Abstract:The rapid assessment of earthquake disasters can provide important information support for government departments to determine key rescue areas, deploy rescue teams, and allocate rescue materials. Based on the rapid earthquake disaster assessment system newly developed in Yunnan Province, the rapid assessment of earthquake disaster loss caused by the Yangbi, Yunnan M6.4 earthquake on May 21, 2021 was completed. The practical application results showed that the technical indexes of the upgraded and optimized seismic quick assessment software are significantly improved, i.e., the system stability, operation efficiency, abundance of emergency products, and information push service. The disaster assessment results, which are basically consistent with the actual results, can meet the new requirements of emergency response in the Internet era.

Abstract:On May 21, 2021, an M6.4 earthquake occurred at Yangbi county, Yunnan Province. 28 groups of acceleration data were obtained by the CDSMON. In this paper, 84 three-component acceleration records were processed, and corresponding ground motion parameters were calculated. Horizontal PGA and PGV contour maps near the epicenter were drawn, and the results showed that the trend and shape are similar to the results of post-earthquake intensity survey. The corresponding source duration of T _d (5%-95%) is between 10.22 s and 13.06 s, which is basically consistent with the inversion results of source rupture process. To summarize the spectrum characteristics of the earthquake, the acceleration response spectra recorded by six typical stations were analyzed and compared with the seismic design spectrum. The study results can provide a reference for seismic fortification in the study area.

Abstract:Based on the air-gun source signals from November 1, 2020 to May 30, 2021, recorded by 15 stations within 50 km of the epicenter of Yangbi M_S6.4 earthquake on May 21, 2021, the time series of travel time changes of Sg phase at 15 stations were extracted with the cross-correlation time delay detection technique, and the travel time changes of each station before and after the M_S6.4 earthquake were analyzed. The results showed that: (1) About 10 days before the earthquake, the travel time of 4 stations began to appear abnormal. Among them, the travel time of stations Ey211 and Ey213 showed a " V" -shaped structure, and the travel time of stations Ey210 and CHT showed an upward trend. (2) In the short term after the earthquake, the travel time of most stations showed obvious trend change. The change trends of stations on both sides of the Weixi-Qiaohou-Weishan fault were obviously different. The travel time of stations EYA, HDQ, and YSW09 at the east of the fault showed an upward trend, and the most significant change was in the HDQ station, with a travel time difference of 0.067 s. All stations at the west of the fault began to show a significant trend decline on the day of the M_S6.4 earthquake (or 1~2 days after the earthquake). The travel time decline lasted 4-9 days, and the travel time difference varied from -0.053 s to -0.201 s. The maximum decrease in travel time showed at 53 285 station, and the minimum decrease was at CHT station.

Abstract:The coseismic deformation field of 2021-05-21 Yangbi M_S6.4 earthquake in Yunnan Province was obtained by using Sentinel-1A satellite data and D-InSAR technology. The results showed that the coseismic deformation field of the Yangbi earthquake is distributed along the long axis near NW, and the signals of ascending and descending deformation are opposite. The maximum slip along line of sight is 0.1 m. Slips are mainly distributed in 2-12 km along strike and 1-9 km along down-dip direction, and the maximum displacement is 0.35 m. The seismic rupture is 9.8 km long and 4 km wide. The slip focus on the range of 3-6 km underground, and the slip angle is -146.7°. The coseismic deformation field and slip distribution model implied that the earthquake is a right-lateral strike-slip event, with rupture not reaching the surface. The inversion results of fault model showed that the moment magnitude of the mainshock is M_W6.1, and the seismogenic structure is a NW-trending right-lateral strike-slip fault. It is inferred that the seismogenic structure of the 2021 Yangbi M_W6.1 earthquake is a NW-trending blind secondary fault on the west side of Weixi-Qiaohou fault.

