Numerical investigation of the effects of soil-structure and granular material-structure interaction on the seismic response of a flat-bottom reinforced concrete silo

In this work,a numerical study of the effects of soil-structure interaction(SSI)and granular material-structure interaction(GSI)on the nonlinear response and seismic capacity of flat-bottomed storage silos is conducted.A series of incremental dynamic analyses(IDA)are performed on a case of large reinforced concrete silo using 10 seismic recordings.The IDA results are given by two average IDA capacity curves,which are represented,as well as the seismic capacity of the studied structure,with and without a consideration of the SSI while accounting for the effect of GSI.These curves are used to quantify and evaluate the damage of the studied silo by utilizing two damage indices,one based on dissipated energy and the other on displacement and dissipated energy.The cumulative energy dissipation curves obtained by the average IDA capacity curves with and without SSI are presented as a function of the base shear,and these curves allow one to obtain the two critical points and the different limit states of the structure.It is observed that the SSI and GSI significantly influence the seismic response and capacity of the studied structure,particularly at higher levels of PGA.Moreover,the effect of the SSI reduces the damage index of the studied structure by 4%.

Seismic Methods for Exploration and Exploitation of Gas Hydrate

Seismic and rock physics play important roles in gas hydrate exploration and production.To provide a clear cognition of the applications of geophysical methods on gas hydrate,this work presents a review of the seismic techniques,rock physics models,and production methods in gas hydrate exploration and exploitation.We first summarize the commonly used seismic techniques in identifying the gas hydrate formations and analyze the limitations and challenges of these techniques.Then,we outline the rock physics models linking the micro-scale physical properties and macro-scale seismic velocities of gas hydrate sediments,and generalize the common workflow,showing the frequently-used procedures of building models with detailed analysis of the potential uncertainties.Afterwards,we summarize the production techniques of gas hydrate and point out the problems regarding the petrophysical basis and abnormal seismic responses.In the end,considering the geological and engineering problems,we come up with several aspects of using geophysical techniques to solve the problems in gas hydrate exploration and production,hopefully to provide some important clues for future studies of gas hydrate.

Comparison of North American Seismic Screening Methods Applied to School Buildings

An ongoing project at McGill University is aimed at developing an adapted seismic screening method for schools in the province of Qu6bec, Canada. As part of this project the ＂FEMA 154 Rapid Visual Screening of Buildings for Potential Seismic Hazard＂ and the ＂NRC92 Manual for Screening of Buildings for Seismic Investigation＂ were used to assess 102 school buildings located in the city of Montr6al. Results for both methods are in reasonable agreement, with 65% of the buildings requiring a detailed evaluation according to FEMAI54 and 50% according to NRC92. Findings highlighted the particular characteristics of educational facilities： they are low rise buildings with high incidence of structural irregularities. Accounting for them in the screening phase is essential, and is better achieved by NRC92. However, this method is largely based on expert opinion, which makes it difficult to update, while FEMA154 uses a rational methodology for calculating vulnerability scores based on the capacity spectrum approach. The FEMA154 analytical procedure allows updating and adapting the method to its use outside its intended scope.

Methods for Estimating Mean Annual Rate of Earthquakes in Moderate and Low Seismicity Regions

Two kinds of methods for determining seismic parameters are presented, that is, the potential seismic source zoning method and grid-spatially smoothing method. The Gaussian smoothing method and the modified Gaussian smoothing method are described in detail, and a comprehensive analysis of the advantages and disadvantages of these methods is made. Then, we take centrai China as the study region, and use the Gaussian smoothing method and potential seismic source zoning method to build seismic models to calculate the mean annual seismic rate. Seismic hazard is calculated using the probabilistic seismic hazard analysis method to construct the ground motion acceleration zoning maps. The differences between the maps and these models are discussed and the causes are investigated. The results show that the spatial smoothing method is suitable for estimating the seismic hazard over the moderate and low seismicity regions or the hazard caused by background seismicity; while the potential seismic source zoning method is suitable for estimating the seismic hazard in well-defined seismotectonics. Combining the spatial smoothing method and the potential seismic source zoning method with an integrated account of the seismicity and known seismotectonics is a feasible approach to estimate the seismic hazard in moderate and low seismicity regions.

Comparative Analysis of Application of Seismic Wave Reflection Method in Advanced Geological Prediction

Seismic wave reflection method is an advanced geophysical detection method in tunnel geological prediction.It is more sensitive and effective in detecting geological anomalies such as fault fracture zone and karst.In order to verify the prediction efficacy and accuracy of the seismic wave reflection method with different instruments and equipment(tunnel geological prediction[TGP]/tunnel seismic prediction[TSP])and different vibration modes(hammering,explosives),a comparison test was carried out in Jinping Tunnel.The test results showed that the time-consumption of the hammering source was short,which can greatly reduce the impact on the construction site;different vibration sources methods of seismic wave reflection can predict the unfavorable geological sections accurately.

