Experimental and computer researches of hollow-core slabs oscillations

Abstract

The results of a free oscillations study of a reinforced concrete slab model, the prototype of which is a floor slab PK 30.12-8, manufactured at the enterprise LLC Velikodolinsky R/CC Plant, are presented. A stand for dynamic tests was developed, the testing of which was performed on a metal I-beam. For numerical analysis by the finite element method, engineering programs for calculating SCAD, ANSYS, and LIRA-CAD software were used. As a result of preliminary static tests, it was found that the cracking process in the slabs begins at the seventh stage of loading, with a load of 16.6 kN, which is approximately 0.6 of the actual breaking load Fult . In this regard, when determining the frequencies and forms of free oscillations, the authors proceed from the fact that deformation is elastic in nature not only in the absence of an external static load, but also when it changes in the range from 0 to 0.5 from the actual breaking load. With the onset of cracking, deformation becomes non-linear, and the modulus of elasticity of the material changes significantly. Based on these considerations, the frequencies of free vibrations were experimentally determined in the absence of an external load and the initial modulus of elasticity of the material, and then with a constant static load varying in the interval (0,50,9)Fultwith the step of 0.1 Fult with the corresponding values of the modulus of elasticity determined during static tests. The results of the experimental determination of the first five natural frequencies and their calculation in SCAD, ANSYS and LIRA-CAD are presented. An analysis of the obtained values shows good comparability of the experimental and calculated data. ANSYS and PC LIRA-SAPR give almost the same results, while the results of calculations in SCAD differ from them by 1.5-3%. At the same time, the frequency spectrum calculated in SCAD is lower than in the other two programs. The experimentally obtained frequency values were higher than in numerical simulation. Regardless of the deformation nature, the smallest discrepancy between the experimental and numerical values is observed for the lowest vibration frequency (within 6.5%). For other spectrum frequencies, this discrepancy averages 10–10.5%.