FREQUENCY MONITORING IN A STRUCTURE ON SOFT SOIL BY MEANS OF N4SID IDENTIFICATION METHOD

Frequencies are identified in a reinforced concrete structure composed by a building of 22-storey founded on soft soil, in Mexico City. This structure suffered damaged during the earthquake in 1985 being subsequently repaired. Since 2008 and by means of accelerometers, ambient vibration and seismic records have been registered. The objective of this paper is to analyze the use of N4SID subspace identification method to monitoring the frequencies of the building. To achieve this, ambient vibration records and moderate intensity earthquakes records are used in the identification process, where N4SID results are compared with those ones by using minimization modal method. Results are consistent in identifying the most representative vibration frequencies. The advantage by using N4SID subspace identification method is on a low-cost computer processing, its online implementation is feasible.