An Improved Stochastic Finite-Fault Method Based on Energy

2015 ◽  
Vol 744-746 ◽  
pp. 878-883
Author(s):  
Ju Fang Zhong ◽  
Jun Wei Liang ◽  
Zhi Peng Fan ◽  
Luo Long Zhan
Keyword(s):  
Ground Motion ◽  
Amplification Factor ◽  
Response Spectrum ◽  
Near Field ◽  
Energy Accumulation ◽  
Accumulation Curve ◽  
Finite Fault ◽  
Acceleration Time Histories ◽  
Time Histories ◽  
Finite Fault Method

Owing to the simulated ground motion energy distribution by stochastic finite-fault method is not reasonable, near-field bedrock strong ground motion acceleration time histories are used to study. Fourier transform is adapted to analysis the variation of the energy accumulation curve with frequency. The results show that the record energy accumulation curve is a steep rise curve, 80% of total energy of the vertical ground motion is concentrated on the 2.5-15Hz, while the horizontal is mainly concentrated on the 2-11Hz. An improved stochastic finite-fault method is proposed by multiplying an amplification factor in some frequency. The results show that multiplying an amplification factor, the simulated acceleration energy accumulation curve matches to the record acceleration energy accumulation curve, and the peak of simulated acceleration response spectrum tends to the record acceleration value.

Comparison of Seismic Analysis of Jacket Structures Using Response Spectrum and Time Domain Procedures

2013 ◽  
Author(s):  
Partha Chakrabarti ◽  
Atul Rikhy
Keyword(s):  
Linear System ◽  
Ground Motion ◽  
Time Domain ◽  
Response Spectrum ◽  
Ground Acceleration ◽  
Soil System ◽  
Soil Stiffness ◽  
Acceleration Time ◽  
Acceleration Time Histories ◽  
Time Histories

In seismically active areas of the world an offshore jacket structure has to be designed for seismic loads. Since the structure must meet both strength and ductility requirements, a two stage design for Strength Level Earthquake (SLE) and Ductility Level Earthquake (DLE) is generally used. Normal procedure for designing such a structure for SLE condition is to use Response Spectrum method of analysis (RSA). The main advantage of RSA is that it is computationally very efficient. Time Domain Analysis (TDA) is used mostly to analyze DLE condition. A response spectrum depicts the maximum response to a ground motion of a single degree of freedom system having different natural periods but the same degree of damping. A design response spectrum is a smoothened average of several earthquake motions. It is a property of the ground motion with a given recurrence interval at the particular region of interest. RSA is a frequency domain analysis technique based on mode superposition approach. API RP 2A specifies that the modal responses be combined using a Complete Quadratic Combination (CQC) of modal responses. For the directional response combination, API RP 2A recommends applying 100% of the spectral acceleration for the two orthogonal lateral directions and 50% for the vertical and using the Square Root of Sum of Squares (SRSS) combination to obtain the maximum response. With this approach it is possible to conduct only one analysis, with any reference system, and the resulting structure will have all members that are designed to equally resist earthquake motions from all possible directions. RSA based on mode superposition is valid strictly for a linear system. A jacket structure with its pile-soil system is not truly a linear system due to soil nonlinearity. Therefore, linearization of the pile-soil system is necessary. The stiffness of a pile is dependent on the pile head loads. Thus the response from the RSA will be very much load or deformation dependent for the pile-soil stiffness. Software used here for the analyses has an iterative analysis option for obtaining the appropriate linearized stiffness. TDA is a step by step time integration procedure for the entire system including the piles and there is no linearization involved for the foundation stiffness as the pile-soil stiffness at discrete points of the pile are calculated at each time instant within the program. The TDA is more precise for the given time history but more time consuming as a series of ground acceleration time histories are normally required for the TDA approach. The results from RSA are expected to be conservative especially for the design of piles. However, this can only be confirmed from a series of TDA performed using ground acceleration time histories. This paper demonstrates that more accurate and less conservative results can be obtained by using a combination of RSA and TDA even for SLE condition. However, several simulations for TDA are required for confidence in the design to ensure that all structural elements have achieved the maximum conditions. Essentially, RSA can be used for jacket member design and TDA can be used specifically for pile design. Thus the authors believe the design of an entire jacket could be more economical if this combined approach is judiciously used.

