Damping in buildings for wind-resistant design based on a stick-slip model

I am posting a download link to a copy of my dissertation here for those of you who are interested.




Damping is said to be one of the most important parameters in the wind-resistant structural design of buildings. But, damping is also known to have high uncertainty, which leads to low reliability in the design. Current estimation formulas and early research on structural damping, particularly, are associated with stick-slip mechanism. But these current models have only shown this qualitatively. In the end, these models fitted formulas to databases of full-scale experimental data. This dissertation therefore aims to quantitatively study the stick-slip mechanism itself to derive a theoretical expression, and finally, to apply the derivation to actual physical structure data to illustrate that stick-slip damping is indeed a valid model. The study starts from a very simple one-degree-of-freedom (1DOF) system with one stick-slip component (1SSC), to a more complicated 1DOF system with a large number of SSC (NSSC). The study also briefly touches on the damping of SSC inside MDOF systems. The study of MDOF with NSSC systems is necessary because actual physical structures are such.

The study starts in Chapter 1 with an extensive literature review that covers the significance, history, methodologies, current practices, and issues in current practices in damping estimation. Then in Chapter 2, damping amplitude dependency due to one stick-slip component is characterized by carrying out a parametric analysis using results of free vibration response analysis of a 1DOF model, which is meant to represent a mode of vibration, with one stick-slip component. The stick-slip component is essentially a nonlinear element with a force-displacement relationship similar to an elasto-plastic damper. A theoretical expression is subsequently derived for such a very simple system and validated against the numerical results.

In Chapter 3, a parametric analysis is next performed considering various probability distributions and parameters for 1DOF systems with a large number of stick-slip components to characterize damping in such systems. An analysis of MDOF systems is also presented, showing that the 1DOF approach is valid. The findings also show that damping due to stick-slip components always show an increase and then subsequent decrease with amplitude. This has been observed from actual full-scale measurement data. Using a few examples, it can be shown indeed that damping in real structures can be characterized using a stick-slip damping model. The results also show that damping could also reach a maximum and maintain a constant level for one order of magnitude, at least for one case. This suggests that current damping predictor models are valid, but here, it is qualified that they are valid only for a narrow amplitude range on which such models were derived from.

Based on the preceding results, a framework for deriving structural damping predictor models based on stick-slip mechanism is proposed in Chapter 4. Simple applications, including modification of existing models and through one example damping measurement on a 300m-high tall concrete building in Hong Kong, are presented to show how the framework can be applied.

In Chapter 5, damping estimation using a stick-slip model is illustrated for a laboratory-scale and a full-scale experimental model, where measurements were carried out on the basic structure (without stick-slip component) and on the structure with stick-slip components. This helped to clearly identify the damping effect of the stick-slip components. Damping estimation is also applied to a 200m-high steel building, and three other full-scale buildings. The effects on wind response are also discussed, showing that the increase in wind loads using this model would not be so large.

As concluded and summarized in Chapter 6, this study has shown that a stick-slip model could indeed be used to describe the primary mechanism behind structural damping in buildings, which could be used for estimating damping in wind-resistant design.

You can download the whole dissertation at this link: http://sdrv.ms/1bqrAQ8

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