Abstract:The concept and geometric design of a novel friction "plastic hinge" structure with high safety and low cost were proposed to achieve the seismic objective of accurate energy dissipation and repairable damage under large earthquakes. Based on the design theory of the beam-column ductility steel joint structure, the mechanical property theory and working mechanism of the structure were deduced, and the static elastoplastic analysis of the steel frame structure was conducted. Through the finite element software ABAQUS, the numerical analysis model of five working conditions were established, and the cyclic reciprocating displacement load analysis of the finite element model was conducted to explore the seismic performance of the new friction "plastic hinge" structure. The results showed that only the shear failure of shear bolt occurred in the model, indicating that it can realize the accurate energy dissipation and rapid repair of the structure. The model had good rotational performance, which can meet the requirement of story drift angle. The friction energy dissipation increased with increasing prestress and friction coefficient of the rotary load bolt. The bearing capacity of the theoretical analysis and that of the finite element analysis were 15.92 kN and 15.84 kN, respectively, basically agreeing with each other. The equivalent viscous damping coefficient of shear bolts in shear stage and friction stage were 0.318 and 0.671, respectively. The formation and development of the friction "plastic hinge" in a steel frame can meet seismic performance requirements, and the pushover analysis can be used as an effective way to evaluate the seismic performance of the structure.

Abstract:Extreme disasters such as earthquakes, fires, and collisions can cause the partial or widespread collapse of building structures. Existing research on the resistance of building structures to progressive collapse has mainly considered the contribution of the slab to the beam stiffness, but not the continuous tension of the rebar, which implies that the contribution of the slab to the whole structure is conservatively evaluated. In this study, we selected as the research object the composite joints of a circular concrete-filled steel tubular structure. Using ABAQUS software, we established a numerical model with two different boundary conditions for the steel end in the plate. We analyzed the joint failure mechanism during failure of the vertical middle column and observed the influence of the constraint conditions of reinforcement in the plate on the bearing capacity of the joints' girder and catenary mechanisms. The results show that there are four stages in the joint collapse process:the beam mechanism, transformation mechanism, catenary mechanism, and failure stages. By comparing the resistance curves under two different constraint conditions, we found that the bearing capacity of the beam mechanism is increased by about 7% when considering the tensile action of reinforcement in the plate, whereas the bearing capacity of the catenary stage is not obvious.

Abstract:After an earthquake shock, reinforced concrete frame structures feature complex stiffness degradation, and the simulation results are considerably distorted. Therefore, analysis and simulation were performed considering the stiffness degradation law to study the resilience of a reinforced concrete frame structure under earthquake impact. The hysteretic curve of the reinforced concrete frame structure under earthquake was extracted, and different characteristic points were obtained via finite element analysis to form the skeleton curve of restoring force model. According to the skeleton curve and stiffness degradation rule of the restoring force model, the hysteretic curve was constructed to simulate the restoration process of the reinforced concrete frame structure after the earthquake. The restoration experiment simulation results of the reinforced concrete frame structure showed that the story drift was less than 5 mm, and the errors of absolute story acceleration and column bottom lifting were both less than 0.1 mm. The bending moment gap could be closed, and there was no yield phenomenon in the structure, indicating that the simulation results are reasonable.

Abstract:To study the seismic vulnerability of brick masonry structures with openings in their walls, we used ABAQUS finite-element-analysis software to construct a model of the walls of a brick masonry structure, and established reasonable wall-model and numerical-simulation parameters. Comparing our simulated values with the test values obtained in previous research, we verified that the model parameter values were reasonable. Using measured mechanical change data, we analyzed the earthquake vulnerability of a brick masonry structure. The analysis results show that with increases in the number of wall openings, the load capacity of the wall decreases, the horizontal bearing capacity increases, and the relative degradation rate of the wall stiffness increases. The more openings there are in a wall, the faster the lateral stiffness of the brick masonry structure decreases. Therefore, the seismic vulnerability of a brick masonry structure is more obvious as the number of wall openings increases.

Abstract:This study aims to understand the progressive collapse mechanism of concrete-filled steel tubular (CFST) frame-core wall hybrid structures when local components are destroyed. Under the failure condition of columns and core walls on the 1st, 17th, and 33rd floors, nonlinear dynamic analysis of a 33-story CFST frame-core wall hybrid structure is carried out based on ABAQUS fiber beam and multi-layer shell elements by using the material constitutive subroutine iFiberLUT. The anti-progressive collapse mechanism of the remaining structure is also studied. When the components are destroyed, the lowest displacement response of the upper node occurs on the 1st floor, a larger displacement response occurs on the 17th floor, and the largest one occurs on the 33rd floor. Compared with that in the failure condition of the shear wall, the vertical displacement of the upper joints is greater and vibrations are more obvious when a column is destroyed. The influence of different working conditions on the core wall is weak, and the core wall enhances the film effect of the floor slab; it also improves the anti-progressive collapse capacity of the structure. Moreover, the path of inertial forces follows the "shortest path principle" when typical components are destroyed. The slab and core wall effectively improve the redundancy load path and integrity of the hybrid structures.

