Abstract:It is convenient and economical to repair eccentrically braced steel frames with replaceable shear links after an earthquake, but few studies have focused on it domestically and internationally. Therefore, 16 groups of web-connected shear links connected by bolts with eccentrically braced steel frames were designed and analyzed through numerical simulations. The effect of changing the parameters (section size, length of the energy dissipation section, stiffener spacing, stiffener arrangement, and comprehensive parameters) on the hysteretic performance and the skeleton curve of web-connected shear links under low-cyclic reversed loading was discussed, and the simplified restoring force model of shear links was established. The results show that section size is the parameter that primarily influences the energy dissipation of the web\|connected shear links. The proposed restoring force model is in good agreement with the simulated skeleton curve, which can be used as a reference for elastic-plastic analysis of such shear links.

Abstract:Taking the Haven Bridge as the engineering background, we studied the dynamic response of pile foundations during earthquakes in the case where bridges cross active faults in strong seismic zones. The finite element software Midas GTS was applied to establish a numerical model of the pile-seabed rock-fault coupling action in areas characterized by strong earthquakes. The dynamic time-history response characteristics of the acceleration, displacement, bending moment, and shear force of the bridge pile foundation under the action of 5010 seismic wave with different intensities (0.20g-0.60g) were investigated. The results showed that the upper loose soil with a large thickness had an amplifying and filtering effect on the acceleration of the pile body, while the bedrock had a largely negligible effect. The horizontal displacement at the top of the pile foundation in the hanging and foot walls of the fault increased with the increase in the input seismic intensity, while the moment of reaching amplitude was consistent. The permanent settlement appeared 50 s after the vertical displacement time-history response at the top of the pile foundation in the hanging and foot walls, and the permanent bending moment appeared 40 s after the time-history response at the maximum bending moment section of the pile. Emphasis must be on appropriately designing the flexural capacity at the bedrock interface and at the interface between the soft and hard soils of the upper overburden as well as on designing the shear capacity near the pile top and the bedrock face. The pile foundation of the hanging wall should be designed on the basis of the dynamic parameters, such as the pile acceleration, bending moment, and horizontal displacement at the pile top, while the pile foundation of the foot wall should be designed on the basis of the dynamic shear stress.

Abstract:In this paper, the internal force law of the south bank section and wind tower structure of Dalian Bay subsea immersed tube tunnel under the action of earthquakes and the structural damage characteristics in the elastoplastic stage were studied. In addition, a three-dimensional refined model of an immersed tube-plant-wind tower was established, and the ABAQUS built-in constitutive model of concrete damage was used to perform seismic response analysis of the structure under two seismic conditions using mode-superposition response spectrum and time-history analysis methods. Results show that the maximum displacement values in the X and Y directions are 1.11 and 5.56 mm, respectively, both appearing at the top of the structural ventilation tower. Moreover, the modal mass participation coefficients in the X and Y directions are 90.52% and 92.07%, respectively, both meeting the requirement of seismic code, and the bending moment at the junction of two lanes of the immersed tunnel is the largest, reaching 5 069 kN·m. Under rare earthquakes, the maximum story drift ratio of the structure is 1/2 798, and the maximum damage of the structure appears at the time of seismic wave peak. By observing the damage, the structural concrete is uniform, and no broken phenomenon is observed. The maximum tensile damage coefficient is 0.893-0.94, appearing at the fresh-air duct and roof of the fresh-air room. Therefore, enhancing the bending resistance at the connection between the two lanes of the immersed tunnel and adding reinforcement at the top plate of the fresh-air duct and fresh-air room are necessary to improve the tensile capacity.

Abstract:To improve the seismic performance and construction fault tolerance of prefabricated assembled piers, this paper proposes a new connection method for assembled piers: assembled piers connected with ultra-high-performance concrete (UHPC) around piers. A cast-in-place bridge pier specimen and an assembled pier specimen connected with UHPC around the pier were designed and fabricated. A quasi-static test was performed on two specimens, and a three-dimensional solid nonlinear finite element model of the assembled pier specimen was established. The seismic performance and associated influencing factors of the proposed assembled pier were analyzed by performing a numerical simulation. The results showed that the assembled pier specimen connected with UHPC around the pier exhibited a similar lateral performance and self-resetting capability as the integral cast-in-place pier, and their seismic performances were the same. The fitting degree between the hysteretic curves of the nonlinear finite element model and the actual pier specimen was high, verifying the reliability of the modeling method and the accuracy of the simulation results. The height of the UHPC connection had little influence on the seismic performance of the assembled pier, and only the lap length of the reinforcement needed to be ensured. The axial compression ratio, column height, and lapped reinforcement ratio had evident effects on the seismic performance of the assembled bridge pier. When the axial compression ratio was between 0.1 and 0.3, the stiffness and horizontal bearing capacity of the specimen increased with the increase in the axial compression ratio. When the column height increased from 2.0 m to 2.5 m, the horizontal bearing capacity and accumulated hysteretic energy dissipation of the assembled pier decreased with the increase in the column height; when the reinforcement ratio was increased from 1.01% to 1.57%, the horizontal bearing capacity and residual displacement of the assembled pier were evidently improved compared with those of the original specimen.

