• Volume 41,Issue 2,2019 Table of Contents
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    • >结构抗震
    • Comparative Study on the Seismic Performances of Undergroundvs. Above-Ground Reinforced Concrete Structures withRectangular Cross Sections

      2019, 41(2):271-277. DOI: 10.3969/j.issn.1000-0844.2019.02.271

      Abstract (820) HTML (0) PDF 7.46 M (834) Comment (0) Favorites

      Abstract:The seismic performance of underground structures differs from that of above-ground structures due to the confinement effect of surrounding soil. This paper compares the seismic performances of underground structures, considering soil-structure interaction (SSI), with above-ground structures, without considering soil, by means of the Pushover analysis method. Two kinds of reinforced concrete single-story structures with rectangular cross sections were chosen, including single-span and two-span. The research results showed that the seismic deformation of underground and above-ground structures is different. Under similar conditions, namely, with the same structure size and initial axial compression ratio, the elastic inter-story drift limit of underground structures was less than that of above-ground structures, and the plastic hinge for underground structures appeared earlier. The deformability of the underground single-span structure was weaker because of the shear deformation constraint of the surrounding soil. While the deformability of the central column of the underground two-span structure was nearly the same as that of the above-ground structure, the deformability of the lateral wall of the underground two-span structure was a bit weaker than that of above-ground two-span structure. In conclusion, even with the same structure size and initial axial compression ratio, the seismic performances of underground structures and above-ground structures are different. Therefore, existing research concerning above-ground structures is not applicable to underground structures.

    • Seismic Response of Long-span Suspension Bridges underMulti-support Excitation Based on Artificial Seismic Waves

      2019, 41(2):278-285. DOI: 10.3969/j.issn.1000-0844.2019.02.278

      Abstract (793) HTML (0) PDF 7.39 M (724) Comment (0) Favorites

      Abstract:To study the seismic response of long-span suspension bridges under multi-support excitation, an improved power spectrum model based on an existing power spectrum model is proposed and applied to the synthetic process of artificial seismic waves. A full-bridge finite element model for the suspension bridge with a main span of 720 m over a reservoir was established with Midas civil, and the seismic response of the bridge under multi-support excitation and different wave velocities was analyzed with a large-mass method. The results showed that under multi-point excitation, the internal force response and displacement response of the main tower and the displacement response of the main beam of the long-span suspension bridge are all affected by the traveling wave effect, the attenuation effect, the incoherence effect, and the superposition effect of seismic waves after attenuation, and the value of final response is determined by the combined effects of attenuation and superposition of seismic waves. Under 500 m/s multi-point excitation and the combined effects of superposition and attenuation of the seismic wave after attenuation, the axial force response of the main tower, the longitudinal shear response at the bottom of main tower, and the shear force and bending moment response at the beam of the left tower showed the maximum reinforcement effect. Under multi-point excitation and different wave velocities, (1) the relative variance rate of longitudinal displacement response of the main tower was greater than zero and almost unchanged; (2) the relative variance rate of longitudinal displacement response at the two sides of main beam reached maximum value when the wave velocity was 1 000 m/s; and (3) the vertical displacement response of the main girder reached the maximum value at 500 m/s, and was gradually close to than under uniform excitation with the increase of wave velocity.

    • Damping Shake Technology of the Shock Absorption Layer ofFault-crossing Tunnels in a Dangerous MountainousArea with High-Intensity Earthquakes

      2019, 41(2):286-291. DOI: 10.3969/j.issn.1000-0844.2019.02.286

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      Abstract:To improve the damping performance of fault-crossing tunnels in dangerous mountainous areas with high-intensity earthquakes, based on the Menggushao tunnel engineering of Lixiang Railway, this paper used the finite differential software FLAC3D to study the damping effect of the shock absorption layer of the fault-crossing tunnel under different setting modes. Results showed that if the shock absorption layer is set between the primary support and surrounding rock, the lateral displacement, the vertical displacement, the maximum principal stress, the minimum principal stress, and the maximum shear stress will decrease by 4.17%, 14.32%, 47.89%, 25.93%, and 27.74%, respectively, and the minimum safety factor will increase by 34.62%-59.40%; If the shock absorption layer is set between the primary support and secondary lining, the lateral displacement, the vertical displacement, the maximum principal stress, the minimum principal stress, and the maximum shear stress will decrease by 3.72%, 7.73%, 16.11%, 20.21%, and 20.73%, respectively, and the minimum safety factor will increase by 0.04%-28.38%. The damping effect of the shock absorption layer, set between the primary support and surrounding rock, is better than that set between the primary support and secondary lining. This study is of great significance for the damping design and damping shake technology of fault-crossing tunnels.

    • Shaking Table Tests on the Seismic Performance of UltrahighVoltage Interconnected Electrical Equipment

      2019, 41(2):292-298. DOI: 10.3969/j.issn.1000-0844.2019.02.292

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      Abstract:To investigate the damping effect of a lead damper on ultrahigh voltage (UHV) interconnected electrical equipment, we carried out a shaking table test on an interconnected coupling system comprising a UHV arrester and a capacitor voltage transformer. The equipment frequency and the strain and acceleration of some key components were measured using white noise sweep, seismic test, and damping test. The test results show that the maximum strain response of the arrester is larger than that of the transformer. The arrester of the interconnected coupling system is a vulnerable device. With dampers added, the frequency of the interconnected equipment slightly decreases; thus, the dampers cannot affect the normal operation of the electrical equipment. The top acceleration response and maximum strain response for the arrester and transformer device of the coupling system after adding dampers are greatly reduced under the action of seismic waves with large peak acceleration. The damping efficiencies of the maximum strain response for the arrester and transformer are 75% and 50%, respectively, and the damping effect is significant. The application of dampers greatly enhances the seismic capacity of the interconnected coupling system.

