دانلود رایگان مقاله افزایش طول دوره اساسی ساختمان RC در طول توالی ازدحام لرزه Pollino

Abstract

A primary school in Rotonda was monitored during an on-going seismic sequence in the Pollino area, Southern Italy. The Reinforced Concrete (RC) building is a typical three story building with a concrete frame, bearing pre-cast slab flooring, concrete block internal walls and pre-cast external infill slabs. The monitoring began in September 2011 with a single station on top of the building, and after the ML = 5 mainshock occurred in October 2012 a network was completed with accelerometers on each floor and real-time streaming data was transmitted to the Istituto Nazionale di Oceanografia e Geofisica Sperimentale (Udine-Northern Italy). The school suffered no visible damage during the sequence. The real-time monitoring of the Rotonda school proved to be important for two reasons: (1) the large range of magnitudes and recorded peak accelerations allowed the study of the non-stationary frequency response; (2) the results also show how a simple, real-time monitoring system using cost-effective accelerometers could be used as a tool to provide information on the damage state and usability of the school.

7. Conclusions

During the Pollino (Southern Italy) seismic swarm we installed inside the Rotonda school a monitoring system with real time data transmission that was set up in a short time after the mainshock, substituting a pre-existing single station, trigger monitoring. Permanent instrumentation can then provide relevant detection of changes based on observation of period elongation. It was then possible for Civil Protection authorities to gain useful information in deciding if a building is safe for use, requires inspections or has to be abandoned, according to the three thresholds usually adopted after earthquake crisis for building inventory. This requires a continuous recording also since the frequency recovery may be long, that may also provide false alarm situation if the interpretation of the period elongation is not complete. The building in Rotonda provided another very important result in the discussion about the importance of temporary vs permanent period elongation for damage assessment. The building suffered during the mainshock a spectral acceleration at the top floor reaching almost 2 g, which caused a period elongation of about 50% that was completely recovered attime ofthe first recorded aftershock three hours later and thus has to be considered a purely temporary variation. Since post-event, onsite verification showed that the building suffered no damage, this suggests that to testify onset of damage, the presence of a permanent variation seems to be more important than a temporary variation even if it is a large one. Finally, cost-effective MEMS accelerometers proved to be reliable for the identification of main dynamic parameters of buildings even when weak ground motion occurs (below 0.01 g) and for relatively stiff buildings (frequency >1 Hz). We hope that this could open the way to a widespread, real-time building monitoring in the same way that MEMS based instruments are now used to build extra-dense networks to map ground shaking in California [33] and in New Zealand [34]. A first attempt of cost-effective accelerometric monitoring of strategic building for civil protection purpose will start this year in the North-Eastern region of Italy ([35]).