Radar interferometer application for remote deflection measurements of a slender masonry chimney

Seismic vulnerability of many cultural heritage masonry structures has been vital the recent years especially in seismic prone countries such as Italy. Due to the frequency of the seismic motions in time and due to many limitations, concerning the available knowledge and the seismic design of these stiff masonry structures, there is the necessity of non-contact and quick ambient response recordings so as to provide a structural integrity assessment. In order to improve the knowledge about the dynamic behavior of the slender masonry structures two main different analyses are necessary. The first goal is a territorial level assessment for the determination of the seismic ground motion. The second one concerns the knowledge of the dynamic characteristic of the existing structures. Recently, radar technique has been advanced by the development of microwave interferometers which serve non-contact vibration monitoring of large structures. The main characteristic of these radar systems, is the possibility of simultaneously measuring the dynamic deflection of many points on large structures. As a result, ambient vibration measurements can provide the identification of the modal properties of a structure. This paper reports a set of on-site applications of radar interferometer technique, aiming at evaluating the capability of measuring the vibration response of a slender masonry chimney in the Leonardo campus of the Politecnico di Milano. The results of the investigation highlight the accuracy and the simplicity of the technique for fast dynamic response measurements as well as the capability to detect temperature effects on the fundamental frequencies on the structure.