• Volume 39,Issue 6,2017 Table of Contents
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    • >地震工程
    • Influence of the Taihe Palace Foundation Bed on the SeismicPerformance of Its Superstructure

      2017, 39(6):981-995. DOI: 10.3969/j.issn.1000-0844.2017.06.0981

      Abstract (654) HTML (0) PDF 10.34 M (930) Comment (0) Favorites

      Abstract:Taihe Palace is located in the front part of the Forbidden City, Beijing, China, and is composed of foundations, a wooden frame, tou-kung (bracket sets), a roof (hip type), and filler walls. The beams and columns of the building are connected by a tenon-mortise joints. Taihe Palace represents the apotheosis of Chinese ancient timber buildings. Its foundation bed is composed of a stylobate and high platform. To effectively protect Chinese ancient timber buildings, Taihe Palace is taken as an example to study the influence of its foundation bed on the seismic performance of its superstructure. Based on its constituent characteristics such as the foundation bed, free-standing column root, tenon-mortise connection between beam and column, and bracket sets (tou-kung) on the column tops, two finite element models of the building, with and without the foundation bed, were built. Using modal analysis, the influence of the foundation bed on the natural vibration characteristics of the upper structure was studied. Using response spectrum analysis under an 8-degree intensity of frequently occurring earthquakes, the influences on the distribution of internal force and deformation of the upper structure were discussed. Using time history analysis under an 8-degree intensity of seldom-occurring earthquakes, the influences on the acceleration and displacement response of the upper structure were analyzed. Results show that when the foundation bed is considered as part of the whole structure, the basic frequency of the structure decreases and the participation coefficients of its main modes increase. Compared with the structure without a foundation bed, under the 8-degree intensity of frequently occurring earthquakes, the principle tension and compression stresses in the timber part increase separately; in the filler wall, the principle tension and compression stresses decrease and its deformation increases. The main reason is that the foundation bed itself participates in the vibration, which decreases the stiffness of the whole structure. In addition, the peak stress values of the foundation bed are all with permissible limits. Under the 8-degree intensity of seldom-occurring earthquakes, although its vertical response slightly decreases, its acceleration and displacement in the horizontal direction obviously increase. Thus, it is necessary to consider the dynamic magnification effects of the foundation bed on the upper structure of Taihe Palace.

    • Influence of Isolation and Collapse Prevention Bearings and Locationof Stairwells on the Seismic Performance of Frame Structures

      2017, 39(6):996-1004. DOI: 10.3969/j.issn.1000-0844.2017.06.0996

      Abstract (727) HTML (0) PDF 2.90 M (849) Comment (0) Favorites

      Abstract:To study the influence of isolation and collapse prevention bearings at the end of a stair plate and location of the stairs on the seismic performance of reinforced concrete frame structures, three groups and six models including isolation collapse prevention supports were built using the ETABS software. The effect of frame structures with isolation and collapse prevention bearings and stairwell location on the vibration, internal force, and failure mechanism were analyzed by modal analysis, response spectrum analysis, and pushover analysis. The calculation results show that the location of the stairwell has little impact on torsion of the frame structures after adding isolation and collapse prevention bearings, and the vibration in the two major axes directions of the frame structure is similar, that is, the internal force of the stair columns is significantly reduced. When the layout of the stairwells is in the side span, the internal force of the stair columns is stronger when the frame is subjected to an earthquake in the direction perpendicular to the ladder. The frame beams have improved the structural seismic performance by dissipating the earthquake energy. The overall stability of the stairs can be guaranteed with the isolation and collapse prevention bearings, and the failure of the stairs is delayed during a major earthquake.

    • Seismic Response Analysis of Long-span Rigid Frame-continuousGirder Bridges in High Intensity Region

