PSI - Issue 64

Alessandra De Angelis et al. / Procedia Structural Integrity 64 (2024) 327–334 De Angelis et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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direction and 4 in the transverse direction) and cast-in-place r.c. slabs with a total height of 22 cm. The foundation system consists of a trellis of reversed "T" r.c. beams in the longitudinal direction of the building. The building presents a r.c. stair developing around an elevator. All the internal and external infill masonry walls are double brick walls with variable thickness. For the external perimeter, infill walls made with an internal layer of hollow clay bricks and an external layer of solid clay brick separated by an air gap are used while double hollow clay brick walls are used for internal partitions. At the semi-basement all the external perimeter walls are made of concrete. An example of plan with the distribution of external and internal infill walls is shown in Fig. 1a together with a longitudinal cross-section of the building (Fig. 1b).

Fig. 1. Building case study: (a) plan of the 2nd floor, (b) transverse cross-section and c) longitudinal cross-section

As already said, a first AVT (AVT n.1) was performed on the building in its as-built configuration using 20 uniaxial piezoelectric accelerometers to measure only the horizontal motion of the building. The roof, second, first and ground levels were instrumented in two corners with two monoaxial accelerometers measuring in two orthogonal directions and two pairs of sensors were added in the centre of the first and second level to evaluate the in-plane behaviour of the floor. A detailed description of the AVT can be found in De Angelis & Pecce (2018); here the main results of the experimental test are briefly recalled in terms of frequency and damping ratios in Table 1. The experimental mode shapes are graphically represented in Figure 2. As you can see, the first mode is translational in the transverse direction; the second and third mode, instead, are rototranslational; in particular, they both have counter clock wise rotation component with reverse translational components. The higher modes (fourth and fifth) are local and associated with independent movements of the individual alignments of frames, perhaps due to the deformability of the floors in its plane.

Table 1. Natural frequencies and damping ratios (AVT n. 1). Mode f [Hz] ξ [%] 1 3.19 2.16 2 3.89 3.57 3 4.16 3.86 4 8.69 3.09 5 9.88 3.49

Fig. 2. Experimental mode shapes (AVT n.1)