Abstract:Paleoearthquake refers to the prehistoric and historically unrecorded earthquake events according to the stratigraphic records. The advantage of the stratigraphic record is that it can make up for the transience and limitation of the historical and instrumental records and reduce the uncertainty in the seismic risk assessments (SRA). Only a few decades ago, recording of earthquakes by instruments started. Measuring historical earthquakes only reach the scale of thousands of years. The study of paleoearthquake can extend the seismic records to the scale of ten thousand years and span multiple occurrences of periods of earthquakes, which enables us to recognize the long-term activity habits of faults and helps us estimate the risk of future earthquakes over long periods of time. Paleoearthquake plays an important role in predicting the earthquake risk, and it becomes an indispensable branch of the earthquake disaster prevention information system. The Jiuxi Basin, located in the northern margin of the Qilian Shan and the western end of the Hexi Corridor, is a Cenozoic compressive basin surrounded by active faults. There are many active faults around and inside the Jiuxi Basin. There have been many medium to strong historically unrecorded earthquakes, which have caused the highly destructive earthquakes. Based on the summary of the previous paleoseismic data and supplementary investigation, it is found that most paleoearthquake along the active faults in the Jiuxi Basin conform to the earthquake model characteristics, with a recurrence interval of approximately 3-5 ka. According to the empirical formula, the magnitude of each earthquake is approximately 6.8-7.2. The occurrence of earthquakes in Jiuxi Basin is characterized by clustering from the perspective of regional paleoearthquake. There have been three cluster periods since Holocene, each of which lasts about 2 ka. The seismic risk for the Yinwashan and Baiyanghe faults is high in terms of recurrence characteristics and elapsed time.

Abstract:The explicit finite element analysis method and the viscoelastic artificial boundary are used to study the topographic effect of valleys and the influence of valley topography on surface ground motion subjected to incident SV waves. The results show the following:(1) The incident direction of the ground motion can affect the site response, and the amplification of surface response along the incident direction of the ground motion is larger than those in other directions. (2) Compared with the amplification effect of single hill topography on the surface ground motion, the presence of adjacent hills has little effect on the shape of the Fourier spectral ratio curve of the ground displacement but has significant effect on the peak ground displacement value, and the effect decreases with the increase of the distance between adjacent hills.

Abstract:In this study, we analyzed and summarized the observation data from the Gansu precursor network before and after the Minxian-Zhangxian M_S6.6 earthquake in Gansu on July 22, 2013, and found that there were obvious anomalies at seven stations, 4 observation methods, and 14 test items before the earthquake, including long-term, mid-term, short-term, and impending anomalies. Most epicenter distances with anomalous measuring points were within 200 km. In addition, different degrees of co-seismic effects were recorded by the water level, flow rate, and water temperature measuring point data. Obvious co-seismic responses were recorded by most measuring points of the deformation observation. The measuring points of the recorded co-seismic responses have no obvious relation with the location, direction, and distance of the epicenter.

Abstract:How to recognize anomaly images from the observation data of earthquake precursory networks is always an important topic for earthquake monitoring and forecasting personnel. In order to improve the work efficiency of abnormal image recognition and make full use of the existing experience and knowledge of abnormal image recognition, an exploratory research on the rapid CNN-based identification of anomaly images was carried out. The results show that the CNN-based abnormal image recognition method proposed in this paper has high accuracy, and can realize the rapid recognition of abnormal images. Due to the lack of training samples with specific observation means and specific influencing factors, further research is needed to apply this method to automatic recognition of abnormal images in the whole network.

Abstract:Based on the records of four-component borehole strain gauge of Sheshan station in Shanghai during the six western Pacific typhoons,the methods of wavelet decomposition and predominant polarization direction were applied to extract the significant low-frequency disturbance signals excited by the typhoon,and the characteristics of disturbance signal in time-frequency domain and spatial domain were then analyzed in detail.The results showed that in the low frequency range,the dominant period of disturbance signal excited by the typhoon is 2-4 min;the signal energy varies with the progress of typhoon,and is mainly related to the magnitude of typhoon,the location of typhoon center (sea or land),and the distance between the station and the typhoon center.As the typhoon center approached the coast,the disturbance signals recorded by the four components of Sheshan station began to increase,but the signal intensity recorded in different directions were not consistent.The predominant polarization direction of the signal is 160° and closely related to the strike of the coastline where the station is located.Finally,based on the time-frequency and spatial response characteristics of the disturbance signal,and the records of surface wind speed and ocean buoy,it is considered that the low-frequency disturbance signal recorded by the component strain gauge has a good correlation with the offshore wave height,and the typhoon disturbance signal recorded by the strain gauge is generated by the infragravity waves from the offshore area.