      2017, 39(6):1005-1010. DOI: 10.3969/j.issn.1000-0844.2017.06.1005

      Abstract (758) HTML (0) PDF 6.08 M (973) Comment (0) Favorites

      Abstract:Considering the geological structure activity in the Wenchuan earthquake fault zone, the seismic performance of bridges in the area must be considered in design. As is a typical case of a long-span rigid frame-continuous girder bridge in a mountain area, the Yangjigou left line bridge was selected in this study in order to investigate the seismic response of this kind of bridge in the high intensity region. Multiple finite element models were developed with Midas software, and the horizontal seismic waves in the longitudinal and transverse directions of the bridge were considered. By comparing the results of the response spectrum and time-history analysis, the dynamic response characteristics of the bridge structure were obtained, which can provide a reference basis for the design of long-span rigid frame-continuous girder bridges. The analysis results reveal that the response spectrum method should not be adopted in order to analyze the rigid frame-continuous system, when it is a single-pier rigid frame. When carrying out a time-history analysis on the seismic performance of bridges in the high intensity region, we do not only have to adopt suitable seismic waves, but also have to select artificial waves converted from local seismic parameters as the seismic excitation source. Due to construction restrictions in mountainous areas, bridge piers may have unequal heights. The internal force concentration caused by the great stiffness of the short pier can be avoided by changing the cross-section shape of the pier, and the connection mode between the girder and pier, in order to adjust the internal force distribution.

    • Seismic Response of Deep-buried Circular TunnelsUnder No-slip Interface Conditions

      2017, 39(6):1011-1017. DOI: 10.3969/j.issn.1000-0844.2017.06.1011

      Abstract (611) HTML (0) PDF 8.21 M (843) Comment (0) Favorites

      Abstract:The seismic response of underground structures is mainly determined by the soil deformation induced by seismic wave propagation and soil-structure interaction. The ovalization of tunnel lining during the process of shear wave propagation reduced the effective bearing capacity of lining. The resulting change of shape of tunnel section generates circumferential strains in the tunnel lining, which can cause cracking and/or crushing of concrete and reduce the carrying capacity of the lining. Since the dimension of a typical lining cross-section was small, in comparison to the wavelength of the dominant ground motion, and the inertial effects in both the lining and the surrounding soil were relatively small, therefore, the response of the cross-section induced by seismic motions could be considered as a response to an imposed uniform strain field. Transversal behavior is usually studied by analyzing the response of the cross-section to an imposed uniform strain field by using the pseudo-static approach. In general, most pseudo-static approaches are developed based on the relative stiffness method, which can take soil-structure interaction into account. In this paper, the available closed-form solutions under no-slip interface conditions (no relative shear displacement), which are developed based on the relative stiffness methods, were reviewed, and then the seismic response of a circular tunnel was analyzed, both analytically and numerically, in order to investigate the seismic response of tunnels subjected only to shear waves. The research is of great interest for evaluating the reliability of analytical solutions as well as the reliability of numerical approaches.

    • Damage Analysis of Panel Structures in Reinforced ConcreteBuildings Subjected to Continuous Vibration

      2017, 39(6):1018-1023. DOI: 10.3969/j.issn.1000-0844.2017.06.1018

      Abstract (651) HTML (0) PDF 1.33 M (844) Comment (0) Favorites

      Abstract:To analyze the degree of damage to panel structures in reinforced concrete structures under continuous vibration we need to perform regression calculations on a large amount of data; therefore, we cannot determine the bearing capacity of such panels quickly and effectively enough to avoid building damage. Here to simplify the calculation process in the traditional method, a new method for analyzing the degree of damage to panel structures in reinforced concrete structures under continuous vibration is proposed. The parameters of the building materials, reinforcing material, panel cross-section, and unit material were determined and a finite element model of the reinforced concrete panel structure established. Through analysis of the internal and external forces that destroy panel structures under continuous vibration, the overall degree of failure of the panel was determined. The experiment results show that this new method can effectively determine the shear bearing capacity and flexural bearing capacity of panels, and thereby help avoid building damage due to panel structures losing their supporting force.

    • Invulnerability Estimation Model of Buildings withComplex Networks under Strong Earthquakes

      2017, 39(6):1024-1028. DOI: 10.3969/j.issn.1000-0844.2017.06.1024

      Abstract (652) HTML (0) PDF 1.22 M (799) Comment (0) Favorites

      Abstract:The seismic hazard environment and associated vulnerability of urban buildings are key factors affecting the seismic ability of buildings with complex networks under strong earthquakes. However, evaluating the seismic capacity of buildings is problematic because pre-assessment results are not adequately accurate, and it is only possible to determine the degree of damage using a damage assessment after the building has been destroyed by an earthquake. This study proposes a seismic capacity evaluation method for buildings with complex networks. In consideration of risk factors affecting buildings during earthquakes, peak ground acceleration is used as a parameter to evaluate and analyze the invulnerability of complex building networks under strong earthquakes. In addition, seismic ability indexes are proposed to evaluate the seismic performance of complex building networks. The seismic capacity level is then obtained using seismic capacity assessment criteria, and simulation experiments are conducted. The effectiveness of the proposed method is also confirmed using data of actual earthquake damage.