Dynamic behavior of single-layer latticed cylindrical shells subjected to seismic loading

The single-layer latticed cylindrical shell is one of the most widely adopted space-fl'amed structures.In this paper,free vibration properties and dynamic response to horizontal and vertical seismic waves of single-layer latticed cylindrical shells are analyzed by the finite element method using ANSYS software.In the numerical study,where hundreds of cases were analyzed,the parameters considered included rise-span ratio,length-span ratio,surface load and member section size.Moreover,to better define the actual behavior of single-layer latticed shells,the study is focused on the dynamic stress response to both axial forces and bending moments.Based on the numerical results,the effects of the parameters considered on the stresses are discussed and a modified seismic force coefficient method is suggested.In addition,some advice based on these research results is presented to help in the future design of such structures.

Effective wave identification and interference analysis of the seismic reflection method in mines

Through discussion of the time-distance curve characteristics of the direct waveand from the front,side and rear of the reflection waves of the seismic reflection methodfor advanced exploration in mines,and analysis of several major interference waves inmines,the differences in time-distance curve,frequency,apparent velocity between theeffective wave and interference wave in the seismic reflection method for advanced explorationare obtained.According to the differences,the effective wave is extracted andthe interference wave is filtered and the system's precision and accuracy is improved.

Seismic stability evaluation of embankment slope based on catastrophe theory

An evaluation method for the seismic stability of embankment slope was presented based on catastrophe theory. Seven control factors, including internal frictional angle, cohesion force, slope height, slope angle, surface gradients, peak acceleration, and distance to fault were selected for analysis of multi-level objective decomposition. According to the normalization formula and the fuzzy subject function produced by combination of catastrophe theory and fuzzy math, a recursive calculation was carried out to obtain a catastrophic affiliated functional value, which can be used to evaluate the seismic stability of embankment slope. Fifteen samples were used to verify the effectiveness of this method. The results show that compared with the traditional quantitative method, the catastrophe progression owns higher accuracy and good application potential in predicting the seismic stability of embankment slope.

Seismic hazard analysis for central-western Argentina

In this study, we present a PSHA（Probabilistic Seismic Hazard Analysis） for the city of San Juan, which is located in the central-western region of Argentina（30°S-35.5°S; 66.5°W-71°W）. In addition to crustal earthquakes provided by catalogues, recent paleoseismological and neotectonic investigations have permitted to consider events which occurred during the last 400 years.Four seismogenic sources that could cause damages to the studied site corresponding to Precordillera,Western Sierras Pampeanas, Basement of the Cuyana Basin and Cordillera Principal were identified.Based on the evaluation of the contribution of these sources,maximum moment magnitudes above 7.5（Mw） are expected.High values of SA（spectral acceleration）（0.2 and 1 s periods） and PGA（peak ground acceleration） were found in the city of San Juan, which suggests that it is located in a zone of high seismic hazard.Finally, the obtained SA spectra were compared with the seismic-resistant construction standards of Argentina INPRES-CIRSOC 103 [1]. Results suggest that for the city of San Juan and for a return period of475 years, it covers the seismic requirements of the structures.

Time exposure acoustics in seismic exploration

An analysis of a passive seismic method for subsurface imaging is presented in which ambient seismic noise is employed as the source of illumination of subsurface scatterers. The imaging algorithm can incorporate new data into the image in a recursive fashion which causes image background noise to diminish over time. Under the assumption of spatially-incoherent ambient noise, an analytical expression for the point-spread function of the imaging algorithm is derived. The point-spread function （PSF） characterizes the resolution of the image, which is a function of the receiving array length and the ambient bandwidth.

Numerical modeling of global seismic phases and its application in seismic phase identification

Earthquake data include informative seismic phases that require identification for imaging the Earth's structural interior.In order to identify the phases,we created a numerical method to calculate the traveltimes and raypaths by a shooting technique based upon the IASP91 Earth model,and it can calculate the traveltimes and raypaths for not only the seismic phases in the traditional traveltime tables such as IASP91,AK135,but also some phases such as pPcP,pPKIKP,and PPPPP.It is not necessary for this method to mesh the Earth model,and the results from the numerical modeling and its application show that the absolute differences between the calculated and theoretical traveltimes from the ISAP91 tables are less than 0.1 s.Thus,it is simple in manipulation and fast in computation,and can provide a reliable theoretical prediction for the identification of a seismic phase within the acquired earthquake data.