Abstract:The fault motion coordination ratio method can be applied to analyze the crustal strain accumulation in Yunnan area. Based on the observation data of 11 cross-fault flow monitoring sites for more than 30 years, the three-dimensional activities on the sites were first calculated, and then the coordination ratio parameters of fault activity were obtained. The results showed that:(1) The sites of Lijiang, Yongsheng, Jianchuan, Shiping, and Jianshui have good reflecting effect to historical earthquakes with magnitude 6-7. There are anomalies in the sites of Jianchuan, Shiping, and Jianshui recently, and the strain accumulation and abnormal fault activities are show along the Jianchuan and Shiping-Jianshui faults; (2) Combined with the original cross-fault observation data and the three-dimensional activity time series curve, it is considered that the crustal deformation anomalies are distributed in Jianchuan, Xiaguan, and Yongsheng of northwestern Yunnan, and near Eshan, Shiping, and Jianshui of central Yunnan; (3) It is considered that after the Jiuzhaigou M7.0 earthquake in Sichuan Province, the stress accumulation in southern part of the North-South seismic belt may be accelerated, so more attention should be paid to the risk of moderate and strong earthquakes in Yunnan.

Abstract:In actual calibration analysis of drilling strain observation, the strain coupling coefficient of the drilling surface is directly obtained from drilling strain observation data through harmonic analysis of tide. However, the method is difficult to use to fully reflect the internal link between the observed drilling strain and stratigraphic strain. This study measures the inner and outer diameter and the elastic parameters of the steel tube as well as the drilling radius and the elastic parameters of the cement sheath paper by using the TJ-2C strain gauge and a four-layer coupling medium drilling model of "stratum-equivalent elastic layer-cement sheath-steel tube." The relations between the drilling coupling coefficient in different strata and the elastic modulus of the drilling equivalent elastic layer are obtained. The analysis results of the volumetric strain from 40 TJ-2C strain gauges show that the tidal factors are distributed from 0.01 to 1.86. The tidal factor mean value of the granitoid bedrock is 0.83, and that of limestone or sandstone bedrock is 0.57. Hence, the tidal factor in the hard formation is higher than that in the soft formation. Based on the four-layer model, the equivalent elastic modulus of the equivalent elastic layer reflects the coupling state of the borehole. For the same type of bedrock formation, the poor coupling between the probe and the formation will lead to the decrease in the elastic modulus of the equivalent elastic layer, leading to a decrease in the tidal factor. The borehole is assumed to be in the decoupling state when the equivalent elastic modulus is less than 0.5 GPa. The statistics show that about 30% of boreholes in China are in decoupling state. The study results are important in conducting seismic analysis and forecasting work by using drilling data.

Abstract:High-resolution seismic reflection surveys are an irreplaceable geophysical method for investigating active faults in thick overburden areas. To identify the spatial location, property, and activity of the northern section of the Xiadian fault, a shallow seismic exploration was carried out, and seven high-resolution shallow seismic exploration survey lines were laid out with a total length of approximately 22 km. To ensure that the detection results could reveal the geological structure characteristics of greater depth and higher resolution, the observation system used unilateral vibroseis excitation and obtained reliable original data. The fine data processing found that the characteristics of the seismic reflection time profile vary and the fault features are clear. The accurate location of breakpoints and fault development characteristics were obtained. Results show that the Xiadian fault is a normal fault with a SE tendency and a dip angle of approximately 69° and it is also a Holocene active fault. The spatial distribution and shallow structural characteristics of the Xiadian fault in the range of approximately 20km are shown, and the fracture trend of the Xiadian fault within the range of the interpretation survey line is approximately N40°E.