    • Study on Seismic Stability of a Tunnel Portal Section based onthe Strength Reduction Method

      2017, 39(6):1029-1036. DOI: 10.3969/j.issn.1000-0844.2017.06.1029

      Abstract (660) HTML (0) PDF 5.66 M (892) Comment (0) Favorites

      Abstract:Recently, the strength reduction method (SRM) has gained importance in static and dynamic fields of Geotechnical Engineering. Based on this method, the dynamic safety factor of slopes and tunnels has been studied by scholars. As a complicated 3-dimensional structure, the tunnel portal section is partly influenced by the interaction between the surrounding rock, slope, and lining of the structure. Seismic stability research is now mostly conducted for qualitative descriptions. To evaluate the dynamic stability of such projects and provide references for design and construction, quantitative indexes should be developed. According to the shaking table test, a numerical model of a 3-dimensional tunnel portal section is built, in which the SRM is adopted to acquire a dynamic safety factor of this section. In this study, the plastic energy criteria (PEC) combined with the catastrophe theory (CT) is used as the failure judgment of the model in deciding the safety factor. Using the CT, the critical changing point of the reduction factor-plastic energy curve is decided. The safety factor of the model then becomes the reduction factor at this critical point. Results show that the PEC combined with the CT have a small error and exhibit the advantages of simplicity and convenience compared with other failure criterion such as displacement criterion, non-convergence criterion and the criterion of plastic zone connection. The dynamic safety factor of the model is smaller than the static safety factor, which is in accordance with the law that structures exhibit lower stability under dynamic loading. The dynamic safety factor is 1.52 for the model, indicating that the portal section in simulating is rather stable, which agrees with the shaking table test results. The results show that the PEC combined with the CT is feasible in such engineering cases, which could provide reference for similar projects.

    • Analysis of the Response Acceleration Method Related to the SeismicDesign of Underground Rail Transit Structures

      2017, 39(6):1037-1045. DOI: 10.3969/j.issn.1000-0844.2017.06.1037

      Abstract (778) HTML (0) PDF 2.88 M (1366) Comment (0) Favorites

      Abstract:Obtaining a proper displacement time history is the most important procedure in the seismic design of underground rail transit structures when using the response acceleration method. This paper develops a practical method for obtaining displacement time histories by effectively eliminating baseline drift difficulties. The principles and basis of choosing a seismic design method is clarified by presenting the seismic design procedure for underground rail transit structures. Based on expounding the fundamental principles of the response acceleration method, a one-dimensional equivalent linearization approach is proposed. Discussions on the parameters that influence the effectiveness and precision of the calculation results for soil seismic response are presented. For the acceleration time-history curves derived from the one-dimensional soil seismic response calculation, this paper puts forward an approach which eliminates the drifting problem induced by long period random components of acceleration by properly simulating its second-order parabolic baseline equation. Therefore, displacement time history without baseline drift can be obtained by natural integration. Meanwhile, this paper describes the procedure and approach in which the baseline drift problem in an integral displacement time history can be effectively solved by properly applying the numerical analytical software Origin Pro. Taking the Beijing Metro line 3 as an example, this paper illustrates how every pertaining technical procedure and analytical calculation in the response acceleration method can be achieved. This study emphasizes that the analysis of soil seismic response and determination of displacement time histories are relatively complicated and specialistic. Therefore, special analytical engineering consultation work should be carried out accordingly. When the acceleration response spectra and time histories acquired through the one-dimensional soil seismic response approach are objective and reasonable, then the equivalent shear modulus under different probabilities of exceedance applied in FEM are trustworthy. Furthermore, the baseline drift problem must be appropriately handled when displacement time histories are obtained by the integral method. The abovementioned pertaining results are objective and trustful, therefore, soil-underground structure seismic response can be truly simulated by FEM.