Abstract:To improve the accuracy of seismic performance analysis of wooden structures, a multi-scale modeling analysis method was used in this paper. By using the multi-point constraint method, the mortise-tenon joints and beam-column members were set as the critical and non-critical regions, respectively. Based on the idea of multi-scale modeling, solid elements were adopted for fine-scale modeling in key areas, while beam elements were used for ordinary-scale modeling in non-critical areas. The coordination of macro-structure model and local micro-model could then be realized on different scales, and the seismic performances of solid elements and beam elements in modeling under different scales were compared. The experimental results showed that the multi-scale finite element numerical analysis can simulate the overall dynamic response of wooden structures and accurately analyze the boundary conditions. Through multi-scale and large-scale hierarchical modeling, local and global seismic performance analyses can be conducted, which are highly accurate and can improve the efficiency of seismic analysis.

Abstract:At present, landscape architecture design often pays more attention to the view of the building while neglecting safety and stability. This leads to poor seismic response of the landscape building as a whole. Therefore, adding a retaining wall can effectively improve its earthquake resistance. For this reason, a type of retaining wall for landscape buildings with some seismic performance was designed in this paper. The composite fiber material, building refuse, and fiber rope retained in the construction process were used as the filling material of the earthen wall. To maintain the stability of the soil wall, tensile material of certain tensile strength was added to the earth fill. Because the landscape architecture usually pays attention to the visual effect of appearance, the design of "altering flat ground into slope" was used. Plants of a certain visual impact were installed on the wall surface to increase the self-weight of the earthen wall and to promote the stability of the overall structure of the soil wall. The stress state of infinite inclined backfill behind the retaining wall was then analyzed, and the rhombic micro-element was chosen as the research object to calculate the earth pressure strength of the retaining wall. The experimental results showed that the optimized design of the retaining wall structure can effectively enhance the overall seismic capacity of the landscape building.

Abstract:In this paper, we propose a method for identifying the instantaneous modal parameters of a time-varying structure based on a continuous wavelet transform. First, we selected a random impact load as the input excitation of a time-varying structure. Then, under the assumed time-varying condition in a short time span, we established a principle for identifying the time-varying parameter based on the continuous wavelet transform. We identified the instantaneous modal parameter using only the output response of the structure, and performed a numerical simulation of a 3-DOF time-varying structure system. The results show that this method can accurately identify the instantaneous modal parameter of a time-varying structure. Finally, we designed and tested a two-layer steel frame model with variable quality parameters, and the results further verified the validity and feasibility of the proposed method.

Abstract:Evaluating the damage resistance of reinforced concrete structures has great engineering significance, but the current evaluation method based on single-factor superposition has a large error factor. To solve this problem, in this paper, we propose a method for evaluating the seismic vulnerability of reinforced concrete structures based on multiple fuzzy analysis. Based on the Park-Ang seismic damage model, we introduce normalized cumulative energy dissipation parameters to obtain the inter-story damage of the building structure, and we obtain the integral damage values of a post-earthquake building structure via a weighted average. Then, we use the story-drift-ratio parameters to calculate the story drift ratio of the post-earthquake structure. We take the integral damage values of post-earthquake structures and the story drift ratio as the multi-factor domain to perform a multiple fuzzy evaluation of the structural damage resistance. We select the mathematical model and membership function of the fuzzy damage assessment to calculate the weight of each factor and the comprehensive damage index of the structure. The experimental results show that the accuracy of the proposed method based on multiple fuzzy analysis is greater than 95%, which confirms its effectiveness for evaluating the damage resistance of reinforced concrete structures.

Abstract:The occurrence of earthquake disasters poses a great threat to the safety of human life and property. To ensure the safety of buildings during earthquakes, determination of the load, initial stiffness, ductility coefficient, and vertical displacement of buildings is required. If the gravity load is higher than the peak value, the building safety cannot be guaranteed. To analyze the gravity load capacity of the top floor of a building during a horizontal earthquake, we established a three-story, three-span building model to test the lateral stiffness of the building under gravity load. Then, we studied the influence of the gravity load on the detected stiffness of the top structure of the building during a horizontal earthquake. We selected five specimens from the model, and analyzed their material properties, experimental results, and load displacements. The peak load of the building, as determined by the gravity load displacement curve of the experimental model, was 700 kN. That is, when the peak load of the top floor of the building exceeds 700 kN, the safety of the building cannot be guaranteed.