Application of the Common Offset Seismic Reflection Method to Urban Active Fault Surveys

The method and principle of common offset seismic surveys as well as the field data gathering and processing technique were introduced briefly. Through two urban active fault survey examples in Fuzhou and Shenyang, the efficiency and limitation of using the common offset seismic reflection technique to carry out urban active fault surveys were probed. The results show that this technique has the properties of high resolving power, better reconstruction of subsurface structures, and real-time analyzing and interpretation of investigation results on site. This method can be used to quickly locate objects under investigation accurately in the areas with thinner Quaternary overburdens and strong bedrock interface fluctuations.

Deformation-based longitudinal equivalent stiffness beam model for shield tunnel and its application in seismic deformation method

In the longitudinal seismic deformation method for shield tunnels,one of the most commonly used is the longitudinal equivalent stiffness beam model(LES)for simulating the mechanical behavior of the lining.In this model,axial deformation and bending deformation are independent,so the equivalent stiffness is a constant value.However,the actual situation is that axial deformation and bending deformation occur simultaneously,which is not considered in LES.At present,we are not clear about the effect on the calculation results when axial deformation and bending deformation occur simultaneously.Therefore,in this paper,we improve the traditional LES by taking the relative deformation as a load and considering the coordinated deformation of axial and bending degrees of freedom.This improved model is called DNLES,and its neutral axis equations are an explicit expression.Then,we propose an iterative algorithm to solve the calculation model of the DNLES-based longitudinal seismic deformation method.Through a calculation example,we find that the internal forces based on LES are notably underestimated than those of DNLES in the compression bending zone,while are overestimated in the tension bending zone.When considering the combined effect,the maximum bending moment reached 13.7 times that of the LES model,and the axial pressure and tension were about 1.14 and 0.96 times,respectively.Further analysis reveals the coordinated deformation process in the axial and bending directions of the shield tunnel,which leads to a consequent change in equivalent stiffness.This explains why,in the longitudinal seismic deformation method,the traditional LES may result in unreasonable calculation results.

An alternative practical design method for structures with viscoelastic dampers

Viscoelastic dampers（VEDs） are one of the most common passive control devices used in new and retrofit building projects which reduce the structure responses and dissipate seismic energy during an earthquake.Various methods to design this kind of dampers have been proposed based on the desired level of additional damping,eigenvalue assignment,modal strain energy,linear quadratic regulator control theories,and other approaches.In the current engineering practice,the popular method is the one based on the modal strain energy that uses the inter-story lateral stiffness as one of the main variables for damper design.However,depending on the configuration of the structure,in some cases the resulting interstory lateral stiffness can be very large.Consequently,the dampers size would also be large producing much more damping than that effectively necessary,resulting in an increase of the overall cost of the supplemental damping system and causing excessive stress on the structural elements connected to the dampers.In this paper an alternative practical design method for structures with VEDs is proposed.This method uses the inter-story shear forces as one of the main variables to accomplish the damper design compared to what was done in previous studies.Nonlinear time-history analyses were conducted on a 7-story reinforced concrete（RC） structure to check the reliability and effectiveness of the proposed method.Comparisons on the seismic performance between the structure without dampers and that equipped with VEDs were carried out.It is concluded that the proposed method results in a very suitable size of dampers,which are able to improve the performance of the structure at all levels of earthquake ground motions and satisfying the drift requirement prescribed in the codes.

Spectral-element simulations of elastic wave propagation in exploration and geotechnical applications

We apply the spectral-element method（SEM）,a high-order finite-element method（FEM） to simulate seismic wave propagation in complex media for exploration and geotechnical problems. The SEM accurately treats geometrical complexities through its flexible FEM mesh and accurately interpolates wavefields through high-order Lagrange polynomials. It has been a numerical solver used extensively in earthquake seismology. We demonstrate the applicability of SEM for selected 2D exploration and geotechnical velocity models with an open-source SEM software package SPECFEM2D. The first scenario involves a marine survey for a salt dome with the presence of major internal discontinuities,and the second example simulates seismic wave propagation for an open-pit mine with complex surface topography. Wavefield snapshots,synthetic seismograms,and peak particle velocity maps are presented to illustrate the promising use of SEM for industrial problems.