Abstract:At 21: 48 on May 21, 2021, an M_S6.4 earthquake occurred in Yangbi County, Dali Prefecture, Yunnan Province (25.67°N, 99.87°E), with a focal depth of 8 km. In this paper, the coseismic deformation field and the seismogenic structure of theM_S6.4 earthquake were analyzed with the two-pass DInSAR technique and the ascending and descending SAR data from sentinel-1A satellite before and after the earthquake, and geometric parameters of the fault were inverted based on the Okada elastic dislocation model. The research results are as follows: (1) The coseismic deformation field caused by the earthquake is about 19 km long and 20 km wide; (2) The maximum deformation along ascending radar line of sight (LOS) and descending radar LOS are about 8.2 cm and 8.7 cm, respectively; (3) The strike, dip and rake of the earthquake fault is 313.7°, 87° and 175°, respectively. The fault slip is right-lateral strike-slip with a maximum value of 0.79 m. The seismic moment obtained by inversion is 1.48×10¹⁸ N·m, and the moment magnitude is M_W6.1. Under the tectonic background of southward extrusion of Sichuan-Yunnan block, right-lateral strike-slip occurred along the Weixi-Qiaohou fault and the Honghe fault on the west boundary of the block. This earthquake is the reflection of right-lateral strike-slip activity along the south branch of Weixi-Qiaohou fault.

Abstract:120 strong motion observation records obtained from the M5.6, M6.4 and M5.2 earthquakes in Yangbi County, Yunnan Province on May 21, 2021 were processed and analyzed in this paper, and the ground motion parameters of records were obtained.Then the peak acceleration contour maps of the three earthquakes were drawn, and their long axes were all distributed in the NW-SE direction.By comparing the actual PGA observations of the three earthquakes with the attenuation relationship of Yu Yanxiang^[1] and Wang Suyun^[2], we found that the actual observations were more consistent with the predicted values of Yu Yanxiang.Finally, the acceleration response spectre of typical stations were compared and analyzed, and it is found that the larger the magnitude is, the more obvious the long-period component is; the smaller the magnitude is, the larger the amplitude attenuation is.

Abstract:Based on the field investigation of the damage of civil structure buildings caused by Yangbi M_S6.4 earthquake in Yunnan Province, the reinforcement performance and damage characteristics of civil structure houses in the earthquake-stricken areas were analyzed.The analysis results showed that the damage of civil structure houses can be reduced after seismic reinforcement.Through the comparative analysis of damage characteristics of similar earthquakes, analysis of reinforced and unreinforced structures, and the strong motion records, it can be concluded that the seismic reinforcement of civil structure buildings can reduce the macro intensity by 1-2 degrees.Furthermore, the effects of earthquake prevention and disaster reduction of seismic strengthening on civil structures were evaluated, and some suggestions on seismic strengthening and intensity evaluation were put forward.

Abstract:On May 21, 2021, an M_S6.4 earthquake occurred in Yangbi County, Yunnan Province. In this paper, we analyzed the statistical characteristics of earthquake anomalies from the geoelectric field stations within 200 km around the epicenter with the shifting correlation method and the dominant azimuth α of geoelectric field. The conclusions are as follows: (1) The statistical analysis results of historical events around the epicenter showed that the abnormal phenomena of geoelectric field usually appeared about 20(±5) days before the earthquake, such as Midu, Xiangyun and Eryuan stations; (2) The dominant azimuth α of geoelectric field at Eryuan and Xiangyun stations began to change about 15 days or earlier before the YangbiM_S6.4 earthquake; (3) When the local geoelectric field station is on the same seismogenic fault (or fracture zone) with the seismic event, it is more likely to observe the earthquake anomaly. In addition, based on the existing magnetotelluric sounding results in the study area, the electrical structure characteristics under geoelectric field stations sensitive to earthquake are preliminarily explored. We found that when the survey area is located on the resistivity boundary, it is easier to observe the abnormal changes of seismic electric field. The findings of the study are expected to provide a technical support for the site selection of geoelectric field stations and the analysis of seismic anomalies.