    • Seismic Risk Assessment of Buildings in Major Chinese CitiesBased on the Nonlinear Time-history Analysis of Cities

      2019, 41(2):299-306. DOI: 10.3969/j.issn.1000-0844.2019.02.299

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      Abstract:It is of profound significance to assess the national-scale seismic risk of urban buildings for seismic disaster prevention and mitigation. the nonlinear time-history analysis of cities, building seismic risk assessment of mainland cities was conducted in this work. First, the urban buildings database was established according to the macroscopic indicators provided by the Nationwide Census and China City Statistical Yearbook. Then, ground motion intensities of the specific sites was obtained from the Global Earthquake Activity Rate Model 1 (GEAR1) method and the 5th seismic ground motion parameters zonation map of China. Then, site classifications of the cities were obtained using the corresponding relationship between the ground slope and the shear wave velocity, through which the ground motion input could be further determined. Finally, based on the dynamic elastoplastic analysis of urban buildings, the seismic economic loss risk and extensive damage and collapse risk were assessed. Using the methods cited above, a map of building seismic risk of mainland cities is given. The results showed that:(1) the method proposed in this work can assess the building seismic risk of mainland cities based on the publicly available data; (2) high seismic economic loss risk regions are mainly located in areas where the intensity of design-based earthquakes given by the 5th seismic ground motion parameters zonation map of China is more than 0.3g; (3) after consideration of urban population and GDP, the building seismic risk of the eastern and central cities will increase significantly due to higher density of population and wealth; (4) differently-selected ground motions have little impact on the seismic economic loss risk but has a greater impact on the extensive damage and collapse risk. The outcomes of this work can provide a useful method for future works on building seismic risk assessment of mainland cities.

    • Seismic Performance of Vertically Reinforced Earth-RetainingWalls Based on Limit Analysis

      2019, 41(2):313-318,384. DOI: 10.3969/j.issn.1000-0844.2019.02.313

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      Abstract:When using the National Concrete Masonry Association method of studying the seismic performance of vertically reinforced earth-retaining walls, the external power of the wall could not be comprehensively calculated, and there was a high deviation in the results of the seismic performance analysis. Therefore, the limit analysis method was used in this paper to analyze the failure mode of a vertically reinforced earth-retaining wall, and an expression of the movement limit of the retaining wall was obtained. According to the expression, the external power of the retaining wall (including the external power of the soil weight and the external power of earthquake action) was calculated, and its seismic performance analyzed. The experimental results showed that the maximum external power of each layer of the vertically reinforced earth-retaining wall was 18.5 kN·m and 20 kN·m, respectively, which did not vary significantly from the actual maximum external power (18 kN·m). The study indicates that seismic performance analysis with this method is consistent with actual conditions and can be applied to actual projects.

    • Influence of Support Settlement on the Seismic Behaviorof Large-span Steel Structure Corridors

      2019, 41(2):319-325. DOI: 10.3969/j.issn.1000-0844.2019.02.319

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      Abstract:The influence of support settlement on the seismic impact analysis of long-span steel structure corridors is often overlooked, but is very important. In this paper, such an influence was studied, and a stress model of the long-span steel structure in earthquakes was established. Incorporating settlement amount into the model, the additional internal force of the corridor (including steel frame and steel truss) under earthquake impact was calculated. The additional bending moment diagram of the corridor was then drawn using structural mechanics, and the seismic impact expression of the settlement on the steel frame of the connecting corridor was obtained. The internal force change of the steel truss structure connected with the corridor under different settlement levels was analyzed with SAP2000 software. The maximum bending moment and maximum axial tension of the upper and bottom chords on the corridor were then calculated under earthquake conditions. The experimental results showed that after support settlement, the maximum dynamic coefficients of the upper chord and web member were 0.17 and 0.15, respectively, which was closer to the relative code value (0.16) than the results achieved through the traditional time-history analysis method.

    • Comparative Analysis of the Seismic Behavior of RecycledAggregate Concrete at Low Temperature

      2019, 41(2):326-331. DOI: 10.3969/j.issn.1000-0844.2019.02.326

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      Abstract:As a building material, the seismic performance of recycled aggregate concrete (RAC) at low temperature needs to be analyzed before use. At present, the cost of RAC is low, and the demand is large in China. However, seismic performance at low temperatures is uncertain if directly applying the RAC to construction engineering. In view of this problem, a comparative analysis of the seismic resistance of RAC at low temperatures was presented in this paper. The low temperature seismic structure model of RAC was designed through the material ratio of RAC and experimental construction. According to the indicators, low temperature frost resistance, acceleration change, damage index, stiffness stability, and layer displacement change were compared and analyzed. The results of the comparative experiments showed that:(1) with decreasing oxygen content, the heat conservation effect is reduced, and the strength and frost resistance of RAC are also reduced; thus, the durability and stability of RAC are poor, and the seismic behavior is poor; (2) after an earthquake, the displacement and acceleration between the floors vary greatly, so the stability of the floor cannot be guaranteed; and (3), as the displacement and seismic load increase, the RAC gradually undergoes cracking changes. The stiffness decreases rapidly, and the degree of stiffness degradation is large, indicating the low temperature seismic performance of RAC is poor.

    • Design and Analysis of the Isolated Bearings for a High-riseShear Wall Structure in Xichang City

      2019, 41(2):332-339. DOI: 10.3969/j.issn.1000-0844.2019.02.332

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      Abstract:An isolation design and seismic performance analysis of the rubber bearing for a reinforced concrete high-rise shear wall structure in Xichang City were performed in the study. A buried fracture zone, the secondary fault of the Zemuhe fault is in the east of the engineering site, and the seismic fortification intensity of Xichang City is 9 degree. Therefore, the near-field influence coefficient was selected as 1.5, and a seismic isolation design of the structure was carried out with software SAP2000. The maximum value of the earthquake reduction coefficient of inter-story shear force and overturning moment under a moderate earthquake was 0.24, which was significantly reduced compared to the non-isolated structure. The surface pressure and horizontal displacement of the isolated structure subjected to the rare earthquake can satisfy requirements of the design code. A dynamic elastic-plastic time-history analysis of the structure under rare earthquakes was conducted using the program ABAQUS, and the results showed that the structure could meet the objective of no collapse under a severe earthquake.

