This work investigates suitability of low cost Micro-Electro Mechanical System (MEMS) sensors in strong motion related studies, particularly in dense arrays utilized in producing quick shaking intensity maps. Two types of MEMS sensors and a reference sensor are tested under excitations of sweeping waves and scaled earthquake recordings. Transfer functions and correlation coefficients are compared. As for earthquake recordings, comparisons are carried out in terms of basic strong motion parameters and elastic response of structures that influences the design majors. The performance of the MEMS-50 sensor is also investigated on free field conditions. Different sensing characteristics are compared by performing time frequency analyses of small earthquake ground motion recordings of the MEMS-50 based accelerometer and of a co-located reference accelerometer. Test results show that the MEMS-50 sensor is able to record the mid-frequency dominant strong motion parameters with high correlation, where the high frequency components of the ground motion are underestimated. Such a difference in strong motion parameters on the other hand, does not manifest itself on empirical instrumental intensity estimations. Strong motion parameters from the reference and MEMS sensors converge to the same seismic intensity level. Hence a strong motion network with MEMS-50 sensors could be a modest option to produce peak ground velocity-based damage impact of an urban area under large-magnitude earthquake threats in the immediate vicinity. MEMS-5, which is an upper quality ensemble, is recommended for wide range of application including peak ground acceleration-based and peak ground velocity-based rapid shake maps.
Titreşim testleri ve sinyal analizleri Titreşim verileriyle mühendislik yapılarının dinamik davranışlarının tanılanılması Sonlu eleman yapı modelinin güncellenmesi ve güncellenmiş yapının yönetmelik çerçevesinde hasar görebilirlik analizleri
Fatih mosque, a landmark structure in Istanbul, has suffered structural damage during 1999 Kocaeli earthquake. Using spectral, time-domain (OKID/ERA for SISO and MIMO models) and T-F domain (WT, HHT) techniques on ambient vibrations, damage identification has been performed. Results of parametric and spectral analyses indicate close global peaks. Northwest arch (O 3 ) that was expected to move in harmony with other arches cannot display such a consistent behavior and produces additional local frequency at 24Hz due to damage. Southeast arch (O 1 ) also has comparable damage producing another locality at 38Hz. Extending linear approaches into nonlinear-nonstationary methods, decompositions in WT and HHT improved the results in the temporal-frequency energy distribution. Estimated individual and global structural behavior are consistent with visually inspected damage states for O 3 and O 1 . On a global scale, damage additionally generates significant nonstationarity on the neighbors in touch. Northeast arch (O 2 ) is affected strongly by the anomalies appeared at stations O 3 and O 1 . Especially neighbor stations O 6 and O 7 located at the springing points of the arch (O 3 ) and others O 5 and O 6 located at the springing points of the arch (O 2 ) are strongly affected due to tension rod failure causing the dome base to open outwards.T-F analysis detects and localizes any anomalous system behavior and can adequately capture the system dynamics of any instrumented part of the structure at any particular time epoch. For historical masonry structures with vulnerable components like large central dome and arches that have low redundancy, there is a need to develop automatic signal/image processing through, machine vision, and pattern recognition for early diagnosis and warning of gradual deteriorations.
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