Strain, tilt, and rotation associated with strong ground motion in the vicinity of earthquake faults

1982 ◽  
Vol 72 (5) ◽  
pp. 1717-1738 ◽  
Author(s):  
Michel Bouchon ◽  
Keiiti Aki
Keyword(s):  
Ground Motion ◽  
Rotational Velocity ◽  
Near Field ◽  
Strike Slip ◽  
Phase Velocities ◽  
Crustal Structures ◽  
Time Histories ◽  
San Fernando ◽  
Earthquake Faults ◽  
Strong Ground

abstract In the absence of near-field records of differential ground motion induced by earthquakes, we simulate the time histories of strain, tilt, and rotation in the vicinity of earthquake faults embedded in layered media. We consider the case of both strike-slip and dip-slip fault models and study the effect of different crustal structures. The maximum rotational motion produced by a buried 30-km-long strike-slip fault with slip of 1 m is of the order of 3 × 10−4 rad while the corresponding rotational velocity is about 1.5 × 10−3 rad/sec. A simulation of the San Fernando earthquake yields maximum longitudinal strain and tilt a few kilometers from the fault of the order of 8 × 10−4 and 7 × 10−4 rad. These values being small compared to the amplitude of ground displacement, the results suggest that most of the damage occurring in earthquakes is caused by translation motions. We also show that strain and tilt are closely related to ground velocity and that the phase velocities associated with strong ground motions are controlled by the rupture velocity and the basement rock shearwave velocity.

scholarly journals Near-Field Ground Motion Modal versus Wave Propagation Analysis

2010 ◽  
Vol 17 (4-5) ◽  
pp. 611-617 ◽  
Author(s):  
Artur Cichowicz
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Response Spectrum ◽  
Near Field ◽  
Spectral Characteristics ◽  
Beam Model ◽  
Drift Spectrum ◽  
Localized Deformation ◽  
Dominant Period ◽  
Strong Ground

The response spectrum generally provides a good estimate of the global displacement and acceleration demand of far-field ground motion on a structure. However, it does not provide accurate information on the local shape or internal deformation of the response of the structure. Near-field pulse-like ground motion will propagate through the structure as waves, causing large, localized deformation. Therefore, the response spectrum alone is not a sufficient representation of near-field ground motion features. Results show that the drift-response technique based on a continuous shear-beam model has to be employed here to estimate structure-demand parameters when structure is exposed to the pulse like ground motion. Conduced modeling shows limited applicability of the drift spectrum based on the SDOF approximation. The SDOF drift spectrum approximation can only be applied to structures with smaller natural periods than the dominant period of the ground motion. For periods larger than the dominant period of ground motion the SDOF drift spectra model significantly underestimates maximum deformation. Strong pulse-type motions are observed in the near-source region of large earthquakes; however, there is a lack of waveforms collected from small earthquakes at very close distances that were recorded underground in mines. The results presented in this paper are relevant for structures with a height of a few meters, placed in an underground excavation. The strong ground motion sensors recorded mine-induced earthquakes in a deep gold mine, South Africa. The strongest monitored horizontal ground motion was caused by an event of magnitude 2 at a distance of 90 m with PGA 123 m/s2, causing drifts of 0.25%–0.35%. The weak underground motion has spectral characteristics similar to the strong ground motion observed on the earth's surface; the drift spectrum has a maximum value less than 0.02%.