Abstract:An M_S6.4 earthquake occurred in Yangbi County, Yunnan Province on May 21, 2021, and an M_S7.4 earthquake occurred in Maduo County, Qinghai Province on May 22, 2021. The data from twelve geoelectric stations within 500 km of Yangbi epicenter and 8 geoelectric stations within 500 km of Maduo epicenter were analyzed, respectively. The results showed that: (1) The dominant azimuth angles of eight stations around the epicenter of Yangbi earthquake showed abnormal changes before the earthquake, while those of other four stations showed no obvious anomalies; The correlation coefficients of seven stations decreased significantly in 2-6 months before the earthquake, while those of other five stations showed no obvious abnormal change. (2) The dominant azimuth angles of four stations around the epicenter of Maduo earthquake showed abnormal changes before the earthquake, while those of other four stations did not change obviously; The correlation coefficients of five stations decreased significantly and the variation range was obviously narrowed in 2-6 months before the earthquake, and those of other three stations did not show obvious abnormal changes. (3) The anomalous changes of dominant azimuth and correlation coefficient of geoelectric field during the two earthquakes are synchronous or quasi synchronous in time.

Abstract:Combined with the seismicity anomalies recorded in the daily tracking word before the Maduo M7.4 earthquake, we systematically sorted out the characteristics of grouping activities of M6 earthquakes in the Qiangtang Block, the low-frequency activities of M5 earthquakes in mainland China, the significant enhancement of moderate seismic activities in the northeastern Tibetan Plateau, and the temporal and spatial anomalies of the seismic swarm activities in the northeastern Tibetan Plateau. We not only summed up the prediction significance of several indexes, but also evaluated the prediction efficiency of some important indexes. Meanwhile, through the temporal and spatial distribution characteristics of Luqu earthquake swarm, we concluded that the Luqu area is a stress-sensitive area; the Luqu earthquake swarm has a good prediction significance for the occurrence of moderate and strong earthquakes in the surrounding area, and should be used as an important index in the subsequent earthquake monitoring process.

Abstract:An M_S7.4 earthquake occurred in Maduo County, Qinghai Province on May 22, 2021.To explore the seismogenic structure of the earthquake and the distribution characteristics of aftershocks, this paper selected the seismic observation reports from Qinghai Seismic Network in a space range of 33-36°N, 97-99.5°E from May 1 to June 3, 2021.After double difference relocation, the overall residual was reduced by an average of 0.23, and the depth was randomly distributed within 5-25 km.According to the earthquake migration direction and local geological structure, it is believed that the seismogenic structure of the M_S7.4 earthquake is Kunlun Pass-Jiangcuo fault.A series of small earthquakes were triggered by the main earthquake and then occurred along the east section of Maduo-Gande fault.The earthquake may cause some connection between the two faults.A new fault was generated by the earthquake and then connected with the Maduo-Gande fault, so that the two faults crossed and connected, forming a new fault structure.

Abstract:On May 22, 2021, an M_S7.4 earthquake occurred in Maduo County, Qinghai Province. A few hours later, an M_S4.4 earthquake occurred in Maqu County, Gansu Province, 200 kilometers away from the epicenter. In this paper, the focal mechanism solution of the Maqu M_S4.4 earthquake was inverted by using the data of three-component broadband digital waveform recorded by regional seismic networks in Gansu, Qinghai, and Sichuan Province. The results showed that the strike, dip, and slip angle of the seismic plane are 105.6°, 74.1°, and -38.7°, respectively. Referring to the focal mechanism solution of the Maduo M_S7.4 earthquake, it is found that the focal mechanism solutions of the two earthquakes are in good agreement, showing obvious characteristics of left-lateral strike-slip. The calculation results of static Coulomb failure stress showed that the tensile stress on the unit area (m²) of the epicenter of the Maqu M_S4.4 earthquake from the epicenter direction of the Maduo earthquake is about 0.2 bar (≈0.02 MPa). Based on the epicentral distance, occurrence time and fault distribution of the two earthquakes, it is preliminarily determined that the Maqu M_S4.4 earthquake should be a triggered earthquake of the Maduo M_S7.4 earthquake in Qinghai Province.

