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The design, programming and implementation of a cost effective wireless structural health monitoring system (wSHMs) is presented, able to monitor the seismic and/or man-made acceleration in buildings. This system actually operates as a sensor network exploiting internet connections that commonly exist, aiming to monitor the structural health of the buildings being installed. Key-feature of wSHMs is that it can be implemented in Wide Area Network mode to cover many remote structures and buildings, on metropolitan scale. Acceleration data is able to send, in real time, from dozens of buildings of a broad metropolitan area, to a central database, where they are analyzed in order to depict possible structural damages or nonlinear characteristics and alert for non-appropriateness of specific structures.

Abstract. This work studies the effect ambient seismic noise can have on building constructions, in comparison with the traditional study of strong seismic motion in buildings, for the purpose of structural health monitoring. Traditionally, engineers have observed the effect of earthquakes on buildings by usage of seismometers at various levels. A new approach is proposed in which acceleration recordings of ambient seismic noise are used and horizontal to vertical spectra ratio (HVSR) process is applied, in order to determine the resonance frequency of movement due to excitation of the building from a strong seismic event. The HVSR technique is widely used by geophysicists to study the resonance frequency of sediments over bedrock, while its usage inside buildings is limited. This study applies the recordings inside two university buildings attached to each other, but with different construction materials and different years of construction. Also there is HVSR application in another much older building, with visible cracks in its structure. Sensors have been installed on every floor of the two university buildings, and recordings have been acquired both of ambient seismic noise and earthquakes. Resonance frequencies for every floor of every building are calculated, from both noise and earthquake records, using the HVSR technique for the ambient noise data and the receiver function (RF) for the earthquake data. Differential acceleration drift for every building is also calculated, and there is correlation with the vulnerability of the buildings. Results indicate that HVSR process on acceleration data proves to be an easy, fast, economical method for estimation of fundamental frequency of structures as well as an assessment method for building vulnerability estimation. Comparison between HVSR and RF technique shows an agreement at the change of resonance frequency as we move to higher floors.