Monday, April 8, 2013
Special Mechanical and Civil Engineering Seminar
Early Warning, Aftershock Reliability, and Life Cycle of Degrading Structures: Performance-Based Earthquake Engineering at Three Scales
Iunio Iervolino, Associate Professor, Dipartimento di Strutture per l’Ingegneria e l’Architettura, Università degli Studi di Napoli Federico II
Time scales of seismic risk may be defined as: (i) real-time, that is during the event; (ii) near-real-time, that is in the aftershock sequence of a major earthquake; (iii) long-term life cycle of degrading structures. The seminar will present research developments to address risk assessment at these three scales.
(i) The tool to manage seismic risk in real-time is earthquake early warning (EEW). The basic elements of an EEW system are: seismic instruments, a processing unit for the data measured by the sensors, and a transmission infrastructure spreading the alarm to the end users. This alarm may trigger security actions, manned or automated, expected to reduce the seismic risk in real time. While, reasonably, to date the most of the research in this ﬁeld was led by seismologists, comparatively little attention was given by earthquake engineering. The key design points for EEW applied to a speciﬁc structure are: (a) the estimated earthquake potential on the basis of the EEW information; (b) the available time before the earthquake strikes or lead time; and (c) the system performance (proxy for the loss) associated to the case the alarm is issued. These issues are discussed in the talk and some results are presented, as well as a prototypal application. The final aim is to illustrate a possible performance-based approach to the design of structure-speciﬁc EEW.
(ii) Major earthquakes (i.e., mainshocks) typically trigger a sequence of lower-magnitude events clustered both in time and space. Because the structural systems of interest might have suffered some damage in the mainshock, possibly worsen by damaging aftershocks, the failure risk may be large until the intensity of the sequence reduces or the structure is repaired. The talk will present closed-form approximations for the aftershock reliability of simple damage-cumulating structures. Results show that, in the case hypotheses apply, the developed models may represent a handy tool for risk-informed tagging by stakeholders and decision makers.
(iii) Stochastic modeling of deteriorating structures at the scale of the life of the construction may include continuous degradation of structural characteristics and cumulative damage due to point overloads, such as earthquakes. The talk illustrates age-dependent models for life-cycle structural assessment, in terms of failure probability either absolute and conditional to different knowledge about the damage history.