Abstract:Load/unload response ratio (LURR) is an earthquake prediction method based on the dynamic evolution law of rock stress-strain relationship. Using Benioff strain as the response, this paper analyzed the evolution characteristics of LURR anomalies within 400 km of the epicenter of 2021 Maduo M_S7.4 earthquake in Qinghai Province and its surrounding area, and found that the LURR reached the highest value one month before the earthquake and fell back half a month later, indicating that the rock medium in the seismogenic zone has entered the end of yield stage. On this basis, the evolution law of short-term and impending anomalies of outgoing long-wave radiation (OLR) value from May 14 to 25 was analyzed by using the OLR data from NOAA satellite. The results showed that: before the earthquake, significant and continuous short-term and impending abnormal changes of OLR occurred only in the northern part of the epicenter and showed a trend of expanding toward the epicenter. In terms of time, the entire evolution process experienced six stages: initial temperature increase-abnormal expansion-peak value-anomaly weakening-earthquake occurrence-anomaly disappearance. The short-term and imminent anomaly characteristics of LURR and OLR before the earthquake indicated that the LURR high value before the fall reflects the end of yielding stage of rock medium. To a certain extent, OLR can characterize the cumulative state of tectonic stress of active faults in a critical state. The comprehensive study of evolution characteristics of the two physical parameters before the earthquake can be helpful to more accurate evaluation of seismic activity trend.

Abstract:On May 22, 2021, an M7.4 earthquake occurred in Maduo County, Qinghai Province. In this study, the cave strain observation data of Tongren, Tangchang, Wudu, and Guza stations from May 1 to 22 were selected and processed with the multi-scale wavelet decomposition method. The results showed that at scale 11, the amplitude of NS components at two close stations increased significantly before the earthquake. Generally, the smaller the epicentral distance is, the larger the deformation amplitude is. There were obviously different characteristics of the vector trajectories during May 10-14 and 16-20. In addition, the multi-scale wavelet decomposition of geomagnetic vertical component at Dawu and Hezuo stations showed that the amplitude increased in the same period (scale 18), which also confirmed the reliability of the strain anomaly. We believe that this strain anomaly is the eastward pushing result of the Qinghai-Tibet block, and is related to the consequent MaduoM7.4 earthquake. Combined with the research results of other scholars, we inferred that this may be related to the movement of the high conductive layer beneath the epicenter. However, this is only a preliminary study, and the detailed seismogenic environment and mechanism need to be further studied.

Abstract:On May 22, 2021, an M7.4 earthquake occurred in Maduo County, Qinghai Province. Before the earthquake, the water temperature recorded by two sets of observation equipment at Gonghe seismic station showed synchronous rise-decline change from February 28 to March 3, 2021, and the observed values ranged from 0.047 ℃ to 0.075 ℃ and 0.007 ℃ to 0.24 ℃, respectively. On March 21, the anomaly ended, and 62 days later, the Maduo earthquake occurred. Through a contrastive analysis of hydrochemical components during different periods, the conclusions are as follows: (1) The hydrochemical types were HCO₃-Na and HCO₃·SO₄-Na, and the degree of water-rock reaction was weak. (2) The chemical ions (Na⁺, Mg²⁺, Ca²⁺, and ) had obvious response to the fluctuation after the anomaly appeared. (3) The Na-K-Mg triangle diagram showed that the water samples were distributed in the area of partial equilibrium water after the anomaly appeared, which was greatly different from the immature water area during the normal period. The results showed that due to the regional stress adjustment after the anomaly appeared, the middle and deep hot water was mixed with the partial equilibrium water of medium salinity when it flowed through the rock stratum to the surface, resulting in significant changes in the salinity and hydrochemical components of water. Based on the analysis of the anomaly characteristics and historical earthquake cases, it is considered that this anomaly is a reliable earthquake precursor anomaly.