Abstract:Particle size is one of the important factors that affect loess seismic subsidence. In this study, samples were collected from the muddy debris of Aiqi Gully mud volcano and nine samples were obtained from the sedimentary sections in surrounding mud volcano area. Laser test was used to determine particle size. Particle size parameters such as median value (M_d), mean value (M_z), standard deviation (σ_φ), skewness (SK₁), and kurtosis (K_G) were analyzed. Results show that the Aiqi Gully volcano samples are dominated by silt (56%) and clay (44%). The particle size distribution is characterized by partial modality and positive skewness. The particle size of the sedimentary stratum samples are dominated by silt, which accounts for 60%-70%, and the clay contents considerably vary in different strata. Some sediment samples contain 15%-20% clay and 10% very fine grains. The grain size characteristics are similar to those of Tianshan loess. The clay content in the loess directly affects its seismic resistance, that is, the anti-seismic resistance of the loess increases with increasing clay content. The sedimentary grain size significantly increases in the clay component after transformation by mud volcanic sedimentation. Therefore, the sediments are gradually transformed from silty loess to clay loess by mud volcanic activity. The stability of the clay loess is high, thereby improving the seismic resistance of the sediments. However, the seismic resistance of the loess is affected by many factors. As such, further study is needed to quantitatively analyze the influence of mud volcano activity on the site seismic subsidence disaster.

Abstract:The Sanweishan fault extends along the northwest margin of Sanweishan, with a total length of 175 km. On the basis of its geometric characteristics, the fault can be divided into three segments, namely, the western segment (Xishuigou-Shugouzi), the middle segment (Shugouzi-Shigongkouzi), and the eastern segment (Shigongkouzi-Shuangta). The tectonic activity intensity and geomorphological development degree of each segment are obviously different. On the basis of fault scarp measurement and regional chronological comparison, the vertical slip rate of the western segment of the Sanweishan fault is approximately 0.1 mm/a and that of the middle and eastern segments is relatively low. To further quantify the influence of the Sanweishan fault on the topography and geomorphology of the study area, we use the geomorphic factors (i.e., elevation, slope, channel steepness index, and stream gradient index) to quantitatively analyze the geomorphic features of each segment. Results show that the value of the western segment is larger than that of the middle and eastern segments, indicating that the uplift rate of the western segment is higher than that of the two other segments. This finding further indicates that the topography has a good response to tectonic activity. From the comparison between lithology, rainfall, and tectonic activity, we propose that the segmentation of the Sanweishan fault is the main reason for the differential uplift of each segment. Moreover, new activities of the Mingshashan fault accelerated the differential uplift of the west segment of the Sanweishan fault.

Abstract:Based on the GPS data of the Weihe Basin and its adjacent areas from 2009 to 2014 and the calculation method of continuous deformation field and strain field proposed by Shen, the horizontal deformation field and strain rate field of the Weihe Basin and its adjacent areas were obtained. Combined with the data of tectonic geology and seismic catalogue, the present crustal deformation and tectonic characteristics of Weihe Basin and its adjacent areas were studied in this paper, and the following conclusions were obtained:(1) The difference of GPS deformation field in the western and eastern parts of the southern margin of the Ordos block is obvious. The deformation field along the Liupanshan-Longxian-Baoji fault zone is dominated by compression, and the deformation field in the Xi'an-Xianyang area of the middle Weihe Basin is characterized by EW extrusion and SN extension; (2) The areas with significant changes in principal strain rate, shear strain rate, and surface strain rate are located along the Liupanshan-Longxian-Baoji fault zone in the southwestern margin of the Ordos block, the Chang'an-Lintong fault and Weinan fault in the central part of the Weihe Basin, and near the Hancheng fault and Shuangquan-Linyi fault; (3) In future, it is necessary to be alert to the seismic risks in the Liupanshan-Longxian-Baoji fault zone, Chang'an-Lintong fault and Weinan fault, as well as near the Hancheng fault and Shuangquan-Linyi fault.