Abstract:To verify the effect of the application of a fluid viscous damper (FVD) and friction pendulum bearing (FPB) in large-span and long-unit bridges with a seismic isolation system, we established a finite element model of a prestressed-concrete continuous-beam bridge. By inputting three artificial seismic waves with a 50-year exceedance probability of 2%, we conducted an isolation study of the bridge with an individual or combined use of an FVD and FPB. With respect to energy dissipation, we determined the combined action mechanism of an FVD and FPB in large-span and long-unit bridges. The results indicate that if only an FVD is used, the FVD will dissipate energy effectively because of its long-period characteristics, but seismic damage to a fixed pier cannot be avoided. Using only an FPB will cause bearing displacement beyond the design specifications under longitudinal (horizontal) strong earthquakes. The isolation mechanism operating under the combined action of FVD and FPB is that the FPB provides a weak connection between the pier and beam, generates relative velocity between them, and thus facilitates the effective dissipation of energy by the FVD. In addition, the FPB serves as an auxiliary energy dissipation device, with the FVD being the main energy dissipation device controlling the beam displacement. Compared with the use of only the FPB, the combined system may increase the energy input to the structure, thus resulting in an intensified seismic response.

Abstract:The steel-truss structure is widely used in long-span buildings, so it is of practical significance to analyze its seismic response. In this paper, we describe our construction of finite element models of a long-span main and auxiliary steel-truss structures and discuss their seismic responses. Based on the two elements of stiffness and mass, we perform a natural vibration analysis of the natural vibration characteristics of the large-span main and auxiliary steel-truss structures. We then analyze the structural mechanical properties of the structures using the modal decomposition response spectrum method, and analyze the seismic response of the steel-truss structures with respect to their mechanical properties. The simulated results show that the structural stiffness of the steel structures is good. These study results provide a preliminary basis for the seismic design of large-span main and auxiliary steel-truss structures.

Abstract:In the design of long-span spatial steel structures, reasonable selection of the support and upper hanger combination has an important influence on the seismic resistance of the structure. However, such factors are not taken into account in present designs. The main purpose of this paper is to comprehensively select the suitable support and hanger structure for the long-span spatial steel structure, in the hope of better seismic performance. First, three kinds of widely-used contemporary structures were listed. Second, some seismic constraint conditions, such as bearing capacity, stress-strain, and tensile deformation, were presented. Considering seismic constraints, the selection model for the support and hanger with anti-seismic capacity were given along with a concrete calculation example. The support and hanger of long-span spatial steel structure was selected, with a certain seismic capacity considered. The experimental results of the long-span spatial steel structure showed that the seismic level of the core steel structure with the model was obviously improved compared with the traditional random hanger selection method.

Abstract:To study the influence of the design parameters of sector lead viscoelastic damper on seismic performance of the reinforced frames, precise finite element model corresponding to the experimental retrofitted frame specimens was built based on ABAQUS and validated by test results. Three key parameters of sector lead viscoelastic damper influencing the seismic performance of retrofitted frames were studied:sector effective radius, viscoelastic layer width and lead core diameter. Analysis results indicate that increases of sector effective radius, viscoelastic layer width and lead core diameter of sector lead viscoelastic damper can significantly enhance the initial stiffness, yielding force and lateral bearing capacity of the retrofitted frames. In particular, augment of sector effective radius reveals an obvious raise on seismic performance of the retrofitted frames. However, to avoid local stress concentration of columns and beams, an exaggerated sector effective radius shall be avoided when strengthening existing structures. Furthermore, the size of lead core diameter of sector lead viscoelastic damper has little contribution on the later bearing capacity of the reinforced frames.

Abstract:The dynamic interaction mechanism of soil and large-diameter belled piles is an important factor in earthquake engineering research. Based on the Lagrangian FLAC^3D program, we established three-dimensional numerical models of the dynamic belled pile-soil interaction and dynamic equal-diameter pile-soil interaction under seismic loading to investigate the difference in the seismic responses of the large-diameter belled pile and conventional equal-diameter pile. We used the Mohr-Coulomb elastic model to consider the nonlinear characteristics of the soil around the pile and the linear elastic model to simulate the pile itself. We then used the model cutting method to set the interface between the pile and its surrounding soil. Under the input of a 5·12 Wenchuan seismic wave, we performed a numerical calculation and analysis of the seismic responses of the two pile foundations. The results show that the anti-seismic performance of the large-diameter belled pile is better than that of the conventional equal-diameter pile. A comparison of the acceleration time history curves with a dramatic difference shows that the belled pile is not sensitive to the dynamic displacement response.