    • Seismic Response Analysis of the Base Isolation of a Frame Structure

      2019, 41(2):340-346. DOI: 10.3969/j.issn.1000-0844.2019.02.340

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      Abstract:Based on the principle of structural dynamics and the basic theory of the finite element method, the finite element analysis software SAP2000 was used to establish an analytical model for an actual frame structure base isolation building and a similar non-isolated building, respectively. The dynamic time history analysis method was applied to analyze the horizontal seismic responses of the two models. The results showed that the horizontal seismic response of the base-isolated building was much smaller than that of the non-isolated building, and the natural period of the superstructure of the base-isolated building was significantly larger than that of the non-isolated building. Moreover, the interstory shear force, basement shear force, and the relative displacement and acceleration of the floor were lower than those of the non-isolated building. In general, isolation bearings can significantly reduce the adverse effects of horizontal ground motion on a structure and thus deserve propagation.

    • Influence of Buckling-Restrained Braces on the SeismicStrengthening Performance of Building Structures

      2019, 41(2):353-359. DOI: 10.3969/j.issn.1000-0844.2019.02.353

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      Abstract:The influence of buckling-restrained braces on building structure is not considered in the current methods of structural reinforcement with outriggers. The connection between the outrigger and the building structure is unstable, thus leading to poor seismic strengthening performance of the structure. Therefore, herein, the influence of buckling-restrained braces on the seismic strengthening performance of a building structure is analyzed in detail, and the seismic reinforcement scheme of the structure is designed. The buckling-restrained brace and the structure are fixed by the high-strength bolted joints through connecting steel plates. The influence of buckling-restrained braces on the seismic strengthening performance of a structure was studied. The study was based on the relationships among bracing deformation and story drift, bearing capacity, displacement-checking calculations of the buckling-restrained braced frame under frequent earthquakes, and the elasto-plastic displacement-checking calculation of the buckling-restrained brace under the influence of rare earthquakes. The experimental results showed that after adding a buckling-restraint brace to the structure, the ratio of the first period of torsion to the first period of translation was decreased by 0.14; the stiffness ratio of the masonry wall to the building structure in the X and Y direction was decreased by 6.9 and 8.0, respectively, and the maximum vertex displacement was reduced by 15.4 mm and 29.3 mm, respectively. This indicated that the seismic reinforcement performance of the structure was greatly improved.

    • Seismic Response of Continuous Skewed Bridges Consideringthe Bidirectional Pounding Effect

      2019, 41(2):360-369. DOI: 10.3969/j.issn.1000-0844.2019.02.360

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      Abstract:To study the influence of bidirectional collision on the seismic response of continuous skew girder bridges, the Kelvin-Voigt model was used to simulate the longitudinal collision phenomenon at the expansion joint of the abutment, and the simplified hysteresis model was used to simulate the lateral collision process between the link stopper and main beam. Therefore, a parametric comparison study on a three-span skew continuous bridge was conducted. The study shows that the effect of bidirectional collision on the lateral displacement of the main beam is much larger than that of longitudinal collision, and the abutment clearance has the greatest influence on the plane angle of the main beam:the plane angle decreases with the increase of the abutment clearance. The effect of lateral collision on the curvature deformation of the pier is much larger than that of the longitudinal collision, particularly the influence of the intensity of the link stopper. When the intensity of the link stopper increases from 0% to 50%, the mean values of the longitudinal and lateral curvatures of the pier increase 13.43 times and 7.21 times, respectively. With the increase of the skew angle, the longitudinal displacement of the butt of beam increases continuously, and the lateral displacement and plane rotation angle first increase and then decrease; the longitudinal curvature of the bottom of the pier continues to grow, and the lateral curvature alternately increases and decreases. The longitudinal collision effect first weakens and then increases, which is opposite of the lateral collision effect. Because the effect of the lateral collision on the pier is much larger than that of the longitudinal collision, it is advisable to reduce the lateral collision effect when the skew angle is 15°-45°.

    • >岩土工程
    • Influence of the Uncertainty of Backfilled Soil onSite Seismic Response

      2019, 41(2):370-377. DOI: 10.3969/j.issn.1000-0844.2019.02.370

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      Abstract:Ground motion characteristics are relatively affected by the local conditions of the site, and the site often needs backfill and foundation treatment before construction. Therefore, it is necessary to study the influence of the backfilled layer on the seismic response of the site. In this paper, we analyzed the two-dimensional seismic response of a nuclear power site with the software MIDAS GTS NX, i.e., thickness, shear wave velocity, and density of controlled boreholes at the site. Time histories of input ground motion have a great impact on ground motion parameters, thus the results of these parameters can vary significantly. To maximize the response of the structure and narrow the gap between earthquake action on the structure and the actual earthquake action, five time-history samples were fitted as the input seismic ground motion, and three models with different shear wave velocities of backfilled soil layer were established. The results showed that, with constant thickness of backfilled soil and constant total thickness of the model, the horizontal peak acceleration of the surface decreases with increasing shear wave velocity of the backfilled soil, but the amplitude was gradually reduced. The surface horizontal peak acceleration will no longer be affected when the shear wave velocity reaches a certain value. We also found that with increasing shear wave velocity of backfilled soil, the spectral value of the entire response spectrum will generally decrease.

