PSI - Issue 78

Leandro Pancottini et al. / Procedia Structural Integrity 78 (2026) 1103–1110

1105

Infills were modeled as "diagonal strut elements" (compression-only), using an updated phenomenological model (Decanini and Fantin, 1986; Cardone and Perrone, 2015; Sassun et al., 2016) that considers their mechanical and geometric characteristics, including openings (Figure 2). The constitutive model for the equivalent struts was implemented in OpenSees with the Concrete01 material (Noh et al., 2017). Foundations were not modeled, assuming a fixed-base condition for the structure.

Figure 2: Mansory Infill panels with percentage of openings (from 100% yellow to 0% red): (a) IFns; (b) IFsm; (c) IFsc.

3. Non-Linear Analysis Result 3.1. Modal Analysis The masses were distributed node by node to accurately represent their true distribution. Table 2 presents the results of the modal analysis for the first three vibration modes of each of the six models.

Table 2: Modal parameter for BF and IF models Model Type

BFns

BFsm

BFsc

Mode

1

2

3

1

2

3

1

2

3

T [s]

2,87 1,65 1,43 1,63 1,55 1,45 2,18 1,44 1,12

Dir.

Y Rot

X Rot

X Y Y X Rot

Model Type

IFns

IFsm

IFsc

Mode

1

2

3

1

2

3

1

2

3

T [s]

1,35 0,93 0,82 1,09 0,92 0,80 1,22 0,92 0,79

Dir.

Y X Rot

Y X Rot

Y X Rot

The modeling of staircases significantly influences the seismic response of buildings. Their inclusion in the model increases structural stiffness and reduces the fundamental period (BFsm and BFsc models) compared to a model without stairs (BFns). This also induces a variation in the position of the center of stiffness and an increase in torsional effects, the magnitude of which is correlated with the eccentricity of the stair. Similarly, the integration of infill walls (IF models) contributes to the stiffening of the structure. In such scenarios, the vibration modes become regularized: the first two are translational, and the third is rotational. 3.2. Non-Linear Static Analyses (Pushover) Non-linear static (pushover) analyses were conducted to evaluate the impact of staircases and infills on structural responses. Pushover curves, generated with uniform force distributions proportional to masses for the principal directions and in both pushing directions (Figure 3), showed a notable difference in stiffness and base shear between the X and Y directions. This disparity is attributable to the building's design for gravity loads only, with a predominant orientation of frames and beams in the X direction. The inclusion of staircases (BFsm and BFsc models) led to an increase in base shear in the Y direction (parallel to the knee beams), while the effects in the X direction (perpendicular) were negligible. The IF models exhibited