PSI - Issue 78

Franco Braga et al. / Procedia Structural Integrity 78 (2026) 2176–2183

2182

5.3. Comparison in terms of Global Reactions The following table shows the global reaction induced at the foot of the building by the seismic action as codified by Law 1684 of 1962, i.e. the one adopted for the project, by that foreseen by the NTC08 code and by that recorded by the accelerometers installed in the Romolo Capranica school (AMTS). GLOBAL REACTION Earthquake X(L.1684/62) Earthquake Y(L.1684/62) SLV1 (NTC08) SLV2 (NTC08) AMTS1 AMTS2 It is easy to see how: - the seismic action codified in 1962 is far lower than that of the more recent NTC08 (the difference is only partially offset by the different verification method used in the two cases); - the 1962 standard considered two orthogonal earthquake directions separately (with a constant distribution with height, not the "inverse triangular" one as required by modern codes), while in 2008 the code requires combining an earthquake in one direction with 30% of the earthquake in the orthogonal direction; - the shears obtained by considering the AMTS spectra are more severe than those obtained with the NTC08 spectra; in fact, the AMTS1 combination has a N-S shear almost double that of the SLV1 combination, while the AMTS2 combination has both shears very high, close to the E-W shear of the SLV2. 5.4. Comparison in terms of structural safety checks The results of the combined axial load and bending moment checks for the first-order columns, performed using the formulas reported in § 4.1.2.1.2.1 of the NTC08, considering the stresses related to the "standard" earthquake (NTC2008), were compared with those of the checks performed with the stresses related to the stresses caused by the actions of the event recorded on August 24, 2016 [AMTS]. The column reinforcements were deduced from the original design drawings. The comparisons in terms of safety factor (S.F. = capacity/demand ratio) are reported below. Tx (N-S) [kN] Ty (E-W) [kN] 644 0 3959 1213 2974 7290 2226 2559 0 644 918 817

Fig. 7. Comparison in terms of combined axial load and bending moment safety factor

Fig. 8. Comparison in terms of shear safety factor The results presented above clearly show that the earthquake experienced by the analyzed buildings on August 24, 2016, was more severe than that prescribed by the seismic code in force at the time of the event (NTC08). This is because the safety factors—already significantly lower than unity, as the building structures had been designed according to the 1964 regulations, which considered loads much lower than those currently codified—were, in some cases (e.g., central columns), reduced by up to an order of magnitude. The final activity involved comparing the displacement demands by calculating the interstory drift for seismic