Earthquake Action Research Articles

Slope Stability Analysis for a Large Hydropower Station in China

Hydropower plants (including the switching station) built in the middle and southern section of the north–south zone of China are always situated in complex geological settings of transition zones from strong to weak earthquakes with active faults. It is of great importance to carry out careful evaluation of the slope stability considering various loading scenarios to ensure safe operation of the power stations. By using the rigid body limit equilibrium method and the finite element method, the effects of long-term load and seismic load on slope stability for a large hydropower station were studied. The results show that the slope safety factors of the station meet the stability requirements when the slope is under long-term load and under the action of the Wenchuan and Lushan earthquake loads. The stability of the slope is guaranteed. However, the risk analysis of the slope stability under the action of the design earthquake load shows that the slope safety factor is less than the accidental working condition safety factor of 1.05. Under the action of a strong earthquake, the crumbling block gravel soil layer in the shallow natural slope slides and destabilizes, which is obviously beyond its protection capacity, and therefore, effective seismic defense measures should be developed to ensure the safety of the personnel and equipment operating in the power station and switching station.

Unified Mechanism of Rock Burst Induced by Coal Mine Earthquake and Its Activity and Response Characteristics

The occurrence regularity of the coal mine earthquake under the influence of hard roof, fault, and mining was studied by theoretical analysis, field investigation, and monitoring data analysis for the phenomenon of rock burst induced by coal mine earthquakes. The dissipation characteristics of coal mine earthquake energy propagation considering a hypocenter scale were described, and the coal mine earthquake response characteristics were analyzed. The two principles of rock burst induced by hard rock fractured type coal mine earthquakes and the three principle of rock burst induced by fault were described. Based on this, the unified mechanism rock burst induced by different types of coal mine earthquakes was proposed. The results show that the microseismic energy increases sharply and decreases sharply when mining in the fault area. The amplitude and frequency of support resistance increased before and after the heavy coal mine earthquake occurred. The periodic characteristics of the coal mine earthquake in the 43upper 13 working face of the Dongtan coal mine show that there are 50 m small periods within 100 m large periods. The multiparameter field monitoring can make it possible for instantaneous capture of the coal mine earthquake dynamic responses. The unified rock burst mechanism induced different types of coal mine earthquake and is the difference energy between the superposition energy of the rock burst source region and the energy consumed by coal-rock instability increases suddenly under the action of coal mine earthquakes. Meanwhile, the violent rock burst accident occurs when the stiffness condition is satisfied.

Seismic performance analysis of shallow-buried large-scale three-box-section segment-connected pipeline structure under multiple actions

To ensure the safety operation of inter-basin water transfer project, it is important to understand the seismic performance of shallow-buried large-scale segment-connected pipeline structure under earthquake and other multiple actions. In this paper, a 3D FE model is built in details for the seismic assessment of large-scale prestressed concrete inverted-siphon shallow-buried under riverbed, and a method is proposed to realize multiple interactions of the viscoelastic boundary elements to finite elements, the compressible fluid to structure and the sealed joints made of rubber belt between adjacent segments. The inverted-siphon is longitudinally composited by 58 segments in total length of 858.64 m, and transversally consisits of three rectanguler-section boxes with net dimension of each box of 6.5 m width and 6.6 m height. The main influencing factors are set as the thickness of overburden soil, the flow condition and the engineering geological condition. The time-history analysis is carried out on the 3D FE model under Elcentro seismic wave excitation. The numerical analyses figures out the main vibration modes and vibrational frequency of this inverted-siphon, reveals the regions of peak tensile stress appeared on the concrete surface and the risk sealed joints with extremum relative displacement. This provides a scientific reference to take specific prevention measures of anti-earthquake, based on a deep understanding to the seismic cracking of concrete and the tearing broken of sealed joints for this kind of segment-connected pipeline structure.

Analysis of the Seismic Performance of a Masonry Structure with RC Frames on the First Story with Concrete-Filled Steel Tubular Dampers

The concrete shear walls of masonry structures with RC frames on the first story are low-rise shear walls with a height–width ratio of less than 1. The strength, stiffness, and ductility of these low-rise shear walls are not matched, resulting in poor seismic performance. Based on the idea of the passive control theory and multi-seismic defensive lines, the scheme of a masonry structure with RC frames on the first story with a concrete-filled steel tubular (CFST) dampers is proposed in this paper. To explore the seismic mitigation effect of CFST dampers applied to a masonry structure with RC frames on the first story, the seismic performance under low-reversed cyclic loading of the frame with the CFST dampers is first compared with that of the energy-dissipated low-rise concrete shear wall proposed by previous researchers and the ordinary low-rise concrete shear wall. Furthermore, the response of the masonry structure model with RC frames on the first story with CFST dampers and two other comparative structural models under earthquake action are discussed. The results show that a masonry structure with RC frames on the first story with CFST dampers has a fuller hysteretic loop, lighter pinching, better energy dissipation ability, and better seismic performance. Compared with the other two structures, the energy dissipation capacity of the masonry structure with RC frames on the first story with CFST dampers is significantly improved, by 1.25~1.5 times. The amplification effect of the deformation angle allows the CFST dampers to play a significant role in energy dissipation, whereas the main structure still undergoes a small deformation. The CFST dampers can dissipate more seismic energy to protect the main structure from damage and improve the seismic performance of masonry structures with RC frames on the first story.

