INFLUENCE OF THE TYPE OF FINITE ELEMENTS ON THE RESULTS OF DYNAMIC ANALYSIS OF A BRIDGE SPAN

Abstract

Increasing traffic volumes, increasing weight and speed of vehicles, as well as trends in modern bridge construction towards the use of new materials and lightweight structures increase the sensitivity of bridges to dynamic impacts and make traditional static calculations using a dynamic coefficient insufficient. A key aspect of ensuring reliability and durability is the accurate determination of dynamic characteristics, in particular natural frequencies and vibration forms, to prevent dangerous resonance phenomena. The purpose of this paper is to study the natural vibrations of a typical reinforced concrete road bridge span structure using the finite element method (FEM) and to compare the results obtained using different approaches to finite element modeling. The study was carried out in the LIRA-FEM software package by performing a modal analysis. Two objects are considered: a single reinforced concrete beam of a 24 m long span structure and a complete bridge span structure of the same length, consisting of five beams connected by a monolithic slab. Two computational models were created for each object: the first one using a combination of universal spatial rod and plate finite elements; the second one using universal spatial volumetric (eight-node isoparametric) finite elements. The first three shapes and their corresponding frequencies of natural oscillations are determined. The analysis of the results for an isolated beam showed a relatively small difference in the values of natural frequencies between the rod and volume models, which indicates the acceptability of using simpler models for individual beam elements. However, for the complete span structure, significant differences in frequencies between the two modeling approaches were found. This demonstrates the critical importance of choosing an adequate type of finite element to accurately model the dynamic behavior of complex spatial systems. The results confirm the effectiveness of FEM for the dynamic analysis of bridges and emphasize the need for a careful approach to the creation of computational models.