Influence of Uncertain Source Parameters on Strong Ground Motion Simulation with the Empirical Green's Function Method

A combined stochastic and Green's function approach was developed to simulate strong ground motions in Southwest Western Australia (SWWA) in a previous study. Although it was demonstrated that adopting the source parameters derived from other regions yielded reasonable simulation of ground motions in SWWA as compared with a few available strong motion records, the effect of source parameter variations on simulated ground motions was not known. This article performs a statistical study of the effects of random fluctuations of the seismic source parameters on simulated strong ground motions. The uncertain source parameters, i.e., stress drop ratio, rupture velocity, and rise time corresponding to the empirical source models are assumed to be the respective mean value of the parameter and normally distributed with an assumed coefficient of variation. The Rosenblueth's point estimate method [Rosenblueth, 1981 Rosenblueth, E. 1981. Two-point estimates in probabilities. Applied Mathematical Modelling, 5: 329–335. [Crossref], [Web of Science ®] , [Google Scholar]] is used to calculate the statistics of the simulate ground motion parameters corresponding to different magnitudes and epicentral distances. The accuracy of the Rosenblueth's point estimate method in estimating the mean and standard deviation of ground motion PGA, PGV, and response spectrum is proven by simulating the ground motions from an ML6.0 and epicentral distance 100 km event with both the Rosenblueth's point estimate method and the Monte Carlo simulation method. A sensitivity analysis is preformed to investigate the effect of random fluctuations of each source parameters on strong ground motion simulation. A coefficient of variation model for ground motion parameters is developed based on the simulated data as a function of the variations of the three source parameters and earthquake magnitude, which can be used in probabilistic predictions of earthquake ground motions with uncertain source parameters.     

Wavelet-Based Damage Detection in Reinforced Concrete Structures Subjected to Seismic Excitations

The feasibility of using output-only model-free wavelet-based techniques for damage detection in reinforced concrete structures subjected to seismic loads is explored through the analysis of the results of a full scale shake table test of a reinforced concrete bridge column recently performed at the NEES Large High Performance Outdoor Shake Table. The evaluated approaches are based solely in the analysis of the acceleration time histories recorded in the structure. The viability of using numerical models to validate this type of damage detection methodologies is also evaluated. Wavelet analyses were capable of identifying the rebar fracture episodes and partially identified the frequency shifts in the structure as the inelastic demand increased. It was also found that, depending on the methodology employed, the use of numerical models to validate damage detection techniques can oversimplify the actual problem and/or induce spurious irregularities.     

Experimental and Numerical Seismic Response of a 65 kW Wind Turbine

A full-scale shake table test is conducted to assess the seismic response characteristics of a 23 m high wind turbine. Details of the experimental setup and the recorded dynamic response are presented. Based on the test results, two calibrated beam-column finite element models are developed and their characteristics compared. The first model consists of a vertical column of elements with a lumped mass at the top that accounts for the nacelle and the rotor. Additional beam-column elements are included in the second model to explicitly represent the geometric configuration of the nacelle and the rotor. For the tested turbine, the experimental and numerical results show that the beam-column models provide useful insights. Using this approach, the effect of first-mode viscous damping on seismic response is studied, with observed experimental values in the range of 0.5–1.0% and widely varying literature counterparts of 0.5–5.0%. Depending on the employed base seismic excitation, damping may have a significant influence, reinforcing the importance of more accurate assessments of this parameter in future studies. The experimental and modeling results also support earlier observations related to the significance of higher modes, particularly for the current generation of taller turbines. Finally, based on the outcomes of this study, a number of additional experimental research directions are discussed.     

Optimum Design of Bridge Abutments Under High Seismic Loading Using Modified Pseudo-Static Method

This article focuses on the optimum design of bridge abutments when subjected to earthquake loading. Planar failure surface has been used in conjunction with modified pseudo-static approach to compute the seismic active earth pressures on an abutment. The proposed modified Mononobe-Okabe method considers the effects of strain localization in the backfill soil and associated post-peak reduction in the shear resistance from peak to residual values along a previously formed failure plane, phase difference in shear waves, and soil amplification along with the horizontal seismic accelerations. Four modes of stability viz. sliding, overturning, eccentricity, and bearing capacity of the foundation soil are considered in the analysis. The influence of various design parameters on the seismic stability of abutments is presented. The optimum values of base width of the abutment needed to maintain the stability are obtained against four modes of failure, based on the suggestions of Japan Road Association, Caltrans Bridge Design Specifications, and U.S Department of the Army.     

