Ray Ruichong Zhang

Signatures of the Seismic Source in EMD-Based Characterization of the 1994 Northridge, California, Earthquake Recordings

In this article we use empirical mode decomposition (EMD) to charac- terize the 1994 Northridge, California, earthquake records and investigate the sig- natures carried over from the source rupture process. Comparison of the current study results with existing source inverse solutions that use traditional data processing suggests that the EMD-based characterization contains information that sheds light on aspects of the earthquake rupture process. We first summarize the fundamentals of the EMD and illustrate its features through the analysis of a hypothetical and a real record. Typically, the Northridge strong-motion records are decomposed into eight or nine intrinsic mode functions (IMFs), each of which emphasizes a different oscillation mode with different amplitude and frequency content. The first IMF has the highest-frequency content; frequency content decreases with an increase in IMF component. With the aid of a finite-fault inversion method, we then examine aspects of the source of the 1994 Northridge earthquake that are reflected in the second to fifth IMF components. This study shows that the second IMF is predominantly wave motion generated near the hypocenter, with high-frequency content that might be related to a large stress drop associated with the initiation of the earthquake. As one progresses from the second to the fifth IMF component, there is a general migration of the source region away from the hypocenter with associated longer-period signals as the rupture propagates. This study suggests that the different IMF components carry information on the earthquake rupture process that is expressed in their different frequency bands.

Vibration analysis of medical devices with a calibrated FEA model

Abstract This study presents vibration analysis of medical devices by a finite element analysis (FEA) model calibrated with test data. The medical device under investigation is the Lifepak500 automated external defibrillator (AED), a product that is frequently exposed to vibration and shock in transportation means such as ambulances and medical-evacuation helicopters. In structure, the AED is a plastic case that contains a printed circuit board (PCB) with various attached electronic components such as capacitors, resistors, inductors, and integrated circuits. In this study, an FEA model of the AED is established with the use of ANSYS based on design specifications and static tests. The model is first calibrated with various static and dynamic tests to verify that the static displacements at selected locations, PCB twist angles, and first three natural frequencies predicted by the FEA model are consistent with those obtained by the tests. The model is then used to examine the dynamic characteristics and vibration transmissibility of the PCB within both rigid and flexible medical device cases. Finally, random vibration analysis of the PCB is presented. This study shows that the predicted frequency data favorably agrees with test data (within 7% error range), while predicted vibration amplitudes are in a reasonable range at major PCB locations when compared with the test data, but do not always agree well at the locations where the PCB has more complicated structural features and boundary conditions. The established FEA model predicts the reliability and functionality of current design of the AED from a vibration viewpoint. It can also help engineers improve the PCB mechanical design and product reliability when used in harsh vibration environments.

Editorial: the empirical mode decomposition and the Hilbert-huang transform

1Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, USA 2Department of Electrical and Computer Engineering, University of Delaware, Newark, DE 19716, USA 3Departments of Mathematics and Statistics and Molecular Physiology Biophysics, The University of Vermont, Burlington, VT 05405, USA 4Civil Engineering Specialty, Division of Engineering, Colorado School of Mines, Golden, CO 80401, USA

Surrounding Rock Deformation Mechanism and Control Technology for Gob-Side Entry Retaining with Fully Mechanized Gangue Backfilling Mining: A Case Study

To counter the technical difficulties faced by gob-side entry retaining (GER) under multiple complex mining geological conditions in China, this paper introduces a GER method with fully mechanized gangue backfilling mining. A similar materials simulation experiment was conducted to simulate the gob-backfilled GER process by using the similar model test system containing an independently developed horizontal pushing load device. The experimental results show that the compaction speed of the backfilling area (BFA) can be improved, and the main roof subsidence can be reduced by increasing the horizontal pushing load and reducing the attenuation rate of the stress in BFA. The designed roadside backfill body (RBB) containing a flexible cushion is adaptive to the given deformation of the main roof, thus reducing the stress concentration of the RBB. The field test results show that when a 2 MPa horizontal pushing load is exerted in the BFA, arranging a 200 mm high-water-material flexible cushion can cause the BFA to swiftly change to the compaction stage. After stabilized deformation, the roadway section satisfies the design and application requirements. The feasibility and rationality of the GER with the fully mechanized gangue backfilling mining are proved, providing a safe, efficient, and environmentally friendly mining method without using a coal pillar.