Abstract:The ridge line is usually the starting point of mountain disasters caused by earthquakes. An accurate identification of the location of the ridge line while monitoring such mountain disasters is crucial to facilitate the development of relevant preventive measures. However, detection of the ridge line in PolSAR images containing buildings with high scattering intensity can be challenging due to some imaging issues of synthetic aperture radar (SAR), resulting in misjudgments. A recognition method combining the region-growing method and the variogram is proposed in this paper to address this problem. During the recognition process, the collected image is first segmented by the region-growing method. Then, the texture variations and other features are clustered and analyzed by the Fuzzy C-means method, and the similarity is assessed to obtain the building area. The ridge line can then be extracted by comparing this with the mixed image. A comparative analysis of the experimental results for the proposed method show significantly improved extraction accuracy as compared with the threshold segmentation method. Thus, this study can provide a new idea for the detection of ridgelines in PolSAR images.

Abstract:This study aims to explore the disaster mechanism, fracture development behavior, and initiation time of accumulation landslides during post-earthquake rainfall, taking the Jiangdingya landslide in Zhouqu County, Gansu Province, as an example. Four groups of post-earthquake rainfall tests with the same seismic intensity and different rainfall intensities were performed using a shaking table and an artificial rainfall model. The results revealed the following: (1) The earthquake causes shear failure of the slope, which is eroded by soil loss due to post-earthquake rainfall, with an obvious shear outlet at the slope foot. Thus, post-earthquake rainfall induces local instability in the accumulation landslide. (2) The earthquake causes shear cracks and dislocations in the middle of the slope and “arc-shaped” tensile cracks at the rear edge. During post-earthquake rainfall, the crack deformation intensifies with an increase in rainfall intensity, and sudden deformation occurs during the rainfall. (3) Given the same seismic intensity, there is an exponential relationship between the initiation time of the landslide and the rainfall intensity and a logarithmic relationship between the soil settlement deformation and the rainfall intensity. The results presented in this paper can provide a reference for the early warning and prevention of accumulation landslides during post-earthquake rainfall.

Abstract:The loess-mudstone interface landslide in Chenzhuang Village, Lixian County, Gansu Province, was investigated in this study. A dynamic numerical simulation of the instability mechanism and stability of the landslide subjected to ground motion at various artificial calculation sites was conducted based on an analysis of the seismic geological environment and basic characteristics of the landslide. Results show that the deformation and failure of the Chenzhuang landslide are associated with a composite failure mode of tension and shear when subjected to ground motion. The process of instability can be summarized as follows: ground motion due to an earthquake → tension at the bottom of rock mass → increase in shear stress at the upper part of the main slip section of the potential slip surface → emergence of a shear strain concentration zone → extension and penetration of the shear strain concentration zone → landslide instability. The stability of the Chenzhuang loess-mudstone interface landslide decreases with an increase in the ground motion, and the landslide is in an unstable state when subjected to bedrock ground motion with a exceeding probability of 2% in 50 years.

Abstract:The loess in the landslide area of the Heifangtai irrigation district in Gansu Province was taken as the research object in this study. The salt content and the chemical characteristics of the soil and water in the landslide area were investigated. A series of triaxial consolidation undrained shear tests was conducted on remolded loess with different soluble salt contents and moisture contents to explore the effects of the salinity and moisture content on the shear strength of the loess in this region. The results showed that (1) The soluble salt contents in the samples ranged from 0.15% to 4.55%, and the main components were Na₂SO₄ and NaCl. (2) The hydrochemical analysis showed that the irrigation water infiltrated and dissolved the soluble salt in the plateau loess, which was discharged and enriched at the slope foot in the form of spring point seepage. (3) The shear strength of the samples increased with the increase in the soluble salt content and decreased with the increase in the water content. (4) Under the conditions of different soluble salts and water contents, the cohesion varied from 4.2 kPa to 57.1 kPa, and the internal friction angle varied from 23.1° to 33.5°. The cohesion was more sensitive to changes in the soluble salt and moisture contents.

