Abstract:In this paper, the seismic phase observation report and waveform records of M≥3 earthquakes in Puyang and its adjacent area during 2008-2018 were collected. Based on the velocity model of wide-angle reflection/refraction profile of artificial earthquake, the absolute location of 287 M≥1 earthquakes in the study area was carried out by using the Hypo2000 seismic location method. Meanwhile, taking the absolute positioning result of Hypo2000 as the initial position, the double difference location of 153 M≥1 earthquakes within 25 km around Pucheng town was carried out. The results showed that after relocation, two branches are shown both in the profile of epicenter and focal depth of the small earthquake cluster in Pucheng town: the main branch of earthquake swarm is distributed along the Liaocheng-Lankao fault, and the branch composed of a few earthquakes is distributed in the east side of the Yellow River fault. Combined with the interpretation results of deep seismic reflection profile, it is inferred that the Liaocheng-Lankao fault is the main seismogenic structure of the small earthquake cluster in Pucheng town, and the seismogenic fault of the branch of few earthquakes in the west is the Yellow River fault zone. The small earthquake activity is also closely related to the water injection activities in oilfield production.

Abstract:In this paper, three common stacking methods, i.e., linear stacking, spectrum whitening stacking, and phase-weighted stacking, were used to process the experimental data of air-gun source in Ansha reservoir. The practical application effects of the three methods were analyzed and evaluated from the aspects of signal-to-noise ratio, waveform correlation, and seismic phase travel-time difference. The results showed that: (1) The phase-weighted stacking method has the strongest ability to improve the signal-to-noise ratio, but both of it and the linear stacking method can not effectively eliminate strong interference. The spectrum whitening method can weaken the influence of strong interference, resulting in accurate recognition of signal. For the waveform with low signal-to-noise ratio, the spectrum whitening method is better than linear superposition in improving signal-to-noise ratio, and vice versa. (2) With the reference of linear stacking results, the correlation of phase-weighted method is high, and the travel-time difference is basically zero, but the signal with small amplitude in the waveform may be suppressed, thus affecting the discrimination of waveform signal with small amplitude value; when the signal-to-noise ratio of the station is high, the waveform correlation is poor, and there is a certain travel time difference. Then the waveform before the arrival of seismic phase may be amplified, which makes the first arrival of seismic phase fuzzy, and affects the picking accuracy.

Abstract:Based on 28 698 P wave polarity data of 6 245 natural earthquakes recorded by Liaoning seismic network in the last decade, we calculated the 0.25°×0.25° tectonic stress field of Liaoning and its adjacent areas by considering the weight of different epicenter distance. The inversion results in the study area were then analyzed in combination with corresponding tectonic background. In general, the inversion results indicated that the principal compressive stress axis is mainly NE and NEE, and the dip angle is small; the principal extensional stress axis is mainly NW and NNW, with local distribution of near NS, and the dip angle is almost horizontal. The results are consistent with those of previous studies. The pitch angle of principal extensional stress axis of most grid points is smaller than that of principal compressive stress axis, showing that Liaoning and its adjacent areas are in a stress state of tension. It is related to the subduction of the Eurasian plate by the Pacific plate in NWW direction and the consequent upwelling of upper mantle asthenosphere. In addition, the results also showed that local tectonic stress field at the junction of geological structure divisions is relatively complex and uneven. The nodal strike inverted by composite focal mechanism solution is consistent with the main fault orientation in the study area.

Abstract:In this paper, the double-difference tomography method was used to relocate the Zigui, Sanxia M4.7 earthquake swarm on March 27 and M4.5 earthquake swarm on March 30, 2014. The inversion results showed that at depths of 0-5 km, the high-velocity zones of P-wave are mainly distributed in the northern and middle sections of Xiannushan fault and the north section of Jiuwanxi fault, and the low-velocity zones are mainly distributed along the Tianyangping fault; the high-velocity zones at depth of 8 km are distributed in the east side of Jiuwanxi fault; the high-velocity anomalies at depth of 11 km are only distributed in the junction zone of Gaoqiao fault and Zhoujiashan-Niukou fault. The low-velocity zone below the earthquake concentration area (8-12 km) is relatively stable. Large earthquake events are mainly distributed in high-velocity zones or high-low velocity junction zone, while few earthquakes are distributed in the low-velocity zone. Local high-velocity body provides the material basis for instantaneous fracture of rocks, and the gradient zone between it and the low-velocity body often develops seismogenic structures. A large number of fractures exist in the depth range from the surface to 5 km and 5-10 km, indicating that shallow earthquakes are still in the range of reservoir permeability, while deep earthquakes are irrelevant to fluid permeability. There are both reservoir-induced earthquakes and tectonic earthquakes in the earthquake swarm.

