PSI - Issue 37

G. Gusev et al. / Procedia Structural Integrity 37 (2022) 425–430 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 4. (a) The dependence of the deformation energy on the average compressive stresses in a representative volume; (b) the dependence of the deformation energy on the loading time steps.

The Figure 4 shows the dependence of the deformation energy on the average compressive stresses in a representative volume and on the loading time steps. Dependencies are constructed for a representative volume of a critically loaded node of a reinforced concrete structure. This criterion is used as follows. First of all, the problem of finding the limiting deformation energy for a representative volume of the node is solved. Next, the deformation energy is calculated in the same volume, but in an elastic formulation for the same model. The graphs show how they differ. And then we should talk about the mutual correspondence of energies at a certain stage of loading. This is necessary in order to assess the condition of reinforced concrete units as part of the whole building, since the solution of the problem of finding the ultimate deformations of the soil surface occurs in an elastic formulation. This approach is somewhat crude and has a number of assumptions. These include the dependence of the deformation energy of a representative volume on the properties of concrete and reinforcement, on the percentage of reinforcement in the concrete body and on the geometry of the node itself. But the assumption is made that for these forms of stress-strain state and other things being equal, the deformation energy can be compared and brought into line with the stated criterion. The criterion in this case is the work of external forces, which is necessary for destruction in a representative volume. This approach requires further study and organization of a large number of field experiments. Work is underway in this direction. To test this approach at this stage, the values of the main stresses in a representative volume were compared with the strength limits of the reinforced concrete structure, which are determined by the rule of mixture for composite materials based on the actual strength of the materials. This approach has paid off. A match was found. Further, taking into account the calculated limiting deformation energies, the behavior of various types of structures in the deformation zone of the Earth's surface was analyzed. The Figure 5 shows the dependences of the limiting deformations of the ground surface in the vicinity of the building for different stores of monolithic and prefabricated frame reinforced concrete houses. The maximum deformations of the soil surface correspond to the previously determined level of deformation energy in reinforced concrete, which is critical. The graphs also indicate the boundary, which is determined from the regulatory documentation. It can be seen that for different types of foundation structures there are big differences in the ultimate deformations both among themselves and from the standard value. It is safe to say that the normative literature requires correction. It can be seen that for some types of buildings the limits can be increased, while for others they need to be significantly lowered. These results formed the basis of the newly developed regulatory document, which is used at potash salt mining enterprises in the Urals. The behavior of a huge number of frames with different values of spans and different number of floors. Calculations were carried out for serial large-panel buildings. For each series of calculations, similar dependences are compiled and the limiting deformations of the soil surface in the vicinity of buildings are determined.