Abstract:Herein, the parametric modeling method was employed in the analysis and design of damping structures. An optimal damper arrangement scheme was developed by presetting objectives and iterative optimization calculations for the energy dissipation structure of a B-level high-rise residential building in Tianshui City. Perform 3D and ETABS software were used to analyze the structural response during frequent and rare earthquakes to assess the seismic performance of the energy dissipation structure. The analysis results show that during small earthquakes, the story displacement, story drift ratio, story moment, and story shear of the energy The setting of ring beams and structural columns is an important measure to improve the overall seismic performance of rural buildings. In this study, a series of shaking table tests considering soil-structure interaction (SSI) was performed on rural buildings with ring beams and structural columns. The 1/4 scaled model of the structure used in the test was manufactured and placed on a foundation soil model. One natural and two artificial seismic waves were selected, and the input seismic amplitudes were 0.1g (7-degree), 0.2g (8-degree), and 0.4g (9-degree). The test results showed that under the action of a 0.4g (9-degree) earthquake, only slight cracks were induced around the corners of doors and windows of the longitudinal wall, and the failure mode was intact, indicating good seismic performance of rural buildings with ring beams and structural columns. With the increase in the seismic action, the acceleration amplification coefficient of the structural model decreased gradually, while the response of the story drift gradually increased. When the seismic intensity is high, the influence of the SSI effect on the acceleration transfer coefficient from the soil layer to the structure should be appropriately considered.

Abstract:Herein, the parametric modeling method was employed in the analysis and design of damping structures. An optimal damper arrangement scheme was developed by presetting objectives and iterative optimization calculations for the energy dissipation structure of a B-level high-rise residential building in Tianshui City. Perform 3D and ETABS software were used to analyze the structural response during frequent and rare earthquakes to assess the seismic performance of the energy dissipation structure. The analysis results show that during small earthquakes, the story displacement, story drift ratio, story moment, and story shear of the energy dissipation structure are reduced by ＞6.5%, which meets the design requirements. During large earthquakes, the frame columns, frame beams, shear walls, and viscous dampers of the structure can meet the requirements of performance-based design, and the story drift ratio can meet the code limit. Accordingly, the structure can achieve the design goal of “no collapse during large earthquakes.” This study provides a reference for preset damping targets and the optimal layout of dampers in practical applications.

Abstract:To reduce the impact of earthquakes on the story drift of building structures, the relationship between the story drift control and the seismic performance of buildings was analyzed considering the shear at the bottom of the structure. A method for calculating the story drift of buildings was developed to determine the lateral displacement of beams, columns, and joints after shearing. The constraint conditions of the story drift limit were set based on these calculations. The story drift was controlled by reducing the beam and column spacings of the frame, the transformation between the plan structure and the three-dimensional structure, and implementing the bending-shear system. The seismic performance was tested and verified for an actual practical project. The results show that the error in the calculation of story drift was ＜3.5%. Furthermore, the ranges of the story drift under the Kobe wave and the El-Centro wave were 0.43-0.82 mm and 0.40-0.42 mm, respectively. After adjustment and control, maintaining the story drift in the range of 0.4-1.1 mm can improve the seismic performance of the building.

Abstract:A typical brick-vault hall of the Kaiyuan Temple in Suzhou City was selected as the research case for studying the mechanical properties and weak locations of the brick-vault hall heritages built during the Ming Dynasty in China under the action of earthquakes. The Rhino three-dimensional model of the brick-vault hall of the Kaiyuan Temple was established and imported into ANSYS Workbench to generate a finite element model. The natural frequency, mode shape, displacement response, and stress response of the brick-vault hall under the action of earthquakes were obtained using finite element analysis. Results show that the structure of the brick-vault hall of the Kaiyuan Temple has high symmetry and torsional stiffness. The vertical earthquake has little effect on the structure, while the seismic action in the depth direction has a considerable impact. From the perspective of stress, using the response spectrum analysis for brick-vault halls is safe, whereas using the time-history analysis for brick is safe from the perspective of displacement. The weak locations of the brick-vault hall of the Kaiyuan Temple under the action of earthquakes include the corner and top of the two layers of door and window arches, as well as passage arches in the width and depth directions, the gable end wall, and the middle and end of the roof.