Abstract:In this paper, based on the three-component broadband digital waveform data recorded by Gansu seismic network from January 2010 to August 2020, the characteristics of non-natural seismicity in Honggu District of Lanzhou City were analyzed by adopting the spatial distribution of epicenter location, waveform characteristics, and Fourier spectrum characteristics. The results showed the waveform characteristics and Fourier spectrum characteristics of a large number of seismic events in Honggu District are significantly different from those in other areas. Through preliminary analysis, it was found that the typical seismic phase characteristics of non-natural earthquakes in Honggu District are closely related to the exploitation of mineral resources in the area. The study on the characteristics of non-natural earthquakes in Honggu District can be helpful to quickly and accurately identify the earthquake types around Lanzhou, and also has positive scientific significance for the risk assessment and prevention of earthquake disasters in Lanzhou area.

Abstract:In this paper, the spatial correlation method was used to analyze the diurnal variation anomalies of geomagnetic vertical components obtained from 151 stations before and after the Minxian-Zhangxian M_S6.6 earthquake in Gansu Province. The results showed that: (1) On July 3 and July 4, 2013, the diurnal variation of geomagnetic Z components of 16 and 17 stations near the epicenter appeared obvious anti-phase anomalies, respectively, and there was a clear boundary between the two anomalies; (2) The S-transform method was used to calculate the correlation coefficient of the daily variation of Z component at Tianshui and Lanzhou stations on both sides of the boundary, and it is found that the daily variation of geomagnetic Z component on July 3 and July 4 both had a negative correlation at about 6 h. Therefore, it is considered that the anti-phase anomaly caused by daily variation anomaly of geomagnetic Z component before the Minxian-Zhangxian M_S6.6 earthquake is mainly at about 6 h. In addition, the mechanism of the anomaly was explained.

Abstract:The geomagnetic data of Enshi station, Jiangdong station in Fuling, Huangshui station in Shizhu, and Xiannushan station in Wulong from January 2012 to November 2017 were selected and the anomalies were analyzed. Then the calculation results of geomagnetic harmonic amplitude ratio and load/unload response ratio of each station were obtained. The geomagnetic anomalies before and after the Wulong, Chongqing M5.0 earthquake on November 23, 2017 were analyzed by combining with the geological structure background near the earthquake epicenter. The analysis results indicated that the variation characteristics of most harmonic wave amplitude ratios are similar to those of earth resistivity, showing a process of "down-turning-recovery". The M5.0 earthquake occurred in the early stage of turning upward. During the earthquake, the changing trend of geomagnetic harmonic amplitude ratios of stations with small epicentral distance are not synchronous, but their change amplitudes are roughly the same; the changing trend of geomagnetic harmonic amplitude ratios of stations with large epicentral distance are relatively synchronous, and their change amplitudes are large. In addition, the study also showed that the temporal and spatial distribution of abnormal high value of geomagnetic load/unload response ratio before the earthquake has a good corresponding relationship with the epicenter position.Keywords: geomagnetism; harmonic wave amplitude ratio; Wulong earthquake; tectonic setting

Abstract:Some researches have shown the existence of thermal-infrared radiation anomalies before moderate to strong earthquakes. Sichuan-Yunnan Block has been considered in this study due to the occurrence of frequent moderate to strong earthquakes in recent years. In Sichuan-Yunnan Block, anomalies analysis of the thermal-infrared radiation based on remote sensing is essential and significant. We used the moderate resolution imaging spectroradiometer (MODIS) or terra thermal-infrared data from April 2004 to June 2017 to analyze the thermal-infrared radiation anomalies in detail. Then, we researched the thermal-infrared anomalies before M≥5.5 earthquakes occurred in Sichuan-Yunnan Block. The results showed that: (1) obvious anomalies of thermal-infrared radiation appeared before the M≥6.0 earthquakes occurred in the study area; (2) infrared anomalies appeared before earthquakes are not randomly distributed, but are restricted by related blocks; and (3) researches on Ninglang M5.7 earthquake and Ludian M6.5 earthquake indicate the correlation between the epicenter and the region of enhanced radiation before the earthquakes occurred.