Abstract:Taking the vertical wing wall of the intake of a nuclear power plant as the background, in this study, we used the FLAC^3D program to simulate the dynamic response of the vertical wing structure under earthquake action. Combined with the PL-Finn constitutive model, we studied the dynamic response law of the wing wall structure under dynamic load, and quantitatively evaluated the safety of the wing wall's revetment structure with respect to the structural displacement time history, structural deformation, excess pore water pressure ratio, and liquefaction area. The analysis results show that the structure experiences regular residual deformation due to the liquefaction-induced flow of sand, which increases with earthquake intensity. The horizontal and vertical deformations are caused by the earthquake inertial force and sand liquefaction. The horizontal residual deformation at the top of the wing wall structure under the action of SL1 was 0.05 m, and the vertical residual deformation was 0.07 m. Under the action of SL2, the horizontal residual deformation at the top of the wing wall structure was 0.26 m, and the vertical residual deformation was 0.16 m. Compared with the input ground motion of the bedrock, we found the horizontal and vertical accelerations at the top of the wing wall structure under the actions of SL2 and SL2 to be amplified by 4-5 orders of magnitude, whereby the closer the acceleration is to the top of the wing, the more significant is the amplification effect. The conclusions obtained in this paper can serve as reference for similar projects in the future.

Abstract:To study the influence of different evaluation methods on the overstrength factor of partially-restrained steel frames with concealed vertical slit RC infill walls (PSRCW), a ten-story PSRCW structure located in an area with a fortified aseismic intensity of 8 was designed. The standard PSRCW was extended to 40 PSRCW specimens using the Latin hypercube sampling method, and the randomness of materials (including steel, steel bar, and concrete) was considered. The hysteretic and skeleton curves of 40 PSRCW specimens were obtained using the cyclic pushover method, and the overstrength factor of the PSRCW structure was determined by the probabilistic method at the 95% confidence level. In addition, two groups of 22 near-fault and far-fault earthquake waves recommended by the ATC-63 specification were selected to conduct incremental dynamic analysis (IDA) on the structure; the same probabilistic method was then adopted to evaluate the overstrength factor of this standard PSRCW structure. The evaluation method plays an important role in the overstrength factor of PSRCW structures. The overstrength factors of the PSRCW structure considering the randomness of materials are calculated to be 1.3 and 1.73 by the cyclic pushover method for the generalized power loading distribution mode and the uniform lateral loading distribution mode, respectively. In addition, the overstrength factors of the PSRCW structure considering the randomness of near-fault and far-fault earthquake waves are determined by the IDA method to be 2.42 and 2.45, respectively.

Abstract:Under the action of earthquakes, some key components of underground structures may be damaged, and the stability of the whole structure may deteriorate. Based on the traditional response displacement method, a new response analysis method of displacement time-history is proposed, and the characteristics and solution procedure of the method are introduced. Seismic response analysis of the Daikai subway station in Kobe, Japan, was conducted using the proposed method, which takes several aspects, e.g., the soil-structure interaction, material nonlinearity, geometry nonlinearity, coupling effect of horizontal shock and vertical shock, and the time-space effect of ground motion propagation, into consideration simultaneously. As the deformation and damage failure of the metro station obtained by the proposed method agreed well with actual results, the method is suitable for seismic analysis of underground structures.

Abstract:To study the seismic performance of the connection system of precast concrete with a metallic damper, numerical simulation analyses of the connection system and ordinary prefabricated assembly frame are carried out; the influence of different design parameters of the damper on the seismic perfor-mance of the system is also analyzed. The connection system of the metallic damper shows better seismic performance than ordinary precast concrete frames, which could delay beam end damage, and effectively solve difficulties associated with construction of the subsequent concrete casting area at the beam end. Decreases in metallic damper height improve the energy dissipation ability but reduce the initial stiffness and bearing capacity. In addition, as the height of the energy dissipator increases, the larger the mid-span bending moment of the member and the earlier it yields. However, the oversize of the energy dissipator leads to severe bending deformation.

Abstract:Based on a practical project environment, in this study, we studied the failure mechanism of a sandy soil embankment subjected to freeze-thaw cycles, and introduced a novel moisture-transfer test device. We used this device to measure the space-time distribution of the temperature, water, and stress fields of typical sandy soil specimens from the main dike of the Heilongjiang River during freeze-thaw cycles. The test results show that the damage to the embankment is related to its uneven settlement. We found the change in the water content gradient to be due to the temperature change, which changes the stress field, and the water content and temperature gradients have a linear relation. The stress increases at the top of the soil column during the initial freezing period and decreases after it has stabilized, with the stable freezing depth occurring at about 1 m.

