PSI - Issue 48

G. Gusev et al. / Procedia Structural Integrity 48 (2023) 169–175 Gusev et al/ StructuralIntegrity Procedia 00 (2023) 000–000

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Relative stiffness K is defined as the ratio of the reaction in the column in the case of nonlinear calculation, to the maximum reaction obtained from the calculation in the elastic formulation for the corresponding loading steps. Energy of deformation was calculated for the volume of the column at the junction with the slab. The height of the fragment for which the value of strain energy is estimated was 700 mm. According to the results of calculations and assessment of relative stiffness, it is clear that up to a certain loading step (pt. A on the diagram) the fragment behaves as an elastic body. At the following loading steps (up to pt. B) the absolute stiffness of the fragment decreases which is connected with the growth of cracks in the tensile zone of concrete section which corresponds to the protective layer of tensile reinforcement. The effective height of the section decreases. Further on the interval pt. B - pt. C, the column reinforcement in the tensile zone of the section, taking a significant part of the deformation energy, which leads to an increase in the absolute stiffness of the load-bearing fragment, is included in the work. At the loading section between pt. C and pt. D the cracks in the tensile zone of the section pass through the stretched reinforcement, and the absolute stiffness of the section continues to decrease. Defects begin to accumulate in the compressed zone of the section. Their growth starts from the corners of the column, at the junction with the foundation slab. The zone of failure in the compression area in this section is localized in the area of the protective layer of the reinforcement and does not go beyond it. After reaching the loading step, which corresponds to pt. D on the graph, the area of the fractured concrete in the compression zone reaches the compressed reinforcement, including it in the work. Further, the absolute stiffness of the fragment decreases significantly. The defects in the tensile and compressed zones of the column grow in volume. This deformation continues fleshing out until pt. E on the graph, which corresponds to the general loss of the carrying capacity of the fragment due to loss of integrity and the beginning of plastic deformations in the reinforcement. Up to pt. E throughout the entire loading interval, the rebar deformed as an elastic body.

Fig. 3. Dependence of the relative stiffness of the fragment on the strain energy at all stages of loading.

Fig. 4. Strain energy of the 300x600x700 mm volume of the most loaded column depending on the deformations of the soil mass in the foundation vicinity according to the calculations of the general problem.