Pipe concrete as a complex material, which effectively combines the advantages of steel and concrete, is used in the construction of high-rise and long-span structures and has good prospects for expanding the scope. At present, this is prevented by the relatively poor knowledge of the steel shell interaction with the concrete core under operational loads, when, due to the difference in the coefficients of transverse deformation of steel and concrete, the shell can detach from the core and lose its stirrup effect, which significantly increases the concrete strength. In the article in a linear-elastic formulation, the Lame problem is applied to a circular cylinder subjected to internal (for the shell) and external (for the core) uniform radial pressure, as well as an external centrally applied the longitudinal compressive force. The formulas for determining the stresses and radial displacements in the shell wall and core are obtained. The recommendations on providing the conditions for the joint operation of the shell and core, which are relevant, in particular, for the pipe-concrete kinematic racks of foundations protecting the buildings under seismic effects, are given.
Pipe-concrete structures are effectively used in the high-rise and long-span structures’ construction. This complex material has the properties that distinguish them from the conventional metal and reinforced concrete structures. However, the wider use of pipe concrete in construction, despite a large number of studies, is constrained by the lack of documents governing the calculation, design, production process technology and rather significant discrepancies in the experimental data of various authors on determining the interaction forces of the concrete element’s case and core. This is explained by the influence on their size: the method of applying the load (axial or with eccentricity, to the entire cross section or only to the core), its action duration, the ratio of the wall thickness to the cross section size, deformability and strength of concrete, the ratio of steel and concrete amount in the cross section. In this paper, based on the solution of the Lame problem for a circular cylinder, we obtain the formulas for the interaction forces between the core and the case, taking into account various factors. The yield strength of the case steel and the ultimate deformation of the concrete core are accepted as the criteria for the structure’s strength. Axial compression is considered without loss of shape stability, i.e. with a structure length not exceeding the five cross-sectional diameters, which usually corresponds to the length of columns in civil buildings.
The problem of determining the coefficient of averaging the deformations in tensioned reinforcement when calculating reinforced concrete structures according to the limiting states of the second group is considered. An assessment is made of the effect on it of the adhesion stresses distribution type between the reinforcement and the concrete.
The problem of determining stresses in a stretched reinforcement of inflexible eccentric-compressed reinforced concrete elements is considered when the height of the compressed zone in the limit state exceeds its boundary value corresponding to the condition of equal strength of the section. Instead of the generally accepted linear dependence of the stresses under consideration on the height of the compressed zone, an elliptic relationship more expedient from different points of view has been proposed.
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