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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The load-carrying capacity was assessed by comparing the equivalent stresses according to Mohr's theory for brittle bodies with the ultimate allowable stresses for the reinforced concrete structure in the tensile or compressive region depending on the percentage of reinforcement of the section, taking into account the mixture rule. The reinforced concrete elements were modeled in the volumetric formulation with generalized physical and mechanical characteristics. Thus, the deformation state of soil in the vicinity of the foundation was determined to be consistent with the limit value of the building. For example, the ultimate foundation soil deformations in the vicinity of the foundation for a monolithic reinforced concrete frame with a height of 5 floors, with a spacing of the bearing elements of 6 meters, with a section of columns-pillars of 300x600 mm were about 6.2 mm/m. The ultimate ground deformations are deformations, which correspond to the value of ultimate equivalent stresses, in the calculation of which the strength characteristics of concrete and reinforcement. In a similar way, the ultimate ground deformations have been determined for different variations of the structural design of buildings on different types of foundations. Further, in order to obtain a more qualitative assessment of the deformation process of reinforced concrete elements of monolithic structures, the boundary problems of the deformation behavior of the joints of monolithic columns with foundation slab were solved numerically (Figure 2). The numerical solution was obtained taking into account the physically nonlinear deformation of both the concrete body and the reinforcement body. Models of load bearing elements in the form of structural fragments were created. The boundary conditions and loading parameters were adopted on the basis of previous calculations in a series of more general statements. The task was to model the process of bearing frame fragment failure under the action of SSS caused by ground undermining conditions. Three fundamentally different loading schemes were used. The first one was bending of the column along its long side considering vertical load, the second one was oblique bending of the column considering vertical load, and the third one was oblique bending of the column. Problems have been solved taking into account forces of inertia by transient analysis method up to complete collapse of bearing elements. Figure 2 shows isofields of general strain intensity for one of the loading steps in the case of the first variant of loading conditions.

Fig. 2. Intensity of general strains for the model of the bearing fragment of the building - ground floor column.

Based on the results of the solution, the dependence of the relative stiffness of the supporting fragments (K) on the deformation energy (U) at all loading steps, which correspond to the proportion of load increment (figure 3 results for the variant of column - foundation slab coupling) was plotted. Line 1 is the bending of the column along the long side considering the vertical force, line 2 is the oblique bending of the column considering the vertical force, line 3 is the oblique bending of the column. Line 4 in Figure 4 is the result of the solution in the linear-elastic formulation, necessary to determine the relative stiffness of the fragment. The results are given for columns of 300x600 mm cross-section size with the percentage of reinforcement equal to 7%.