    • Stress Characteristics of Soil around Belled PileFoundations under Wind and Wave Loads

      2019, 41(2):378-384. DOI: 10.3969/j.issn.1000-0844.2019.02.378

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      Abstract:Foundation soils around the belled pile foundation exhibit complex stress response characteristics when subjected to horizontal wind and wave loads. Based on the finite element program ABAQUS, finite element models of the belled pile and the equal diameter pile were established for the bearing characteristics of the single pile foundation of the offshore wind turbine. The stress characteristics of soils around the belled pile under wind and wave loads were analyzed, and the laws of the principal stress axis rotation angle of the soil around the belled pile and the equal diameter pile were compared and analyzed. The results showed that the deviation stress and principal stress direction angle of the soil around the upper pile change when the belled pile is subjected to wind and wave loads. With increasing distance between the soil around the pile and the belled pile, the rotation amplitude of the principal stress direction angle of the soil around the pile decreases gradually to a relatively stable value. The rotation amplitude variation laws of the principal stress direction angle of the soil around the belled pile and the equal diameter pile are different.

    • Experimental Study of the Dynamic Characteristics of FrozenSilty Clay under Uniaxial Step Cyclic Loading

      2019, 41(2):385-391,398. DOI: 10.3969/j.issn.1000-0844.2019.02.385

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      Abstract:To study the dynamic characteristics of frozen clay, uniaxial step loading tests were carried out at different temperatures (-0.6, -1.0, -1.5℃) and different frequencies (0.5, 1.0, 1.5, 2.0, 3.0 Hz). The results showed that the influence of temperature and loading frequency on the dynamic stiffness, damping property, and residual strain characteristics of soil becomes increasingly apparent with increasing dynamic strain amplitude. The backbone curves linearly change, and at constant dynamic strain amplitude, the dynamic stiffness increases as the temperature decreases and the frequency increases. The damping ratio increases first and then decreases gradually with increasing dynamic strain amplitude, and slightly increases at the end of loading. With the same dynamic strain amplitude, the damping ratio decreases with decreasing temperature and increasing frequency. The residual strain linearly increases with the number of cycles under the same load; the higher the loading grade, the faster the residual strain grows. At different temperatures and frequencies, dεpd/dt increases with increasing dynamic strain amplitude, and at constant dynamic strain amplitude, dεpd/dt increases with increasing temperature and decreasing frequency.

    • Influence of a Semi-circular Canyon Site on Ground SurfaceDisplacement Due to Incidence of Elastic Waves

      2019, 41(2):392-398. DOI: 10.3969/j.issn.1000-0844.2019.02.392

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      Abstract:The surface displacement responses of a semi-circular canyon site subjected to normal incidence of SH and P waves were studied using a numerical simulation method. Results were compared and analyzed with the corresponding analytical solutions. Subjected to P waves, the Rayleigh wave was generated on the semi-circular canyon site, and had certain influence on the displacement response amplitude of the free surface of the site. In the canyon, the normalized displacement amplitude in the Z direction was quite different from that without consideration of the Rayleigh wave, though there was no change at the canyon edge. There was a compression effect in the extension direction from the canyon to both sides. The normalized displacement amplitude in the X direction had no significant change in the canyon, but changed in the extension direction from the canyon to both sides.

    • A Comparative Study of Different Equivalent Linear Analysis Programs

      2019, 41(2):399-405. DOI: 10.3969/j.issn.1000-0844.2019.02.399

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      Abstract:In this paper, to evaluate the applicability of four equivalent linear analysis programs, i.e., SHAKE 2000, DEEPSOIL, EERA, and Strata, the bedrock seismic wave was chosen as the input motion on a deep site. The initial shear modulus was determined according to the shear wave velocity and density of the soils, and the corresponding modulus decay curves and damping ratio curves were assigned. Surface acceleration time-histories, the corresponding acceleration response spectra, and the Fourier amplitude spectra were obtained by using the four programs. In addition, the maximum shear strain and peak ground acceleration vs. depth for the site were plotted. The results showed that the acceleration response spectra and the Fourier amplitude spectra obtained by the four programs were identical. The plots of maximum shear strain and peak ground acceleration vs. depth obtained by program Strata were different from those of the other three programs due to different division of soil layers. The differences among the four programs were summarized as well. The dynamic properties of soil can be comprehensively considered using DEEPSOIL with more formulas, and the random vibration theory proposed by Strata could be used for equivalent linear analysis.

    • Use of a BP Neural Network Algorithm with Activation Functionto Predict the Subgrade Subsidence and DeformationInduced by Strong Earthquakes

      2019, 41(2):406-411,475. DOI: 10.3969/j.issn.1000-0844.2019.02.406

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      Abstract:In the current mode of railway subgrade deformation prediction after strong earthquakes, the algorithm fails to consider the nonlinear properties of the activation function, resulting in incomplete extraction of nonlinear deformation features and errors in the characteristic data. Based on this, the back-propagation (BP) neural network algorithm, incorporating the activation function, was proposed to predict the subgrade subsidence deformation after strong earthquakes. The nonlinear activation function of ReLU was compensated for by bipolar S factor, so as to optimize the BP neural network algorithm and solve the problem of characteristic number extraction in nonlinear subgrade deformations. Using the data standardized normalization method, the deviation data of all the characteristic data extracted and corrected was normalized to obtain the subgrade deformation characteristic data set. The subgrade subsidence deformation after a strong earthquake could then be predicted. Combined with the measured results, the prediction experiment was carried out using Matlab. The results showed that the proposed hybrid method can effectively predict the deformation degree of railway subgrade subsidence under horizontal earthquake action, and the error of predicted value is within acceptable limits.