Abstract:The Loess Plateau is seated on the upper and middle stream of the Yellow River in northern China, covering an area of 440 000 km², with loess deposit thickness ranging from several meters to more than 500 meters. The Loess Plateau is one of the most tectonically active areas of the world and one of the most seismically active regions. More than 1.4 million people have been killed by the earthquakes in the region. The Wenchuan M_S8.0 earthquake in 2008 collapsed or seriously damaged enormous buildings, houses, and infrastructure. The field investigations, observations, and analyses indicate that a large number of casualties and tremendous economic losses were caused not only by the collapse and damage of houses with poor seismic performance, but also by the amplification effects of site conditions, topography, and the thickness of loess deposits on ground motion. The morphological characteristics of slopes determine the predominant frequency, which may amplify the incident seismic wave with the same or similar frequency range, and thus, increase the slope dynamic response and even trigger landslides. The field investigations of the Wenchuan earthquake indicate that the amplification effects of site conditions and topography on ground motion were very obvious in loess regions. In this paper, we chose a typical loess site for temporary strong motion array and numerical analysis, and aim to explore the dynamic response characteristics of the loess slope. The results reveal the following:(1) The minimum predominant frequency occurred at the slope crest. The highest peak ground acceleration (PGA) amplification coefficient reached 1.98 at the slope crest. The phenomenon of the low predominant frequency corresponding to the high PGA amplification at the slope top may be related to the ratio of slope height to the wavelength of incident wave. The PGA amplification was maximum when the ratio was 0.2. (2) The amplification effects are more predominant with increase in slope gradient. The predominant period amplification coefficient of response spectrum at the slope top may reach 5. The numerical results are basically consistent with the ground motion observations, and thus, they have high scientific and practical significances for engineering seismic fortification in loess regions.

Abstract:To gain a better understanding of the deformation behavior of Jiaxing Quaternary sedimentary soils, we collected total 34 undisturbed soil samples. The analysis results revealed that the variation characteristics of the normalized dynamic shear modulus ratio (G/G_max) and damping ratio (λ) with increasing shear strain (γ) are strongly influenced by the sedimentary facies and geological time. For the same sedimentary facies, the more recent the geological time, the larger is the dynamic shear modulus ratio and the smaller is the dynamic damping ratio. For the same geological time, we found the dynamic shear modulus ratio of the alluvial-lacustrine deposit to be largest, and the dynamic damping ratio the smallest. Moreover, we suggest recommended values for the dynamic shear modulus ratios and dynamic damping ratios of soils of different sedimentary facies and geological time in Jiaxing area. Furthermore, we used FLAC^3D modelling software to perform a dynamic response analysis of the soils at one typical engineering site using the recommended and measured values and verified the applicability of the recommended values. These study results can be used as reference in the seismic risk assessments of engineering projects.

Abstract:To study the site hazard effect induced by the dynamic interaction among ground fissure, metro tunnel, and surrounding rock under the load of subway vibration, the geological environment of the ground fissures in Xi'an and the actual engineering design of Xi'an Metro Line 2 were selected as the background. A physical model test with a similar scale of 1:5 was designed using the similarity theory. Then the shield tunnel, surrounding rock material, and ground fissures were reasonably designed. A vibrator was used in the model test to simulate the load of metro train vibration, and fixed-point excitation and moving-point excitation were both applied to analyze the dynamic response among ground fissure, metro tunnel, and surrounding rock under subway vibration load. The analysis results can provide a scientific basis for the safe running of subways.

Abstract:The microtremor survey can be used to evaluate geologic interfaces with large differences in their geotechnical properties. Using the microtremor survey method to obtain the S-wave velocity profile, we then compared the stratigraphic strata at the Haokou middle school in Qianjiang City with the borehole results obtained by the earthquake monitoring project at the site. The results show that this method has the advantages of high resolution of the stratigraphic structure and good exploration of strata with different geotechnical properties, which can provide an important basis for understanding the stratigraphic stratification.

Abstract:To evaluate the relationship between micromechanisms and different physical and chemical improvement methods on the seismic subsidence loess engineering site, soil samples were obtained along the Baoji-Lanzhou High-speed Railway, and dynamic triaxial and SEM microstructural tests were conducted. Combining image processing software with the appropriate threshold, the evolution law of microstructure deformation of samples was applied and studied. Results showed that:(1) Physical improvement is the most effective way to eliminate macropores and porous pore structures; moreover, the particle size distribution and structure can be also adjusted. (2) Chemical modification affects the strength of the loess from the aspect of particle contact and intergranular cementation; moreover, the participation of different chemical reactions can produce unique glass beads or flocculent fine structures, which can greatly reinforce the strength of loess and play a role in filling, cementing, or buffering in strong earthquakes. (3) The differences between loess microcosmic parameters and residual strain coefficients, with the above improved methods before and after strong earthquakes, were compared, and it was found that they are in good agreement, indicating that the microstructure can generally reflect the residual deformation strength of the loess.

