PSI - Issue 78

Alessandro Pisapia et al. / Procedia Structural Integrity 78 (2026) 568–575

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(a) (b) Fig. 2. Influence of the in-plane flexural stiffness on the seismic effects in the case of three vertical frames: Lateral support (a); Central support (b) 2.2. Floor diaphragm with four vertical frames The same consideration provided in the case of the floor regular diaphragms with three vertical frames can be easily extended to the case with four vertical frames. According to the scheme shown in Fig.3, the expressions of ∞ ⁄ and ∞ ⁄ are given by: ∞ = 2 3 � 1 − 1 − 6 5+6 +12 � ∞ = 4 3 � 1+ 1 2 1 − 6 5+6 +12 � (4) Fig. 4 provides the influence of the in-plane flexural stiffness of the diaphragm on the seismic effects of the vertical frames.

Fig. 3. Theoretical model of a diaphragm with four vertical seismic-resisting frames.

The same considerations made for the case with three vertical frames also apply to the case with four vertical frames. Additionally, it is worth noting that the effects of shear deformability are less pronounced compared to the previous case. Moreover, it is also worth highlighting that, in accordance with the analyses shown in Figs. 2 and 4, the case with three vertical frames appears to be more critical.