Development of 3D Synthetic Ground Motions Compatible to Design Spectra

• Main Author: Adi Yasa, P.
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/39603
• Institution: Institut Teknologi Bandung

Seismic load is one of the important factors that must be considered, especially in earthquake-prone areas like Indonesia. The earthquake load in design, always depends on the response spectral that applies to the spesific site. For certain cases such as, nonlinear dynamic analysis, it is not enough based on the response spectrum on a site, But it requires earthquake data in the form of time series for design or safety check. Especially for Indonesia, there are still many areas that do not have earthquake data in the form of adequate time series to carry out nonlinear dynamic analysis. Therefore, spectral matching between the time series acceleration of earthquake to design code spectral, is solution to overcome the limited earthquake data in various regions in Indonesia. Spectral matching mostly are carried out independently for each direction, where the major earthquake direction is adjusted to the major target, minor direction to minor target, and vertical direction to vertical target. However, if it did independently, the correlation coefficient between the directions tends to be small, so the relationship between the componens of earthquake is not strong enough. Besides that, in applying Non-Linear Time History Analysis (NLTHA) the three earthquake’s components are analyzed simultaneously, this process illustrates the relationship between three componens of earthquake. Hence, in this study spectral matching is did in three dimensions (3D) with aim to provide strong correlation coefficient between its components. This research has developed several methods of 3D spectral matching in the frequency domain, so we could obtain the best method to make 3D accelerogram respond spectral very closely to target from the spectral code. When did spectral matching, it was carried out in dimensionless for all earthquake’s components and spectral design targets. Non-dimensional or dimensionless was did to obtain a non-dimensional artificial time series earthquake, which could be applied practically in various locations of the site that you wanted to review. In order to provide the best results when applies 3D spectral matching in frequency domain, there are three important steps that need to be added to the conventional frequency domain method. First, adjusting the original earthquake time interval which aims to filter noise at high frequencies, to tighten frequency intervals, and to optimize the amount of data in matching the spectra, or in other words, to increase capturing data at important frequencies. Second, making adjustments or renormalization the resultant of PGA every fifth iterations, this is intended to provide certainty that results PGA from spectral matching are close to the target. And the last is to use high and low band pass filter during modification of Fourier Amplitude Spectral (FAS), that aims to remove unadjusted frequencies, and to avoid aliased Fourier transforms by ensuring that FAS is close to zero at the end of the frequency. 3D spectral matching would apply for 20 different earthquakes to obtain a collection of 3D artificial time series compatible with seismic code spectral. Where the entire response spectral from the 20 earthquakes gave very good results on the spectral target on T / Tv ? 10. To apply time series results from spectral matching, which only need to scale ordinate and abscissa from each time series acceleration, with the resultan of PGA (AoG) and characteristic time (Tv) from the seismic zone and certain types of soil. Then, it will automatically obtain appropriate response spectral on the site being reviewed. Correlations of twentieth pairs of earthquake’s components from 3D spectral matching illustrate, the correlations between components for the same earthquake tends to be quite large, this can be seen especially for the Park-02 earthquake, Chi-Chi and San Salvador. Correlation coefisient with a large value indicates that componen has strong relationship between others components. Strong relationship between the components in the same earthquake is very reasonable, that because the correlation of components for some original earthquakes also tends to be quite large. In addition, the correlation of components for different earthquakes tends to be smaller, this is to ensure variations in the twenty types of earthquakes from 3D spectral matching that can be obtained.