Abstract:On May 22, 2021, an M_S7.4 earthquake occurred in Maduo County, Guoluo Tibetan Autonomous Prefecture, Qinghai Province.Based on the intensity survey of Maduo earthquake, this paper focused on the damage of houses in six key areas and the destruction of bridges and roads in meizoseismal area.The earthquake was characterized by high magnitude and light casualties. Only a few civil structures and brick and wood structures near the epicenter collapsed; some brick-concrete and frame structures showed stairwells and infill walls cracking, and most houses were basically intact.Through investigation, we also found that the Yematan No.1 and No.2 Bridges and Changma River Bridge all experienced different degrees of collapse and damage, thus providing the data support for the division of intensity map.Meanwhile, a statistical analysis of secondary geological disasters caused by the M_S7.4 earthquake was carried out, and some comments and suggestions on post-disaster reconstruction and seismic fortification were also put forward.

Abstract:The intensity distribution of Maduo, Qinghai M7.4 earthquake in 2021 was evaluated rapidly by using the Qinghai seismic intensity attenuation model and the ground motion parameters attenuation model based on the shortest fault distance, and the evaluation results were compared with the actual intensity map. The research results showed that the two models can both get the quick evaluation results of earthquake intensity distribution within 1 minute after the official quick report, thus providing reference for emergency command and rescue work in the shortest time. The calculation results of Qinghai seismic intensity attenuation model have a certain reference value in the general range, but there is a deviation from the actual results in the severely affected areas. The PGV-v_S30 calculation results of the ground motion parameters attenuation model are more precise than those of the Qinghai seismic intensity attenuation model, thus having a good practical application value in the evaluation of high intensity area. Compared with the empirical relationship between surface rupture and magnitude proposed by RAN Hongliu, the empirical relationship proposed by Wells is more applicable in Qinghai area. The research results of this paper are applied in the emergency response of this M7.4 earthquake, and provide important data support for the government emergency command and emergency rescue.

Abstract:On May 22, 2021, an M7.4 earthquake occurred at Maduo County, Qinghai Province.16 sets of three-component acceleration records of the main shock were obtained by CDSMON.In this paper, 48 three-component acceleration records were processed by baseline correction and filtering, and corresponding ground motion parameters were calculated.To analyze the spectral characteristics of this earthquake, the acceleration response spectra of six typical stations were analyzed and compared with the seismic design spectra of buildings in China.The actual observation records of PGA, PGV, and S_a (T=0.1 s, T=1.0 s, T=2.0 s, T=5.0 s) were compared with several ground motion prediction models widely used in China to study the influence field of the M7.4 earthquake.Through the analysis of S_a-S_d curves, the possible relationship between the large displacement of ground motion near the fault area and the bridge unseating damage was discussed.

Abstract:The phenomenon of microwave fluctuation impending strong earthquake is a type of abnormal pulsation record; its dominant frequency of spectrum focuses on 11-16 Hz and frequency spectral morphology appears fairly orderly. Based on the data from " real-time monitoring and tracking system of microwave fluctuation impending earthquake in Lanzhou" , the events of microwave fluctuation impending earthquake recorded by stations within 200 km of the Maduo M7.4 earthquake on May 22, 2021 were analyzed. It is considered that the EW channel of Bayan Har station, 67 km from the epicenter, was abnormal before the earthquake, which reaches the anomaly tracking index proposed by Yang Liming. The events of microwave fluctuation impending earthquake were recorded by eight seismic stations before the earthquake, and more events were recorded in the south of the epicenter than in the north.

Abstract:On May 22, 2021, an earthquake with a magnitude of 7.4 occurred in Maduo County, Guoluo Prefecture, Qinghai Province. The Huanghe Town and its surrounding area, 7 kilometers away from the epicenter, were the stricken areas of the earthquake (Ⅷ degree). Based on the earthquake field work, the earthquake disasters of a total of 1 019 buildings with brick-concrete structure, brick-wood structure, and civil-wood structure in the study area were investigated. Among them, brick-concrete structure houses accounted for 67.71%, and most of them were basically intact or slightly damaged; brick-wood structure houses accounted for 29.24%, and most of them were slightly or moderately damaged; civil-wood structure houses accounted for 2.45%, and most of them were completely destroyed. Based on the investigation results, relevant opinions on earthquake prevention and post-disaster reconstruction are put forward: (1) Professional personnel should be organized to inspect the houses after the earthquake and report to relevant departments; (2) Bricks-concrete, frame, and light steel structure houses are recommended for post-disaster reconstruction; (3) The supervision and construction standards for self-built houses need to be strengthened.