    • Comparative Analysis of Dynamic Responses ofSoil Layers under Blast Wave

      2019, 41(2):412-417. DOI: 10.3969/j.issn.1000-0844.2019.02.412

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      Abstract:The ground motion parameters of bedrock and soils were acquired by field experiments, using an artificial blast wave as the seismic source. Field drilling was conducted and the corresponding data was obtained, and then, the seismic response analysis was carried out by equivalent linearization. The rationality of the conclusion is discussed through comparisons between the calculated and measured values. The peak acceleration comparison results show that the equivalent linearization method is better for class Ⅱ sites, and the calculated values of surface peak acceleration match well with the measured values. For class Ⅲ sites, there are relatively large discrepancies between the calculated and measured values, which vary with the overburden thickness. According to the comparison results of acceleration response spectrum, both the calculated and measured values of peak ground acceleration response spectrum are larger than those of bedrock input, and the measured values are greater than the calculated values. The width of the acceleration response spectrum is closely related to the site category, and the width of the acceleration response spectrum of class Ⅲ site is significantly larger than that of class Ⅱ site; moreover, the measured values of the two types of sites are both larger than the calculated values.

    • Dynamic Response and Influencing Factorsof Ground Fissure Sites in Xi'an

      2019, 41(2):418-427. DOI: 10.3969/j.issn.1000-0844.2019.02.418

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      Abstract:Ground fissures are densely distributed in the Xi'an area. Buildings that are "near the seam and built" are very common, which influences land use and planning in the urban zones. To research the dynamic effects of the ground fissures, this paper chose the Xi'an ground fissure site as the object of the research. After performing the shaking table test and FLAC3D numerical simulation, the dynamic response characteristics, such as acceleration amplitude of the ground fissure site, were analyzed. On this basis, the influence of different types of seismic waves, the fracture surface's dip angle at the ground fissure, the intensity of ground motion, and the soil dislocation on both sides of the ground fissures were further analyzed. The results showed that the ground fissures had an obvious effect on the dynamic response of the site, and that the peak acceleration, in a certain range, was zonal in distribution, i.e., the peak acceleration at the ground fissure was the largest. With increasing distance from the ground fissure, the peak acceleration gradually declined, becoming stable; the range of the zonal distribution was about 30 m in the hanging wall, and about 20 m in the footwall. The dynamic response of the ground fissure site showed an obvious "hanging wall effect," i.e., the peak acceleration of the hanging wall was slightly larger than that of the footwall. The ground motion intensity had an obvious effect on the dynamic response of the ground fissure site, while the dip angle of the ground fissure, seismic waves, and the soil dislocation on both sides of the ground fissures had no obvious effect on the dynamic response of the ground fissure site.

    • Application of a Sand-Filling Monitoring Method for Immersed TunnelsBased on the Frequency Spectrum Features of Elastic Waves

      2019, 41(2):428-435. DOI: 10.3969/j.issn.1000-0844.2019.02.428

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      Abstract:The sand-filling reinforcement method is widely used in the foundation treatment of immersed tunnels. However, noise during construction on complex sites will interfere with monitoring. The application and research of real-time sand-filling monitoring and detection methods has been an important issue in civil engineering. In this paper, based on the propagation characteristics of elastic waves in a multi-layered media, a non-destructive monitoring method based on the frequency spectrum characteristics of elastic waves was presented. With the full-scale model test of immersed tunnel sand filling, the response waveform of elastic waves before and after the change of lower media was obtained, and the frequency spectrum was analyzed. The horizontal layer dielectric model of the immersed tunnel was established to get the elastic wave response waveform data of the lower medium and waveform spectrum. The change range of dominant frequency of the structure before and after sand filling was set as the filter band to reduce the interference of noise on the construction site. The monitoring results obtained by the visualization window, and those obtained by the frequency spectra, were compared, and a visualization nephogram was adopted to real-time detect the sand-filling schedule of the building foundation. This research can provide the scientific basis for sand-filling construction of immersed tunnel foundations.

    • Duncan-Zhang Model Parameters of Red MudstoneBased on Triaxial Tests

      2019, 41(2):436-444. DOI: 10.3969/j.issn.1000-0844.2019.02.436

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      Abstract:The red mudstone in the Lanzhou area formed in arid and semi-arid environments has different physical and mechanical properties than that in other areas. This study investigates the red mudstone roadbed filling of Lanzhou-Haikou Maintenance Project in G6 Beijing-Tibet Expressway. Through a large number of conventional triaxial tests, the influences of the water content on the mechanical properties and Duncan-Zhang model parameters of the red mudstone were studied. The results show that the stress-strain curve of the red mudstone in the Lanzhou area satisfies the hyperbolic model under different moisture contents. When the moisture content is less than the optimum content, the failure mode is shear failure; when the moisture content is greater than the optimal moisture content, the failure mode is drum failure. With the increase of water content, the internal friction angle gradually decreases more than cohesion because the water content has different effects on the cohesion and internal friction angle. The mathematical model was used for fitting, and it was determined that the relation between the cohesion and water content and the relation between the internal friction angle and water content featured a quadratic parabola and logarithmic curve, respectively. The failure ratio, Rf, of Duncan-Chang model parameters under different moisture contents fluctuates within the interval (0.869, 0.984); the K value decreases linearly with the increase of water content, and the n value increases linearly with the increase of water content.

    • A Method of Predicting Sand Liquefaction Based on RS-PCA-GA-SVM

      2019, 41(2):445-453. DOI: 10.3969/j.issn.1000-0844.2019.02.445

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      Abstract:Sand liquefaction is a harmful natural disaster, and it is of great importance to evaluate and predict sand liquefaction in the field of geological disaster prevention and control. In this paper, the rough set theory (RS) was used to perform attribute reduction on six initial evaluation indices, including magnitude, depth of soil, epicentral distance, groundwater level, standard penetration test blow count, and earthquake duration, all of which affect sand liquefaction. After removing redundant or interference information, we obtained a data set based on four core predictors. The principal component analysis (PCA) method was then used to extract the principal component from the four-core evaluation indices. The support vector machine (SVM) was used to train the data set, and the genetic algorithm (GA) was used to optimize the parameters. Finally, the RS-PCA-GA-SVM prediction model for sand liquefaction was established. Combined with the actual data of sand liquefaction, the predicted result of the proposed model was compared with that of the back propagation (BP) neural network model based on the improved Levenberg-Marquardt algorithm (LM-BP). The calculated results showed that the accuracy of sand liquefaction prediction results based on a RS-PCA-GA-SVM model are much better than those of the LM-BP neural network. The discriminant results were in good agreement with the actual situation and can be applied in practical engineering.

