A New Method for Propagation Analysis of Earthquake Waves in Damaged Buildings: Evolutionary Normalized Input-Output Minimization (NIOM)

The authors have developed a new method for wave propagation analysis--called evolutionary normalized input/output minimization (NIOM)--that models time-variant wave propagation by considering the time-variant statistical correlation between the strong motions recorded at different levels in the building. The NIOM results for actual damaged and undamaged buildings (which experienced the 1994 Northridge earthquake or the 1971 San Fernando earthquake), as well as those from an analytical elastic building model, were compared. All of these results showed two clear peaks that correspond to the incident and reflected waves propagating through the building in the vertical direction. The wave travel time was determined from these two peaks. In the case of the damaged buildings, the travel time increased during the earthquake; however, in the cases of the undamaged buildings and the elastic model, it remained almost constant during the earthquake. It was found that the change in the travel time is related to the change in the structural properties and to the degree of damage to a building. These results show that evolutionary NIOM is an effective new method for investigating the change in structural properties and the damage to buildings.