    • >土动力学
    • Dynamic Deformation Characteristics of Remolded RedClay Under Bi-directional Dynamic Load

      2017, 39(6):1046-1053. DOI: 10.3969/j.issn.1000-0844.2017.06.1046

      Abstract (562) HTML (0) PDF 1.47 M (502) Comment (0) Favorites

      Abstract:The dynamic shear modulus and damping ratio are important parameters for describing the dynamic characteristics of the soil. In this study, the dynamic deformation characteristics of red clay under bi-directional dynamic load was investigated by using a SDT-20 dynamic triaxial apparatus. The impact of moisture content, consolidation stress, consolidation ratio, and radial dynamic load amplitude, on the dynamic deformation characteristics of red clay, such as the hysteresis loop, dynamic shear modulus, dynamic stress-strain relationship, and damping ratio, were analyzed. The experimental results show that when the phase difference was 0 and all other conditions were the same, the dynamic shear modulus of the red clay decreased with the increase of radial dynamic load amplitude. The relationship between the dynamic shear strain of the red clay and vibration frequency was approximately demonstrated by an exponential function under a bi-directional dynamic load, and there was a critical cycle number Ndc. With the increase of moisture content and consolidation stress, the failure mode of red clay changed from tensile damage to compression damage. Tensile damage was more likely to happen with the increase of radial dynamic load amplitude. The change of the damping ratio did not present a certain rule with the increase of dynamic shear strain under bi-directional dynamic loading. When the dynamic shear strain was less than 1%, there was no regular pattern in the change of the damping ratio, while the dynamic shear strain was more than 1%, and the damping ratio was stable with the increase of dynamic shear strain. The radial dynamic load amplitude had no obvious impact; however, the moisture content had an effect on the damping ratio. When the moisture content was less than 20%, the damping ratio increased with the increase of moisture content; while the moisture content was more than 20%, its influence on the damping ratio was negligible. This study could be used as a reference for the further design of dynamic deformation characteristics and numerical calculation.

    • Reflection of SV Wave at the Free Surface of Saturated Soils

      2017, 39(6):1054-1061,1096. DOI: 10.3969/j.issn.1000-0844.2017.06.1054

      Abstract (661) HTML (0) PDF 2.70 M (601) Comment (0) Favorites

      Abstract:Based on the elastic wave equation for a fluid-saturated porous medium, in this study, we analyzed the reflection of an SV wave at the free surface of saturated soils. Then, under incident SV waves, we calculated the displacement, velocity, acceleration, and stress responses in the free field of saturated soils. Based on the analytical solutions to these responses, we established a static-dynamic coupling finite element method model to consider the following factors:(1) We used a Duncan-Chang constitutive model during the initial stress field balance step and the Davidenkov constitutive model during the earthquake input step. (2) We used a viscous-spring artificial boundary for saturated porous media and applied some springs and damps on the artificial boundary to simulate energy propagation in saturated soils. (3) We generated the wave input by the equivalent load of the earthquake on the node of the artificial boundary. (4) We considered soil elements as 4-node plane strain pore pressure elements (CPE4P). We then compared the numerical results with our analytical solutions and drew the following conclusions:(1) No vertical displacement response appears under vertical and grazing incidences of SV waves. (2) Peak horizontal displacement response occurs when the incident angle of an SV wave is about 45°. (3) The peak vertical displacement response is reached when the incident angle of an SV wave is about 60°. The above conclusions show good agreement with the analytical results. As such, the proposed numerical model provides a good basis for building soil-structure dynamic interaction models.

    • Effect of Variability in Soil Dynamic Parameters on the Ground MotionParameters of a Site Surface in the Tianjin Area

      2017, 39(6):1062-1069. DOI: 10.3969/j.issn.1000-0844.2017.06.1062

      Abstract (617) HTML (0) PDF 1.44 M (766) Comment (0) Favorites

      Abstract:In recent years, seismic safety evaluation has been conducted at many engineering sites in the Tianjin area where dynamic nonlinear soil parameters can be obtained. In this study, we collected 83 seismic safety evaluation reports in this area and obtained 1 650 groups of dynamic triaxial data on soil from 202 boreholes. We then determined the representative values and their standard deviations of different types of soil at different intervals and different depths. A typical site Ⅲ is taken as an example. By using the equivalent linearization method to calculate the seismic response of the site under different ground motion intensities and phases, we studied in detail the influence of variability in the dynamic shear modulus ratio and damping ratio of the overlying soil on the peak ground acceleration and response spectrum of the site. The results show that the peak ground acceleration and ground response spectrum of the site increase or decrease with an increase or decrease, respectively, in the soil dynamic shear modulus ratio. However, the acceleration and spectrum increase or decrease with a decrease or increase, respectively, in the soil dynamic damping ratio. Under the input of a great earthquake, the soil dynamic shear modulus ratio decreases, and the peak ground acceleration and medium and high frequency portions of ground response spectrum decrease clearly. The change in the dynamic damping ratio also has a certain impact on peak ground acceleration and the ground response spectrum, but this is not as obvious as the change in the soil dynamic shear modulus ratio. Under the input of moderate and small earthquakes, variability in the soil dynamic shear modulus ratio and damping ratio have little impact on the peak ground motion acceleration and ground response spectrum.