Abstract:On August 8, 2017, an M_S7.0 earthquake occurred in Jiuzhaigou area, Sichuan Province. Based on the results of previous research, the seismogenic structure of the earthquake was analyzed and the stress state before the earthquake was calculated. The results showed that the M_S7.0 earthquake was affected by tectonic activity and historical strong earthquakes, and occurred in the stress loading area caused by historical strong earthquakes. In addition, based on the integrity evaluation of the earthquake catalogue of China Earthquake Network since 1990, the spatial images of seismic b-value in the epicenter area and adjacent areas before the Jiuzhaigou M_S7.0 earthquake were calculated by adopting the maximum likelihood method. The calculation results showed that the M_S7.0 earthquake occurred in the region with significant low b-value and high stress anomalies of northern Sichuan (0.82>b>0.75). Therefore, the historical strong earthquakes in the study area may promote the occurrence of the Jiuzhaigou M_S7.0 earthquake.

Abstract:This paper investigated the temporal and spatial change of land cover type within 5 km around the deformation stations in China by using the GlobeLand30 product and MODIS-MCD12Q1 land cover dataset from 2000 to 2018. Then taking the vertical pendulum observation as an example, the relationship between the total land cover changes around deformation stations and the background noise of instrument observation was explored. The results showed that: (1) Cultivated land and forest are the main land types within 5 km around the fixed deformation stations in China. From 2000 to 2010, the proportion of artificial surface increased from 11.8% to 14.5%, while the area of cultivated land and grassland decreased by 2.2% and 1.6%, respectively. The area of cultivated land converted to man-made surface is the largest in the study area, with a total value of 525 km². (2) The decrease of cultivated land and the increase of man-made surface are the most severe in North China seismic region; the decrease of grassland type and the increase of bare land type are the main types in Xinjiang seismic region; the increase of grassland type and the decrease of man-made land surface are slightly in Northeast China seismic region.The change of land cover around stations in different seismic regions of mainland China is different. The area of cultivated land decreased while the artificial surface increased acutely in North China; Xinjiang seismic zone was mainly decreased in grassland and increased in bare land; the grassland in Northeast seismic zone increased while the artificial surface decreased slightly. (3) During 2001-2018, the forest area in the study area increased slowly and the cultivated land continued to decrease, especially in 2005-2016; the artificial surface continued to increase steadily year by year. (4) In 2016, the background noise observed by the vertical pendulum tiltmeter had a certain correlation with the total annual land cover change around the station. However, due to the influence of ocean motion, the noise level of the instruments in South China seismic zone was not positively related to the change of surrounding environment.

Abstract:Along the northeastern margin of the Tibetan Plateau, which is located at the intersection of the Tibetan Plateau, the Ordos, and the Alxa Block, a group of arc-shaped faults characterized by reverse strike-slip and strong new activity are developed. With frequent historical and modern strong earthquakes, the northeastern margin of the Tibetan Plateau is an ideal area for discussing the relationship between modern small earthquake-intensive areas and historical strong earthquakes. In this paper, based on the seismic instrument monitoring catalog of the study area since 1970, 21 earthquake intensive areas are divided by using the calculation method of density at grid nodes. Through the analysis of time distribution characteristics of small earthquake activities in each earthquake intensive area and previous research results of historical earthquakes and active faults, the corresponding relationship between earthquake intensive area and historical strong earthquake is comprehensively judged, and the duration of historical strong earthquake intensive area with different magnitudes are summarized. Meanwhile, this paper also presents the limited conditions for using the calculation method of density at grid nodes to check the historical earthquakes in the northeastern Tibetan Plateau. The results show that about 66.7% of the earthquake-intensive areas in the study area correspond to historical strong earthquakes, and there is a close correlation between them; The larger the magnitude of the earthquake, the longer the duration of the concentrated area. The fitting relationship between them is: T=4.38×10^-7×M^10.91.

