Master's lecture in Civil Engineering - Rajan Dhakal

Master's student: Rajan Dhakal

Title: System identification and seismic analysis of residential RC building in Kathmandu, Nepal

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Faculty: Faculty of Civil and Environmental Engineering

Advisor:  Rajesh Rupakhety, Professor

Other member of the masters committee: Said Elias Rahimi, Post Doc at the Earthquake Engineering Research Centre, University of Iceland

Examiner: Sigurbjörn Bárðarson, Engieneer at Norconsult ehf

Abstract

This study focuses on experimental system identification, numerical modelling and seismic analysis of an existing reinforced concrete frame building located in Kathmandu, Nepal. System identification is performed with basic theoretical background along with brief introduction to different methods. Demonstrations of the different methods are depicted using response simulated from known simple single degree of freedom (SDOF) and multi degree of freedom (MDOF) systems which are then used for system identification. As a case study, system identification of a four-storied reinforced concrete building located in Kathmandu, Nepal is considered. Two methods of system identification techniques--Welch spectral method and N4SID method--are used for estimation of modal properties. The estimated natural periods of the building are 0.264s and 0.266s for the two fundamental modes of vibration in the two principal directions. The corresponding damping ratios are estimated to be 6.3% and 6.9%.  Finite element models with and without soil flexibility are created on Etabs2017 to study overall differences in the model properties compared to results from system identification. The estimated natural periods are 0.226s and 0.207s for model with rigid soil and 0.275s and 0.259s for model with flexible soil for the first two fundamental modes of vibration in the two principal directions. Study finds that the natural periods of the structure, estimated by finite element model, significantly depend on supporting conditions. When the structure is assumed to be built on rigid soil, the estimated vibration periods are lower than those identified from ambient vibration. While, estimated natural periods for model with flexible soil support are very close to those identified from ambient vibration. This shows the importance of modelling soil flexibility for accurate dynamic characterization of buildings using finite element model.