A comprehensive understanding of the dynamic behavior of a tree can play a key role in the tree stability analysis. Indeed, through an engineering approach, the living tree can be modeled as a mechanical system and monitored observing its dynamic properties. In the current work, procedures of dynamic identification used in civil engineering are applied to the case study of a black locust (Robinia pseudoacacia L.). The tree was instrumented with 13 seismic, high-sensitivity accelerometers. Time histories of the tree response under ambient vibration were recorded. Three representative sections of the trunk (the collar, the diameter at breast height, and the tree fork) were equipped with three accelerometers, in order to obtain lateral and torsional vibrations. Moreover, two pairs of accelerometers were fixed on the two main branches. The results show that it is possible to identify the natural frequencies of a tree under ambient vibrations, thanks also to the support of a preliminary finite element model. Even though the optimal position is under the tree fork, the sensors fixed at the diameter at breast height allow a clear identification of the main peaks in the frequency domain.

The paper concerns an experimental study on the wind pressures over the surface of a worldwide known Gothic Cathedral: Notre Dame of Paris. The experimental tests have been conducted in the CRIACIV wind tunnel, Prato (Italy), on a model of the Cathedral at the scale 1:200, reproducing the atmospheric boundary layer. Two types of tests have been conducted: with and without the surrounding modeling the part of the city of Paris near the Cathedral. This has been done, on the one hand, for evaluating the effect of the surrounding buildings onto the wind pressure distribution on the Cathedral, and, on the other hand, to have a wind pressure distribution plausible for any other Cathedral with a similar shape. The tests have been done for all the wind directions and the mean and peak pressures have been recorded. The results emphasize that the complex geometry of this type of structures is responsible for a peculiar aerodynamic behavior that does not allow estimating correctly the wind loads on the various parts of the Cathedral based on codes and standards, which are tailored for ordinary regular buildings.

Urban trees are subjected to stressful conditions caused by anthropogenic, biotic, and abiotic factors. These stressors can cause structural changes, increasing the risks of branch failure or even complete uprooting. To mitigate the risks to people’s safety, administrators must assess and evaluate the health and structural stability of trees. Risk analysis typically takes into account environmental vulnerability and tree characteristics, assessed at a specific point in time. However, although dynamic tests play a crucial role in risk assessment in urban environments, the high cost of the sensors significantly limits their widespread application across large tree populations. For this reason, the present study aims to evaluate the effectiveness of low-cost sensors in monitoring tree dynamics. A low-cost micro-electro-mechanical systems (MEMS) sensor is tested in the laboratory and the field using a pull-and-release test, and its performance is compared with that of seismic reference accelerometers. The collected data are analyzed and compared in terms of both the frequency and time domains. To obtain reliable measurements, the accelerations must be generated by substantial dynamic excitations, such as high wind events or abrupt changes in loading conditions. The results show that the MEMS sensor has lower accuracy and higher noise compared to the seismic sensor; however, the MEMS can still identify the main peaks in the frequency domain compared to the seismic sensor, provided that the input amplitude is sufficiently high.