Abstract:In this paper, the infrared brightness temperature background field and the anomaly detection model were established by the statistical method to extract the infrared brightness temperature anomalies in North China, and the evolution process of anomalies before the Tangshan M4.8 and Baodi M4.0 earthquakes in 2012 were analyzed. The results indicated that:(1) The monthly background field of infrared brightness temperature has the annual variation characteristics of being higher in summer and lower in winter, which is in line with the seasonal variation law, and the infrared brightness temperature has a negative correlation with the elevation; (2) Based on the K-value data of brightness temperature over the same period in previous years, it was found that strong K-value anomalies were shown in the south of Tangshan fault zone before the Tangshan M4.8 earthquake on May 28, 2012, and 8 hours before the earthquake, the maximum value reached 3.3. Before the Baodi M4.0 earthquake on June 18, a weak anomaly of infrared brightness temperature also existed.

Abstract:Based on the second sampling observation data from fluxgate instruments at eight stations in Qinghai area, the geomagnetic vertical intensity polarization method, which is popular at present and with clear physical mechanism, was used to extract seismic magnetic anomalies based on the variation characteristics of polarization background field. The study results showed that It was shown that the high value anomalies of synchronous polarization at multiple stations has a certain ability to reflect M_S ≥ 5.0 earthquakes in Qinghai area within 2 months, and the epicenter is basically located in the region of high polarization value if the observation stations are evenly distributed.

Abstract:To solve the problem of propagation characteristics of thermo-elastic waves in saturated porous media, based on the theory of porous media and the generalized thermo-elasticity model, the reflection problem of plane S waves at the boundary of saturated porous thermo-elastic media is studied in this paper. The thermal-fluid-solid coupling model of elastic waves in saturated porous media is established, based on the wave equations for saturated porous media considering fluid-solid coupling and the generalized thermo-elastic basic equations considering thermal-elastic coupling. By introducing the potential function and considering the adiabatic boundary conditions of free-water permeability, the theoretical expressions of amplitude reflectivity of four reflection waves on the boundary of saturated porous thermo-elastic media are given by theoretical derivation. The effects of some parameters, i.e., the incident frequency of plane S waves, the incident angle, and the thermal expansion coefficient, on amplitude reflectivity of the four reflection waves are analyzed by numerical calculation. Results showed that the amplitude reflectivity of each reflected wave increases with increasing frequency and thermal expansion coefficient, and is also affected by the change of incident angle of the plane S-wave. These conclusions are significant for theoretical research into soil dynamics and related exploratory projects.

Abstract:In this study, we analyzed the air-gun source and background noise signals recorded by mobile stations around the Hutubi air-gun launching station from June 2016 to December 2017. To study the wave-velocity characteristics before and after the Hutubi M6.2 earthquake in December 2016, we used the cross-correlation time-delay detection method and the moving window cross-spectrum method, respectively. The preliminary results are as follows:(1) before and after the Hutubi M6.2 earthquake, the air-gun source signals recorded by the mobile stations showed no obvious wave-velocity changes, whereas the fixed Shitizi station (27 km away from the earthquake) showed obvious wave-velocity anomalies prior to the M6.2 earthquake, which may be related to different signal propagation paths; (2) the background noise signals recorded by mobile stations caused abnormal variation in the wave velocity, which was related to the Hutubi M6.2 earthquake; and (3) air guns mainly emit body wave signals and background noise mainly occurs as surface wave signals. Their different ray paths may be the main reason for the different wave-velocity characteristics.

Abstract:Based on the historical earthquake data during 1993-2017 in China, the applicability and accuracy of four existing models for evaluating seismic fatality with different earthquake magnitudes and different regions were comparatively analyzed. The results showed that:(1) when M<6.0, the evaluation results of four models are basically consistent with the actual number of deaths, and all of them are suitable for the rapid post-earthquake casualty assessment; when 6.0 ≤ M<7.0, there is a large gap between the evaluation results of four models and the actual death toll, and the the evaluation results of Liu Jinlong's model after parameter correction are relatively good; when M ≥ 7.0, the evaluation results of the four models are not ideal, and need to make artificial correction in combination with the geographical environment and economic conditions of the earthquake area. (2) In Yunnan, Sichuan, Gansu, Xinjiang, and Tibet, the results of GB/T 30352-2013 are better than the other three models; in Sichuan, Yunnan, and Gansu, the influence of secondary geological hazards should be taken into account, otherwise, it may lead to large evaluation error. The study results can provide technical support for governments and emergency management departments at all levels to improve their emergency response capacity for earthquake disasters.