Abstract:To evaluate the dynamic response characteristics of polar cranes in nuclear power plants under earthquake, a simplified finite element model of polar crane with containment was established in this paper.Then the numerical simulation for seismic response of the model was carried out under the action of Los Angeles earthquake wave with adjusted amplitude.Natural frequencies of the polar crane were computed, and the first order frequency of polar crane fixed on containment wall is 2.44 Hz.The results showed that the strength of large girder of polar crane meets the standard requirement under seismic load of code.Under the action of typical three-directional Los Angeles earthquake, the gantry wheel and trolley wheel are always in compressive state, and there is no rail jump phenomenon.Compared with peak acceleration of input seismic wave on the basement of containment, the maximum vertical peak acceleration on mid-spans of large beam and small beam of polar crane increases by 107% and 126%, respectively.

Abstract:Railway mountain tunnels passing through the reverse fault in seismic active zone are easily affected by the reverse fault slip, and at present, relevant research experience is not much. In this paper, the numerical analysis method was used to analyze the dynamic response of hinged lining tunnels under seismic load and active fault movement. The results showed that the influence of reverse fault movement on the deformation of shallow strata is greater than that of deep strata, but the maximum additional deformation appears near the deep fault plane. The larger the dislocation distance is, the greater the maximum additional deformation value is. The fault activity has a significant impact on the safety of tunnel structure, and grouting reinforcement can not change the vibration spectrum characteristics of lining during earthquake, so the design scheme of reserved repair space for single-layer lining should be adopted. Under the two working conditions of over-excavation design, the displacement variation law and vibration spectrum characteristics of lining are consistent. Through monitoring and measurement, it is found that the compressive stress of the support tends to be stable after about 2 months. The conclusions can provide a reference for the structural design and construction of similar projects in future.

Abstract:To model the seismic behavior of corroded reinforced concrete columns accurately, in this paper, based on the existing research results, a bond-slip constitutive model between corroded steel bar and concrete under cyclic loads was established. The validity of the bond-slip model was then verified by the ABAQUS finite element analysis software. The friction bond stress and bond degradation coefficients in the bond-slip model were further corrected by analyzing the error between the numerical calculation results and the test results, and a more reasonable bond-slip constitutive model between corroded steel bars and concrete was established. The validity of the modified model was verified by comparing the numerical results with the experimental results again. The results showed that the modified bond-slip model can better reflect the hysteretic performance of corroded reinforced concrete columns under cyclic load. The results can provide a theoretical reference for the numerical analysis and calculation of corroded reinforced concrete structures under earthquake.

Abstract:To reduce the discreteness of lignin fiber-improved loess samples obtained in laboratory tests, unconfined compressive strength tests were carried out on the improved loess samples prepared by dilution mixing method and direct mixing method, respectively. By comparing the change rates of dry density and the discreteness of unconfined compressive strength of samples prepared by the two mixing methods, the effect of mixing methods on the strength of samples was analyzed. The results showed that the change of dry density of improved loess samples prepared by dilution mixing method is more stable before and after curing, and the dispersion degree of dry density change rate of samples with the same content is less than that of samples prepared by direct mixing method. The samples prepared by the two mixing methods can both reflect the basic trend that the unconfined compressive strength of improved loess is affected by the content. However, test results of unconfined compressive strength of the samples prepared by dilution mixing method are more stable, which can better reflect the effect of the change of lignin fiber content on the strength of improved loess samples.