Selection and Scaling Time History Records for Performance-Based Design

2017 ◽  
pp. 1-35
Author(s):  
Yasin M. Fahjan ◽  
F. İlknur Kara ◽  
Aydın Mert
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Time History ◽  
Design Code ◽  
Uniform Hazard Spectra ◽  
Acceleration Time ◽  
Acceleration Time Histories ◽  
Recent Developments ◽  
Time Histories ◽  
Strong Ground

Recent developments in performance-based analyses and the high performance of computational facilities have led to an increased trend for utilizing nonlinear time-history analysis in seismic evaluation of the performance of structures. One of the crucial issues of such analysis is the selection of appropriate acceleration time histories set that satisfy design code requirements at a specific site. In literature, there are three sources of acceleration time histories: 1) recorded accelerograms in real earthquakes scaled to match design code spectrum/uniform hazard spectra/conditional mean spectrum, 2) artificial records generated from white noise spectra to satisfy design code spectrum, and 3) synthetic records obtained from seismological models. Due to the increase of available strong ground motion database, using and scaling real recorded accelerograms is becoming one of the most contemporary research issues in this field. In this study, basic methodologies and criteria for selecting strong ground motion time histories are discussed. Design code requirements for scaling are summarized for ASCE/SEI-7-10, EC8 and Turkish Seismic Codes. Examples for scaling earthquake records to uniform hazard spectra are provided.

scholarly journals A Procedure to Select Earthquake Time Histories for Deterministic Seismic Hazard Analysis: Case Studies of Major Cities in Taiwan

2017 ◽  
Author(s):  
Duruo Huang ◽  
Wenqi Du
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Ground Surface ◽  
Strong Motion ◽  
Response Spectra ◽  
Dynamic Responses ◽  
Motion Time ◽  
Acceleration Time Histories ◽  
Time Histories ◽  
Deterministic Seismic Hazard

Abstract. In performance-based seismic design, ground-motion time histories are needed for analyzing dynamic responses of nonlinear structural systems. However, the number of strong-motion data at design level is often limited. In order to analyze seismic performance of structures, ground-motion time histories need to be either selected from recorded strong-motion database, or numerically simulated using stochastic approaches. In this paper, a detailed procedure to select proper acceleration time histories from the Next Generation Attenuation (NGA) database for several cities in Taiwan is presented. Target response spectra are initially determined based on a local ground motion prediction equation under representative deterministic seismic hazard analyses. Then several suites of ground motions are selected for these cities using the Design Ground Motion Library (DGML), a recently proposed interactive ground-motion selection tool. The selected time histories are representatives of the regional seismic hazard, and should be beneficial to earthquake studies when comprehensive seismic hazard assessments and site investigations are yet available. Note that this method is also applicable to site-specific motion selections with the target spectra near the ground surface considering the site effect.

An Improved Source Model for Simulation Near-Field Strong Ground Motion Acceleration Time History

2013 ◽  
Vol 438-439 ◽  
pp. 1474-1480
Author(s):  
Ju Fang Zhong ◽  
Long Wei Zhang ◽  
Jun Wei Liang
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Response Spectrum ◽  
Near Field ◽  
Time History ◽  
Source Spectrum ◽  
Acceleration Time ◽  
Acceleration Time History ◽  
Spectrum Model ◽  
Strong Ground

The key to near-field strong ground motion simulation based on stochastic finite fault method is to determine the spectrum of ground motion. We present an improved source spectrum model for simulation near-field strong ground motion acceleration time history. We combine Masudas source spectrum model with scaling factor Hij to keep radiation energy conservation and reflect the energy decrease with frequency at low to mid frequencies. We calculate the Fourier amplitude spectrum Fa, accelerate response spectrum Sa, velocity response spectrum Sv and displacement response spectrum Sd of simulation time histories. By comparative analysis of the laws of spectrum values (Fa, Sa, Sv, Sd) with the variation of frequency or period, we discusses the effects of sub-fault dividing scheme, the method of determining scale factor and source spectrum model on spectrum values (Fa, Sa, Sv, Sd). The results show that sub-fault dividing scheme has slightly effect on the model presented in this paper, and the model enable to reflect the sink laws of source spectrum value in mid-to-low frequencies well. We demonstrate that the improved model is superior to other commonly used models.

