The Internet of things concept empowered by low-cost sensor technologies and headless computers has upscaled the applicability of vibration monitoring systems in recent years. Raspberry Shake devices are among those systems, constituting a crowdsourcing framework and forming a worldwide seismic network of over a thousand nodes. While Raspberry Shake devices have been proven to densify seismograph arrays efficiently, their potential for structural health monitoring (SHM) is still unknown and is open to discovery. This paper presents recent findings from existing buildings located in Bucharest (Romania) equipped with Raspberry Shake 4D (RS4D) devices, whose signal recorded under multiple seismic events has been analyzed using different modal identification algorithms. The obtained results show that RS4D modules can capture the building vibration behavior despite the short-duration and low-amplitude excitation sources. Based on 15 RS4D device readings from five different multistorey buildings, the results do not indicate damage in terms of modal frequency decay. The findings of this research propose a baseline for future seismic events that can track the changes in vibration characteristics as a consequence of future strong earthquakes. In summary, this research presents multi-device, multi-testbed, and multi-algorithm evidence on the feasibility of RS4D modules as SHM instruments, which are yet to be explored in earthquake engineering.

The purpose of the paper is to show the great influence of nonlinear seismology in the analysis of the soil deposit response. Some elements about nonlinear seismology, the complexity of the seismic phenomenon are presented, and how we perceive seismic input for constructions at the surface of the earth. Further is presented the nonlinear behaviour of soil deposits during strong earthquakes as it results from resonant column tests (in laboratory) and from the spectral amplification factors (in situ records). The resonance phenomenon between natural period of a structure and soil deposit during strong earthquakes is analysed. All these studies have in common nonlinear behaviour of the soil deposit during strong earthquakes, in fact, the site where a new construction is built or an old one is rehabilitated and needs an optional assessment for mitigation seismic risk. All these studies stand up in supporting nonlinear seismology, the seismology of the XXI-st century.

Processed parameters from sensors located on seismically isolated buildings (maximum acceleration, spectral acceleration and oscillation periods) are compared against free-field ground motion to evaluate the improvement in seismic response for these buildings. The study is carried out for three structures in Bucharest, the capital city of Romania. The data used in this research correspond to moderate magnitude earthquakes, 4.2 ≤ M_W ≤ 5.5 generated from the Vrancea-intermediate-depth seismic area, with focal depths greater than ~90 km. The methodology helps to evaluate amplification/reduction in the seismic motion, and confirmed that base-isolation devices reduce the seismic parameters’ amplitudes of the structure directly above the isolating layer. The effectiveness of the base-isolation technique is further assessed by comparing the amplitude of the seismic parameters recorded under and above the earthquake protection devices. The results show a clear decrease in the values right above the isolating system, supporting the efficiency of base-isolation systems. The outcomes provide necessary empirical data for refining seismic design and improving the resilience of critical structures. The work contributes to the mitigation of the seismic risk in the city area, thus targeting a more resilient urban community and sustainable city through implementation of modern base-isolation systems for the retrofitting of vulnerable buildings exposed to a high risk of seismic hazards.

The impact of natural hazards on structures and infrastructures is a critical issue that needs to be properly addressed by both public and private entities. To better cope with seismic hazard and to mitigate the risk, long-term multi-sensor infrastructure monitoring represents a useful tool for acquiring information on their condition and vulnerability. However, the current increasing data volume collected using sensors is not suitable to be processed with classical standalone methods. Thus, automatic algorithms and decision-making frameworks should be developed to use this data, with minimum intervention from human operators. A case-study for the application of advanced methods is focused on the headquarters of the Institute for Atomic Physics, a 11-story reinforced concrete building, located near Bucharest, Romania. The instrumentation scheme consists of accelerometers installed at the basement, at an intermediate floor and at the top of the structure. The data were continuously recorded, starting with December 2013. More than 80 seismic events with moment magnitude, MW, larger than 3.8 were recorded during the monitoring period. The current study covers the long-term evolution and variation of dynamic parameters (one value per hour), based on both ambient noise sources and small and medium magnitude seismic events. The seasonal variation of these parameters will be determined, as well as their daily variation and the differences between values obtained from ambient noise and from earthquake-induced vibrations. Other atmospheric parameters (e.g. temperature, precipitation, wind speed) will be considered in future studies. The goal of the PREVENT project, in the framework of which the research is performed, is to collect multi-disciplinary data and to integrate them into a complex monitoring system. The current study achieved the first step, focusing on data from the seismic sensors and setting up the premises for a multi-sensor, multi-parameter, more reliable infrastructure monitoring system.