Abstract:Landslides occur frequently in China,especially in the western regions,with largely concealment and harmfulness.Early identification of potential landslides is pretty essential for disaster prevention and mitigation.The traditional methods,such as manual inspection and geodetic survey,are difficult to carry out and time-consuming in mountainous areas.Interferometric Synthetic Aperture Radar (InSAR),as a new remote sensing measurement method,can accurately and efficiently identify the hidden dangers of landslides in wide regions.In this study,based on 111 Sentinel-1 C-SAR images and GPS three-dimensional velocity field in the Liujiaxia-Lanzhou section of the Yellow River Basin,the permanent scatterer InSAR (PS-InSAR) technology was used and calibrated to get the line-of-sight (LOS) deformation field of the study area from October 2014 to December 2019.One potential landslide area,which was located in the Yongjing County,was detected.This potential landslide area has never been mentioned before,but its size and magnitude are much larger than those of Heifangtai landslide area.Compared with GPS and previous results,the accuracy of the InSAR results was verified.Based on the historical data of strong earthquakes and field survey,it is found that this potential landslide area may be related to the Lanzhou M7.0 earthquake in 1125 and the Jiuzhaigou M_S7.0 earthquake in 2017.This study can provide data and technical support for disaster prevention and mitigation in the study area.

Abstract:Due to the special tectonic location and strong Neotectonic activities in the Bailongjiang River Basin, there are rare researches on the exploration of buried active faults in the area. The high-density electrical method, which is flexible, efficient, and easy to implement, is very suitable for the Bailongjiang River Basin with complicated terrain, whereas, there exists a serious problem of multiplicity of solutions under the complex geological environment. Based on huge amounts of geophysical data, this paper studied the electrical anomaly characteristics of hidden active faults in the basin, and divided the electrical characteristics into five categories. Among them, four categories can be used as the basis for fault identification, which mainly showed the electrical characteristics of "high (low) resistance background, low (high) resistance band". There were two reasons why electrical anomalies are difficult to be identified, namely "field layout" and "geological background". The study results showed that the electrical abnormal response of hidden active faults in Bailongjiang River Basin can be followed, and some of them can be used as the basis for qualitative or quantitative description of hidden active faults. The results can provide important reference value for the exploration of hidden active faults in the study area with high-density electrical method.

Abstract:The buildings in historical and cultural districts are characterized by high density, confined space, and insufficient evacuation capacity, and existing shelters are difficult to meet the requirements of earthquake refuge, so it is imperative to improve the seismic resilience of historical and cultural districts. In this paper, the evaluation and planning methods of shelters in historical and cultural districts were analyzed. The spatial model of road network and environmental elements was first established based on ArcGIS 10.2. Then the inductive analysis and special analysis were adopted to determine the quantitative index for shelters. Finally, with spatial network and overlay analysis, GIS analysis and visual analysis, the planning and layout methods for shelters in historical and cultural districts were proposed. A case study of 14 historical and cultural districts in Tianjin was implemented to evaluate the invulnerability of road and the effectiveness of existing shelters, and then areas with high level suitability were selected as alternative locations. For those districts where current shelters cannot meet requirements, quantitative analysis methods including set covering model, maximal coverage model, and minimal facility location model were developed to optimize the shelter layout. Therefore, the scientific and practical application of the shelter planning method proposed in this paper were verified.

Abstract:Curved bridges may bear earthquake disasters during service, resulting in structural damage or even collapse. To evaluate the seismic performance of existing bridges, a seismic performance evaluation method of curved girder bridges based on damage analysis was proposed in this paper. The finite element model of an old curved girder bridge was established, then based on the principle of damage analysis, the component damage model which can describe the seismic response characteristics of curved girder bridge was proposed. The damage indexes of each component of the bridge were calculated by inputting different ground motions into the finite element model. Combined with the checking coefficient of the old bridge, the whole damage index of the bridge was inferred from the damage index of each component. The results showed that: (1) Under different ground motions, the main girder will cause impact damage, the bearings at both ends of the bridge are prone to shift, and the piers will cause displacements both along the transverse and longitudinal direction of the bridge. (2) The damage degree of main girder, bearing, bridge pier, and other components caused by different ground motions is quite different; the seismic response of each component will affect the seismic performance of whole bridge, among which, the pier has the greatest impact, and the pier displacement exceeding the limit value may lead to collapse; (3) Repeated collision of the main girder will aggravate the damage degree of bridge, and the bearings at both ends of the bridge are more likely to be damaged under earthquake.