Abstract:As a country covered by a large area of frozen soil, China's railway network in cold regions is generally affected by the frost heave of the foundation soil. Although research has focused on the frost heave characteristics of foundation soils, the railway-foundation soil interaction under longitudinal nonuniform frost heave deformation remains unexplored. Based on the theory of double-layer beam on elastic foundation, this study established a mechanical model of a railway-sub-rail foundation under the action of nonuniform frost heave deformation. An analytical solution of the model was derived, and the effects of the elastic coefficient of the interlayer and frost heaving on the displacement and internal force of the track were analyzed by combining with an example. The results showed that the elastic interlayer could effectively reduce the frost heave deformation and stress response of the rail, which is conducive to rail operation. The length of the transition section between the rail and the sub-rail foundation and the shear force and bending moment at the concave convex bending section increased with the increase in the frost heave displacement. The frost heave force acting on the sub-rail foundation was gradually transferred to the track with the increase in the elastic coefficient of the interlayer. The length of the transition section was only related to the amount of frost heave. The proposed calculation method and the conclusions obtained from the analysis can provide scientific guidance for the design, operation, and maintenance of railways in cold regions.

Abstract:To study the application effect of the borehole shear test on loess, a series of tests under different primary normal stress and different normal stress increments were carried out on the typical Q₃ loess in the eastern suburbs of Xi'an. The test results show that shear strength increases in a curvilinear trend with the increase in normal stress, and there is a critical normal stress value. Beyond this value, there is a good linear relationship between the shear strength and normal stress. It is in good agreement with the Mohr-Coulomb strength criterion, and the measured shear strength parameters have little difference. In a multi-stage loading test, the smaller the increment in normal stress, the greater the shear strength associated with the same normal stress. Compared with the multi-stage loading test, the shear strength measured by the single-stage loading test under the same normal stress is smaller, and the deviation degree increases with the increase in normal stress. At low normal stress, it is difficult for the shear teeth to be pressed into hard soil, resulting in low cohesion and a large internal friction angle. Therefore, it is suggested that shear plates should be developed to suit different soft and hard soils and a normal displacement observation system should be added to judge the press of the tooth tip into the borehole wall during the application of normal stress.

Abstract:Many uncertain factors exist when establishing the empirical criteria with traditional methods. Thus, comprehensive research on the liquefaction criteria for complex sites needs to be conducted. In this paper, 49 groups of sand samples from the emergency repair project of immersed pipe of the Baotou section in Shanghai were studied. This paper first adopted the standard penetration test method to qualitatively evaluate the sandy silt soil within 20 m of the research area. With the use of the absolute difference percentage method proposed in this paper, 35 groups of soil samples with accurate discriminant results and 14 groups with discriminant errors were divided. Then, referring to the theoretical thought of discriminant analysis, the physical and mechanical parameters such as average particle size D₅₀, uneven coefficient C_u, specific penetration resistance P_s, standard penetration point depth d_s, groundwater depth d_w, and standard penetration blow count N_63.5 were added to the liquefaction evaluation. Finally, with the use of the soil samples with accurate discriminant results, a distance discriminant analysis model suitable for the engineering geological characteristics of the research area was established to quantitatively evaluate the soil layers of samples with discriminant errors. Research results show that the established comprehensive evaluation system for sand liquefaction comprehensively and objectively evaluates the sand liquefaction in the study area from multiple perspectives. Through reasonable anti-liquefaction and subsidence measures, the steady progress of subsequent projects is guaranteed, and a reference for the stability evaluation of sand liquefaction in sites with similar geological conditions is provided.

Abstract:To explore the influence of nonuniform seismic wave input on the seismic response of reinforced concrete (RC) structures, a large 2D finite element model for the dynamic interaction between an RC frame structure and a foundation was built based on the OpenSees software platform. Numerical calculations of the RC frame structure were performed by inputting El-Centro seismic waves at incidence angles of 0°, 15°, 30°, and 35°. The internal forces of the frame columns and the story drifts of the structure were compared and analyzed. The results showed that the nonuniform seismic wave input method has an evident influence on the dynamic response of large-scale RC frame structures. With the increase in the incidence angle of the seismic wave, the axial force amplitude of the bottom column of the RC frame structure decreased while the shear force amplitude increased. The bending moment amplitude changed only slightly, and the amplitude of the story drifts increased. The research results have reference significance for the seismic design of large RC frame structures.

