THE EFFECT OF AFTERSHOCKS ON STRUCTURAL LIFETIME

Structures are generally under the risk of earthquake events, especially in regions with high seismicity. However,rather than occur individually, the seismic events tend to happen in sequence of the mainshock and the multiple aftershocks, which would cause additional damage to the damaged buildings in post-mainshock environment and increase the probability of collapse (Figure 1). When a mainshock occurs, it will be generally followed by a sequence of ground motions with relatively lower intensities. These small following seismic events are called “aftershocks”. Despite aftershocks usually having smaller intensities than their preceding mainshocks, their higher rate of occurrence will leave less time for repair or retrofit of the damaged buildings. Furthermore, if a building is considerably damaged in the mainshock event, the aftershocks will be more likely to cause further damage to the building, leading to the extra financial loss and fatalities. The downtime for building repairing after the seismic events would therefore be elongated with the occurrence of aftershocks. Hence, it is necessary to take the mainshock-aftershock sequence effect into consideration when performing seismic risk analysis (Yeo & Cornell, 2005). Most of the seismic risk assessment tools only consider an initially undamaged structure hit by one mainshock event. However, structures may be initially damaged from past earthquakes, and a seismic sequence is commonly made of a mainshock followed by series of aftershocks. In this post-mainshock context, during which the structure is not repaired, the rate of earthquake occurrence is significantly increased (due to the presence of aftershocks) and the physical vulnerability of possibly mainshock damaged buildings may also increase. In this context, the updated knowledge of the vulnerability of the damaged buildings is of critical importance to accurately assess the associated risk and guide building-occupancy policies after a main seismic event (YAO, 2019).

Keywords:

Structural Lifetime , Time-dependent fragility curve , Aftershoks , IDA , Performance