Abstract:According to the disaster characteristics of mountain tunnels in loess areas under strong earthquake, the ground motion amplification effect of the soil around tunnel portal and the tunnel structure were analyzed. Through a 3D numerical model, the acceleration and displacement responses in the slope elevation direction and horizontal direction of the model with different slope, slope height, and portal elevation were mainly studied, and the responses of lining structure were also analyzed. The range of slope reinforcement area and the recommended seismic fortification length of tunnel were proposed. The research results showed that the changes of elevation, slope angle, and portal elevation all have an important impact on the seismic response law and failure mode of the tunnel portal section. The shear failure at the bottom of slope is easy to occur on gentle slope, while the tensile failure at the top of slope is easy to occur on steep slope. With the increase in slope height, the sliding failure range of the slope increases gradually. The existence of tunnel has a significant " restraining" effect on the amplification effect of slope elevation. There is a dynamic response amplification area in the horizontal direction of the portal, ranging from 2.1 to 2.8 times of the tunnel diameter. Based on the dynamic response law of lining along the tunnel length, it is suggested that the minimum seismic fortification length of the portal section of loess tunnel is 3 times of tunnel diameter.

Abstract:To explore the characteristics of wind field around super high-rise buildings, the Gaoyin 117 Building in Tianjin was taken as an example in this paper.The field measurement was conducted through DZZ2 acquisition system to analyze the wind field characteristics around the building, i.e., the average wind speed, the fluctuating wind speed, the turbulence intensity, the turbulence integral scale, and the Von Karman spectrum.The results showed that the variation of longitudinal and lateral fluctuating wind speed does not follow the standard Gaussian distribution; the longitudinal and lateral turbulence intensity is negatively correlated with the average wind speed, and its change degree is related to the range of average wind speed; the longitudinal and lateral integral scale of turbulence increases with the increase of average wind speed; the Von Karman spectrum is more accurate in describing the wind field characteristics around the super high-rise building in a low frequency range.

Abstract:To objectively predict the synthetic earthquake damage of in-service highway girder bridges, an evaluation index system for synthetic earthquake damage prediction of highway girder bridges was established by considering existing problems of in-service bridges during operation. Taking the bridge as the disaster bearing body, a matter-element extension model for synthetic seismic damage of in-service highway girder bridges was established in this paper. Then the entropy method was used to determine the synthetic seismic damage status of the bridge. Taking an in-service girder bridge as an example, the synthetic seismic damage of the bridge was determined by using the above model. The research results show that the synthetic seismic damage level of the bridge is grade III, and the damage level is medium. According to the results, main factors influencing the seismic damage degree of the bridge were analyzed. The evaluation accuracy and reliability of the model was greatly improved by evaluating the synthetic seismic damage level of the in-service girder bridge through a comprehensive analysis of the correlation coefficient of multiple indexes. The study can provide a certain reference for predicting the seismic damage level of bridges, thus having a positive significance for improving the synthetic seismic capacity of bridges.

Abstract:To calculate the bearing stiffness of mountain bridges with different pier heights, it was proposed that the pier top can be regarded as free constraint in the transverse direction and orientation constraint in the longitudinal direction after considering the rotation restraint effect of upper structures. The formulas of bearing stiffness in the transverse and longitudinal directions were derived based on the principle of equal shear force and bending moment at the pier bottom. To verify the correctness of the proposed design method for pier bearings, a 5-span continuous bridge model with different pier heights was established using the OpenSees, and three cases were selected: In case 1, the bearing stiffness for each pier is the same; In case 2, the bearing stiffness in the transverse and longitudinal directions were calculated in terms of free constraint at the pier top; In case 3, the bearing stiffness were calculated in terms of orientation constraint at the pier top. Time-history analysis was conducted on the bridge structure under three ground motion records, and the shear forces at pier bottom were investigated under the three cases. The analysis results show that the base shear forces of each pier in the transverse and longitudinal directions are different in case 1. The base shear forces in the transverse direction are the same, while those in the longitudinal direction are different in case 2. The base shear forces in the longitudinal direction are the same, whereas those in the transverse direction are different in case 3. These results indicate that in the design of bridge bearings, the bearing stiffness in the transverse direction should be calculated as the pier top is free, and those in the longitudinal direction should be calculated as the pier top is orientation constraint.

