ABSTRACT
It has been emphasized throughout the preceding chapters how the damping value of a mode of vibration governs the overall response in that mode of vibration. In the preceding chapters, it has been tacitly assumed that the damping value is constant and that it is based on a mechanism that is known not to be present in structures. In this chapter, the real situation, in which damping changes with amplitude, is explored. The non-linearities involved, whilst not large in absolute terms, make a large difference to the response of a structure. It is quite normal for damping to change by 100% of its value over the amplitude range involved with the response to wind or wave, whilst for earthquakes the value may change by up to 500%. This factor is perhaps rather significant in the conventional differences between such fields of study, and at the same time it emphasizes why they are merely sub-branches of the same systematic approach. Since the response of a structure is inversely proportional to the value of damping, such large differences are the dominant influence in the calculation of the response of a structure.