Probabilistic Seismic Performance Assessment of Classes of Buildings Using Physics-Based Simulations and Ground-Motion Prediction Equations

We discuss the applicability of two different near field representations of seismic input within the capacity-demand diagram method for seismic performance assessment of classes of buildings in urban areas. The two representations of seismic input used are: (1) synthetic accelerograms obtained from 3D wave simulations of random rupture scenarios are used to estimate seismic risk, through the Monte-Carlo approximation; and (2) random realizations of elastic spectral displacement obtained through ground-motion prediction equations. The implementation of the proposed formulation in evaluating the seismic performance of two classes of buildings in the town of Sulmona, Italy, indicates that empirical ground-motion prediction equations, combined with non-iterative methods for estimating the inelastic seismic demand, can produce results comparable to the physics-based simulations.     

Synthesizing Broadband Time-Histories at Near Source Sites; Case Study, 2003 Bam Mw6.5 Earthquake

The main objective of this article is to synthesize the 2003 Bam earthquake. A hybrid method is proposed for synthesizing the near-fault broadband timehistories; a theoretical green's function method and a stochastic finite-fault approach for generating time histories at low and high frequencies, respectively. A genetic algorithm is developed to optimize the differences between synthesized and recorded ground motions.

The proposed technique can be used for dynamic nonlinear analysis of structures and site specific hazard analysis of the regions with lack of sufficient data and also for retrofitting the damaged structures during Bam earthquake, particularly the well-known adobe buildings of Arg-e-Bam.     

Solution Strategies for Three Problems in Empirical Fragility Curve Derivation Using the Maximum Likelihood Method

Solution strategies are presented to address three potential problems in the empirical derivation of fragility functions from empirical data using the maximum likelihood method. The first strategy addresses the case of fragility curves that cross, the second strategy incorporates demand uncertainty in fragility derivation from post-earthquake reconnaissance data, and the third strategy provides a framework for the resolution of conflict between empirical data and expert opinions. The advantages and disadvantages of the proposed solution strategies are discussed and their use is demonstrated by way of suitable illustrative examples.     

Transient and Long-Term Changes in Seismic Response of the Natural Resources Building,Olympia, Washington,due to Earthquake Shaking

The Natural Resources Building (NRB) in Olympia, Washington, was shaken by three earthquakes (Mw = 5.8, 6.8, and 5.0) between 1999 and 2001. Building motions were recorded on digital accelerographs, providing important digital recordings of repeated strong shaking in a building. The NRB has 5-stories above grade with 3 sub-grade levels and a ductile steel-frame elongated in the E-W direction. The upper two floors extend significantly beyond the lower 3 on the southern and eastern sides. N-S motions dominate the fundamental modal vibrations of the building system. In the 1999 Satsop M5.8 earthquake, the frequency of this fundamental system mode was 1.3 Hz during motions of 10% g. The frequency dropped to 0.7 Hz during the 2001 M6.8 Nisqually strong motions. Moreover, the Nisqually recordings reveal both numerous high-frequency transients of up to 0.18 g, several of which are visible on widely spaced sensors, and long-term tilts of some of the sensors. The weaker 2001 M5.0 Satsop earthquake motions showed the frequency remained depressed at less than 1 Hz for the eastern side of the structure, although the western side had recovered to 1.3 Hz. An ambient noise survey in 2008 showed the fundamental frequency of N/S vibrations remains about 1.0 Hz for the eastern side of the building and 1.3 Hz for the western side. These results suggest that in the Nisqually earthquake, the east side of the NRB suffered a permanent reduction in fundamental mode frequency of 37% due to loss of system stiffness by undetermined mechanism.     

Seismic Performance and Modeling of a Half-Scale Base-Isolated Wood Frame Building

The concept of base isolation is a century old, but application to civil engineering structures has only occurred over the last several decades. Application to light-frame wood buildings in North America has been virtually non existent with one notable exception. This article quantitatively examines issues associated with application of base isolation in light-frame wood building systems including: (1) constructability issues related to ensuring sufficient in-plane floor diaphragm stiffness to transfer shear from the superstructure to the isolation system; (2) evaluation of experimental seismic performance of a half-scale base-isolated light-frame wood building; and (3) development of a displacement–based seismic design method and numerical model and their comparison with experimental results. The results of the study demonstrate that friction pendulum system (FPS) bearings offer a technically viable passive seismic protection system for light-frame wood buildings in high seismic zones. Specifically, the amount and method of stiffening the floor diaphragm is not unreasonable, given that the inter-story drift and accelerations at the upper level of the tested building were very low, thus resulting in the expectation of virtually no structural, non structural, or contents damage in low-rise wood frame buildings. The nonlinear dynamic model was able to replicate both the isolation layer and superstructure movement with good accuracy. The displacement-based design method was proven to be a viable tool to estimate the inter-story drift of the superstructure. These tools further underscore the potential of applying base isolation systems for application to North America's largest building type.     

