International Journal of Civil Engineering

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Showing 4 results for Ghodrati Amiri

RELIABILITY OF NONLINEAR STATIC METHOD IN SEISMIC PERFORMANCE PREDICTION OF REINFORCED CONCRETE FRAMES WITH MEDIUM DUCTILITY

Ghodrati Amiri G., Sedighi S.,
Volume 2, Issue 4 (December 2004)

Abstract

In the past decade design procedure changed to �performance-based design� from�force-based design�, by this mean many researchers focused on nonlinear static analysis (NSA)and the procedure named �PUSHOVER�. Advantages of this method are defining the inelasticbehavior of structure without nonlinear dynamic analysis (NDA) effort and also defining plastichinges formation in critical elements, and the order of formed plastic hinges. In spite of these goodadvantages NSA is limited to short and planar structures and application of that in tall andtorsionaly asymmetric structures may yield unreliable results.In this study reliability of NSA is investigated by performing both nonlinear static and dynamicanalysis on six 2D moment resisting concrete frames. Non linear dynamic analysis has been doneby the suggested method in FEMA356 guideline called �Target Displacement Method�. A groupof 4 different lateral increasing loads were used in pushover analysis and 3 different groundmotions were applied in NDA. Results indicate that same responses can be obtained by performingNSA, but errors will be increased by frames height increment.

Earthquake Duration and Damping Effects on Input Energy

M. Khanzadi, G. Ghodrati Amiri, G. Abdollahzadeh Darzi,
Volume 5, Issue 1 (March 2007)

Abstract

According to performance-based seismic design method by using energy concept, in this paper it is tried to investigate the duration and damping effects on elastic input energy due to strong ground motions. Based on reliable Iranian earthquake records in four types of soils, structures were analyzed and equivalent velocity spectra were computed by using input energy. These spectra were normalized with respect to PGA and were drawn for different durations, damping ratios and soil types and then effects of these parameters were investigated on these spectra. Finally it was concluded that in average for different soil types when the duration of ground motions increases, the input energy to structure increases too. Also it was observed that input energy to structures in soft soils is larger than that for stiff soils and with increasing the stiffness of the earthquake record soil type, the input energy decreases. But damping effect on input energy is not very considerable and input energy to structure with damping ratio about 5% has the minimum value.

Determination of Design Acceleration Spectra for Different Site Conditions, Magnitudes, Safety Levels and Damping Ratios in Iran

G. Ghodrati Amiri, F. Manouchehri Dana, S. Sedighi,
Volume 6, Issue 3 (September 2008)

Abstract

By application of design spectra in seismic analyses, determination of design spectra for different site conditions, magnitudes, safety levels and damping ratios will improve the accuracy of seismic analysis results. The result of this research provides different design acceleration spectra based on Iran earthquakes database for different conditions. For this purpose first a set of 146 records was selected according to causative earthquake specifications, device error modification and site conditions. Then the design acceleration spectra are determined for 4 different site conditions presented in Iranian code of practice for seismic resistant design of buildings (Standard No. 2800), different magnitudes (MsO5.5 & Ms>5.5), different damping ratios (0, 2, 5, 10, 20 percent) and also various safety levels (50% & 84%). Also this research compares the determined design spectra with those in Standard No. 2800.

Comparison of Different Methods of Wavelet and Wavelet Packet Transform in Processing Ground Motion Records

G. Ghodrati Amiri, A. Asadi,
Volume 7, Issue 4 (December 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.

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