Abstract:In this paper, a fast broadband indirect boundary element method is developed for the scattering of spherical waves in a three-dimensional half-space local site. The solution model is established by using ANSYS, and the corresponding program is compiled based on the Intel Fortran compiler. The scattering of spherical waves by three-dimensional semi-ellipsoidal basin is studied numerically, and the influence of some parameters, i.e., the frequency of incident wave, the depth of wave source, and the distance between wave source and sedimentary basin on the ground motion characteristics, were discussed in detail. The calculation method was suitable for solving local surfaces with arbitrary complex shapes, and the fine solution in the frequency domain of the 3D seismic response of a sedimentary basin was realized. Results show that the magnification and interference effect of the sedimentary basin increase with the increase in the incident wave frequency. Under the incident high-frequency wave, the displacement in the secondary direction has a certain edge effect due to the superposition of the body wave transmitted from the bottom of the basin, the surface wave converted from the body wave inside the basin, and the body wave transmitted from the edge of the basin. The analysis of displacement spectrum showed that at a low frequency, the principal displacement amplitude of different points on the surface is basically the same; in the high-frequency domain, the displacement spectrum characteristics of different surface locations are different. Compared with the plane wave incident, the displacement amplitude decreases somewhat. On the whole, as the horizontal distance between the expansion wave source and the basin increases, the maximum displacement amplitude in the main direction of the surface decreases, and the displacement focus area in the subsurface direction increases and the distribution is more dispersed.

Abstract:Seismic landslide often causes casualties and property losses, and the response law of slopes under the action of earthquake is significant for studying the stability of seismic slopes. In this work, finite difference software FLAC^3D was used to build multiple models for analyzing the seismic dynamic response of slope considering the topography effect. The topography was mainly considered in three aspects, namely, slope height, slope angle, and slope shape. The selected seismic waves were applied to different models to analyze the slope acceleration and velocity amplification ratio. The influence of the geometry of the slope on its seismic response was also determined. Results show that the slope height has a significant amplification effect on the speed of the slope. The slope angle has a strong amplification effect on the acceleration of the slope. Different slope shapes will cause different acceleration response laws. This study is helpful for stability analysis of seismic slopes and provides reference for seismic design of slope engineering.

Abstract:Extensive research has been conducted on the influence of the geological conditions on the seismic responses of tunnels. However, most existing work has focused on the influence of single parameters. Less emphasis has been place on the influence of multiple parameters and the interactions between them. In this paper, we consider the influences of geological conditions on a typical tunnel of the Huali expressway project. Using orthogonal and uniform design methods, we studied the influences of various geological parameters, including the mechanical parameters of the rock mass, the in-situ stress state of the rock mass, and the mechanical parameters of the joints. The results indicate that the main factor influencing the excavation deformation index is the deformation modulus. Regarding the mechanical parameters of the rock mass, the main factors influencing the tunnel seismic response were found to be the cohesion and internal friction angle. Regarding the stress-state parameters of the rock mass, the main factor influencing the seismic response of the tunnel was determined to be the tunnel depth, followed by the in-plane and out-of-plane lateral pressure coefficients. Among the joint mechanical parameters, the friction angle and tensile strength were identified as the major influence factors.

Abstract:The silty sand in the Yellow River flood area differs from that in other areas. In this study, we investigated the dynamic and anti-liquefaction strengths of silty sand in the Kaifeng area and identified three influence factors:the confining pressure, dry density, and fines content. Based on the results of a dynamic triaxial test, we obtained the dynamic strength and anti-liquefaction strength curves of silty sand in the Yellow River flood area and considered the effects of these three influence factors. The experimental results indicated that the dynamic and anti-liquefaction strengths of silty sand in the Yellow River flood area increase with increases in the confining pressure and dry density, decrease with increases in the vibration time of the dynamic load, and first decrease and then increase with increases in the fines content. The anti-liquefaction strength of the silty sand was determined to be greater than its dynamic strength in this area.

