%0 Journal Article
%T The influence of higher modes vibrations on local cracks in node of lattice girders bridges
%A S. Pradelok
%J Archives of Civil Engineering
%D 2012
%I Polish Academy of Sciences
%R 10.2478/v.10169-012-0013-0
%X Several previous investigations on failure of a certain type lattice girders railway bridge (on so called BJD line) have not convincingly explained reasons nor have they described potential hazards. This paper attempts to provide an answer, employing static, dynamic, and fatigue analysis of the structure, focusing on previously not analyzed vibrations of elements constituting a lattice node. Detailed models of two types of such nodes - damaged and non- damaged were compared, inside carefully defined limits of applicability. The research project was aimed at finding out the reasons behind lattice girders nodes cracking of railway bridge. The study outlines history of several previous investigations, that did not convincingly explained reasons of failure. The lattice girders that are subject of the study are a part of a railway bridge, which consists of six independent, freely supported steel spans. Four of them are mill rolled and two are apparently identical lattice girders. In one of lattice girders some cracking has been noticed. In second, twin lattice girder, supporting the same rail, such cracking does not occur. The research project focused on specific, particular circumstances for comparative investigation. Detailed models of two types of such nodes (damaged and non-damaged), as well as detailed models before and after repair were analyzed. The study suggests that the main reasons of damage are local static and dynamic influences and all real level strains. Modern numeric analysis of bridges provides very accurate results, dependant largely on accuracy of the calculation model. It is therefore necessary to verify theoretical calculation results empirically. Field tests provide good basis for verification and analysis of quality of theoretical models. The paper describes how a specific placement of deflection sensors made possible recording of main natural vibration frequencies in the subject bridge. The empirically detected frequencies confirmed the ones identified by the theoretical analysis. Specific placement of sensors (accelerometers and tensometers) allowed further detection of local vibration patterns in two nodes being subject to the tests. Prevailing part of the power spectrum density was identified near the theoretically obtained natural frequencies of transverse girders near to the dilatation. The analysis, confirmed by the empirical tests, allowed unambiguous explanation of the damage cause, and the reason it appeared only in one of two twin bridge spans.
%K bridge
%K vibrations
%K cracking
%K detailed models
%K dynamic analysis
%K fatigue analysis
%U http://versita.metapress.com/content/t82vw71818786361/?p=991819865f9d42179756c9bfa57ad00b&pi=5