PSI - Issue 78

Franco Braga et al. / Procedia Structural Integrity 78 (2026) 285–292

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configuration and PGA equal to 0.20 g; therefore a rather modest variation and in any case a situation such as not to require the presence of reinforcement in the slab to guarantee its distribution capacity. The percentages change significantly if one considers the presence of a reinforced concrete stiffening core (as already mentioned, consisting of two walls with dimensions equal to 0.20 m x 1 m) positioned in correspondence with "Block 1", therefore in a very decentralised position with respect to the centre of the masses. In this configuration ( Fig.3 b) the maximum value of R is always greater than 100%, and reaches 200% in the case of 8-storey buildings and PGA equal to 0.20 g; therefore a very significant variation and in any case a situation such as to always require the presence of the reinforcement in the slab to guarantee its distribution capacity.

Fig.3 . R as the number of storeys and PGA vary for buildings without a stiffening core (a) and with a stiffening core (b).

The diagrams shown so far refer to the maximum value of R, evaluated referring to all floors. On the other hand, Fig.4 shows the trends of the R parameter at the various floors, for a single value of the PGA (PGA = 0.15 g), showing the situation in the absence of a stiffening core, Fig.4 a, and in the presence of a stiffening core, Fig.4 b; it is interesting to note that the diagram of Fig. 4 b, referring to constructions that have a stiffening core, has the highest values of R at the top floor (R always greater than 100%), while the values at all other floors are significantly lower, R never exceeding 60%.

Fig.4 . R evaluated at the different floors of buildings without a stiffening core (a) and with a stiffening core (b) induced by the earthquake with PGA equal to 0.15 g.

This means that, in the event of an earthquake, while the columns of the lower floors are normally more stressed than those of the upper floors, the stresses in the floors have an inverse trend, being greater at the top floor and significantly lower at the first levels. It can therefore be stated that, both in the presence and in the absence of stiffening cores, at the first levels of reinforced concrete constructions, which are normally the critical floors in the event of an earthquake,