Sensor Systems for Structural and Health Monitoring

The present research project aims at producing new scientific methodologies for designing spatially distributed sensors or dense sensor networks for the monitoring of engineering structures. Recently, the use of such sensor systems has been facilitated through cost reductions in smart sensor technology as well as advances in wireless technologies; however, there remains a lack concerning the proper structural interpretation of the measured sensor signal. Therefore, the project will focus on feasible spatial distributions or properly located and weighted dense sensor networks enabling an accurate sensing of structural entities with a well-posed physical meaning, such as relative displacements between the members of a structural system, or slopes of displacement fields, to mention only two examples. In this project, we will particularly focus on strain type sensors, such as piezoelectric materials. In the first part of the project we will concentrate on spatially distributed strain type sensors for structural monitoring of elastic or viscoelastic structures under dynamic loadings; both, for linear and nonlinear problems. Starting from three-dimensional continuum formulations, formulations applicable to elements and systems of structural mechanics, such as beams, plates, shells and frame structures, will be deduced. The spatial distribution of the sensors is represented by statically admissible stresses of the structure under the action of fictitious quasi-static force loadings. Such stress distributions are known to be non-unique and they can hardly be calculated analytically; hence, numerical methods will be used for their calculation. Based on the knowledge of spatial sensor distributions, the individual sensors of a dense network of strain type sensors will be located throughout the structure and the assignment of proper weights will result into a combined sensor signal, which approximates the spatially distributed sensor in an optimal manner. Moreover, multiple tunings of the sensor weights will yield as many different desired outputs as may be needed, resulting in the design of multi-purpose sensor networks for structural and health monitoring. We will use the non-uniqueness of statically admissible stresses to design multi-purpose sensor networks, which are able to detect local damage occurring in the structural elements and systems by directly measuring the jumps of those structural entities that experience discontinuities at certain points, lines or surfaces. In order to validate the developed sensor methodologies a significant part of the project will be dedicated to numerical and experimental investigations. Experimental work will be carried out concerning the use of strain type sensor networks to monitor structural entities directly related to either the vibrations of the structure or to local damage. The oriented basic research at the border between fundamental and applied research conducted in the present project will stimulate the increased practical application of dense sensor networks for structural and health monitoring of sensitive engineering structures.