Keywords: diagnostic systems, magnetic methods, construction monitoring, civil engineering, structural health monitoring.

Monitoring of civil engineering structures is an important issue as a result of the rapid development of modern building techniques and the growing fatigue wear of concrete and steel structures such as market halls, bridges etc. Adaptation of these systems is essential for online assessment of the technical state of these structures and could limit the possibility of catastrophic disasters.

This paper presents a concept of a comprehensive diagnostic approach that could increase the reliability of the diagnosis of the early stages of the development of structure defects. Therefore as a solution a distributed monitoring system based on different available signal sources [1] capable of evaluating the current technical state of the construction is being developed and tested. As a source of information data from fibre Bragg grating (FBG) sensors, classical strain gauges, passive magnetic field and acceleration sensors are considered [2].

Magnetic sensors are used for measuring changes in the magnetic field of the structure which occurres as a result of the elastic deformation of truss member [3]. An exemplary procedure of a construction's diagnosis consists of using magnetic measurements for finding the critical object's nodes, and then constant monitoring of stress limits that take into account the range of the permanent and elastic deformation.

The approach proposed in this paper and used in the system assumes the use of a verified and validated finite element numerical model for inferring the causes of changes in the dynamic response of the structure. Changes in the dynamic properties of the structure, detected by the SHM system permits inferences to be made on the technical state of object. Changing loads or the development of cracks influence the modal parameters of the structure monitored. As a result of the use of the finite element model it is possible to reduce number of acceleration sensors thus reducing costs and processing power.

The implementation of the distributed monitoring system [4] makes it possible to implement the automation of the analysis, decrease costs related to the maintenance of large scale infrastructure structures and to increase the reliability of a structure.

1

A. Galezia, S. Gontarz, M. Jasinski, J. Maczak, S. Radkowski, J. Senko, "Distributed system for monitoring the large scale infrastructure structures based on analysis of changes of its static and dynamic properties", Second International Workshop on Smart Diagnostics of Structures, Krakow, Poland, 2011.

2

S. Radkowski, S. Gontarz, J. Maczak, M. Kujawinska, G. Dymny, K. Malowany, "Experimental comparative testing of steel structures by strain gauges, Digital Image Correlation and magnetic field methods", The Eighth International Conference on Condition Monitoring and Machinery Failure Prevention Technologies, Cardiff, 2011.

3

S. Gontarz, S. Radkowski, "Impact of Various Factors on Relationships Between Stress and Eigen Magnetic Field in a Steel Specimen", Magnetics, IEEE Transactions on, 48(3), 2012. doi:10.1109/TMAG.2011.2170845

4

J. Maczak, "Structure of distributed diagnostic systems as a function of particular diagnostic task", 20th International Congress on Condition Monitoring and Diagnostic Engineering Management, Faro, Portugal, 2007.

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