Measuring and Modelling Building Amplification Using Seismological Data

Ground motion produced by earthquakes induces a dynamic response in buildings, which can vary depending on the characteristics of the ground motion, as well as the building’s structural properties. The interaction between these factors determines the amplification of ground motion acceleration within the building. Specifically, the building’s response modifies the period content of the ground motion, amplifying periods that are near to the building's natural periods of vibration, which causes acceleration to be perceived differently at each floor of the building. Understanding the amplification of acceleration within a building is a key aspect of assessing the forces imposed on nonstructural components. Despite ongoing advances in structural earthquake resilience, the understanding and demonstration of building amplification and the resulting demands on nonstructural components is limited. This was demonstrated in the 2010 & 2011 Canterbury, 2013 Cook Strait, and 2016 Kaikōura earthquakes where the potential for nonstructural damage was highlighted, and has since prompted review on the current understanding of acceleration demands and nonstructural performance as described in the New Zealand building code. In this study, over a decade of structural array data from the GeoNet Building Instrumentation Programme is compiled and processed to examine the response of three instrumented mid- to high-rise buildings in Wellington to over 800 earthquakes in New Zealand with a focus on how ground motion is amplified within buildings. Fourier based analysis techniques are employed to observe and determine relationships between ground motion intensity and building amplification on a floor by floor basis. Additionally, real records of building response data are used to verify and evaluate newly proposed amplification models. Key findings reflect building behaviour varies significantly under weak versus strong ground motions, with structural properties observed to respond dynamically with increasing ground motion intensity. Both temporary and permanent elongation of the building's natural periods are observed during and following records of strong ground motion, such as during the 2013 Cook Strait and 2016 Kaikōura earthquakes, suggesting a reduction in structural stiffness. Existing amplification models based on modal superposition are tested using real ground motion data, and a new model is proposed that operates within the Fourier domain. The proposed model is evaluated using residual modelling techniques to compare the influence of structurally related parameters on model performance.