Abstract:The results of rock stick-slip dislocation experiments in the laboratory show that one stick-slip dislocation process includes three stages generally:pre-slip stage, stick-slip stage, and stop-slip stage. We found the stick-slip dislocation process is often not a single point stick-slip dislocation process, but is composed of multi-point stick-slip dislocation process, showing the characteristic of multi-point stick-slip dislocation in the different parts of the fault. A strong earthquake of magnitude M_W7.9 occurred at Wenchuan, China, on May 12, 2008. The process of coseismic stick-slip dislocation and stop-slip process of the earthquake were recorded perfectly by the digital seismograph of Global Seismographic Network's (GSN) 74 seismic stations and the deep borehole water level digital instrument of Zhouzhi seismic station, China. After analyzing these recordings, we find that multi point stick-slip dislocation process during the Wenchuan M_W7.9 earthquake. According to the observational evidence, the stick-slip dislocation process may be composed by four sub-stick-slip dislocation events.The duration time of whole process of stick-slip dislocation is more than 86.6 s. We infer to the Wenchuan M_W7.9 earthquake may be a result of elastic rupture and stick-slip dislocation commonly. It is a kind of "stick-slip dislocation + elastic rupture" mechanism. After analyzing the recording of deep borehole water level digital instrument of Zhouzhi seismic station, we find the results of coseismic stick-slip dislocation process of Wenchuan M_W7.9 earthquake are consistent with the rock stick-slip dislocation experimental results of P. N. Sundaram^[1]. The stick-slip dislocation process can be divided into the stick and the slip two process. The stop-slip phase XsQ and XsR are excited during the stop-slip process of Wenchuan M_W7.9 earthquake. The XsQ and XsR phase are Love type surface wave and Rayleigh type surface wave, respectively. The travel time relationships of P+Xs1, Xs2, Xs3, Xs4, XsQ and XsR phases are given, at Δ=5.3°-121.0°. Studying the Xs phase will be helpful for understanding the processes of the stick-slip dislocation. Studying the XsQ and XsR phase will be helpful for judging disaster loss of the great earthquake.

Abstract:The results of mobile geomagnetic data processing may contain significant trend components, which interfere with the identification of anomalous information, and their removal thus becomes necessary. In this paper, the trend surface analysis method was applied to determine and strip the trend components from mobile geomagnetic data processing results. The results showed that the trend surface analysis method could effectively determine and remove the regional variation components of the lithosphere magnetic field in the monitoring area, and make the spatial distribution of the local anomalous components clearer and more reasonable. This is helpful for the identification of precursory anomalies. The technological ideas adopted in this paper are innovative, and the process of technological treatment is relatively simple, operable, and clear in its physical significance.

Abstract:Based on the broadband records from Fujian Digital Seismic Network, the focal depths of M_L ≥ 3.5 earthquakes in Shunchang area, Fujian Province, during 2007-2017 were determined using the sPL phase. Based on the focal mechanism solutions of these earthquakes, combined with the velocity model of the study area, the F-K method was used to calculate the Green's function at different depths in the corresponding epicentral distance; the theoretical waveform of sPL phase at different depths were then obtained. According to the characteristics of the sPL phase, the broadband records of stations within 30-50 km of the epicenter were selected and filtered. They were compared with synthetic seismograms, and the corresponding depth with the most similar waveform was found. The determination results showed that the focal depth was approximately 12 km.

Abstract:In this study,the geochemical evolution process of CO₂ gas and a series of acid-base equilibrium and redox chemical reactions during seismotectonic activity were systematically studied through the analysis of macroscopic anomalies observed in the seismic risk area of southeastern Gansu.The results showed that deep underground CO₂ gas not only acts as a carrier for other trace gases moving toward the surface but also participates in acid-base balance and redox reactions,which is an important influencing condition for deep underground biochemical reactions.The occurrence of earthquake precursors and macroscopic anomalies is accompanied by abnormal changes in CO₂.Thus,CO₂ gas can be used as a good tracer gas.Therefore,CO₂ monitoring should be paid special attention in the observation of earthquake precursors and the implementation of major anomalies.

