ANALYSIS OF MODES AND FREQUENCIES OF NATURAL VIBRATIONS AND DYNAMIC STRESSES OF BRIDGE ABUTMENT FOUNDATION AND SOIL BASE

Purpose. The purpose of the research work is to determine, during the modal analysis, the modes and frequencies of natural vibrations of the railway bridge abutment together with the pile cap and pile foundation. A separate task of the research is to clarify the dynamic influence of the abutment structure on the possibility of vibrational displacements of the soil base. Methodology. To calculate the pile foundation of the abutment, which interacts with the surrounding massif, it was decided to use the finite element method (FEM) based on Structure CAD for Windows, version 7.31 R.4 (SCAD). To reproduce the features of the pile foundation of the abutment, a flat (quasi-spatial) model was used in the research. All dimensions of the pile cap and piles are adopted according to the design documentation for the construction of an actual overpass. Findings. An analysis of the stress-strain state results of the overpass abutment foundations, taking into account the train load, was performed, which made it possible to obtain a conclusion about the high bearing capacity of all parts of the “pile – pile cap” system for all considered types of load combinations with a safety margin of 8 and 7 times, respectively, which indicates normal operation in the future provided an unchanged state of engineering and geological conditions and loads. The pile material, class C30/35 concrete, fully withstands all types of loads represented by load combinations, taking into account the dynamic coefficient. The modal analysis of the overpass abutment foundations shows that the obtained frequencies and modes for the foundation are equal to 2.5 Hz (fundamental tone) … 6.6 Hz, and from comparing these frequencies with the liquefaction frequencies of wet sands (30 … 50 Hz) it is clear that the support's own vibrations cannot cause vibration-induced liquefaction. Originality. The originality of the conducted research lies in obtaining the parameters of dynamic displacements and natural vibration frequencies during the modal analysis of a railway bridge abutment Practical value. The practical value lies in substantiating the strength of the abutment structure under varying load combinations, as well as in determining that the dynamic impact of the rolling stock does not affect the vibrational displacements of the foundation soils.