Abstract:Since earthquake occurs frequently in the loess plateau, the internal structure of loess with large pores and weak cementation structure will be disturbed by the influence of dynamic loading, while the change of microstructure will be reflected by physical and mechanical properties in later stage. To study the change of loess mechanical properties under the long-term influence of frequent earthquakes, dynamic triaxial tests and consolidation undrained shear tests were conducted on the loess samples. The results showed that when the initial water content of loess samples is 10%, compared to undisturbed loess samples, the deviatoric stress of disturbed samples is significantly increased, and the shear strength index value is increased by 3.42 kPa and 2.67°, but the pore water pressure is reduced. When the initial water content increases to 15%, the long-term effect of historical earthquakes would cause the strength of loess to continue increase in later period. The increment is far more than 10% of the loess samples, and the cohesion and internal friction angle are up to 3.98 kPa and 3.02°. Results of SEM and MIT revealed that the inter particles movement and the pore structure change caused by historical earthquakes are key factors for the increment of loess strength.

Abstract:The physical properties of loess can be used to simply and quickly evaluate its collapsibility. Under the disturbance of different loads and water infiltration, the collapsibility of intact loess varies with the change in its physical properties. To better evaluate the collapsibility of such disturbed loess, on the basis of two indoor tests conducted on a site in Donggang Town, Lanzhou City with a time span of more than 40 years, the correlation analysis method was used to study the relationships among the collapsibility coefficient and the dry density, water content, porosity, saturation, and plasticity index of loess before and after the disturbance. The results show that: (1) Before and after the disturbance, the collapsibility coefficient is negatively correlated with the dry density, water content, saturation and plasticity, and positively correlated with the porosity ratio. After the disturbance, the collapsibility coefficient is generally lower than that before the disturbance, and the influence of the indices on the collapsibility coefficient is weakened. (2) Using the dry density, water content, porosity ratio, saturation and plasticity index as factors reflecting the collapsibility of loess before and after the disturbance, the multivariate linear regression and factor weight analysis were performed to obtain the regression equation and the sequence of factors affecting the loess collapsibility. The research results have certain reference value for estimating the collapsibility of disturbed loess and choosing an appropriate foundation treatment method.

Abstract:There are many problems when using current methods to predict the loss caused by post-earthquake debris flow disasters: long time for prediction, large errors in the results, and low prediction efficiency and accuracy. In this paper, a coupling prediction method for post-earthquake debris flow disaster loss based on GIS technology was proposed. GIS technology was adopted to obtain the information about post-earthquake debris flow disasters. Based on the acquired information, a watershed calculation model, a solid mass calculation model, and a debris flow starting model were established to analyze the starting process of debris flow. Based on the property loss prediction model and personnel loss prediction model, a coupling prediction model of post-earthquake debris flow disaster loss was constructed. The experimental results show that the proposed method has high prediction efficiency and accuracy.

Abstract:With the fast and convenient development of urban rail transit, the environmental vibration caused by subway operation is increasingly prominent. As an industrial filler, Duxseal has good damping performance and can absorb vibration reflection energy. In this paper, it was applied to subway vibration isolation, and a vibration isolation method of Duxseal filled by WIB (wave impeding block) with cylindrical holes (DXWIB) was proposed. Through a three-dimensional ABAQUS finite element model, the vibration isolation effects of WIB, honeycomb WIB (HWIB), and DXWIB were compared and analyzed. The influences of the depth and the thickness of DXWIB on the vibration isolation effect were discussed, and the vibration laws of the subgrade surface and the ground were analyzed. The results showed that the vibration isolation effect of DXWIB is the best, while those of WIB and DXWIB are similar. DXWIB has the best vibration isolation effect when the buried depth is 0.5 m and the thickness is 0.8 m. The vibration law of the subgrade surface is that the vibration source propagates laterally to both sides, and the acceleration shows an attenuation trend. In the process of ground propagation, the peak acceleration increases first, then decreases, and finally increases, and local amplification effect appears at 20 m and 50 m away from the track axis.