Field Measurements and Numerical Simulation of Debris Flows from Dolomite Slopes Destabilized during the 2005 Kashmir Earthquake,Pakistan

A devastating earthquake occurred in Kashmir, Pakistan on October 8, 2005. This earthquake resulted from reactivation of a known active fault later defined as the Balakot–Bagh fault, which caused widespread slope failure throughout its stretch, particularly around Muzaffarabad, the provincial capital of Azad Jammu and Kashmir. This slope failure resulted in a huge amount of debris material which flows in deeply incised creeks during monsoon and hits the inhabitants along the valley in Muzaffarabad. Two GPS measurements are carried out along with channel morphometric parameters and observed changes to investigate the effect of debris flows along these creeks during monsoon. Other than the physical measurements, actual debris flow is simulated using the Depth Average Material Point Method (DAMPM) after carrying out parametric study and calibrating the model for subject topographical and geological settings. The generalized effect of different input parameters of the model on debris flow runout features is studied and discussed in detail. After ensuring validation of the numerical tool, the contribution of a single closed-type check dam to decrease runout intensity to its downstream reach is also investigated for different locations to obtain optimized selection.     

Seismic Damage to Structures in the 2015 Nepal Earthquake Sequences

The 7.8 Mw Gorkha earthquake struck the east of Lamjung in Nepal, followed by a sequence of powerful aftershocks. Chinese Team Six including the authors inspected the seismic damage to civil structures along 10 paths in densely populated areas with a seismic intensity of VII to IX, 40 days after the main shock. The damage was categorized according to structure types and described in detail. Several conclusions are made: powerful aftershocks can significantly affect the failure patterns; geological conditions, structure types, and height have great influence on the level of damage; and the local risky retrofitting technique needs improvement badly.     

Evaluation of the Nonlinear Seismic Response of an Earth Dam: Nonparametric System Identification

A system identification framework is proposed to investigate the nonlinear dynamic response of massive earth dams using the seismic motion recorded by a sparse array of accelerometers. The framework includes a methodical step of nonparametric analyses to characterize the involved loading conditions and response mechanisms. This nonparametric step provides essential information to reduce the indeterminacy of the associated parametric identificatin problem and ensure a proper model selection, calibration, and validation. The proposed framework was applied to the Long Valley earth dam (California) and benchmarked using records of a series of 1980 earthquakes. This article presents the conducted correlation, spectral motion reconstruction, and nonparametric stress-strain analyses. These analyses revealed a complex three-dimensional dynamic response marked by non uniform boundary conditions and a shear stress-strain behavior slightly less nonlinear than what was observed in triaxial tests of soil samples taken from the dam core.     

Simplified Mechanical Model to Estimate the Seismic Vulnerability of Heritage Unreinforced Masonry Buildings

Traditional or historic masonry structures occur in large populations throughout the world, particularly in preserved historical city clusters. Being non-engineered and aging these structures are in urgent need of assessment and seismic repair/rehabilitation. However, traditional masonry presents important challenges to computational modeling, owing to complexity of structural system, material inhomogeneity, and contact interactions that collectively can only be addressed through detailed 3D nonlinear representation. In this article, a simple performance assessment model is developed in order to address the need for preliminary assessment tools for this class of structures. The objective is to be able to rapidly identify buildings that are at higher risk in the event of a significant earthquake, potentially justifying a second round of more detailed evaluation. The proposed model defines the characteristics of a Single Degree of Freedom representation of the building, formulating consistent 3D shape functions to approximate its fundamental mode of vibration considering both in-plane and out-plane wall bending as a result of insufficient diaphragm action. Parametric expressions for the dynamic properties are derived in terms of the important geometric, material, and system characteristics, and are used to express local demand from global estimates. Acceptance criteria are established both in terms of deformation and strength indices to guide retrofit. An application example of the proposed assessment methodology is included to demonstrate the ability of the model to reproduce the essential features of traditional masonry buildings under seismic action.     

A New Seismic Intensity Parameter to Estimate Damage in Buried Pipelines due to Seismic Wave Propagation

A new seismic intensity parameter to estimate damage in buried pipelines due to seismic wave propagation is proposed. This parameter depends on the peak ground velocity (PGV) and the peak ground acceleration (PGA). It is shown that PGV²/PGA is related to displacement, a parameter directly related to ground strain, which is the main cause of buried pipeline damage. For the case of Mexico City, this parameter exhibits higher correlation with damage than PGA or PGV alone. Finally, we presented intensity-damage relations for the Mexico City's primary water system using PGV²/PGA as the measure of seismic intensity.     

