PSI - Issue 78

Federica Rauseo et al. / Procedia Structural Integrity 78 (2026) 473–480

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the Y direction and 250 mm -thick one-way joist slabs. It has a regular re ctangular plan (21.5 m × 11.5 m), with an interstore y height of 3.40 m at the ground floor and 3.05 m at the upper levels. Columns are mostly 300×300 mm², except for a few 300×400 mm² interior columns at the ground level. External beams have a cross section of 300×500 mm², while internal beams are of varying sizes: 300×600 mm², 115×250 mm², and 80×250 mm². Materials and loads reflect typical construction practices of the time, with an average concrete strength of f cm = 18 MPa and AQ42 reinforcing steel with f ym = 322 MPa. In both models, infill walls are neg lected.

Y

X

Fig. 1. Plan view of the case-study building at ground level

2.2. Model A Model A is implemented in OpenSees and simulates the reinforced concrete structure using nonlinear displacement-based beam-column elements (dispBeamColumn) with fiber sections. A corotational formulation is employed to incorporate geometric nonlinearity due to large displacements. The floor system is assumed to behave as a rigid diaphragm. Soil - structure interaction is explicitly included through translational and rotational springs placed at the base of each column, whose stiffness is derived from Gazetas (1991), assuming isolated footings and taking into account both soil properties and foundation geometry. Material behaviour is defined by the constitutive model proposed by Karsan and Jirsa (1969) for concrete while steel is modelled using a bilinear law with kinematic hardening, wrapped within a MinMax material to impose upper and lower strain limits and prevent unrealistically large deformations.

(a)

Fig. 2. (a) 3D Model A - OpenSees; (b) 3D Model B - SeismoStruct