Damage Identification Analyses of a Historic Masonry Structure in T-F Domain

Abstract

Fatih mosque, a landmark structure in Istanbul, has suffered structural damage during 1999 Kocaeli earthquake. Using spectral, time-domain (OKID/ERA for SISO and MIMO models) and T-F domain (WT, HHT) techniques on ambient vibrations, damage identification has been performed. Results of parametric and spectral analyses indicate close global peaks. Northwest arch (O3) that was expected to move in harmony with other arches cannot display such a consistent behavior and produces additional local frequency at 24Hz due to damage. Southeast arch (O1) also has comparable damage producing another locality at 38Hz. Extending linear approaches into nonlinear-nonstationary methods, decompositions in WT and HHT improved the results in the temporal-frequency energy distribution. Estimated individual and global structural behavior are consistent with visually inspected damage states for O3 and O1. On a global scale, damage additionally generates significant nonstationarity on the neighbors in touch. Northeast arch (O2) is affected strongly by the anomalies appeared at stations O3 and O1. Especially neighbor stations O6 and O7 located at the springing points of the arch (O3) and others O5 and O6 located at the springing points of the arch (O2) are strongly affected due to tension rod failure causing the dome base to open outwards. T-F analysis detects and localizes any anomalous system behavior and can adequately capture the system dynamics of any instrumented part of the structure at any particular time epoch. For historical masonry structures with vulnerable components like large central dome and arches that have low redundancy, there is a need to develop automatic signal/image processing through, machine vision, and pattern recognition for early diagnosis and warning of gradual deteriorations.