Abstract:As a country with frequent earthquakes, the high-speed railway network in China is more and more intensive, and many railways are located along the seismic belt, thus endangering their operation safety. Pile-supported subgrade is widely used in high-speed railways in China. Therefore, the seismic response characteristics of pile-supported subgrade under seismic load were analyzed through a three-dimensional numerical model of track-subgrade-foundation, and the influence of calculation parameters, i.e., pile diameter, pile length, pile spacing, and elastic modulus of pile body on the seismic response of subgrade were discussed and contrasted with those of free subgrade. The seismic response characteristics of free subgrade showed that the vibration displacement amplitude of rail in the horizontal x direction is the largest under seismic load, which is 5 times of that in the z direction; the vibration displacement amplitude at the foot of subgrade slope is 25.2 times of that at the surface of subgrade bed. Compared with the free subgrade, pile-supported subgrade has an increasing effect on the horizontal displacement amplitude and acceleration amplitude of the track, but it reduces the vertical values. It also obviously reduces the displacement amplitude and acceleration amplitude of each structural layer of subgrade. It is concluded that the optimal pile diameter, pile length, pile spacing, and elastic modulus of pile-supported subgrade are 0.8 m, 8-10 m, 2 m and 20 GPa, respectively.

Abstract:With the development of traffic construction, more and more roads have to pass near existing buildings. Therefore, the vibration caused by construction or heavy vehicle traffic poses a great security threat to surrounding building structures, and even causes serious damage. In this paper, the vibration control standards of building structures under traffic vibration and the damage mechanism caused by vibration were reviewed, and the research status and methods for the influence of traffic vibration on the safety of building structures were introduced. The development status of vibration reduction and isolation was analyzed, and the fatigue life was innovatively taken as the reference basis for the allowable value of building structure vibration. Based on the summary and analysis of current situation, the existing problems were put forward, and the relevant opinions and suggestions were given, which can provide reference for future related research.

Abstract:Based on the design concept of "strong horizontal joints and weak vertical joints",a series of low-cyclic reversed loading tests were carried out on three L-shape fabricated shear wall specimens with web wall and wing wall connected by mild steel dampers.The test results showed that the overall working performance of specimens is good;the displacement ductility coefficient of specimens is greater than 2.6,showing good deformation performance;the damper has good in-plane performance and can achieve yield energy dissipation.The influence of the yield force of dampers on the axial compression ratio of specimens should be considered to avoid a great difference of the bearing capacity of specimens in two loading directions.

Abstract:The environmental temperature can affect the physical properties of rubber, thus influence the dynamic response of plate rubber bearings under earthquake. In this paper, the finite element method was used to analyze the frictional sliding characteristics of plate rubber bearings. The hysteretic curve and equivalent viscous damping ratio of the bearing were compared with those obtained from normal temperature experiment. Based on a reliable model, the influence of environmental temperature on the friction sliding characteristics of plate rubber bearing was analyzed. Relationship between the temperature and the energy consumption, the equivalent viscous damping ratio, and the starting distance of sliding were also studied. The results showed that: (1) The finite element model can well show the frictional sliding characteristics of plate rubber bearing under horizontal load; (2) Within the temperature range studied in this paper, the lower the temperature, the more energy consumption of plate rubber bearing in the friction sliding process, and the bearing will earlier enter the sliding state. So it is important to control the supporting length of upper structure of the bridge in cold area. (3) With the decrease of shape coefficient, the viscous damping ratio of plate rubber bearing is increased, and the initial sliding distance of the bearing was decreased.