    • >地震科学研究
    • Space-Time Relative Characteristics of SeismicActivity before Strong Earthquakes

      2019, 41(2):454-459. DOI: 10.3969/j.issn.1000-0844.2019.02.454

      Abstract (546) HTML (0) PDF 8.72 M (562) Comment (0) Favorites

      Abstract:Based on the correlation between the temporal variability coefficient of seismic activity before strong earthquakes and the b-value, the relative characteristics of space and time of 40 strong earthquake cases (M>6.5) are discussed in this paper. The analysis indicated that the correlation coefficient curve has the stage feature, which is caused by the b-value being deviated in the relative temporal stage with stress field variation. Next, the three elements of future strong earthquakes were estimated using the feature of the first stage of the correlation process, and some empirical formulas for predicting time and magnitude are given. Finally, the reliability of the first stage of the correlation process is discussed. The research results of this study were not apparent for small and moderate earthquakes.

    • Pre-slip and Stick-slip Phases during the Tohoku, Japan,MW9.1 Earthquake on March 11, 2011

      2019, 41(2):460-468. DOI: 10.3969/j.issn.1000-0844.2019.02.460

      Abstract (882) HTML (0) PDF 17.02 M (886) Comment (0) Favorites

      Abstract:The results of indoor rock stick-slip experiments show that one stick-slip dislocation process often includes three stages:pre-slip, stick-slip, and stop-slip. In addition, the stick-slip process is not a single point dislocation process; rather, it comprises many stick-slip dislocation processes, showing the characteristic of multi-point stick-slip dislocation in different parts of the fault.
      An MW9.1 earthquake occurred near the coast of Tohoku, Japan, on March 11, 2011. After analyzing the waveform records from the Global Seismographic Network (GSN), we identified the Xp phase about 125.5 s prior to the Pn phase from the records of the ERM station (Δ=3.8°). We then identified three stick-slip dislocation phases (Xs1, Xs2, and Xs3) and two stop-slip phases (XsQ and XsR) from the records of 98 stations in GSN. According to the results of stick-slip experiments and observation, we inferred that at the block where the ERM station was located, an impending pre-slip dislocation occurred about 69.1 s prior to the main shock, which excited the Xp phase. Following the main shock, the first stick-slip dislocation occurred during the elastic rupture process. Then, the stick-slip dislocation phase Xs1 was excited. About 27.5 s after the elastic rupture, the second stick-slip dislocation occurred, and the stick-slip dislocation phase Xs2 was excited. About 71.0 s after the elastic rupture, the third stick-slip dislocation occurred, and the stick-slip dislocation phase Xs3 was excited. About 93.1 s after the elastic rupture, the stick-slip dislocation amplitude reached its peak value of Xsm, then entered the stop-slip stage, wherein the stop-slip phase XsQ and XsR were excited. According to the fact that the periods of XsQ and XsR phases are generally greater than 75 s, we suggested that the XsQ and XsR phases may be the surface wave propagating through the mantle. The travel time relationship between XsQ and XsR phases were given. According to the observed evidence that the main shock was accompanied by three sub-stick-slip dislocation events, we suggested that the MW9.1 earthquake may have resulted from the cooperation of elastic rupture and stick-slip dislocation. Identifying the Xp phase from seismic records is helpful in understanding the pre-slip dislocation process before the main shock, with certain precursory significance. Studying the Xs, XsQ, and XsR phases will be helpful in understanding the coseismic stick-slip dislocation processes, and in judging the earthquake disaster loss.

    • Frequency Characteristics of Continuous Gravity before the 2016 Menyuan MS6.4 Earthquake

      2019, 41(2):469-475. DOI: 10.3969/j.issn.1000-0844.2019.02.469

      Abstract (578) HTML (0) PDF 10.30 M (850) Comment (0) Favorites

      Abstract:Based on continuous gravity data at the Lanzhou and Gaotai seismic stations, variations in continuous gravity prior to the Menyuan earthquake that occurred on January 21, 2016 were analyzed. Fast Fourier transform was used to conduct a power spectral analysis on data sampled five days before and two days after the earthquake. The results showed that the frequency amplitude continuously increased, then decreased to a normal value within one day of the earthquake. Furthermore, data from the second sampling, i.e., data sampled 6 days before the earthquake, was filtered, and we found that the gravity disturbance signal was observed within the 48-h preceding the earthquake, with a period of 4-8 s. The frequency characteristics and gravity disturbance signal observed prior to the Menyuan earthquake may reflect a whole seismogenic process before the earthquake, providing a reference for revealing the mechanism of the Menyuan earthquake.

    • A Method for Random Noise Elimination from Seismic Data Based onthe Neural Network-improved Wavelet Transform

      2019, 41(2):476-481. DOI: 10.3969/j.issn.1000-0844.2019.02.476

      Abstract (602) HTML (0) PDF 6.53 M (846) Comment (0) Favorites

      Abstract:The effective signal of seismic data reflects weakly and is affected by multiple waves, so random noise interference inevitably exists. A method of removing random noise from seismic data based on a neural network-improved wavelet is proposed. The neural network model was used to identify the random noise signal. The signal was decomposed by wavelet packet to obtain multi-class random noise signal. The cascaded back-propagation algorithm (BP) network model was used to extract multi-class random noise signals, the random signal suppression of seismic data was realized. The experimental results showed that the improved wavelet method has a better denoising effect on the random noise signals in seismic data, and has strong applicability in suppressing random noise in the seismic data in complex sedimentary geological structures.

