.45 0.54 0.40 0.59 0.34

213 217 214 209

6

1494.9 1711.8

8.3 6.6

667.7 835.7

3.75

332.80

Despite their similar construction typology (URM with tuff blocks and lime mortar), the buildings exhibited notable variability in their seismic capacity. A detailed review of the input parameters and capacity results led to the following findings. Although the computed plan irregularity coefficients β fall within a relatively narrow range (1.0 1 –1.25), they consistently exceed unity, indicating the presence of non-negligible eccentricities between the centers of mass and stiffness. These irregularities introduce penalizing effects in the base shear capacity calculation and thus contribute to the reduced seismic capacity across all buildings The most decisive factor in seismic capacity is the quantity and distribution of effective wall surface area in the critical horizontal direction. Buildings with limited wall area in this direction (e.g., id. 209) exhibited significantly lower base shear capacities, even when their total seismic mass was low. Conversely, buildings with higher and better distributed resisting walls (e.g., id. 214) demonstrated greater capacity and higher I a , LSLS values. The design shear strength τ di varied among the buildings as a result of differing vertical stress conditions, which stemmed from architectural configuration and applied loads. In structures with low axial loads, the calculated τ di values remained close to the lower bound (0.09–0.10 MPa), limiting their shear capacity. Interestingly, the shortest building (209) had the lowest safety index ( I a , LSLS = 0.34), confirming that a reduced number of storeys or lower total mass does not guarantee adequate seismic performance. Rather, a sparse or discontinuous wall layout can critically undermine seismic capacity, also in low excited buildings. 5. Conclusion This study applied the Elevation Level 1(EL1) mechanical model, as proposed in the Italian Guidelines for Cultural Heritage to assess the seismic vulnerability of a representative group of unreinforced masonry buildings in the historic center of Casertavecchia. The evaluation was conducted using geometric data from the GENESIS project and mechanical parameters defined by NTC2018 (Ministero per le Infrastrutture e i Trasporti, 2018), allowing for a consistent and comparative analysis across the case-study buildings. The results show that all assessed buildings exhibit seismic safety indices below the minimum acceptable threshold