This research focused on applying vibration-based model updating to estimate the structural properties of high-rise buildings using a discrete Timoshenko beam model. Previous studies by Moretti et al. [1] and Taciroglu et al. [2] showed limitations in estimating the structural properties of buildings using model updating with a uniform Euler-Bernoulli beam model or a uniform Timoshenko beam model. Both models were not able to describe the third measured bending mode accurately after updating. Moreover, with the uniform Euler-Bernoulli beam model, when only the lowest two bending modes were used to fit the model, the estimates of the rotational stiffness of the foundation around the y-axis, Kr,y, showed significant uncertainty after model updating, with a Coefficient of Variation (CV) of 46.9%. Therefore, this research aimed to improve the accuracy of structural property estimations for high-rise buildings by using a more detailed model.
The model updating method applied in this research was an indirect vibration-based technique, which adjusted the input parameters of the chosen model to minimize the difference between the model output and the measured data. Both the model output and the measured data were in the shape of natural frequencies and mode shapes. The technique was applied to two high-rise buildings: the residential tower New Orleans, which is bending-dominant in behavior, and the office tower Delftse Poort, which is shear-dominant in behavior and exhibits irregular stiffness across its height. The discrete Timoshenko beam models used to approximate the dynamic behavior of these buildings were created using the Finite Element (FE) models of the buildings.
The research findings highlighted several key aspects essential for obtaining more accurate estimations of the structural properties of high-rise buildings. For a more accurate estimation of parameter Kr,y, it is of importance to incorporate shear deformations in the model and to account for irregular stiffness along the height. For the New Orleans, using the discrete Timoshenko beam model led to estimates of parameter Kr,y with low uncertainty, indicated by a Coefficient of Variation of 6.91%. This was an improvement compared to the study by Moretti et al. [1], which showed a Coefficient of Variation of 46.9% using the uniform Euler-Bernoulli model.
Moreover, obtaining accurate values for the bending stiffness was crucial for achieving more precise estimations of the structural properties. It was challenging to determine the bending stiffness values using the FE models. These challenges posed a problem for model updating, as the initial structural property ratios were maintained for both high-rise buildings. Maintaining these ratios gives weight to the initial structural property values. These values must be correct. Otherwise, model updating is limited by the incorrect ratios and will not be able to accurately match the measured modal properties.
For the Delftse Poort, more pure bending modes were needed for better accuracy. The discrete Timoshenko beam model was unable to match the measured second bending mode in the y-direction, as it exhibited twisting, which the model could not represent due to its limitation to pure bending modes. Furthermore, since the discrete Timoshenko beam model requires a single displacement value per height but multiple sensors were used to measure displacements, the measurements had to be averaged. This averaging process may led to a mode shape that deviates from the actual behavior, resulting in an inaccurate representation of reality.