PSI - Issue 44

Paola Sorrentino et al. / Procedia Structural Integrity 44 (2023) 1308–1315 Paola Sorrentino et al. / Structural Integrity Procedia 00 (2022) 000–000

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3. Case study 3.1. Description

The building case study (Figure 1) is a five-storey R.C. building characterized by free plans on the ground floors and by the presence of pilotis. Its height is equal to 16.48m with an interstorey-height of 3.20m. It is characterized by symmetrical plan composed by two rectangles (30mx12m) rotated and symmetrical to their transversal direction. The access to the apartments (four per floor) consists of two stair-blocks, located in the central zone of the rectangles.

B

B’

(a)

y

x

(b)

16.48

13.28

10.08

6.88

3.68

0.00

(c)

Figure 1. (a) Plan, (b) structural plan and (c) cross-section B-B’.

The frames are arranged only in transversal direction and the distance between frames axes is 4.8 m longitudinally and 8 m transversally. The columns are positioned backward from the facades: this solution allows the free design of the façade and the use of ribbon windows, with a clear reference to the 1927 Le Corbusier points of architecture. The stair blocks have frames also in the longitudinal direction. Each frame is characterized by the presence of two columns, backward from the facades. In the orthogonal direction there are perimeter beams loaded by the infill. The beams have a section of 23x80. The columns have hexagonal section at ground floor (that can be approximated to rectangular sections of 45x70) and rectangular on upper floors, having dimensions of 40x67 at the second level, 40x56 at the third one, 35x40 at the fourth level and 23x30 at the fifth one. The frames in correspondence of the stair blocks are characterized by beams and columns having dimension of 50x20 and 40x50, respectively. In the whole building, the concrete slab has a thickness of 20 cm. 3.2. Dynamic characteristics: natural frequencies and modes A simulated design has been carried out to define the geometry and reinforcement of structural elements. In this case the hexagonal sections of columns (pilotis) have been approximated to rectangular sections with dimensions of 45x70, assuming a percentage of smooth reinforcement equal to 0.7% of the concrete area. Smooth reinforcements in percentage of 0.7% and 1% of the concrete area for each column and beam, respectively have been adopted. The implemented materials are C20/25 concrete and Fe32k steel. A modal analysis has been performed to investigate the dynamic characteristics of the structure. In Table 1 the periods and participating mass ratios (given by the ratio between the modal mass and the total mass in the same direction) computed for each mode are listed. From the analysis of the first three vibration modes, it can be noted that the first mode is translational in x direction (longitudinal direction) with a period equal to 1.78s, the second mode is