Multi-sensor measurement of dynamic deflections and structural health monitoring of flexible and stiff bridges

We investigated the response of bridges of different types to controlled and to wind and traffic-induced excitations; the emphasis was on deflections,derived from recordings of geodetic sensors and accelerometers (output-only analysis). Our focus was to push the limits of the existing experimental techniques, in order to cover not only flexible, but also stiff structures, and to present independently validated results. Our study focused on a 700m long, thin-deck cable-stayed bridge, a stiff steel pedestrian bridge, a historic composite (masonry/steel) train bridge and a 30m long, gradually decaying, currently swaying pedestrian timber bridge. Our basic strategy was first to develop data measurement and processing techniques using controlled (supervised learning) experiments, and then, (1) use collocated, redundant and distributed geodetic sensors (GPS/GNSS and Robotic Total Stations, RTS), as well as accelerometers, in order to record bridge excitations, especially con-trolled excitations leading to free attenuating oscillations;(2) develop techniques to denoise recordings of various sensors based on structural/logical constraints and sensor fusion, compensating for the weaknesses inherent in each type of sensor), validate results and avoid pitfalls;(3) monitor the episodic and gradual decay of a pedestrian bridge, through repeated surveys under similar loading and environmental conditions and using similar instrumentation.The output of our studies is to confirm the potential of modern sensors to measure, under certain conditions, reliable mm-level dynamic deflections even of stiff structures (3-6Hz dominant frequencies) and to provide firm constraints for structural analysis, including evidence for changes of first modal frequencies produced by structural decay, even to identify dynamic effects such as foundations response to dynamic loading

Perceived citizens’ satisfaction with climate change stakeholders using a multicriteria decision analysis approach

Summarization: The current need to adjust to the climate change requires urgent action to be taken both by the stakeholders involved in addressing climate change and by citizens. However, in order for citizens to be able to take part in such actions directly or indirectly, they will need to have a positive perception of the relevant stakeholders, so that a mutual relationship of trust and understanding is established. The objective of this study is to examine citizen satisfaction with the actions of the stakeholders involved in climate change. The study was conducted in Greece using a structured questionnaire; 1536 questionnaires were collected from January 2014 to June 2015 and the relevant data were processed using the MUSA method (MUlticriteria Satisfaction Analysis). The results of the study show that the citizens are not particularly satisfied, mainly with the actions of the governmental authorities involved in addressing climate change. In order to motivate citizens to take part in such actions in future, the relevant governmental bodies will need to increase their involvement and substantially improve their actions regarding the reduction of pollutants from industry and business, the level of civil protection and information provision, as well as public awareness and education on climate change.Παρουσιάστηκε στο: Environmental Science and Polic