    • Discussion of the Existence of the Surface Rupture along theSouth Segment of the Minjiang Fault and Causes of theAbnormal Negative Orography on Manaoding

      2019, 41(2):482-488. DOI: 10.3969/j.issn.1000-0844.2019.02.482

      Abstract (600) HTML (0) PDF 21.16 M (1012) Comment (0) Favorites

      Abstract:The existence of the surface rupture along the south segment of Minjiang Fault has been a controversial issue in recent years. The study area is located in the middle segment of the north-south seismic belt, amid strong seismic activity. The 1933 Diexi earthquake in the study area was an important earthquake in modern history, but the seismogenic fault of this earthquake is still not clear. In 2017, the Jiuzhaigou M7.0 earthquake occurred in the study area. Therefore, the seismic risk analysis of the south segment of Minjiang Fault is very important, and the existence of the surface rupture is the first thing to check. In this paper, we denied the existence of the surface rupture along the south segment of Minjiang Fault, and analyzed the causes of the abnormal negative orography on Manaoding.

    • Interference Factors in the Earth Geo-resistivityObservation in Shaanxi Province

      2019, 41(2):489-499. DOI: 10.3969/j.issn.1000-0844.2019.02.489

      Abstract (603) HTML (0) PDF 19.10 M (552) Comment (0) Favorites

      Abstract:Based on the earth geo-resistivity observation data in Shaanxi Province from 2011 to 2018, we analyzed the main factors that affect these observations, including the failure of the observation system, the interference of the natural environment, and the interference of the site environment. In this paper, we calculated the interference amplitude of the observed data, and obtained the time scale of the interference. We then analyzed the form of each type of interference and the morphological characteristics of the observation data curve. Based on this, we proposed methods and made recommendations for interference suppression, and analyzed the physical mechanism of observed data change under the influence of interference factors. In addition, we clarified the basic workflow of data application in earthquake prediction, declared the importance of identifying all types of interference factors accurately, sought ways to solve interference problems, and explored new methods to process interference data.

    • Tracing Tests on the Phenomenon of Microwave FluctuationPreceding Impending Strong Earthquakes

      2019, 41(2):500-506. DOI: 10.3969/j.issn.1000-0844.2019.02.500

      Abstract (626) HTML (0) PDF 10.24 M (973) Comment (0) Favorites

      Abstract:The phenomenon of microwave fluctuation before impending strong earthquakes is a type of anomalous pulsation record; its dominant frequency of spectrum focuses on 11-16 Hz and frequency spectral morphology appears fairly orderly. Microwave fluctuations occurred before the Wenchuan, Yushu, Qingchuan, and other strong earthquakes, and they can be used for predicting the strength of impending strong earthquakes. To conduct a tracing test on such microwave fluctuations, continuous records of microtremors were analyzed using the "real-time monitoring technology system of microtremor in Lanzhou"; these microtremors occurred in the three months before four M ≥ 5.5 earthquakes which occurred in the Qinghai-Tibet Block and Xinjiang area during 2015 and 2016. The reproducibility of the microwave fluctuation of impending earthquakes was verified by the abnormal amplitude change and duration of microwave fluctuation. The tracking test results were in accordance with seismic tracking indexes based on the microwave fluctuation preceding impending earthquakes proposed by Yang Liming.

    • >地震应急
    • Urban Earthquake Disaster Assessment and EmergencyResponse Based on a GIS System

      2019, 41(2):507-512. DOI: 10.3969/j.issn.1000-0844.2019.02.507

      Abstract (663) HTML (0) PDF 2.28 M (545) Comment (0) Favorites

      Abstract:Earthquake prevention and mitigation are key demands of our country. To address the problem of poor flexibility currently existing in our urban seismic response, we applied, in this paper, a GIS system to the urban earthquake emergency and disaster relief response. The established GIS system made use of an earthquake disaster assessment module, database management module, and earthquake emergency response and command decision module to constitute the emergency response framework for urban earthquake disaster relief. This system completed the application analysis of the urban GIS system. In the seismic disaster assessment module, total loss, economic loss, and loss of life caused by earthquake damage were calculated, and satisfactory accuracy in seismic disaster assessment information data was realized. The disaster relief emergency response database in the database management module mainly used vector data, digital orthophoto map data, and other special data to improve the flexibility of the urban emergency response to earthquake relief. In the response and decision-making module, the core server was used to transmit the data information and realize the rapid rescue response. In the study, the GIS system was compared with current methods, and a comparative experiment was carried out on the flexibility of the earthquake relief process and the precision of rescue data. The experimental results showed that the rescue data provided by the proposed system are accurate, and some indices used in the operation process are superior to those of the current research.

    • Power Network Security Detection for a Post-EarthquakeEmergency Power Supply

      2019, 41(2):513-519. DOI: 10.3969/j.issn.1000-0844.2019.02.513

      Abstract (562) HTML (0) PDF 1.18 M (496) Comment (0) Favorites

      Abstract:Current safety detection methods for emergency power supply following an earthquake generally ignore the three-phase current asymmetry of the power grid node; nor are node power of the network, branch current, and network loss calculated. This results in low accuracy in node network safety detection. Based on this premise, a power network security detection method for emergency power supply following earthquakes is proposed. According to the operation parameters of the connectivity matrix power network node, the voltage vector of different nodes was obtained using the power flow calculation. The fast-coupled method was used to optimize the calculation speed of the Newton-Raphson method, and node power, branch current, and network loss values were calculated. Based on the constructed safety detection model of the power network node connectivity, the Monte Carlo method was used to accomplish the power network security detection for emergency power supply following an earthquake. The experimental results showed that the proposed method could effectively detect the safety of power network nodes for post-earthquake emergency power supply. When the vibration acceleration was 0.05 gal, 0.20 gal, and 0.80 gal, the safety test results of the experimental objects were high, medium, and extreme, respectively, which was consistent with the actual results, and indicated that the proposed method can also accurately detect the security of the connectivity of power network nodes.

