Issue 50

C. C. Silva et alii, Frattura ed Integrità Strutturale, 50 (2019) 264-275; DOI: 10.3221/IGF-ESIS.50.22 267   2 1 EI k a   (3) where a is the distance between the parallel beams of the inverted "U-frame" mechanism, α is a coefficient depending on the position of the beam being considered. If the beam is at the end of the slab, α = 2, and for the internal beam, α = 3 (for internal beams with four or more similar beams, one can adopt α = 4). The term (EI) 2 represents the bending stiffness of the homogenized composite section of the slab, disregarding the tensile concrete, per unit length of the beam, taken as the lowest value between the stiffness in the middle of the span and in the internal support. Figure 3. Rotational stiffness of a composite beam (Oliveira [1]). Figure 4. Cracked slab bending stiffness (Calenzani [9]). The steel profile web rotational stiffness is obtained by considering the web as a cantilever plate in the geometric center of the top flange and free in the geometric center of the bottom flange where a force F acts, according to Fig. 5. The relation between the force F and the displacement δ 2 is given by the expression: 3 2 3 o F D h   (4)