Latest issue

International Journal of
Earthquake Engineering and Hazard Mitigation
(IREHM)
September 2013 (Vol. 1 N. 1)

by Amir H. Gandomi (Founding Editor)

Hybridizing Genetic Programming with Orthogonal Least Squares for Modeling of Soil Liquefaction

by Amir H. Gandomi, Amir H. Alavi

Abstract - Precise estimation of the strain energy density required to trigger soil liquefaction, denoted as capacity energy, has been the focus of many studies. The main objective of this paper is to develop a robust prediction model for the soil capacity energy using a novel hybrid technique coupling genetic programming with orthogonal least squares, called GP/OLS. The proposed model was developed upon experimental results collected through a literature review. A traditional genetic programming analysis was performed to benchmark the GP/OLS model. The predictions made by the derived model were found to be more accurate than those provided by the genetic programming and other existing models. A subsequent parametric study was carried out and the trends of the results were confirmed via some previous laboratory studies.

Keywords: Genetic Programming, Orthogonal Least Square, Soil Liquefaction, Capacity Energy, Formulation.

Role of Records During the 2011 off the Pacific Coast of Tohoku Earthquake in Seismic Resistant Design of Nuclear Power Station

by Shuichi Kamagata, Izuru Takewaki

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Abstract - The 2011 off the Pacific coast of Tohoku earthquake (Mw9.0) had two main wave phases. They are precious records produced by the series of large earthquake. This phenomenon can be interpreted using the concept of the consolidated-type earthquake. The after-shock (Mw7.1) occurred near the Oshika peninsula on April 7th as the intra plate earthquake. We mainly analyzed the seismic records which were measured at the underground of the Onagawa Nuclear Power Station (NPS). The typical displacement pulse wave was identified by the Ricker wavelet. The directivity of the ground movement was detected. This agrees with the direction of permanent movement measured by GPS system. From the displacement profile from O.P.17.0m to O.P.-128.4m, the uniform deformation of underground soil was found and was evaluated from the shear strain in the underground. The non-stationary Fourier spectra indicated that the maximum amplitude of seismic record (O.P.-8.6m; Onagawa NPS) was comparable with that of the code-specified S2 artificial wave and this fact corresponds to the small damage of the Onagawa NPS. Furthermore the seismic records at the Kashiwazaki-Kariwa NPS during the Niigata-ken Chuetsu-oki earthquake and at the Hamaoka NPS during the Suruga-Bay earthquake in 2009 were compared with the code-specified design motion (S2 artificial wave). The validity of the current code for the NPS is discussed.

Keywords: Consolidated-Type Earthquake, Inland-Type Earthquake, Onagawa Nuclear Power Station, Directivity of Ground Movement, Amplification in Surface Soil, Relation of Shear Stiffness and Shear Strain, Seismic Design Code, S2 Artificial Wave, Non-Stationary Fourier Spectra, Maximum Amplitude Spectra, Ricker Wavelet, K-Net, Kik-Net.

Influence of Concrete Behaviour Modelling on Nonlinear Response of Oscillators

by A. Azarbakht, F. Masoomian

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Abstract - A set of 4620 single-degree-of-freedom oscillators have been taken into consideration which has different natural periods, different critical damping ratios and different backbone curves. The initial concrete cracking phenomenon was taken into account in the considered backbone curves. Two sets of ground motion records were also selected to be representatives of free-field and near-field events. The incremental dynamic analysis was performed in order to quantify the seismic demand in different intensity levels. Then, the relationship between natural period, ductility factor and strength reduction factor was derived versus intensity measure. Influence of each input variable was also studied in which revealed that the natural period and the concrete initial cracking have significant influence on the seismic demand of oscillators.

Keywords: Strength Reduction Factor, Ductility, Natural Period of Vibration, Nonlinear Spectrum, Near Field, Far Field.

Next Generation Attenuation Models and Time Independent Probabilistic Seismic Hazard of Darjeeling-Sikkim Himalaya

