Davide Trapani

Low Power Wireless Sensor Network for Building Monitoring

A wireless sensor network is proposed for monitoring buildings to assess earthquake damage. The sensor nodes use custom-developed capacitive microelectromechanical systems strain and 3-D acceleration sensors and a low power readout application-specified integrated circuit for a battery life of up to 12 years. The strain sensors are mounted at the base of the building to measure the settlement and plastic hinge activation of the building after an earthquake. They measure periodically or on-demand from the base station. The accelerometers are mounted at every floor of the building to measure the seismic response of the building during an earthquake. They record during an earthquake event using a combination of the local acceleration data and remote triggering from the base station based on the acceleration data from multiple sensors across the building. A low power network architecture was implemented over an 802.15.4 MAC in the 900-MHz band. A custom patch antenna was designed in this frequency band to obtain robust links in real-world conditions. The modules have been validated in a full-scale laboratory setup with simulated earthquakes.

Validation of MEMS acceleration measurements for seismic monitoring with LVDT and vision system

Recent improvements in Micro-Electro-Mechanical Systems (MEMS) and wireless transmission technologies today allow researchers to overcome some of the limitations of tethered structural monitoring systems, such as their high installation and maintenance costs. This paper presents a new-generation monitoring system based on MEMS and wireless transmission. This is an integrated system consisting of a set of small acceleration and strain sensors, distributed within the structure. The sensors have on-board computational capabilities and can transmit recorded data to a remote acquisition unit. This unit automatically records and interprets the data, and provides the user with a damage index representing the structural safety after a seismic event. Specifically developed algorithms which estimate the displacement time histories based on the accelerations recorded during the earthquake are used to perform this task. The aim of this paper is to assess the reliability of these algorithms, by comparing the output of the prototype monitoring system in terms of displacement with data from other measuring systems, such as linear voltage displacement transducers (LVDT) and multiple cameras.

MEMS-based sensors for post-earthquake damage assessment

The evaluation of seismic damage is today almost exclusively based on visual inspection, as building owners are generally reluctant to install permanent sensing systems, due to their high installation, management and maintenance costs. To overcome this limitation, the EU-funded MEMSCON project aims to produce small size sensing nodes for measurement of strain and acceleration, integrating Micro-Electro-Mechanical Systems (MEMS) based sensors and Radio Frequency Identification (RFID) tags in a single package that will be attached to reinforced concrete buildings and will transmit data using a wireless interface. During the first phase of the project completed so far, sensor prototypes were produced by assembling preexisting components. This paper outlines the device operating principles, production scheme and operation at both unit and network levels. It also reports on validation campaigns conducted in the laboratory to assess system performance. Accelerometer sensors were tested on a reduced scale metal frame mounted on a shaking table, while strain sensors were embedded in both reduced and full-scale reinforced concrete specimens undergoing increasing deformation cycles up to extensive damage and collapse. The performance of the sensors developed for the project and their applicability to long-term seismic monitoring are discussed.

Structural Health Monitoring for Seismic Protection of Structure and Infrastructure Systems

Structural Health Monitoring (SHM) of civil-engineering structures is becoming more and more popular both in Europe and worldwide mainly because of the opportunities that it offers in the fields of construction management and maintenance. More precisely, SHM offers several advantages in terms of reduction of inspection costs, because of a better understanding of the behavior of both structures and infrastructures under dynamic loads, seismic protection, observation in real or near real-time, of the structural response and of evolution of damage. Therefore, it is possible to produce post-earthquake scenarios and support rescue operations. In this context, this paper provides a review of different technical aspects of SHM summarizing some sensor validation methodologies for SHM. Following that, recent progresses on SHM of buildings subjected to seismic actions and relevant ways to detect damage are recalled. Moreover, some aspects of SHM of tunnels and bridges are covered. Some related applications that use sensor networks designed by the University of Trento and a startup are described, pointing out the solutions adopted to build reliable SHM systems. Finally, concluding remarks and promising research efforts are underlined.

Uncertainty evaluation of after-earthquake damage detection strategy

After-earthquake assessment of buildings in terms of safety and usability is nowadays performed by technicians who are called to give their judgement based on in-field surveys and visual inspections, often conducting the surveys in the absence of objective data. This implies additional inconvenience for residents and economic losses in the affected area. A near real-time assessment based on objective data related to the seismic response of the structures is possible through the use of monitoring systems that provide observations on the state of the monitored structure, obtaining information on its dynamic response. One of the most reliable parameters that can be correlated to the state of a structure after an earthquake is the ductility demand, expressed in terms of interstory drift. Using acceleration time-history records from the ITACA (Italian Accelerometric Archive) strong-motion database, we investigate the main sources of uncertainties in the estimation of displacement time-histories and interstory drift, using the method of double integration of the acceleration measurements alone. We have found that in general the instrumental uncertainties have less importance than the uncertainties of the model, in particular in the presence of residual displacements at the end of the seismic motion.

Full-scale laboratory validation of a wireless MEMS-based technology for damage assessment of concrete structures

This paper illustrates an experimental campaign conducted under laboratory conditions on a full-scale reinforced concrete three-dimensional frame instrumented with wireless sensors developed within the Memscon project. In particular it describes the assumptions which the experimental campaign was based on, the design of the structure, the laboratory setup and the results of the tests. The aim of the campaign was to validate the performance of Memscon sensing systems, consisting of wireless accelerometers and strain sensors, on a real concrete structure during construction and under an actual earthquake. Another aspect of interest was to assess the effectiveness of the full damage recognition procedure based on the data recorded by the sensors and the reliability of the Decision Support System (DSS) developed in order to provide the stakeholders recommendations for building rehabilitation and the costs of this. With these ends, a Eurocode 8 spectrum-compatible accelerogram with increasing amplitude was applied at the top of an instrumented concrete frame built in the laboratory. MEMSCON sensors were directly compared with wired instruments, based on devices available on the market and taken as references, during both construction and seismic simulation.