Logarithmic decrement of vibrations of aluminum alloy bridges

Abstract

Introduction. The paper presents the materials of theoretical analysis and the results of experimental studies of determining the values of the logarithmic decrement of vibration of aluminum alloy bridges, which is a key factor in calculations of bridge structures for dynamic effects. In the regulatory documentation of the Russian Federation on design of aluminum alloy bridges, there are no data for determination of logarithmic decrement of vibration. The content presents the results of research on this issue and recommendations for eliminating this shortcoming and improving the current regulatory documentation of the Russian Federation. Materials and methods. The factors influencing the values of the logarithmic decrement of aluminum bridge structures have been studied, recommended values of the logarithmic decrement of bridge vibrations depending on the materials used and design solutions are given. The results of analysis of field researches of dynamic parameters of three pedestrian bridges made of aluminum alloy 1915 T1: the bridge with a span of 40.1 m across Ryazanskaya st. in Tula and two bridges with span of 10 m in the floodplain of the Yauza river in Moscow, conducted by the NRU MGSU in 2020 are presented. The bridges have load-bearing structures in the form of vertical side trusses with a triangular diagonal lattice. To identify the values of natural frequencies the bridges were studied in the mode of natural vibrations caused by impact force. Velocities of the motions of characteristic points of the bridges were recorded on the basis of which after computer processing the values of frequencies and decrements of natural vibrations have been calculated. Results. During dynamic tests of the studied aluminum alloy bridges 1915 T1, it has been established that each frequency of the natural vibration corresponds to the value of decrement. By increasing the bridge span values of natural frequencies and their corresponding decrement values significantly decrease, the values of the decrements for the first frequency are affected by the supporting conditions, for the second frequency, the values of the decrements depend only on the material properties and the construction solution. Conclusions. Decrease of vibration decrement values leads to increase of material consumption to ensure standard operating conditions. When designing complex and critical bridge structures using high-strength aluminum alloys the decrement values should be established in the course of scientific and technical support and experimental research of these alloy grades.