PSI - Issue 78

Franco Braga et al. / Procedia Structural Integrity 78 (2026) 285–292

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• by virtue of the previous point, the stress on the edge of block 1 (black dashed line shown inFig.2 a) is considered pure shear; • the seismic action, calculated in correspondence with the horizontal section of the acceleration spectrum S a (T), is evaluated as 2.5∙PGA/q (PGA is the peak ground acceleration, q is the structure factor) even for configurations whose proper period does not fall in correspondence with the horizontal section of the graph of S a (T); • the balance of forces (hence the stresses in the deck planes) refers to the undeformed configuration of the structure. Furthermore, it should be noted that the calculations were carried out using the values of the following variables as a basis • earthquake in the direction parallel to the Y axis; • m equal to 8, n equal to 4 (see Fig. 1); • pillars arranged according to a square mesh of side 5.5 m; • spacing between the pillars, both according to X and Y, equal to 5.5 m; • building dimensions in plan, according to X and Y, 16.5 m x 38.5 m; • number of floors varying from 2 to 8; • reinforced concrete spatial frame with X-Y structural mesh of 4 pillars in the X-direction and 8 pillars in the Y direction • storey height of 3.3 m; • floor slab with a thickness of 4 cm • concrete type C20/25 (maximum calculation tensile stress f ctd equal to 1.06 MPa); • weight of the building concentrated on the floors and evaluated, for each floor, at 10 KN/m 2 ; • pillar rigidity evaluated for α =8 (value corresponding to the most frequent cases, i.e. frames with beams partly emerging, partly thick). Finally, it should be noted that, in order to make the simulation more faithful to possible real situations, the calculation was carried out with and without the presence of a stiffening core positioned in correspondence of block 1 (the stiffening core consists of two reinforced concrete walls parallel to the direction of the earthquake, each having a thickness of 0.20 m and a length of 1 m); the stiffness of the stiffening core was evaluated assuming α =3 (a value attributable to the most common static schemes, due to the high stiffness of the core itself). 3. Stress state, stresses and deformability of the decks The following graphs represent the results of the simulations carried out; they show, in abscissa, the number of floors (2, 4, 6, 8) and the PGA of the seismic action expressed in g (0.10, 0.15, 0.20), in ordinate, the work rate or maximum "exploitation" of the concrete identified in the manner indicated below. The parameter used as a reference for evaluating the structural commitment of the slab in its function of distribution between the columns is represented by the ratio between the shear V and the shear resistant surface of the s∙DY slab section: = ∙ (4) The value σ c of the tensile stress to which the concrete is subjected coincides with the value of τ c since the stress is pure shear; therefore, the work rate or "exploitation" of the concrete is equal to the ratio R = τ c /f ctd which, if greater than 100%, indicates that the limit capacity has been exceeded, i.e. the tensile failure of the slab. In the following graph (Fig.3), which represents a frame configuration with a structural mesh of 4 x 8 columns, no. of floors varying from 2 to 8, PGA varying from 0.10 g to 0.20 g, the exploitation rate R of the concrete varies strongly depending on whether the stiffening core is absent (Fig.3 a) or present (Fig.3 b). In the case of an absent stiffening core (Fig.3 a), the maximum value of R is always less than 100%, varying from approximately 10%, for the 2-storey configuration and PGA equal to 0.10 g, to approximately 44% for the 8-storey