    • A Disaster Information Collection System Based on VisualizationRemote Sensing Technology in Earthquake Areas

      2019, 41(2):520-525,538. DOI: 10.3969/j.issn.1000-0844.2019.02.520

      Abstract (520) HTML (0) PDF 3.92 M (638) Comment (0) Favorites

      Abstract:Earthquake sites are different from general disaster sites, and their disaster areas are relatively large. However, collected disaster information based on remote sensing can prove scattered and confused, and cannot form visual analysis results. To solve this problem, a disaster information collection system for a large earthquake area, based on visualization remote sensing technology, was designed in this paper. The system hardware consisted of a network communication layer, a data collection layer, a database layer, a GIS remote sensing platform layer, and an application layer. The advantages of using remote sensing to gather information was harnessed, and the three-dimensional reconstruction technology of GIS was applied to visualize the disaster information. The experimental results showed that the maximum response time of the system is 1.857 s, and the maximum CPU occupancy and consumption were 80.8% and 1 656 MB, respectively. There was a high degree of recurrence of information visualization.

    • Design of a Computer Online Simulation System forEarthquake Disaster Scenes

      2019, 41(2):526-531. DOI: 10.3969/j.issn.1000-0844.2019.02.526

      Abstract (916) HTML (0) PDF 5.61 M (690) Comment (0) Favorites

      Abstract:The traditional large-scale multi-channel seismic simulation system lacks the visual integration of the earthquake disaster scene, and the viewing effect is poor. Thus, a computer online simulation system of earthquake disaster scenes based on GIS was designed for this paper. The system was composed of a data layer, a logic layer, and an application layer. From two aspects of the system level division and software realization, the online simulation of an earthquake disaster scene was developed. According to the GIS data of the research area and the underlying support of the development components, a 3D pixel set model of the buildings at the scene was constructed using the automated integration function of the disaster scene-generating module in the logic layer. A simulated reconstruction of the disaster scene was then realized through determination of the ground motion field and the three-dimensional coordinate transformation. The experimental results showed that the minimum mean error of the simulated earthquake disaster scene image was only 3.4, and the function and performance of the system could meet actual needs.

    • >技术交流及其他
    • An Earthwork Construction Method of Building Foundationsin Post-earthquake Reconstruction Areas

      2019, 41(2):532-538. DOI: 10.3969/j.issn.1000-0844.2019.02.532

      Abstract (620) HTML (0) PDF 3.72 M (562) Comment (0) Favorites

      Abstract:Considering the influence of seismic activity on building damage, the errors between calculated and actual quantities of earthwork are large in current earthwork foundation construction, resulting in settling and time-consuming construction at later stages. This paper puts forward a method for earthwork foundation construction and applies it to a reconstruction area after an earthquake. We analyzed the problems of water accumulation, rubber soil, and substandard density in the construction site, and proposed corresponding solutions. By calculating the quantity of earthwork per unit area, the total quantity of earthwork in the construction site building foundation was obtained. Using these calculated results, combined with the conditions at the construction site, the duration requirement, and the design scheme, Navisworks software and Revit were adopted to construct a three-dimensional model. According to the simulation results, the construction scheme was adjusted and optimized, and the foundation earthwork construction for the building in the post-earthquake reconstruction area was completed. The experimental results showed that the accuracy of earthwork calculation results with the proposed method is high, and that settling induced by earthquake can be restrained to a certain extent. The construction time is short and the overall construction efficiency is high.

    • A Fuzzy Comprehensive Evaluation Model for Seismic Behaviorof Assembled Steel-Concrete Composite Structures

      2019, 41(2):539-544. DOI: 10.3969/j.issn.1000-0844.2019.02.539

      Abstract (590) HTML (0) PDF 1.18 M (473) Comment (0) Favorites

      Abstract:The current parameterized building information model of assembled steel-concrete composite structures lacks structural information and cannot realize the modification and self-renewal of the drawings of assembled steel-concrete composite structures. Therefore, both the damage assessment effect of structural members and the seismic reinforcement performance are poor. This paper presents a building information model for seismic reinforcement of assembled steel-concrete composite structures. The model framework included a building design model, a structural design model, a seismic reinforcement design of the building, and damage assessment. Through solid definition, attribute definition, and association definition of structural members, the seismic strengthening performance information regarding the steel-concrete composite structural members, i.e., columns, beams, slabs, and walls, was comprehensively described. The accurate comprehensive damage index of structural members was obtained to evaluate the reinforcement grade of the structural members by using a fuzzy reinforcement evaluation method. The experimental results showed that the error between the damage index obtained by the proposed model and the actual damage index was < 0.03, which indicated that the accuracy of the model for seismic reinforcement of assembled steel-reinforced composite structures is relatively high.

    • Coupling Relationship between Noise of a Very BroadSeismometer and the Environment

      2019, 41(2):545-548. DOI: 10.3969/j.issn.1000-0844.2019.02.545

      Abstract (622) HTML (0) PDF 4.58 M (707) Comment (0) Favorites

      Abstract:In this study, the theoretical model of the vertical leaf spring system for very broadband seismometers was analyzed, and the influence of pressure changes on the LP noise of the instrument is discussed. The theoretical analysis showed that the vertical leaf spring system is quite affected by pressure changes. Then, according to the theoretical model of the leaf spring system, a kind of sealing installation method was designed, and the coupling relationship between the noise and the environment (pressure, temperature, and the base deformation) is discussed through experiments. Finally, the power spectrum noise analysis results of the experimental data showed that, after vacuuming, the noise in the three branch directions of the seismometer was reduced, at 100 s, by 10 dB, 5 dB, and 6 dB in the vertical direction, east-west direction, and north-south direction, respectively.

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