Global SH-wave propagation in a 2D whole Moon model using the parallel hybrid PSM/FDM method

We present numerical modeling of SH-wave propagation for the recently proposed whole Moon model and try to improve our understanding of lunar seismic wave propagation. We use a hybrid PSM/FDM method on staggered grids to solve the wave equations and implement the calculation on a parallel PC cluster to improve the computing efficiency. Features of global SH-wave propagation are firstly discussed for a 100-km shallow and900-km deep moonquakes, respectively. Effects of frequency range and lateral variation of crust thickness are then investigated with various models. Our synthetic waveforms are finally compared with observed Apollo data to show the features of wave propagation that were produced by our model and those not reproduced by our models. Our numerical modeling show that the low-velocity upper crust plays significant role in the development of reverberating wave trains. Increasing frequency enhances the strength and duration of the reverberations.Surface multiples dominate wavefields for shallow event.Core–mantle reflections can be clearly identified for deep event at low frequency. The layered whole Moon model and the low-velocity upper crust produce the reverberating wave trains following each phases consistent with observation. However, more realistic Moon model should be considered in order to explain the strong and slow decay scattering between various phases shown on observation data.

Effect of strata restraint on seismic performance of prefabricated sidewall joints in fabricated subway stations

A disadvantage of the conventional quasi-static test method is that it does not consider the soil restraint effect.A new method to test the seismic performance of prefabricated specimens for underground assembled structures is proposed,which can realistically reflect the strata restraint effect on the underground structure.Laboratory work combined with finite element(FE)analysis is performed in this study.Three full-scale sidewall specimens with different joint forms are designed and fabricated.Indices related to the seismic performance and damage modes are analyzed comprehensively to reveal the mechanism of the strata restraint effect on the prefabricated sidewall components.Test results show that the strata restraint effect effectively improves the energy dissipation capacity,load-bearing capacity,and the recoverability of the internal deformation of the precast sidewall components.However,the strata restraint effect reduces the ductility of the precast sidewall components and aggravates the shear and bending deformations in the core region of the connection joints.Additionally,the strata restraint effect significantly affects the seismic performance and damage mode of the prefabricated sidewall components.An FE model that can be used to conduct a seismic performance study of prefabricated specimens for underground assembled structures is proposed,and its feasibility is verified via comparison with test data.

Nonlinear Response of Tunnel Portal under Earthquake Waves with Different Vibration Directions

Tunnel portal sections often suffer serious damage in strong earthquake events.Earthquake waves may propagate in different directions,producing various dynamic responses in the tunnel portal.Based on the Galongla tunnel,which is located in a seismic region of China,three-dimensional seismic analysis is conducted to investigate the dynamic response of a tunnel portal subjected to earthquake waves with different vibration directions.In order to simulate the mechanic behavior of slope rock effectively,an elastoplastic damage model is adopted and applied to ABAQUS software by a self-compiled user material(UMAT)subroutine.Moreover,the seismic wave input method for tunnel portal is established to realize the seismic input under vertically incident earthquake waves with different vibration directions,e.g.,S waves with a vibration direction perpendicular or parallel to the tunnel axis and P waves with a vibration direction perpendicular to the tunnel axis.The numerical results indicate that the seismic response and damage mechanisms of the tunnel portal section are related to the vibration direction of the earthquake waves.For vertically incident S waves running perpendicular to the tunnel axis,the hoop tensile strain at the spandrel and arch foot and the hoop shear strain at the vault and arch bottom are the main contributors to the plastic damage of the tunnel.The strain is initially concentrated around the tunnel foot and spandrel,before shifting to the tunnel vault and bottom farther away from the tunnel entrance.For vertically incident S waves running parallel to the tunnel axis,very large hoop shear strain and plastic damage appear at the tunnel haunches.This strain first increases and then decreases with distance from the tunnel entrance.For vertically incident P waves running perpendicular to the tunnel axis,the maximum damage factor of the slope rock and the maximum plastic strain of the tunnel are significantly lower than for S waves.Moreover,with increasing distance from the tunnel entrance,the plastic damage to the tunnel lining rapidly decreases.

GEOPHYSICAL TECHNIQUES IN DETECTION TO RIVER EMBANKMENTS

Geophysical technologies are very effective in environmental, engineering and groundwater applications. Parameters of delineating nature of near surface materials such as compressional wave velocity, shear wave velocity can be obtained using shallow seismic methods. Electric methods are primary approaches for investigating groundwater and detecting leakage. Both of the methods are applied to detect embankment in hope of obtaining evidence of the strength and moisture inside the body. A technological experiment has been done for detecting and discovering the hidden troubles in the embankment of Yangtze River, Songzi, Hubei, China in 2003. Surface wave and DC multi channel array resistivity sounding techniques were used to detect hidden trouble inside and under dike like pipe seeps. This paper discusses the exploration strategy and the effect of geological characteristics. A practical approach of combining seismic and electric resistivity measurements was applied to locate potential pipe seeps in embankment in the experiment. The method presents a potential leak factor based on the shear wave velocity and the resistivity of the medium to evaluate anomalies. An anomaly found in a segment of embankment detected was verified, where occurred a pipe seep during the 98’ flooding.