INVESTIGATION OF DYNAMIC RESPONSE OF AN INSTRUMENTED BUILDING DURING THE CEPHALONIA 2014 SEISMIC SEQUENCE

Abstract eng:
In the beginning of 2014, the island of Cephalonia in Greece was struck by two major earthquakes: a M6.1 on January 26, 2014 (followed by a M5.5 aftershock on the same day) and a M6.0 on February 3, 2014. Both earthquakes were found to be related to the Cephalonia Transform Fault, a dextral strike-slip fault with a thrust component. Due to the proximity of the epicenters to the island, very high peak ground values were recorded by the permanent strong motion network maintained by EPPO-ITSAK and the NOA’s Institute of Geodynamics, as well as an additional, temporary network deployed by EPPO-ITSAK in the meisoseismal area of the island on January 27 and 28 2014. During the Feb 3 event, a PGA=0.77g was recorded at Havriata village (the highest ever recorded in Greece), while a comparable PGA=0.68g was recorded at the town of Lixouri. In spite of the intensity of the events, the overall response of the building stock in the island was very satisfactory, with rather limited damage. On February 5, 2014 the Earthquake Engineering research team of EPPO-ITSAK instrumented a building in the town of Lixouri with a special accelerometer array in order to record its response to various aftershocks. The selected building is the new administrative building of the Lixouri hospital. The building (a two-storey one with basement) was erected in 2009, according to the 2003 Greek New Seismic Code, which is compatible to a great extend to Eurocode 8 (EC8). Given the intensity of both the 26/1/2014 and 3/2/2014 events (PGA=0.54g and 0.68g respectively at Lixouri), the building exhibited a remarkable behavior, with essentially no damage to either its load bearing structural system or the infill walls. For the instrumentation nine uniaxial sensors were used, in sets of three at three different levels of the building: its basement, the first floor and the terrace (Figure). At each level, two uniaxial sensors were placed in parallel along the floor’s extreme edges, and the third was placed in an orthogonal direction along one of the other two edges. In this way it is possible to record both the translational response of the floor diaphragms along two orthogonal directions, as well as their torsional response. The recorded response of the building to various aftershocks was used to assess its actual dynamic characteristics (eigenvalues, eigenmodes, damping ratios). These were then be used to properly calibrate finite element models of the structure that were developed in order to reliably represent its actual dynamic behavior and to further investigate its overall satisfactory response to seismic excitations, and in particular the two aforementioned major events. The whole effort is expected to help enrich the EPPO-ITSAK’s research contribution on the seismic response of civil engineering structures.

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