    • >地震科学观测
    • Maximum Detective Range of the Large-volume Airgun ActiveSource in Qilian Mountains, Gansu Province

      2017, 39(6):1070-1075. DOI: 10.3969/j.issn.1000-0844.2017.06.1070

      Abstract (822) HTML (0) PDF 19.45 M (644) Comment (0) Favorites

      Abstract:Numerous waveform data, which continuously vary owing to excitation by the large-volume, airgun active source in Qilian Mountains, Gansu Province and are recorded by the Gansu and Qinghai digital seismic network, are stacked in this study. The results reveal that after single excitation, the airgun source signals could be detected by the GLT station located 304 km away from the source; the signals stacked 110 times could be detected by the AXX station located 412 km away from the source; and the signals stacked 4,600 times could be detected by the WTM station located 677 km away from the source. The findings of this study are of great scientific importance for improving the monitoring capability of the large-volume, airgun active source observation system in Qilian Mountains, extracting weak signals, and discussing the velocity change of internal medium in Qilian Mountains.

    • Research and Modification of Short Period Calibration Function ofLocal Earthquake Magnitude (ML) in Ningxia Area

      2017, 39(6):1076-1083. DOI: 10.3969/j.issn.1000-0844.2017.06.1076

      Abstract (674) HTML (0) PDF 7.20 M (733) Comment (0) Favorites

      Abstract:To calculate the deviation, average deviation, and standard deviation between single-station and average magnitudes in the Ningxia area, we performed a residual and multiple regression analysis of the magnitude, and selected 7 345 items of data from 1 782 seismic events recorded by the Ningxia broadband digital seismic network from January 2009 to December 2016. We analyzed the frequency distribution of the magnitude deviations and modified the calibration function of the local earthquake magnitude (ML) to obtain the calibration function of the local uniform magnitude system for the Ningxia region. We obtained the attenuation characteristics of the maximum ground displacement and corresponding calibration function by multiple regression analysis. Our results show that the modified mean square variance of the magnitude reduces from 0.2370 to 0.2289, and the maximum modified magnitude value is 0.51.

    • Analysis of Lithospheric Magnetic AnomalyCharacteristics in Fujian Region

      2017, 39(6):1084-1089. DOI: 10.3969/j.issn.1000-0844.2017.06.1084

      Abstract (599) HTML (0) PDF 21.85 M (771) Comment (0) Favorites

      Abstract:In this study, we obtained information on the characteristics of the lithosphere magnetic field in the study area using four mobile geomagnetic observation datasets recorded in the Fujian region during 2014-2015. In order to separate shallow and deep anomalies, the data was processed with upward continuation, at depths of 5 km, 10 km, 20 km, and 30 km, among others, and the deep anomalies were extracted. The results show that there were obvious geomagnetic anomalies in the Changle-Zhaoan fault zone, which might be related to the geological structure distribution and the seismic activity in the Fujian region.

    • The Application of Comprehensive Prospecting Method in The TaiyuanBasin Dongshan Piedmont Fault

      2017, 39(6):1090-1096. DOI: 10.3969/j.issn.1000-0844.2017.06.1090

      Abstract (609) HTML (0) PDF 12.55 M (752) Comment (0) Favorites

      Abstract:Dongshan piedmont fault of Taiyuan basin in the East, is the north boundary fault in the Taiyuan basin. Previous data indicate that the fault is a late Pleistocene active fault, From Taiyuan city active fault detection and seismic hazard assessment project, the Dongshan piedmont fault detailed exploration, Exploration methods include high density resistivity、shallow seismic exploration and borehole profile exploration. Based on fault location by multi-channel DC resistivity and shallow seismic exploration, using bore associated profile detection of faults accurately positioning, Combined with the sample test to determine the fault era. Multi channel DC exploration confirms the presence of Dongshan piedmont fault and the approximate position, Shallow seismic exploration and bore associated profile determine exact location and upper buried depth of the fault. The latest active age of fault was obtained by drilling age sample. Obtained by detecting:Dongshan piedmont fault was consisted of three faults, Three faults F1, F3 dip westward, F2 dip East, F1 is dominated fault.Fault breakpoint buried about 16.7 m, faulted middle Pleistocene stratum, Fault distance is about 23.96 m. Age of fault activity is middle Pleistocene. The results have corrected the conclusion of the previous studies that it is the late Pleistocene active fault. The results provide a key basis for the seismic hazard analysis of Taiyuan basin, and also play an important role in urban planning and construction of Taiyuan. Compared three methods:multi-channel DC exploration can preliminary determine the fault location, The high resolution seismic exploration and drilling geological section is the effective method to determine the location and activity of the buried faults.

