Modal identification of localised damage in beams and trusses: experimental and numerical results

Mariella Diaferio,Vincenzo Sepe,Gabriele Bellizzotti

doi:10.1007/s40091-019-00243-9

Abstract

The paper discusses the possibility of detecting local damages in complex structures typical of civil engineering, as multispan beams and trusses. Namely, it describes a procedure to identify localised cracks in structures in the elastic range of behaviour using only the values of natural frequencies in the intact configuration and in the damaged one evaluated by means of dynamic tests. The error minimisation procedure described in the paper selects the solution within a set of finite element models that simulate a range of positions and levels of damage, by identifying the damaged configuration as the one whose modal frequencies minimise the least-square difference with the measured data. The accuracy of the method is first investigated by applying it to the damage detection of a two-span steel beam, whose modal frequencies were obtained by means of experimental tests. To explore the accuracy of the proposed procedure, numerically simulated data with random noise were also generated for several positions and levels of damage and for different values of the random noise. The procedure was then extended, by means of numerical simulations, to the case of a beam with two localised damages. Finally, the procedure proposed for multispan beams is adapted to the damage identification of plane truss structures.

Highlights

The last decades have witnessed an increasing attention to health monitoring of civil structures, above all in case of existing buildings, for which retrofitting interventions are often required to guarantee prescribed performances during the time
2009; Rahai et al 2007; Moaveni et al 2008, 2009; Ramos et al 2010; Amani et al 2007). The importance of this tool is confirmed by the recent development of new modal identification procedures (Pioldi et al 2017) which make use of short duration and non-stationary data related to heavy structural damping
In case of a damage localised in small parts of a linear elastic structure, e.g., in few sections of a beam or in a rod of a truss, as considered in this paper, the comparison between dynamical parameters of the damaged and undamaged structures should, allow to identify at least the main characteristics of the damage, as location and severity

Summary

Introduction

The last decades have witnessed an increasing attention to health monitoring of civil structures, above all in case of existing buildings, for which retrofitting interventions are often required to guarantee prescribed performances during the time. The damage detection, i.e. position s and damage level p for a beam, element number # and stiffness reduction r for a truss, is performed by an error function which is defined as the square difference between the non-dimensional variation of the natural frequencies experimentally evaluated and the one obtained through the finite element model of the examined structure.

Results

Conclusion