A case study on model updating of long uniform buildings

In the Structural Health Monitoring (SHM) framework, model updating procedure is an iterative or cyclical process which gives numerical model of structure having modal behaviour close to the dynamic behaviour of real structure. Normally for structures with or without any expansion joints typical model updating procedure is used. But the typical procedure may not be applicable for long uniform buildings having expansion joints since the individual blocks in structure connected with expansion joints tend to vibrate in coherence. This behaviour is confirmed by observing the identicalness of modal frequencies of individual blocks in long uniform buildings. This phenomenon was observed in three selected long uniform buildings. When structures connected with expansion joints vibrate in coherence or when the modal frequency of the connected structures are identical, the numerical models of these structures cannot be updated using typical procedure for the following reasons: (1) Modal parameters from Modal identification of structure doesn’t represent the actual parameters of the individual block since the ambient vibration is not independent and is influenced by interaction between blocks. (2) Modal analysis of analytical model of individual structural blocks gives dynamic parameters which are true to the model. And these two sets of parameters can’t be compared for convergence in model updating procedure. Therefore, to update a numerical model of long uniform buildings with expansion joints having the coherence phenomenon among its individual blocks, a different is needed. Hence, a new approach is proposed where instead of using modal parameters from analytical analysis, the parameters obtained for the structure from modelled floor responses to weak earthquake using Frequency Domain Decomposition (FDD) algorithm are used for checking convergence in model updating procedure. To demonstrate the proposed procedure, two long uniform buildings in which the coherence phenomenon was observed were updated by applying the proposed procedure and results are discussed. Here for the selected buildings, only modal frequencies were used for checking convergence, since mode shapes obtained were not reliable as floor vibration data of intermediate floors were not available.