    • Comparative Study on Seismic Mitigation and Isolation Schemes fora Long-span Railway Steel Truss Continuous Beam Bridge

      2017, 39(6):1097-1104. DOI: 10.3969/j.issn.1000-0844.2017.06.1097

      Abstract (629) HTML (0) PDF 1.65 M (834) Comment (0) Favorites

      Abstract:To investigate appropriate seismic mitigation and isolation schemes and rational optimal parameters for long-span railway steel truss continuous beam bridges, based on a three-span railway steel truss continuous beam bridge with a total length of 504 m, a finite element model was built with the non-linear finite element analysis program SAP2000. The damping efficiencies of different seismic mitigation and isolation devices, such as the friction pendulum, lock-up device, and damper, were compared by the fast non-linear analysis method. The results showed that, since the natural vibration of bridge piers may cause significant earthquake force, the scheme with a friction pendulum system does not show high efficiency. The lock-up device will greatly increase the seismic input energy of this kind of bridge, therefore, it is not recommended in this case; the scheme with a damper can significantly reduce the seismic response of piers with movable bearings; however, it cannot effectively reduce the seismic response of piers with a fixed bearing. A combination of the friction pendulum bearing and damper can effectively control the internal forces and the displacement response of this type of bridge. The conclusions can provide valuable reference for the seismic isolation of long-span railway steel truss continuous beam bridges.

    • >动力响应分析及其他
    • Dynamic Response Analysis of Composite Frames with Concrete-filledSteel Tubular Columns Based on Non-linear Fiber Beam Element

      2017, 39(6):1105-1110. DOI: 10.3969/j.issn.1000-0844.2017.06.1105

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      Abstract:Due to their excellent mechanical performance, such as seismic performance and fire resistance performance, concrete-filled steel tube structures have been widely used in high and super-high building structures. In order to investigate the seismic performance of concrete-filled steel tube structures under the effect of earthquake, this paper developed a finite element model of composite frames with concrete-filled steel tubular columns and steel beams with RC slabs by the separate modulus approach and uniform modulus approach, respectively. By using the ABAQUS software, the two validated calculation models of the separate modulus approach and uniform modulus approach were used in order to perform finite element analysis and elastic dynamic time-history analysis of a 13-story composite frame structure with concrete-filled steel tubular columns and steel beams with RC slabs under three different frequent earthquake waves. The top story displacement versus time curves, acceleration time-history responses, story lateral displacement, and the dynamic magnification factors of the frame, were contrasted based on the two models. The results show that the separate modulus approach and uniform modulus approach did not vary much for the dynamic performance analysis of composite frame with concrete-filled steel tubular columns and steel beams with RC slabs under frequent earthquake. However, the separate modulus approach can be used in elastic-plastic analysis, while the uniform modulus approach needs the expression of the stress-strain curve in elastic-plastic analysis, which requires further study.

    • Dynamic Characteristics Analysis of Widening Embankmentsunder Asymmetric Traffic Loading

