| Summary: | Deformation parameters of concrete are adequately studied under static uploading of samples until fracture. Methods of their determination during unloading (primarily due to the lack of experimental data) is not presented in the regulatory and scientific literature. That hinders the development of calculating methods of loadings for reinforced concrete structures, which vary according to certain cyclical regularities. The basis for computational models development for unloading are the results of the studies with short-term tests of concrete samples, where the sample is loaded to a predetermined level of compressive stresses, and then it is unloaded. The purpose of the research is to establish an analytical connection between stress and deformation parameters of concrete on axial loading and unloading branches with compressive stresses. The subject of the study is: axial and transverse deformation coefficient of transverse deformation volume deformations. The treated cycles have different values of maximum stress, including close to the limit values, taking into account the dilation of concrete. Permanent deformations during unloading are determined in increments of stress and strain by radial method. A connection is established between the initial elastic modulus of concrete and the modulus of deformation during unloading. On the basis of experimental data the analytical determination of the quantities depending on the residual strains for partial or complete unloading was offered. It was found out that in case of increasing stress level at the beginning of unloading the share of transverse strain increases and in case of full unloading, volume deformations increase. In case of unloading from the stress level, when dilatation property is manifested, they change the sign to the opposite, which is, become positive. The authors show a comparison of calculation results of the proposed method with experimental data obtained.
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