Fundamental period elongation of a RC building during the Pollino seismic swarm sequence

Abstract

a b s t r a c tA 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 M L = 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 (UdineNorthern 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.

Structural health monitoring of the Ferrara University before and after the 2012 Emilia (Italy) earthquake, and after the damage repairs

“…24,25 On one hand, we have examples such as the Navelli town hall, which suffered the 2009 Abruzzo earthquake, 26 and the primary school in the Rotonda city struck by the 2010–2014 Pollino swarm. 3 In both cases, the buildings showed multiple temporary period elongations which did not reflect in any increased damage. On the other hand, a permanent period shift accompanied by damage was observed both at a reinforced concrete building located in Bonefro during the 2002 Molise earthquake (Mucciarelli et al, 2004) and at the Mirandola hospital during the 2012 Emilia earthquake.…”

“…50 With this strategy, building frequency variations, either during or after an earthquake, can be easily observed, hence obtaining an immediate indication of the damage evolution. 3,26…”

“…These aspects promoted the current interest in real-time monitoring applications for early warning damage evaluation, which may be conveniently implemented using low-cost sensors. 3,4…”

“…However, this solution is typically costly and feasible only in a restricted set of circumstances. 5–9 An alternative to permanent monitoring is using ambient vibration measurements from which the fundamental period and damping can be retrieved using different techniques, namely, horizontal-to-vertical noise spectral ratio (HVNSR), 10–12 standard spectral ratio (SSR), 13 non-parametric damping analysis (NonPaDAn), 14 random decrement method (RDM), 15 and half bandwidth method (HBW), 16 Trifunac 17 and Gallipoli et al 3,18 confirmed that the fundamental frequency and damping from ambient vibrations are consistent with those obtained by forced vibrations for low input motion and provide a valid reference for a system vibrating within its linear range of behavior. In this study, we estimated the fundamental vibration period and damping of two buildings under low excitation generated by ambient sources such as wind or anthropic activity such as traffic and machinery (in the following, we will generally refer to these signals as “ambient vibration” 11,17,19,20 and weak motions).…”

Forecasting Time-Variable Earthquake Risk for Reinforced Concrete Buildings During Aftershock Sequences Based on Operational Earthquake Forecasting and Resonance Period Elongation

“…Clinton et al [16] and Astorga et al [17] showed the accumulated effect of successive earthquakes on frequency drop, in relation to the amplitude of seismic loading, for long-term structural monitoring. Furthermore, Gallipoli et al [18] reported the co-seismic frequency drop of permanent monitored buildings during main and aftershocks. Post-earthquake experimental surveys for building damage classification have also highlighted residual elongations.…”