Abstract:
A Synchronous noise is a broad — band time series, which looks like random noise but has an absolutely flat power spectrum. It is a much stronger version of the white noise as it has exactly equal magnitude at all the calculated frequencies of its Desecrate Fourier Transformation (DFT). A synchronous noise is effectively used in this work to study the single input and single output nodal response of a structure in detail for different excitation without analyzing the whole structure for each excitation.
Synchronous noise, of same duration and sampling period as that of earthquake, is• first generated. This is to excite the fixed node of the model of structure. The structure is then analyzed and response of the required node for synchronous noise input is determined. Fourier transformation of this nodal response is really the transfer function of the node with respect to the ground motion. Frequency domain convolution between this transfer function and the DFT of any other earthquake excitation of any fixed node gives DFT of the nodal response for earthquake excitation. Inverse DFT of this sequence thus yields the time history response of the node. Thus, for studying the response of a node for different earthquakes, one has to only analyze the structure once with synchronous noise input.
In this dissertation work a plane frame, and then space frame (multistoried building) is studied for earthquake excitation. All this cases, first, time history response of a node is determined analytically using commercially available software for synchronous noise input as well as for a given earthquake excitation. Nodal response of the synchronous noise input is then used to fine the nodal response for the earthquake using the proposed transfer function approach. Earthquake responses determine through analysis and through transfer function is then compared. It shows exactly matches the responses for each case of excitation.