Abstract:To study the influence of a base isolation system on the seismic performance of rotational cable-stayed bridges, the Taichengxi Bridge on the newly-built Fuzhou-Xiamen passenger line was taken as the engineering background. A dynamic model of the entire bridge was established for a nonlinear time-history analysis. Seven seismic waves and five groups of base isolation schemes with curved surface friction pendulum bearings were selected to compare and analyze the seismic performance of the rotational cable-stayed bridge. The results showed that the natural period of the bridge increased, and the global stiffness and seismic response decreased evidently after adopting the base isolation system. Although the curved surface friction pendulum bearing had little influence on the structural deformation, it significantly reduced the internal force; therefore, it can be used as an isolation bearing in rotational cable-stayed bridges. With the adoption of the base isolation system, the bending moment at the bottom of the main pier could be reduced by 44.83%-55.82%, the shear force could be reduced by 40.3%-63.09%, and the maximum displacement in the rigid fixity zone of the tower and girder was 65.53 mm.

Abstract:In this paper, the data, calculation algorithms, and applicability of some traditional magnitudes (M_L, m_b, m_B, M_S, and M_JMA) were first described and compared. Additionally, the theoretical basis and calculation methods of two modern magnitude scales (M_e and M_W) were systematically explored. The determination methods of some moment magnitudes (i.e., M_WW, M_WC, M_Wb, M_wp, and M_dt) were then introduced in accordance with different use data and applicable scenarios. Meanwhile, high-frequency GPS-based observation was increasingly used for the rapid determination of earthquake magnitudes due to the wide availability of GPS observation data. Finally, the time efficiencies of these magnitude determination methods were compared and analyzed, and the applicable scenarios and stability of different magnitude scales were discussed.

Abstract:Research has shown that the propagation direction of seismic waves from bedrock is not perpendicular to the ground surface. The site effect generated by obliquely incident seismic waves is quite different from that generated by vertically incident seismic waves. The site effect under obliquely incident shear vertical (SV) waves is more complicated than that under vertically incident SV waves on account of the existence of total reflection. In this study, a set of mathematical expressions of ground motions was derived based on the theory of homogeneous elastic half\|space seismic wave propagation when SV incident angles were less than, greater than, or equal to the critical angle. The mathematical expressions were then applied to a model example to calculate and analyze the ground motion characteristics under the excitation of total reflected SV waves. The results show that the ground motions generated by SV waves are mainly composed of incident and reflected waves, and the effect of sliding waves could be ignored. The ground motion trajectory exhibits the characteristics of rotational vibration of surface waves. With the increase in the incident angle, the ground horizontal vibration gradually decreases, whereas the ground vertical vibration gradually increases, but neither of them is greater than twice the peak value of the incident wave.

Abstract:Under the background of rising gas radon concentration in Jiayuguan for many years, an unprecedented change occurred in 2017. However, no earthquake matching the amplitude and duration of the anomaly has occurred in the Qilian Mountains seismic belt. On May 22, 2021, an M_S7.4 earthquake occurred in Maduo, which is 570 km away from the radon measuring point in Jiayuguan. An in-depth analysis of the anomaly reliability, anomaly characteristics before the earthquake, anomaly change after the earthquake, and geological structure background was conducted in this study to determine the relationship between the radon concentration anomaly of gas in the Jiayuguan and Maduo earthquakes. Results show that the anomalous characteristics of the gas radon concentration in Jiayuguan are related to the structure where the earthquake occurred. The anomaly of gas radon concentration shows an annual distortion of 1 year or 6 months for earthquakes that occur along the Qilian Mountains seismic zone. By contrast, the anomaly demonstrates a long-term change in the propensity for earthquakes that occur far away from the Qilian Mountains seismic zone. The decreasing rate of radon concentration in Jiayuguan slowed down and then turned to a recovery state after the Maduo earthquake. The measuring points for gas radon concentration in the Jiayuguan and Maduo earthquakes are both located in the northeastern part of the Tibetan Plateau with the same dynamic background and structural correlation. The comprehensive analysis shows that the tendency anomaly of gas radon in Jiayuguan may be related to the Maduo M_S7.4 earthquake. This study is of considerable importance in establishing a reliable anomaly index system and improving earthquake prediction.