      2017, 39(6):1111-1117. DOI: 10.3969/j.issn.1000-0844.2017.06.1111

      Abstract (606) HTML (0) PDF 3.94 M (688) Comment (0) Favorites

      Abstract:A numerical model was established for the widening of a road embankment subjected to long-term asymmetric traffic loading in Shanxi Province, China. The model was created using FLAC3D software, with traffic load simplified to half-sine wave. The geogrid was simulated by FLAC3D structural element, and the soil was modeled by solid element. Mohr-Coulomb criterion was used to estimate the failure of geogrid and soil. The deformation and stability of both unreinforced and reinforced embankment widening under asymmetric traffic load were analyzed. Furthermore, parametric study was conducted to investigate the deformation of reinforced widening embankment under different parameters including:fill properties of the widening embankment, amplitude and frequency of traffic load, and running interval. The results show that the deformation of the widened embankment is only partially restricted by the geogrid, while the global stability of the embankment under asymmetric traffic load is effectively improved. Differential settlement decreases as the fill properties of the widening embankment increases. Through comparative analysis, it was found that the effect of cohesion on the differential settlement is more obvious than that of the compression modulus. Smaller differential settlement can be obtained when the soil properties of the new and old embankments are similar. In practical engineering use, by ensuring the properties of new embankment fill are the same as those of the old embankment fill, differential settlement can be effectively controlled under dynamic load situations, and will not affect the comfort and safety of the vehicle. The increase in amplitude of traffic load only on one side of the embankment will lead to excessive differential settlement and the pavement smoothness will be seriously affected. As the frequency of asymmetric traffic load and running interval increases, embankment settlements gradually decrease, while the differential settlement will remain constant. The findings in this investigation can provide a theoretical basis for the construction of the widening embankment under asymmetric traffic load.

    • Numerical Analysis of Dynamic Response on a New Type of CuttingBed in the Expansive Soil District on the Yun-Gui Railway

      2017, 39(6):1118-1125. DOI: 10.3969/j.issn.1000-0844.2017.06.1118

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      Abstract:This article used FLAC3D finite difference software to study the dynamic response rules of the new cutting bed structure with a new type of waterproof and drainage structure layer set in the bedding. Past studies have proven that a new bed ballast and a new type of waterproof and drainage structure can significantly contribute to the attenuation of dynamic stress. A new type of waterproof and drainage structure layer on vertical dynamic stress and shear stress attenuation can enhance the dynamic stability of the bedding structure, whereas a new bed structure can more effectively control bed dynamic displacement. New bed vibration velocity and acceleration decrease with the increase of depth. Meanwhile, the ballast of vibration velocity and the ensuring acceleration attenuation effect are obvious. The numerical simulation results and in-situ measurement data reveal a matching physical discipline at the vibration velocity and dynamic stress of the new cutting bed structure, indicating that both values decrease along the depth direction. The study's findings can be used and referenced for the design, construction, and dynamic response study of high-speed railway cutting subgrades in special soil areas.

    • Influence of Different Design Parameters on the Damage andFailure Characteristics of High-piled Wharves

      2017, 39(6):1126-1133. DOI: 10.3969/j.issn.1000-0844.2017.06.1126

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      Abstract:Two high-piled wharves with same structure but different design parameters were examined to determine the design influence on damage and failure characteristics. The first wharf comprised eight piles, each with a pile diameter of 1.2 m and a wall thickness of 22 mm. The second wharf comprised six piles, each with a pile diameter of 1.6 m and a wall thickness of 16 mm. The differences in dynamic characteristics and seismic performance of the two wharves were studied using the finite element software ANSYS. Both types of piles were simulated by BEAM188 element and the nonlinear spring was simulated by COMBINE39 element. The results show that under the same condition of load, site, and material usage, the stiffness of the six-pile wharf is greater than that of the eight-pile wharf. When the wharves were examined under the influence of a Tianjin wave, the pile acceleration of the six-pile wharf is larger than that of the eight-pile wharf, with the difference increasing with the strength of the seismic degree imposed. Under a rare earthquake, the displacement at the top of the six-pile wharf is less than that of the eight-pile wharf, but the residual displacement of the six-pile wharf is greater than that of the eight-pile wharf. Under the same condition of load, the ductile capacity of the eight-pile wharf is obvious greater than the six-pile wharf, and the limit plastic rate of the eight-pile wharf is 2.28 times that of the of six-pile wharf. With peak acceleration of 800 gal, the eight-pile wharf approaches the ultimate curvature, whereas the six-pile wharf approaches the ultimate curvature when the peak acceleration is 1 150 gal. Thus, it is important to comprehensively consider the stability and ductility capacity of the structure.