Abstract:The Yardang landform through which the newly built Yuqia-Yiliping railway in Qinghai Province passes was investigated in this study. Field real-time tests were carried out on ground vibrations induced by heavy-haul trains with different speeds, and then the attenuation characteristics of vibration acceleration in the frequency domain and time domain in the Yardang area were analyzed. Through a geological survey, a vibration analysis model of the Yardang slope was constructed. A numerical simulation was carried out to analyze the acceleration and displacement responses of a typical Yardang slope with weak interlayers under different train speeds, and the safety distance was calculated. The results showed that the attenuation rate of vibration acceleration decreased rapidly with the increase in distance. The acceleration attenuated quickly at 2.5-5.5 m and tended to be flat at 5.5-15.5 m. As the distance increased, the high-frequency components were suppressed, and the frequency gradually moved toward the low frequency. The weak interlayer in the lower part of the slope sharply reduced the transmission coefficient and had a good vibration isolation effect. However, the vibration isolation function of the weak interlayer in the upper layer was not significant. Taking the peak vibration velocity (PPV) as the vibration quantity evaluation index, it was found that the influence distance of heavy-haul trains was less than 6.1 m when the speed was below 70 km/h.

Abstract:This study aims to determine the effect of excavation process and retaining structure as a permanent structure in the seismic design of open excavation metro stations. A finite element model of two-story two-span rectangular frame is established by Plaxis2D based on an open cut subway station with cast-in-place pile as the retaining structure in Zhengzhou City. The constitutive model of hardening soil is adopted to assess earthquake resistance. Results showed that under seismic load, the design value of the upper bending moment of the structure is 31% smaller without considering excavation than that considering excavation. The design of the side wall and floor is conservative, with bending moments larger than 87% and 64%, respectively. If excavation is neglected, then the calculation error of shear force on the lower sidewall increases with the depth from 36% to 122%. However, the influence of stiffness reduction of the diaphragm wall on the internal force is less than 5%. Therefore, in the seismic design of structures on this kind of soft soil, the influence of excavation and the diaphragm wall within the design life should be considered. The bottom of the shear wall and the top and bottom of the middle column should also be emphasized.

Abstract:To study the micro-mechanical failure process of high cutting loess slopes during earthquake, a highway slope in loess area was taken as an example in this paper. On the basis of field engineering geological investigation and indoor test, initial state of the high cutting loess slope after excavation was analyzed with the strength reduction method, and then a numerical calculation model of the cutting slope was established by using PFC^2D, and seismic response of the slope was simulated. Through the analysis of some key elements of particle during the process of seismic response, e.g. displacement, coordination number, porosity, stress, and strain rate, instability process of the slope was revealed on meso-level. The results showed that the method proposed in this paper can reproduce the micro-physical and mechanical process of landslides under the action of earthquake, covering the failure mode and process of slope, as well as the temporal and spatial evolution law of stress and strain. The research results has a great significance for understanding the failure mechanism of high cutting loess slopes under seismic action.

Abstract:Pile-sheet retaining wall developed from anti-slide piles could be used as the retaining structure for slope engineering in normal, inundated, and seismic areas. However, the retaining effect of single-or double-row pile-sheet structures in earthquake areas has not been well researched yet. In this study, the practical application of single-and double-row pile-sheet retaining structures is analyzed based on shaking table model test. Soil pressure, soil peak acceleration, and pile displacement are then compared between the two types of piles at different levels of loads. The deformation characteristics of the retained slope under static and dynamic situations are summarized. Results may provide reference for seismic design of pile-sheet retaining structures.

Abstract:In this paper, a novel electromagnetic inertial mass damper (EIMD) is applied to realize the practical semi-active control of a real-life eccentrically braced high-rise building structure subjected to outward dynamic loads such as earthquake. Then, we present a feasible semi-active control strategy based on a linear quadratic regulator (LQR) active control algorithm. The coupled torsional responses of the structure with EIMDs are analyzed at different EIIMD installation positions. Finally, the feasibility and effectiveness of the new control strategy is demonstrated by its application to a real-life 24-story irregularly reinforced concrete frame-shear wall structure with EIMDs, for which the El Centro earthquake records are considered. The simulation results show that (1) the proposed semi-active control strategy is effective and feasible compared with the traditional active LQR control method, and (2) the torsional angle and torsional angle acceleration responses of the structure are obviously suppressed by optimizing the installation positions of the EIMDs.