Abstract:In view of the problems associated with the traditional optimization method for seismic data attribute reduction, i.e., the large amount of computation required in the reduction process and the high CPU occupancy rate, in this paper, we propose an attribute reduction and optimization method for massive seismic data based on principal component analysis (PCA). First, we establish a feature matrix of the seismic data based on the characteristics of seismic samples. The features in the matrix are then clustered and arranged in descending order. We then select the first few data as the seismic data attribute feature results and evaluate the classification information of these results. Next, the classification information is modified using the feature integral criterion to obtain the attribute feature nodes of the massive seismic data. We use PCA to label the principal components of the attribute nodes of the seismic data and establish a global optimization of the semi-supervised dimensionality reduction. The dimensionality reduction results are calculated by eigenvalue decomposition, we solved the problem of over-fitting in the attribute reduction process of massive seismic data, and realized the optimization of the attribute reduction of massive seismic data by combining the PCA algorithm with Fisher discriminant analysis. The experimental results show that the proposed method has a high accuracy and contribution rate of attribute feature selection, and the CPU occupation rate is low during the dimensionality reduction process.

Abstract:The main characteristic of the spatial distribution of geomagnetic low-point time is that it changes with longitude. To solve the analytical formula of the relationship, we first calculated the low-point time sequences and the expected values of the low-point times of 13 geomagnetic stations in Gansu Province. Using nearly three years of data from the national geomagnetic network, the frequency distribution diagram and the normal density curve of the low-point time series were plotted. We then made a linear regression for the relationship between the low-point time of the Z component and longitude of the station, and indicated that the linear regression equation should be infinitely close to the "Greenwich time-longitude" equation. In this paper, the relational expression between the low-point time of the Z component and longitude of the station is first proposed, and the approximation equation of the relational expression is described. The expected value of the low-point time of each station is the normal background value of the geomagnetic low-point time, which is a reference standard to determine whether the geomagnetic low-point time is abnormal. The significance of the above work is to perfect the geomagnetic low-point displacement method proposed by Ding Jianhai.

Abstract:Because of the limited extrusion of the Tibet Plateau from the northwest to southeast, the Sichuan-Yunnan block has one of the highest concentrations and frequencies of earthquakes in China. It is very critical to assess the seismic hazard and explore the geodynamics of this region by quantifying the slip rates of active faults as well as the earthquake occurrence. The Menglian fault, one of the active left-lateral strike-slip faults in Sichuan-Yunnan block, stretches from China to Myanmar. There are no records of earthquakes on the Menglian fault; however, many earthquakes occurred in its vicinity, which may be related to the activity of the fault, such as the Myanna M_S7.3 earthquake of 1995. In China, the Menglian fault has a length of 90 km and a trend of NE-ENE. The fault shows clear geomorphologic characteristic with linear fault scarps (mainly), fault valleys, and fault trenches. Additionally, various offset streams, gullies, and terraces have been formed along the fault, and the observed minimum left-lateral dislocation is about 7 m. Using high-precision Li-DAR measurement, four typical horizontal dislocation geomorphologies were finely measured. According to the obtained age of the geomorphic surface, the average left-lateral strike-slip rate of the fault since the late Quaternary was (2.2±0.4) mm/a. The results were equivalent to the sliding rate of other NE-trending left-lateral strike-slip faults in southwestern Yunnan, reflecting the overall coordination of regional tectonic activities. According to the maximum left-lateral dislocation of (9.5±1.8) km, the initial time of the left-lateral strike-slip of the fault was estimated to be about (4.7±1.6) Ma, in the middle and late Miocene.

Abstract:The current long-distance signal transmission method does not realize parallelism between the transmission channel energy and transmission channel signals, which leads to high distortion of long-distance signal transmissions. To improve the long-distance transmission efficiency of seismic signals, in this paper, we propose a new technique for long-distance signal transmission in the seismic monitoring systems of high-speed railways. By adopting a method using parallel seismic signal energies in the signal transmission channel and parallel signal transmission structures in the transmission channel, we realize the bidirectional transmission of signals in the transmission channel. Based on the channel energy transmission structure and the signal transmission process, we made the transmission channel energy and signal parallel, and controlled the distortion of seismic signals in long-distance transmissions of high-speed railways. The experimental results show that the proposed method has a low packet-loss rate of about 3% and a long-distance transmission delay of only 0.9 s. This represents a low-error and high-efficiency long-distance transmission method for seismic signals in high-speed railways.