    • Numerical Analysis of Low Cyclic Loading Tests ofMega SRC Columns Based on OpenSees

      2017, 39(6):1134-1141. DOI: 10.3969/j.issn.1000-0844.2017.06.1134

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      Abstract:A steel reinforced concrete (SRC) column is a combined specimen constructed by allocating steel in the reinforced concrete in order to bear the external force. Because the SRC column gains the advantages of high strength and stiffness, good ductility, and fine refractoriness, it is widely used in high-rise structures nowadays. From the mixture of steel and reinforced concrete, the force performance and failure mode of the SRC column become more complex than ordinary columns. In this paper, in order to study the numerical simulation methods of the seismic performance of mega SRC columns, based on the finite element software OpenSees, tests on five mega SRC column specimens with different and complex steel sections were carried out under low cyclic reversed load by using the fiber element. Then, the numerical simulation results were compared to hysteretic and skeleton curves. The results indicate that the finite element model based on the fiber element can efficiently simulate the hysteresis response of mega SRC columns, which verifies the rationality and reliability of the numerical model. Meanwhile, a new high-performance multi-layer shell element was used in order to accurately analyze one of the mega SRC column specimens. By comparison to experimental results, the multi-layer shell can adequately simulate the initial stiffness and peak bearing capacity of the specimen. By comparison to the simulation results of the fiber element model, it was found that using fiber element could better simulate the descent of the specimen's bearing capacity, and the results were rather more accurate and efficient.

    • Influencing Factors on End-enhanced Double-steelTube Buckling Restrained Braces

      2017, 39(6):1142-1149. DOI: 10.3969/j.issn.1000-0844.2017.06.1142

      Abstract (674) HTML (0) PDF 7.46 M (870) Comment (0) Favorites

      Abstract:The influence of factors such as constraint ratio, gap-thickness ratio, and diameter-thickness ratio on the ultimate bearing capacity of end-enhanced double-steel tube buckling restrained brace (BRB) is studied using ANSYS software to simulate monotonic loading. Through the secondary development of APDL, the critical constraint ratio value range, critical gap-thickness ratio, and critical diameter-thickness ratio are analyzed. The results show that the constraint ratio is an important factor affecting the stability of BRBs and should not be less than 1.5 without considering initial imperfections. When the constraint ratio meets this requirement, the upper limit of the critical gap-thickness ratio decreases with an increase in the diameter-thickness ratio of the core tube, and the change trend is close to a straight line. The critical gap-thickness ratio should not be more than 0.18. When the constraint ratio meets this requirement, the critical diameter-thickness ratio decreases with an increase in the gap-thickness ratio, and the critical diameter-thickness ratio should not be more than 29. When the diameter-thickness ratio is too large (more than 29), it is prone to high order buckling and failure, resulting in full-section yielding.

    • Lowest-cost Analysis of Buildings DuringPost-earthquake Reconstruction

      2017, 39(6):1150-1155. DOI: 10.3969/j.issn.1000-0844.2017.06.1150

      Abstract (747) HTML (0) PDF 1.08 M (481) Comment (0) Favorites

      Abstract:During post-earthquake reconstruction, the traditional method used to determine the lowest cost of buildings is unable to balance the relationship between costs and construction requirements, which ultimately results in low-cost buildings with low seismic capabilities being built. This study proposes a method for analyzing the lowest-cost required to re-build following earthquakes. The relationship between building cost and demand is analyzed, and basic data are provided. In addition, the IFC building standard is optimized and lowest-cost indexes are defined. Furthermore, analysis factors are comprehensively determined to balance the demand relationship in the value chain. Finally, a lowest-cost analysis model for buildings is presented. Experimental data show that the lowest-cost analysis model not only meets the demand relationship but also realizes the lowest-cost for buildings.

    • Damage Identification Based on Structural Dynamic ResponsesUsing Wavelet Packet Energy Eigenvector

      2017, 39(6):1156-1160. DOI: 10.3969/j.issn.1000-0844.2017.06.1156

      Abstract (557) HTML (0) PDF 1.10 M (1035) Comment (0) Favorites

      Abstract:Monitoring structural dynamic responses is an important factor in structural health monitoring. When a building is subjected to certain vibration excitations, the structure will produce certain vibration responses. Once a structure is damaged, variations occur in its natural frequencies, stiffness, and damping values. The accurate determination of structural damage is a difficult engineering problem in the monitoring of structural dynamic responses. In this paper, we propose a method for extracting structural damage information and identifying structural damage based on the wavelet packet energy eigenvector. Utilizing the decomposed energy eigenvalue of each frequency band as a structural dynamic parameter, we determined differences in the structural state by the observed variation in the energy value and obtained good results. We also analyzed the experimental data with respect to the influence of noise on energy values. In an experiment, we found that the energy eigenvector can be used to identify the structural state and was free of noise. However, it could not be used to extract the energy feature vector after de-noising the observation signal. Therefore, we propose a method for accurately determining situations with structural damage, which is practical and can facilitate structural damage monitoring.

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