Abstract:Earthquake is a natural disaster phenomenon. The low-tower cable-stayed bridge, for its good mechanical and aesthetic performance, has been widely used in recent years. Therefore, seismic design is very important for low-tower cable-stayed bridges. The friction pendulum system can separate the superstructure from the substructure of bridge, thus extending the natural vibration period and friction energy dissipation of the structure, reducing and dissipating the energy transferred to the superstructure of the bridge. In this paper, the low-tower cable-stayed bridge in Jintan Yellow River Bridge of Jingyuan was taken as the analysis model, and the friction pendulum bearing was used to study the seismic isolation effect of the pier body of low-tower cable-stayed bridge. Different seismic waves were input to test the damping effect of the friction pendulum system by using the Midas finite element software. The analysis results showed that the application of friction pendulum bearing system in low-tower cable-stayed bridge is effective.

Abstract:Trains have become a main force in transportation. High-speed trains play an especially important role in economic and social development. High-speed trains produce greater environmental vibration than their more conventional counterparts. Thus, interactions between train transportation systems and human life has become more intense. Therefore, the environmental vibration problem caused by high-speed trains has become a major topic in international research. This paper summarizes the status of research and progress of high-speed trains at home and abroad, and focuses on the theoretical research, numerical calculation, field tests, and train vibration research at different sites. This paper also summarizes the current state and future outlook for vibration propagation characteristics, site effects, vibration prediction, and vibration control of train operation.

Abstract:The effects of elastoplastic static and dynamic response on the structure under multiple loads are discussed to study the damage patterns and characteristics of the wind tower and substructure of an undersea tunnel at the plastic stage. A large three-dimensional finite element model of the wind tower and substructure of an undersea tunnel is established. On the basis of the concrete plasticity and its damage constitutive model, dynamic time history analysis of the structure under different seismic conditions is conducted by using ANSYS and ABAQUS, and the vibration mode, the story drift ratio, and the complete plastic damage destruction coefficient curve are compared and analyzed. Calculation results show that under different earthquakes, the integrity of the structure is good, and the vibration mode and story drift ratio can meet the specification requirements. Under different rare earthquakes, the maximum plastic tensile and compressive damage of the structure occurred at 20 s. The main damage area is in the contact position of the wind tower, human well, and lower column, and the stretch damage coefficient is significantly higher than the compression damage. The results can provide some basis and guidance for seismic design similar to offshore tunnel engineering.

Abstract:Viscoelastic dampers dissipate energy through the shear deformation of viscoelastic materials; thus, they can provide additional damping and reduce structural responses during earthquakes and winds. In this study, a viscoelastic material with loss coefficient of less than 0.5 was developed, and a novel domestic viscoelastic damper was obtained based on this material. An experimental study of the novel viscoelastic damper was conducted by using full-scale specimens. Strain amplitude and loading frequency were chosen as test parameters, and shear storage modulus, shear loss modulus, and loss factor of the damper under different loading schemes were investigated. Low-cycle fatigue tests were also conducted. The test results suggest that the loss coefficient of the damper is about 0.3-0.4 for most cases. The correlation between basic mechanical properties of the damper and loading frequency is small, and the energy dissipation capacity of the damper is stable under different loading amplitudes. The damper shows good deformability as it can maintain stable mechanical properties at a strain amplitude of 150% and is not damaged when the strain amplitude is 350%. The damper also exhibits satisfactory low-cycle fatigue behavior since its mechanical behavior does not change significantly after 30 cycles of loading.

Abstract:The response of subway station structure under coupled ground motion is complex. This paper uses a finite element method for dynamic response research. Dynamic response of the subway station structure was analyzed under the horizontal, vertical, and bi-directional coupled ground motion. Results showed that:(1) Coupled ground motion has little effect on the relative horizontal displacement of the structure, but has a large effect on the relative vertical displacement of the structure. (2) Coupled ground motion can decrease the principal stress of the middle column, but cannot change the distribution of principal stress of the middle column to a large extent. (3) The bottom of the middle columns and joints of the station are weak positions under unidirectional and coupled ground motion, which require more attention in seismic design.