PSI - Issue 78

Francesco Nigro et al. / Procedia Structural Integrity 78 (2026) 1537–1544

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Verderame and Ricci (2018). The model assumes members with plain bars, characterised by a quadrilinear backbone curve involving yield, peak, ultimate and zero strength points. Material properties were selected according to the most common concrete and steel classes of the considered construction age according to Verderame et al. (2012) and Masi et al. (2019).

Fig. 1. Blueprint of the archetype existing RC structure

In the present study, two different models of the as-built buildings have been investigated: the bare frame (BF) structure and the infilled frame (IF) structure, whose nonlinear finite element models are discussed in detail in De Risi et al. (2023) and Di Domenico et al. (2023), for the BF and IF structures respectively. Both RC structural models were analysed by means of non-linear static (pushover) analyses utilising the OpenSees software (McKenna et al., 2000). Each analysis was run up to a target displacement of 300 mm with a displacement increase of 0.30 mm per step, considering two distributions of horizontal forces for each plan direction: a first distribution was adopted being proportional to the 1 st translational vibration mode of the structure while a second distribution was considered being proportional to the storey masses. Then, the N2-Method formulated by Fajfar (1999) was adopted to estimate the displacement and corresponding force demands. Fig. 2 depicts the pushover curves describing the as-built structures, while Table 1 summarizes the main safety indexes  E (intended as the Peak Ground Acceleration capacity-to-demand ratios) characterizing those structures, focusing on the most relevant failure mechanisms for both Damage Limitation (DL) and Severe Damage (SD) Limit States (LSs). Fig. 2 points out that the IF structure is characterized by higher stiffness and maximum base shear force resistance, although its strength degradation appears to be greater than the one characterising the BF structure. Observing Table 1, it may be mentioned that both the BF and the IF structures exhibit very inadequate performance for the Severe Damage LS because of shear failure of columns and beam-column joints. It may also be noted that the presence of the infill walls is able to increase significantly (yet not sufficiently) the safety indexes related to shear failures.

0.30

0.30

BF - Mass Y+ BF - Mode Y+ IF - Mass Y+ IF - Mode Y+ Ductile Failures Shear Columns Joints Compr. Joints Tens.

IF - Mass X+ IF - Mode X+ BF - Mass X+ BF - Mode X+ Ductile Failures Shear Columns Joints Tens.

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RDR [%]

RDR [%]

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Fig. 2. Pushover curves of the as-built BF and IF structures along the X (a) and Y (b) directions