Abstract:To monitor conditions in disaster areas in real time, enhance real-time performance and reduce the error of search and rescue, the application of the Internet of Things technology in earthquake emergency search and rescue of trapped personnel was studied, and applied to the design of an earthquake emergency search and rescue system. The collected data were transmitted through the Internet to the data processing center server by a RFID reader, and then fed back to the monitoring and defense module of the information processing subsystem in the disaster area. If an abnormal situation occurred, the radio frequency module would be turned on to order the in-situ alarm device to respond to the emergency search and rescue signal. The optimal search and rescue route could be calculated with the ant colony algorithm, and the earthquake trapped personnel could be timely searched and rescued. The experimental results showed that the designed system can effectively search and rescue earthquake trapped personnel. The throughput of the system was as high as 90%, the average accuracy rate of search and rescue as high as 97.6%, and the average consuming time was only 0.88 h. The system showed high search and rescue accuracy and efficiency.

Abstract:To improve the accuracy of quality evaluation of post-earthquake recovery and reconstruction projects, this paper presents a quality evaluation system for post-earthquake recovery and reconstruction projects based on the Matlab analytic hierarchy process (AHP). AHP is an effective way to make an accurate decision, but the various indicators for the quality evaluation of reconstruction projects make the data process difficult, and the calculation effect is not good. In this paper, the AHP was combined with Matlab software to obtain accurate analysis results in short time, and a set of new evaluation indices was established. This study provides a new idea for the rapid evaluation of post-earthquake recovery and reconstruction projects, thus having certain reference significance for improving the intelligent level of quality evaluation of post-earthquake recovery and reconstruction projects.

Abstract:When using the WSR model to analyze the cost control problem of seismic structures in building engineering, the cost control effect is poor. A cost control model for aseismic structures of high-rise building was designed in this paper. The hierarchical structure for cost control was constructed, and various schemes for cost control of the high-rise building were obtained. The optimal scheme of cost control was selected by using the three-scale method and the weight vector method. The quality quantification QoS dispatching method was then used to obtain the optimal cost control results for high-rise buildings. The experimental results showed that the designed model can effectively analyze the qualitative characteristics of high-rise buildings and improve the cost control of high-rise seismic structures. The estimated consumption cost can be controlled below 18 000 RMB, and the average analysis time is 0.15 h, indicating the model has the advantages of cost savings, high efficiency, and good control effect.

Abstract:Deflection is an important index for determining bridge stability and safety after an earthquake, but the measurement of bridge deflection is complex and suffers a lot of interference, so the obtained results are problematic. In this study, we designed a method for measuring bridge deflection after an earthquake. Based on the relevant parameters of an actual bridge, we used the conjugate beam method to calculate the initial deflection of a fixed point on a bridge after earthquake. Combined with the deflection curve function of the post-earthquake bridge, we can determine the deflection of the bridge section. To determine the deflection error of a post-earthquake bridge and correct the measured bridge deflection, we replaced the deflection error problem with the difference between the elevations of the monitored and reference points. Experiments involving simply supported and continuous girders verified the accuracy of the proposed method for measuring the deflection of a bridge post-earthquake.

Abstract:Different discussions on the causes of the 1856 Xiaonanhai, Chongqing earthquake disaster are available, and different understandings of the earthquake's origin, magnitude, and epicentral intensity exist. This work analyzed historical earthquake records and the extant traces of the Xiaonanhai earthquake site in reference to previous investigations and studies. It also calculated the magnitudes of earthquakes in the Xiaonanhai area in accordance with the calculated gravitational collapse potential of several large landslides. The earthquake disaster in Xiaonanhai area may have resulted from the superposition of multiple tectonic earthquakes because four earthquakes with M ≥ 5 were located near the Qianjiang Fault Zone. Satellite images revealed the active tectonic features of the fault zone. In addition, numerous earthquakes were distributed near the fault zone. Several possible causes of seismogeological disasters were discussed, and other potential predisposing factors were presented. The Xiaonanhai earthquake may have resulted from the superposition of multiple tectonic earthquakes or from a pure mountain collapse, but other causes cannot be completely ruled out. The further development of scientific practice is needed to uncover and further discuss the mystery of the geological disaster of the Xiaonanhai earthquake.

Abstract:Many methods have been developed to distinguish earthquake foreshock. In this study, we used the rhythm of nine multiplied days in different years to distinguish foreshocks. In this method, we look for earthquakes that conform to the rhythm of nine multiplied days in different years in regions where a small earthquake or earthquake swarm occurred. If one day among the nine in different years occurred close to the day the small earthquake or earthquake swarm occurred, we consider that this small earthquake or earthquake swarm may have been a foreshock. Two examples were identified:the small earthquake before the Yushu M_S7.1 earthquake in 2010 and the small earthquake swarm before the Wenchuan M_S8.0 earthquake in 2008, both of which could possibly have been foreshocks.