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Showing 2 results for Frequency Content

G. Ghodrati Amiri, A. Asadi,
Volume 7, Issue 4 (12-2009)
Abstract

Future design procedures for civil structures, especially those to be protected from extreme and blast related

loads, will need to account for temporal evolution of their frequency content. There are, however, several instances

where acceleration time histories are required as seismic input. For example, to determine the ultimate resistance and

to identify modes of structures’ failure, a nonlinear time history analysis is needed. In other cases, acceleration time

histories are required for linear analyses. Many seismic codes require this type of analysis for buildings which have

irregularities. The process of time-frequency analysis made possible by the wavelet transform provides insight into the

character of transient signals through time-frequency maps of the time variant spectral decomposition that traditional

approaches miss. In this paper an approach is examined and a new method for processing the ground motion which is

modeled as a non-stationary process (both in amplitude and frequency), is proposed. This method uses the best basis

search algorithm with wavelet packets. In this approach, the signal is expressed as a linear combination of timefrequency

atoms which are obtained by dilations of the analyzing functions, and are organized into dictionaries as

wavelet packets. Several numerical examples are given to verify the developed models.


M.a. Rahgozar,
Volume 13, Issue 3 (12-2015)
Abstract

The interactive effects of adjacent buildings on their seismic performance are not frequently considered in seismic design. The adjacent buildings, however, are interrelated through the soil during seismic ground motions. The seismic energy is redistributed in the neighboring buildings through multiple structure-soil-structure interactions (SSSI). For example, in an area congested with many nearby tall and/or heavy buildings, accounting for the proximity effects of the adjacent buildings is very important. To solve the problem of SSSI successfully, researchers indicate two main research areas where need the most attention: 1) accounting for soil nonlinearity in an efficient way, and 2) spatial analysis of full 3D soil-structure models. In the present study, three-dimensional finite element models of tall buildings on different flexible foundation soils are used to evaluate the extent of cross interaction of adjacent buildings. Soil nonlinearity under cyclic loading is accounted for by Equivalent Linear Method (ELM) as to conduct large parametric studies in the field of seismic soil-structure interaction, the application of ELM is preferred over other alternatives (such as application of complicated constitutive soil models) due to the efficiency and reliability of its results. 15 and 30 story steel structures with pile foundations on two sandy and clayey sites are designed according to modern codes and then subjected to several actual earthquake records scaled to represent the seismicity of the building sites. Results show the cross interaction of adjacent buildings on flexible soils, depending on their proximity, increases dynamic displacements of buildings and reduces their base shears. 



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