Nonlinear Response Potential of Real versus Simulated Ground Motions for the 11 March 2011 Tohoku-oki Earthquake

2015 ◽  
Vol 31 (3) ◽  
pp. 1711-1734 ◽  
Author(s):  
Katsuichiro Goda ◽  
Susumu Kurahashi ◽  
Hadi Ghofrani ◽  
Gail M. Atkinson ◽  
Kojiro Irikura
Keyword(s):  
Nonlinear Response ◽  
Main Shock ◽  
Strong Motion ◽  
Motion Generation ◽  
Demand Curves ◽  
Finite Fault ◽  
Time Histories ◽  
Ground Motion Records ◽  
Finite Fault Method ◽  
Simulated Ground Motions

This study compares the nonlinear response potential of generic inelastic single-degree-of-freedom systems subjected to three sets of ground motion records for the 2011 Tohoku main shock. The compared record sets, all for the same sites, are: (1) observed accelerograms at 48 KiK-net strong motion stations; (2) time-histories simulated from the empirical Green's function method; and (3) time-histories simulated using the stochastic finite-fault method (with multiple sub-events). The adopted techniques can capture a realistic source rupture process involving multiple strong motion generation areas in simulations. Statistical analysis of computed peak ductility demands for the three record sets is conducted via cloud and stripe analyses. Results indicate that for the 2011 Tohoku main shock, different record sets produce similar average trends of the inelastic seismic demand curves. This conclusion is applicable to both cloud and stripe approaches and to structural systems with degrading and pinching hysteresis.

Strong motion accelerograph records from the 1993 Napierville earthquake

1995 ◽  
Vol 22 (1) ◽  
pp. 190-196
Author(s):  
René Tinawi ◽  
André Filiatrault ◽  
Pierre Léger
Keyword(s):  
Ground Motion ◽  
Energy Content ◽  
Strong Motion ◽  
Response Spectra ◽  
High Energy ◽  
Period Range ◽  
Attenuation Relationships ◽  
Acceleration Time Histories ◽  
Short Period ◽  
Time Histories

An earthquake of magnitude ML = 4.3 occurred near Napierville, Quebec, on November 16, 1993. An accelerograph at the liquefaction, storage, and regasification plant of Gaz Metropolitain in Montreal, about 55 km from the epicentre, recorded the ground motion. Although the maximum accelerations and velocities from this event are small, the acceleration time histories do confirm the high energy content in the very short period range. The recorded ground motion and corresponding absolute acceleration response spectra are presented and various attenuation relationships, proposed for eastern North America, are utilized to compare the measured and predicted ground motion parameters. Key words: Napierville earthquake, attenuation relationships, acceleration spectra, strong motion records.

Earthquake time histories compatible with the 2005 National building code of Canada uniform hazard spectrum

2009 ◽  
Vol 36 (6) ◽  
pp. 991-1000 ◽  
Author(s):  
Gail M. Atkinson
Keyword(s):  
Ground Motions ◽  
Time History ◽  
Building Code ◽  
Site Condition ◽  
Period Range ◽  
Uniform Hazard Spectrum ◽  
Finite Fault ◽  
Time Histories ◽  
Finite Fault Method ◽  
Site Classes

The seismic design provisions of the 2005 National building code of Canada (NBCC) (NRC 2005) describe earthquake ground motions for which structures are to be designed in terms of a uniform hazard spectrum (UHS) having a 2% chance of being exceeded in 50 years. The “target” UHS depends on location and site condition, where site condition is described by a classification scheme based on the time-averaged shear-wave velocity in the top 30 m of the deposit. For some applications, such as dynamic analysis by time history methods, it is useful to have time histories that represent the types of earthquake motions expected and match the target UHS from the NBCC over some prescribed period range. In this study, the stochastic finite-fault method is used to generate earthquake time histories that may be used to match the 2005 NBCC UHS for a range of Canadian sites. Records are provided for site classes A, C, D, and E. They are freely available at www.seismotoolbox.ca .

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