Design and Parameter Optimization of the Reduction-Isolation Control System for Building Structures Based on Negative Stiffness

In order to improve the damping capacity of building isolation system, this paper studies the damping isolation control system of the building structure based on negative stiffness. In this paper, the dynamic equation of the damping isolation control system is derived and its parameters are optimized by H2 norm theory and Monte Carlo pattern search method. Taking the 5-story building structure as an example, this paper analyzes and evaluates the damping performance of the damping isolation control system of the building structure under the actual earthquake. The results show that negative stiffness can improve the damping capacity of traditional isolation system. Additionally, the negative stiffness ratio under the condition of stability, the smaller the negative stiffness ratio, the stronger the vibration reduction ability of the negative stiffness. The damping isolation control system of building structure based on negative stiffness shows good damping effect under the actual earthquake.

Shaking table test on suspend-dome structure with the center-hung scoreboard under three-dimensional seismic

In order to meet the demand of watching games, the LED display, i.e., the center-hung scoreboard, has been widely used in large stadiums. To investigate the mechanical properties of the suspend-dome structure with the center-hung scoreboard under the action of earthquake, a dynamic scaled model with a geometric similarity ratio of 1:20 was designed. And the shaking table test was performed to study the seismic performance under the actions of 8 degree frequent, seismic precautionary and rare earthquakes. The acceleration, displacement and internal force responses under three-dimensional seismic were analyzed. The results show that the Z-directional acceleration amplification factors of the reticulated shell vertex region are significant and decrease fastest under actions of rare earthquakes, which is the weak point of the model. The influence of the center-hung scoreboard on the structure cannot be ignored in the study of seismic performance. The vertical displacement is the largest in the center and gradually decreases from inside to outside. The maximum displacement under actions of frequent earthquakes is 2.061 mm. The maximum displacement under actions of seismic precautionary earthquakes is 1/556, the maximum displacement under actions of rare earthquakes is 1/242, both of which satisfy the requirement of seismic specifications. The maximum internal force of the ring rod first decreases and then increases from the center to the surroundings. The internal force of the radial rod gradually increases from the edge to the center. Under actions of rare earthquakes, the center-hung scoreboard has more influence on the internal force of the rod. The accuracy of the finite element modeling method is verified by comparing the simulation results and test results of the scaled model, and the reliability of the scaled model is verified by comparing the simulation results of the scaled model and the prototype structure. The structure does not collapse under actions of 8 degree rare earthquakes and does not show apparent failure. The seismic principle that “the structure hasn’t damaged under frequent earthquake, repairable under precautionary earthquake, and doesn’t collapse under rare earthquake” is reached, thus the structural design of the Lanzhou Olympic Sports Complex is reasonable.

Numerical Investigations of Asymmetric Inerter Nonlinear Energy Sink for Vibration Control

Nonlinear energy sinks (NESs) and tuned mass damper (TMD) have achieved excellent control performance. However, their energy and frequency robustness, as well as a large desired slide mass, impede their wide application in practice. To address this limitation, this paper proposes an asymmetric NES that combines two types of inerter NES, the AsymI-1 NES and AsymI-2 NES, to improve the damping robustness of traditional control devices and reduce the damper mass. In addition, the distinction is achieved by adding an inerter between the sliding damper and the top or bottom story. Further, the mathematical formulation of the asymmetric inerter NES is deduced. The working principle of the proposed asymmetric inerter NES is presented, and motion equations of the asymmetric inerter NES-attached system are derived. The proposed asymmetric inerter NES is optimized using impulsive excitation to analyze its energy and frequency robustness. The control performance and wavelet spectrum analyses of the asymmetric inerter NES are conducted under the action of earthquakes. The analysis results show that combining the two asymmetric inerter NESs can help to absorb seismic energy rapidly, limit structural reaction, and ensure good energetic and frequency robustness. Furthermore, the proposed asymmetric inerter NES can significantly decrease the stroke requirement and damper mass.

Quantitative Evaluation of Seismic Performance for Truss Structures Based on the Condition Number of Dynamic Matrix

The quantitative analysis of seismic performance under small and moderate earthquakes is of great significance. However, only using the stiffness distribution index is no longer applicable to seismic performance evaluation, and the influence of mass distribution must be introduced. In this study, under the action of small and medium earthquakes, the equation of motion can be simplified into the equilibrium equation of the dynamic matrix by the quasi-static method. Furthermore, a condition number index of dynamic matrix is proposed to evaluate the seismic performance of truss structures, which can consider both stiffness distribution and mass distribution. Then, the correctness of the proposed index is verified by comparing with the displacement and strain indexes. In addition, the performance of truss structure is studied by the condition number of stiffness matrix, mass matrix and dynamic matrix. It is found that since the condition number of stiffness matrix and the condition number of mass matrix cannot consider both stiffness and mass, it is not comprehensive to use these two indexes to evaluate the seismic performance of truss structures. The evaluation result based on the condition number of dynamic matrix is more reasonable under small and medium earthquakes.