by Sankar Kumar Nath, Manik Das Adhikari

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Abstract - We deliver Next Generation Attenuation (NGA) Model and Time-independent Probabilistic Seismic Hazard Maps of Darjeeling-Sikkim Himalaya based on enriched earthquake catalogue, upgraded tectonic database, seismological database and seismotectonic implications. For consideration of near and far-field source effect, we synthesize a strong motion database by using finite-fault stochastic modeling & frequency wave number (FK) integration. NGA models have been developed for three tectonic types’ in the region viz. normal, strike-slip and thrust faulting. In addition, a regional seismic source characterization is performed using Brune circular crake model. Small to Moderate magnitude earthquakes nucleating at hypocentral depths <70 km in the region recorded by IIT Kharagpur Darjeeling-Sikkim Strong Motion Array (DSSMA) seemed to have Brune stress drop ranging between 0.75 and 147 bars. In compliance with the National Earthquake Hazard Reduction Program (NEHRP) & Federal Emergency Management Agency (FEMA) regulations a geotechnical site characterization is performed using effective shear-wave (S-wave velocity (V_s³⁰) distribution based on soil taxonomy, composition, grain size, lithology and topographic gradient implicating site classes: A (S-wave velocity, β > 1500 m/s), B (β = 760-1500 m/s), C (β = 360-760 m/s) and D (β = 180-360 m/s). Generic site amplification for each site class is estimated as per elevation from the recorded accelerograms of about 300 seismic events in the terrain that has provided a site amplification variation from 2.5 to 8.5 with the predominant frequency ranging between 4.0 Hz to 18.0 Hz. Probabilistic Seismic Hazard Analysis (PSHA) can be performed using both the time-dependent and the time-independent approaches. The present study follows the time-independent protocol using layered polygonal as well as tectonic sources and a logic tree frame work to consider both the epistemic and aleatory uncertainties in the magnitude, rupture distance and the several combinations of attenuation relations already existing for the terrain and also developed as a part of the present investigation. For seismic hazard analysis, the earthquake source model is composed of layered polygonal seismogenic sources, fault seismogenic sources, several combinations of attenuation relations, seismicity parameters and maximum credible earthquakes for all tectonic types prevalent in the region. The hazard maps in terms of Peak Ground Acceleration (PGA), Pseudo Spectral Acceleration (PSA) at 0.2 sec & 1 sec for 10% probability of exceedance in 50 years with a return period of 475 years for Darjeeling-Sikkim Himalaya have been generate in GIS platform. The PGA distribution shows a variation between 0.265g and 0.640g. Maximum hazard distribution is associated with the active tectonics viz Main Boundary thrust (MBT), Main Central Thrust (MCT) and Main Frontal Thrust (MFT). The major urban centers like Gangtok, Mangan and Darjeeling depict higher hazard level to the tune of 0.64g. The design response spectra generated from the estimated PGA and PSA at 1.0 sec & 0.2 sec provide an updated scenario significantly higher than the existing Bureau of Indian Standard (BIS) codal provisions.

Keywords: Seismic Source Attributes, NGA, Seismic Source Zone, Logic Tree Frame Work, PSHA.

Seismicity of Oltenia Region of Romania through the Effects of the Major 1977 Vrancea Earthquake on Related Housing

by M. Calbureanu, R. Malciu, E. Albota

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Abstract - This scientific paper reveals the main characteristics of Oltenia Region in order to evaluate the seismicity of this important zone from Romania South West Region. There are presented the geomorphological map and also the vulnerability map of this region and the damages after the strongest earthquake from Vrancea source (Romania) on the 4^th of March 1977 (MW=7.4). These damages are presented in dynamic conditions of that massive seismic event. The results interpretation and conclusions are done in the context of the real response of the buildings from the territory of Oltenia Region.

Keywords: Damage, Building Damage Evaluation, Seismic Hazard, Performance, Oltenia Seismicity.

Assessing the Risk of Landslide-Generated Tsunamis, Using Translatory Wave Theory

by Jonas Eliasson, Ragnar Sigbjörnsson

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Abstract - The conventional opinion of scientists is that tsunamis are usually generated by earthquakes, but the discovery of the huge landslides on the continental shelf of the North Atlantic Ocean and other possible submarine slides, have changed this view considerably. Such tsunamis may be triggered by earthquakes but the dominating force in generating such a tsunami is alandslide, so landslides may be the major threat. Using estimates of slide scar dimensions that can be compiled from bathymetry data, it is possible to estimate this force. For estimating atsunami, a translatory theory previously devised for super floods on land is suggested as an alternative to theories used by Tinti and others. The data on slide scars and slopes areused to estimate the amplitude of a displacement wave from such an event. The amplitudes are used to obtain wave heights ata reference point outside the breaker zone. Energy transmission formulas are used to find the wave height transfer coefficients from the near field (source area) to the far field (reference point), numerical modeling or CFD (Computational Fluid Dynamics) simulations may be used as well. Tsunami risk from a number of sources ata reference point, are quantified using stochastic processes, and estimations of a hazard curve for the probability of landslide occurrence are carried out. The sensitivity of the hazard curve touncertainties in determining the wave height from the individual sources turns out to be surprisingly high for amplitudes above two meters.

Keywords: Waves, Tsunami, Landslide, Hazard.

Perforation Effect on the Hysteretic Response of Coupled Shear Walls

by A. Asghari, B. Azimi, A. H. Gandomi

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Abstract - Coupled walls are known as efficient lateral load resisting systems. Recently by changing the design codes from strength based design to performance based design, better nonlinear performance of coupling wall systems (CWS) is needed. In order to evaluate the seismic performance of a structure, nonlinear analysis is carried out by many researchers, nonlinear dynamic analysis is one of the newest ones used. The outcome of this analysis is a hysteretic response known as hysteresis loop which indicates the nonlinear behavior of the structure under monotonic loadings. In this study nonlinear dynamic analysis is carried out by SAP2000 S/W in order to evaluate seismic performance of 2D frames. These 2D frames are part of 20, 30 and 40 story buildings which are located in a high seismic zone, the records of El-Centro earthquake is chosen for the nonlinear time history analysis of the frames. The hysteresis response is obtained for all of the patterns, and then the walls on both sides are perforated according to three patterns, chess, rhombic and rectangular. The results of hysteretic response confirm that the perforation, gives better response to the coupling wall systems under monotonic loadings, by using changes the behavior of coupling wall systems from flexural to shear.

Keywords: Concrete Shear Wall, Coupling Beam, Coupling Wall.