An XFEM Model for Seismic Activity in Indian Plate

Empirical approaches based on the available earthquake catalog are popular among engineers to estimate seismic hazard. The seismic activity on individual faults inferred from these approaches is associated with a large number of uncertainties, especially due to lack of data. This article proposes a mechanistic approach to quantify seismic and fault activity, thereby overcoming the difficulties in the existing empirical procedure. A finite element (FE) model for Indian Plate, with the geological ‘cratons’ is developed and subject to plate driving forces namely, the ridge push and the slab pull forces. The material properties and the thickness of both plate and cratons are obtained through inversion using the recently available Global Positioning System (GPS) data. The tectonic faults are modeled using the well-known ‘extended FE method (XFEM)’. The simulated strains at fault level are compared with the computed strain rates from the earthquake catalog. Further, the procedure to quantify fault activity is demonstrated for Gujarat, India.     

An Analytical Study on the Seismic Vulnerability of Masonry Buildings in India

Two analytical models for unreinforced masonry (URM) buildings are proposed with the aim to simulate their seismic response and to estimate corresponding vulnerability functions. The proposed models are implemented in SAP 2000 nonlinear software to obtain capacity curve parameters for representative Indian URM buildings, based on a field survey and statistical analysis. Vulnerability functions are estimated using the obtained capacity curves. Damage Probability Matrices (DPMs) are obtained using the approximate PGA-intensity correlation relationship as per Indian seismic building code and are compared with the commonly used intensity scales and empirical damage data observed after the 2001 Bhuj earthquake.     

Source Effects on the Spectral Characteristics of Strong Ground Motions Recorded in Bucharest Area During Vrancea Earthquakes of 1986 and 1990

The August 30, 1986 (M_W ?=?7.1) and May 30, 1990 (M_W ?=?6.9) Vrancea intermediate-depth earthquakes, despite their almost similar magnitudes, have produced very different spectral contents as shown by the strong ground motions recorded in Bucharest and its surroundings. The differences can be attributed to different epicentral distances and to different values of the stress drop. The characteristics of the seismic ground motions recorded in Bucharest area in the 1986 and 1990 seismic events are discussed in the context of (a) the source characteristics of the two earthquakes and (b) the local soil conditions in Bucharest. Furthermore, an attempt is made to determine the soil factors S defined in EN 1998-1 EN 1998-1. 2004. Design of Structures for Earthquake Resistance – Part 1: General Rules, Seismic Actions and Rules for Buildings, CEN.  [Google Scholar] for the Bucharest area, based on the strong ground motion dataset recorded during the two seismic events.     

Computational Modeling of the Seismic Performance of Beam-Column Subassemblies

Analytical studies are carried out to investigate the effectiveness of finite element modeling procedures in accurately capturing the nonlinear cyclic response of beam-column subassemblies. The analyses are performed using program VecTor2, employing only default or typical material constitutive models and behavior mechanisms in order to assess analysis capabilities without the need for special modeling techniques or program modifications. The specimens considered cover a wide range of conditions, and include interior and exterior seismically and non seismically designed beam-column subassemblies. It is shown that finite element analyses can achieve good accuracy in determining the strength, deformation response, energy dissipation, and failure mode of reinforced concrete beam-column subassemblies under seismic loading conditions.     

Scattering problems of the SH Wave by Using the Null-Field Boundary Integral Equation Method

The scattering problem of seismic waves is an important issue for studying earthquake engineering. In this paper, the null-field boundary integral equation approach was used in conjunction with degenerate kernels and eigenfunction expansion to solve the SH-wave scattering problem of a circular or an elliptical-arc hill. The original problem is divided into subdomains by taking a free-body diagram. One region is an interior boundary value problem. The other is a canyon scattering problem. For the boundary value problem, not only a simply connected domain (elliptical-arc hill problem) but also a doubly connected domain (a circular-arc hill problem containing a circular tunnel or a circular inclusion) is considered. The canyon scattering problem may be addressed in an infinite domain with an artificial boundary of a full plane such that the degenerate kernel can be fully utilized. The null-field integral equation method is used to match boundary conditions. Numerical results are compared favorably with the available data.     

Experimental and Analytical Study of Seismic Soil-Pile-Structure Interaction in Layered Soil Half-Space

The dynamic interaction of pile foundations, embedded in a horizontally stratified soil profile, with superstructures under low to moderate earthquake excitation can be handled in different ways. In this article, the soil-pile-superstructure dynamic interaction problem has been investigated using the coupled finite element-boundary element method. Comparison with shaking table experiments of a small scale model pile shows a good correlation with the proposed method in terms of the kinematic response of pile foundations and the structural response. A parametric study of the proposed model has yielded important results essentially concerning the amplification factors of the pile foundation and the superstructure.