SAFETY EVALUATION OF BUILDINGS BY AFTERSHOCKS

Earthquakes can affect the performance of civil structures significantly. Iran is located on Alpine-Caucasian-Himalayan belt, so earthquakes are major threats for the structural stability and safety in this country. Immediately after a seismic event, safety evaluation of buildings in the earthquake stricken area is essential for decision-making. In otherwords, post-earthquake structural safety assessment is a key to determine whether an earthquake-damaged structure is safe to re-occupy or not. Current assessment practices rely mostly on visual inspections conducted by experts and assign green, yellow or red tags on buildings that are apparently safe, restricted for use and unsafe to occupy, respectively. ATC- 20 is one of the most common guideline for this practice; it has a three-level evaluation methodology: rapid evaluation (emphasis is on the exterior of the building), detailed evaluation (requires a thorough examination of the interior and exterior of the building), and engineering evaluation (when visual inspections are not sufficient to determine damage to the building). Some researchers showed that the assessment results of visual inspections are subjective (Marshall et al., 2013;Galloway et al., 2014). Additionally, in an earthquake stricken area with widespread damage probably there are not enough well-trained engineers for safety assessment of the buildings. Being time consuming is another drawback of this method specially when there is a potential need for multiple inspections of some buildings, it conflicts with the need for rapid decision-making. Hence, there will be a need for a methodology which can complement visual inspections. For this purpose, some decision-support systems are devolved by different researchers. Mitrani-Reiser et al. (2016) introduced the “Virtual Inspector”, which is used to probabilistically estimate building safety and assign corresponding tags. Goulet et al. (2015) proposed a Bayesian probability updating scheme for vulnerability curves in order to reduce the number of buildings to inspect without losing information related to the damage on a city-scale. Jalayer et al. (2009) proposed a methodology could be used for post-earthquake decision-making between a set of viable actions such as, evacuation, shutdown, repair and re-occupancy. Since an important structural-identification application is residual-capacity assessment of earthquake-damaged structures, it can be an attractive method to overcome shortcomings of visual inspection. Reuland et al. (2019) proposed a model-based data interpretation method for determining structural safety based on system identification through ambientvibration measurements. There are several system identification methods based on structural response. A guideline for using the response-based methods is given in Table 1 based on the pros and cons of those methods (Xuan Kong et al., 2017). As ambient vibration measurements have a very low amplitude of excitation, using forced vibration measurements under aftershocks can be a natural response to this drawback; after a rare earthquake there is the imminent risk of aftershocks with rich frequency content which creates the opportunity for an objective post-earthquake assessment. This paper is focused on the safety evaluation of a building with a moment resistance frame, previously damaged by a mainshock, through aftershocks. The outcomes of this study can be useful for creating a new support decision system for post-earthquake safety evaluation of earthquake-damaged structures.

کلیدواژه ها:

System identification ، Post-earthquake building assessment ، Decision-support system ، Structural safety ، Forced-vibration measurements