Keywords: optoelectronic, radar, optical fibre, digital signal processing, numerical simulation, finite element methods, resonance frequencies, natural modes.

Technological innovation provides the ability to establish a system of continuous or discontinuous control of certain parameters which is called monitoring. The process of knowing the properties and structural response of a building, particularly heritage construction and those located in seismic zones, involves a complex, costly and operationally difficult to spot tests, samples, laboratory testing and structural analysis. This work is often impractical for the cost and time required.

The present work is focused on finding laser interferometric methods using technology able to capture and develop the embryonic state of excitement through the dynamic auscultation of an environmental nature (mainly wind and environmental noise).

The aim of the paper is to survey the testing methods using optical and interferometric microwave technologies that are able to provide some preliminary tests for the structural assessment of historical constructions by means of natural, environmental and induced force excitations. In the current work structural assessment in two slim constructions: a) industrial chimney placed in Aldaia (Valencia) and b) Gilet (Valencia) church bell tower.is presented.

The project is undertaken is based on the combination of three technologies:

1. the interferometric laser to follow the small displacements in 5 cm diameter circles and their vibrations,
2. radar interferometric for measuring the sub-milimetric displacements and vibration,
3. deformation by optical fibre using Bragg grating sensor arrays.

The analysis involves a digital signal processing in the time and the spectral domain and the response assessment compared with the numerical simulation of the construction.

In this way, the measurements have been obtained by providing the optical sensor and piezoelectric at the top of the structure that is the point where, for the flexural excitement is the most significant deformation caused by lower energy excitation, both corresponding to the first mode of vibration of the cantilever. It has been relatively easy to obtain the value of the frequency corresponding to the first mode of vibration.

A sharp difference between the frequency of vibration obtained by modelling the structure with the finite element method and that obtained with the Optoelectronic method is observed. This is mainly results from the modelling of the structure where the surface irregularities that exist in the structure in the form of cracks have not been reproduced in the numerical model.

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