Abstract:With the development of urban transportation along the coast and rivers in China, the urgency of constructing submerged immersed tunnels is constantly increasing, and their seismic performance also becomes an important content of concern. Taking the northern bank section of a submarine tunnel project as the research object, a three-dimensional finite element model of immersed tunnel-soil-pile foundation-caisson was established based on ANSYS software. The water stop and shear bar were simulated by COMBIN39 element, and their physical and mechanical properties were simulated by non-linear F-D curve. The contact effect between pile and soil was described by thickness-free contact element, and the radiation effect of far-field foundation was reflected by setting viscoelastic artificial boundary. The calculation results showed that under the action of rare earthquakes, the caisson interface has a large stress due to the change of interface material and the consequent stress concentration phenomenon. The displacement of upper water stop at tube joint is larger than that of lower water stop, so it is easier to be damaged. It can provide a reference for seismic safety evaluation and optimal design of immersed tunnels and similar structures.

Abstract:Taking the Tianjin Z2 line as an example, the longitudinal seismic analysis of the shield tunnel is carried out by the response deformation method. The ABAQUS finite element analysis software was used to establish a 3D beam-spring model for seismic analysis. According to the actual tunnel bolt connection, the ring-ring joint is simulated by springs. The maximum free-field horizontal displacement amplitude under earthquake is applied by sine-wave mode in the axial and lateral directions of the shield tunnel. By adjusting the displacement amplitude with 1/0.85 or 0.85/1 between the axial and lateral directions of the shield tunnel, the coupling effect between the axial and lateral directions are considered. The internal forces and joint opening of the shield tunnel for 4 coupling cases are obtained, and some conclusions valuable for engineering design are presented.

Abstract:In this paper, a two-dimensional contour plot of relative acceleration is drawn through outdoor experiments, and the area division is carried out according to the vibration of soil around pile. Furthermore, the changes of soil vibration area around single pile with different geometric size are analyzed. The results show that there are vibration strengthening areas in front of and on both sides of the single pile, and the vibration strengthening phenomenon in front of the pile is stronger, especially at the pile corner. With the ratio of pile length to wavelength in a range of 0.109-0.840, the areas of vibration isolation zone and reflection zone increase greatly, while the area of diffraction zone decreases rapidly; when the ratio increases from 0.840 to 0.962, the areas of vibration isolation zone, reflection zone, and diffraction zone change little. The ratio of pile diameter to wavelength has a great influence on the vibration area around the pile. As the ratio increases from 0.013 to 0.163, the areas of vibration isolation zone and reflection zone increase by 0.249 m² and 0.129 m², respectively, while the area of diffraction zone decreases by 0.088 m². The ratio of source distance to wavelength has a great influence on the area of vibration isolation zone and reflection zone. When the ratio is in the range of 0.163-0.961, the areas of vibration isolation zone and reflection zone decrease rapidly; when the ratio is in the range of 0.961-1.068, the change trend tends to be gentle, and the area of diffraction area only increases by 0.037 m².

Abstract:Restriction of system frequency is one of the key points in the design of offshore wind turbines. The dynamic loads of operating offshore wind turbines can cause the horizontal displacement of the monopile foundation, which will decrease the stiffness of the pile-soil system, so that the natural frequency of the offshore wind turbine system will be further influenced. Based on the software platform ABAQUS, a numerical model is developed to analyze the system natural frequencies of offshore wind turbines supported on monopiles. Effect of the horizontal displacement of the foundation in the operating state on the natural frequencies of the offshore wind turbine system is further investigated. The numerical model considers the variation of the cross-sectional geometry of the wind turbine tower; the pile-soil interaction is simulated by a p-y curve method. The tower and monopile are modeled using beam element, and the pushover analysis is used to obtain the equivalent springs providing the foundation response at the pile-cap level. Results indicated that the lateral displacement of the monopile will reduce the natural frequency of the system. It has little effect on fundamental frequency, but has a significant effect on higher frequencies. In general, the influence of the operating state of the wind turbine on the natural frequency of the wind turbine system can be neglected.

Abstract:Software ABAQUS was used to establish a three-dimensional solid finite element model of a 2-story 1-span reinforced concrete plane frame structure for pseudo-dynamic analysis. The model takes into account the plastic damage of concrete, the elastic-plastic mixed hardening properties of steel, the structural damping, and the cumulative effect of plastic damage caused by continuous earthquakes. The calculated results of displacement and restoring force are in good agreement with existing pseudo-dynamic test results, then the structural damage, the plastic energy dissipation distribution mechanism, and the stress-strain relationship of concrete and steel bar are further analyzed. The results showed that the plane frame structure is basically in the elastic stage under small and medium earthquakes, and enters the plastic stage under large earthquake. The concrete at the beam-column joints is easier to be crushed than that at the bottom of column, and the first floor beam is easier to be destroyed than the second floor beam. The plastic energy consumption of beam is much larger than that of column, indicating that the frame is a typical "strong column and weak beam" structural system. The modeling method adopted in this paper can effectively reflect the damage process of the structure, and can be conveniently used for seismic performance evaluation of practical projects.

