Ambient and Forced Vibration Testing and Finite Element Model Updating of a Three Storey Post-Tensioned LVL Building

Abstract

The Nelson Marlborough Institute of Technology (NMIT) Arts and Media building was recently constructed in 2011 and consists of three seismically separate complexes, the Media building, Workshop building and Arts building. The Arts building is focused on herein as it showcases the use of coupled post-tensioned LVL shear walls which are part of the innovative "Pres-Lam®" system developed by the University of Canterbury. Experimental testing was combined with the use of finite element modelling to obtain an understanding of the buildings dynamic performance with in the linear range. This research was part of a larger instrumentation program developed to investigate the wind and seismic response and long term deformations of the NMIT building The objective of this research was to determine the value of testing of a 'real' building while it was under construction. Ambient testing was performed at three stages during construction and was combined with Forced Vibration Testing (FVT) for the final stage. Results from the testing were analysed using the Peak Picking, Enhanced Frequency Domain Decomposition, and Data Driven Stochastic Subspace Identification methods. A comprehensive Finite Element (FE) model was created of the building which was updated with the results from the FVT using sensitivity based iterative updating. It was shown that the addition of non-structural elements such as the cladding and the staircase increased the natural frequency of the first mode and second mode by 19% and 24% respectively. The addition of the concrete floor topping as a structural diaphragm significantly increased the natural frequency of the first mode but not the second with an increase of 123% and 18% respectively. The elastic damping of the NMIT building at low level vibrations was identified as being between 1.6% and 2.4%. Unexpected floor performance meant that the FE model did not correlate well with the experimental results. Updating however improved the correlation of the model with the first and fourth mode. The results show that there is significant value in performing this kind of testing in the development of an instrumentation program.