Issue 46

I. Shardakov et alii, Frattura ed Integrità Strutturale, 46 (2018) 383-390; DOI: 10.3221/IGF-ESIS.46.35 387 (a) (b) Figure 4: Impulse load: (a) – force evolution. (b) – Fourier transform. Scheme Vibrogram Fourier transform a b c Figure 5: Vibrograms and corresponding Foutier transforms for three loading schemes. A NALYSIS OF CHANGES IN VIBROGRAMS CAUSED BY CRACK INITIATION he proposed model (1)-(5), which passed the verification procedure, was used for numerical analysis of changes in the vibration parameters of the RC structure in the period of nucleation and propagation of cracks. The most probable places for crack formation in the structure are the connections of vertical columns with floor slabs and cross beams. In accordance with Fig. 6, we considered a fragment of the structure, for which we simulated the subsequent nucleation of cracks at the crossbar-to-column connections. Four crack nucleation stages were identified: the crack T1 appeared at the first stage, and cracks T2, T3 and T4 were successively formed at the next three stages. The numerical experiment consists in solving successively the problems of the dynamic deformation response of the structure to equal, locally applied impulse loads at all stages of crack nucleation. The examined structural fragment, the schemes of loading and registration of deformation response correspond to the scheme shown in Fig. 3b. To characterize the external force action, we used the parameters of the force impulse, determined experimentally at the stage of verification of the mathematical model. As before, the implementation of the numerical experiment was based on the finite element method using the ANSYS software package. To simulate the crack, we excluded from the calculation one layer of finite elements for concrete adjacent to the face of the column, retaining yet the finite elements for the reinforcement to provide simulation of its integrity. As already mentioned, the evolution of crack formation was determined by a sequence of 4 stages: the first stage is associated with the formation of crack T1 followed by successive nucleation of cracks T2, T3, and T4 at the next three T