Abstract:Although the numerical methods proposed in recent years overcome the possible divergence phenomenon when applying the complex damping model to solve the structural dynamic response, the calculation process is complicated and cannot express the structural dynamic characteristics and the change law of response with structural parameters. This paper derived the analytic forms of natural frequencies and mode functions of each order of a horizontal shear structure by referring to the mathematical solution of tridiagonal Toeplitz matrix eigenvalue problem. Through Fourier transform of the motion equation, the analytical equation of transfer function of the structure under complex damping theory was obtained, and the dynamic characteristics of the structure and the variation of the response with structural parameters were expressed intuitively. The results showed that the analytical method based on the complex damping model overcomes the time-domain divergence problem. Then we compared it with the time-domain numerical calculation method and found that the time-history curves of displacement response obtained by the two methods are consistent with each other, and the peak displacements are basically the same. In addition, by comparing the dynamic responses of the two methods when underlying stiffness changes, the curves of the analytical method are smoother and the discrete error of numerical method is avoided.

Abstract:The intake tower with characteristics of tall tower body and thin wall is an important part of water conservancy project. It easily suffers structural instability and damage under earthquake. In view of the poor anti-sliding and anti-overturning ability of intake tower, the method of setting cast-in-place piles was proposed to improve the dynamic stability of tower foundation in this paper. Taking the intake tower of a water diversion project in Gansu Province as an example, the influence of cast-in-place piles on the dynamic stability of intake tower foundation was analyzed from three aspects: the stress of intake tower body from pile foundation, the shear force and bending moment of pile foundation, and the distribution of foundation displacement. The results showed that the cast-in-place piles can reduce the stress value at the middle and lower part of tower and improve the stress distribution; besides, after adding cast-in-place piles, the displacement value near the tower bottom decreases and there is no obvious potential slip arc surface. In conclusion, the dynamic stability of intake tower foundation is improved by setting pile foundation.

Abstract:To investigate the characteristics of dynamic parameters of model soil mixed with sawdust and sand, a series of dynamic triaxial tests were carried out to study the hysteresis loop's characteristics of this kind of soil, and the variation characteristics of dynamic shear modulus and damping ratio with the number of cyclic loading were also discussed. The test results showed that in the process of cyclic loading, the hysteretic circle showed a gradual increase in area and its shape developed from leaf to crescent as the loading level increased. The dynamic shear modulus of the model soil was basically constant and the damping ratio fluctuated under different cycle. With the increase of load level, the mean value of dynamic shear modulus decreased, and that of damping ratio increased. Lastly, the distribution of dynamic parameter curves of model soil are similar to those of common sandy soil, but the dynamic shear modulus is smaller and the damping ratio is larger.

Abstract:Six methods for the determination of characteristic period based on ground motion records were studied in this paper, i.e., ATC3-06 method, ASCE7-16 method, probability method (97%), peak value method, peak value reduction method, and smoothing method. The distribution of characteristic periods obtained by these six methods were compared by using 1 491 ground motion records. The influence of different calculation methods and different seismic events on the distribution of characteristic period were studied, and the correlation of these methods was also analyzed. The results showed that ATC3-06 characteristic period reflects the ratio between sectional spectral velocity and sectional spectral acceleration, while ASCE7-16 characteristic period considers the influence of site factors based on the ratio between simplified sectional spectral velocity and sectional spectral acceleration; Probability method (97%) reflects the characteristic period with the area ratio contained in characteristic period of response spectrum. The calculated characteristic periods of eight earthquakes calculated by six methods are distributed mainly from 0.2 s to 1.2 s, accounting for 80% of the total. There is a good correlation among ATC3-06 method, ASCE7-16 method, probability method (97%), peak value reduction method, and smoothing method.