Actual ground-exposure determination and its influences in structural analysis and design

Abstract Wind exposure categories are currently used to account for the influences of different ground roughness in wind profile that is fundamentally important to wind-resistant structural analysis and design. Since each classified exposure covers a relatively large spectrum of ground roughness with constant indices such as exponent α , this results in uncertain wind-resistant structural analysis and design for structures in each and every categorized exposure. More importantly, such an uncertainty is not only quantitative but also qualitative in terms of aerodynamic instability assessment and economic loss estimation. This study proposes a method to determine the actual wind exposure and estimates its influences in wind-resistant structural analysis and design. In particular, this paper first provides a review of wind exposure categories and illustrates the shortcomings of its use in structural analysis and design. It then introduces a method to determine the actual ground exposure. The method generates formulae for the actual ground roughness exponent on the basis of measured data from both wind-tunnel and full-scale experiments, of ground roughness-induced wind energy dissipation analysis, as well as of current Chinese and other countries’ loading codes. Through examples of hypothetical and practical engineering projects, this study finally investigates the influences of the actual ground roughness exponent on wind-induced structural responses and economic loss estimation, as well as on wind-resistant structural design.

An Alternative Approach to Characterize Nonlinear Site Effects

This paper examines the rationale of a method of nonstationary data processing and analysis, referred to as the Hilbert-Huang transform (HHT), for its application to a recording-based approach in quantifying influences of soil nonlinearity in site response. In particular, this paper first summarizes symptoms of soil nonlinearity shown in earthquake recordings, reviews the Fourier-based approach to characterizing nonlinearity, and offers justifications for the HHT in addressing nonlinearity issues. This study then uses the HHT method to analyze synthetic data and recordings from the 1964 Niigata and 2001 Nisqually earthquakes. In doing so, the HHT-based site response is defined as the ratio of marginal Hilbert amplitude spectra, alternative to the Fourier-based response that is the ratio of Fourier amplitude spectra. With the Fourier-based approach in studies of site response as a reference, this study shows that the alternative HHT-based approach is effective in characterizing soil nonlinearity and nonlinear site response.

Dynamic Bridge Substructure Condition Assessment with Hilbert-Huang Transform: Simulated Flood and Earthquake Damage to Monitor Structural Health and Security

Modal vibration tests combined with the Hilbert-Huang transform (HHT) method were used to analyze previous recordings of controlled field-vibration tests of one concrete pile substructure of the Trinity River Relief Bridge No. 4 in Texas in its intact, minor-, and severe-damage states. Piles were excavated and broken to simulate flood and earthquake damage to a bridge substructure. The HHT algorithm is unique in that it reveals the quantitative difference in the instantaneous frequency of sound and damaged structures, consistent with the damage states and with what a simple structural model predicts. This approach differs from traditional modal vibration analyses in that a short-lived shift downward in resonant frequency can be seen in the HHT from a damaged member, whereas this shift is often lost due to the averaging effect of a modal vibration analysis. Accordingly, an HHT-based structural health monitoring procedure is discussed.

Seismic wave motion modeling with layered 3D random heterogeneous media

Abstract A generalized earthquake-wave-motion model is established in this study, which considers 3D random heterogeneous media, together with existing models for sources and realistic geological profiles for sedimentary basins and irregular topography. The model can be used not only to examine the influences of random heterogeneous media, but also to explore the multiple interactions of source, site (irregularity and/or heterogeneity), and wave interference on spatial variations of ground motion. Specifically, the earth is modeled as a layered half-space with 3D weak-random heterogeneity media. Seismic waves are generated by a shear-dislocation source buried in one of the layers and then propagated through the modeled earth medium. A first-order perturbation approach together with wave propagation theory is used to solve the problem at hand for wave motion response, which is found as the superposition of the mean and scattered wave responses. The mean wave response is obtained as a wave-motion solution for a layered half-space without heterogeneity subjected to a buried seismic dislocation source. The scattered wave field is obtained as a wave-motion solution for the same layered half-space without heterogeneity subjected to virtual distributed body forces that mathematically replace the heterogeneity. The explicit expressions for the responses in both mean and scattered wave fields are derived in this study. A computational procedure for the wave-motion responses is also presented in detail.

An Experimental Investigation on the Mechanical Properties of Gangue Concrete as a Roadside Support Body Material for Backfilling Gob-Side Entry Retaining

Development of a safe and economical roadside support body (RSB) material is the key to successful backfilling gob-side entry retaining (GER). By means of laboratory tests, this paper studied the effects of the water-cement ratio, aggregate content, and age on the contractibility and resistance increasing speed, compressive strength, and postpeak carrying capacity of the concrete with gangues as an aggregate. It also discussed the rationality and adaptability of gangue concrete as a RSB material for backfilling GER. The experimental results show that the compressive strength of gangue concrete increases with age, and that the strength of gangue concrete demonstrates a nonlinear decreasing trend with the increase of the cementing material’s water-cement ratio. The water-cement ratio in the range of 0.46–0.60 has the most significant regulation effect on the strength of gangue concrete. Mixing with a certain amount of coal gangue enhances the postpeak carrying capacity of concrete, preventing the sample from impact failure. The field experimental results report that as a RSB material, gangue concrete can meet the design and application requirements of GER with gangue backfilling mining. A RSB material featuring high safety, high waste utilization rate, fast construction speed, and low costs is provided.