Advances in the study of simultaneous occurrence of strong wind and earthquake and their effects on structures

<p indent="0mm">With the increasing demand for sustainable development of engineering structures, the study of engineering structures under the joint action of multi-hazards is receiving more and more attention from scholars and engineers. Are the simultaneous occurrence of strong wind and earthquake, as two major hazard loads, still uncertain as a coincidental event? To clarify the possibility of simultaneous occurrence of two hazards, this paper summarizes the current research status that strong wind and earthquake can occur simultaneously from two aspects, respectively, strong wind triggers earthquake and earthquake causes strong wind, collects data on the simultaneous occurrence of strong wind and earthquake in some areas from various factors, provides data support for the coupling phenomenon of simultaneous occurrence of strong wind and earthquake, and reviews the current research progress of engineering structures under the simultaneous action of strong wind and earthquake. It reviews the progress of related research on engineering structures under the simultaneous effects of strong wind and earthquake. The results show that: (1) Strong wind can trigger microseismic, slow earthquake, and normal earthquake by affecting waves and geological structures, and earthquakes can trigger strong wind by causing changes in atmospheric temperature and electromagnetic waves, and there is a coupling phenomenon between strong wind and earthquake. (2) The probability of simultaneous occurrence of strong wind and earthquake varies greatly in different regions, and the wind speed surface fitting can better meet the temporal and spatial relationships for collecting data on the simultaneous occurrence of strong wind and earthquake. (3) Engineering structures under the simultaneous effects of strong wind and earthquake are more prone to damage and destruction, and structural design standards should be adjusted or energy-consuming damping devices should be installed to improve their performance. Therefore, it is still necessary to improve the data related to the simultaneous occurrence of strong wind and earthquake and their mechanism of action. The comprehensive consideration of the effects of strong wind and earthquake on engineering structures is an important research direction in this field in the future.

Cyclic Behavior of Rectangular Bridge Piers Subjected to the Coupling Effects of Chloride Corrosion and Bidirectional Loading

The degradation of seismic performance for RC bridge piers induced by chloride corrosion has previously been studied by treating the earthquake as a unilateral cyclic loading. Such studies do not consider the true response of the pier under the joint effect of corrosion damage and real multi-dimensional earthquake action. Thus, in the present study, the cyclic behavior of rectangular bridge piers subjected to the coupling effects of chloride corrosion and bidirectional loading was numerically investigated. First, the corrosion-induced deterioration of material mechanical properties is introduced. Second, the numerical model of two corroded piers is built and validated with the test results in the literature. Then, the time-dependent biaxial seismic performance of a rectangular bridge pier under the circular-shaped (CS) biaxial displacement pattern, square-shaped (SS) biaxial displacement pattern, uniaxial displacement in the X-direction (UX) pattern, and uniaxial displacement in the Y-direction (UY) pattern is analyzed using the validated model. The simulation results conclude that the trajectory of biaxial loading paths and corrosion levels significantly influence the peak force, deformation capacity, and dissipated energy of the piers. The biaxial loading path effect for the corrosive pier includes two stages with different biaxial force trajectory characteristics. Compared with the uncorroded pier, the corrosion level of 13.7% and biaxial loading induces up to a 40% reduction in strength and a 54% decrease in the residual ultimate displacement of the corroded pier. For the same corrosion degree, the dissipated energy under the SS biaxial displacement path is the largest among the four loading paths.

The influence of earthquake characteristics on the seismic performance of reinforced concrete buildings in Australia with varying heights

In Australia, most of the existing buildings were designed before the release of the Australian standard for earthquake actions in 2007. Therefore, many existing buildings in Australia lack adequate seismic design, and their seismic performance must be assessed. The recent earthquake that struck Mansfield, Victoria near Melbourne elevated the need to produce fragility curves for existing reinforced concrete (RC) buildings in Australia. Fragility curves are frequently utilized to assess buildings’ seismic performance and it is defined as the demand probability surpassing capacity at a given intensity level. Numerous factors can influence the results of the fragility assessment of RC buildings. Among the most important factors that can affect the performance-based seismic assessment of buildings are the building height and the characteristics of the earthquake. Despite this, very few studies accounted for the earthquake characteristics and the influence of height on the vulnerability of buildings in Australia. Consequently, the combined effect of building height and the characteristics of the earthquake were investigated in this study. This was achieved through numerical modeling and time-history analyses of three typical two-, four-, and nine-story RC frame buildings in Australia. Moreover, these buildings were subjected to three different types of ground motions which were: short- and long-duration, and near-fault earthquakes. Fragility analysis was then conducted for the three buildings under all the selected earthquake suites. It was noted from the median values of the fragility curves that the four-story and the nine-story RC buildings were 17% and 18% more susceptible to damage in comparison with the two-story building under short-duration earthquakes. Moreover, it was also noted that the median value of the vulnerability increased by 33%, 40%, and 50% for the two-, four-, and nine-story buildings, sequentially, when subjected to near-fault compared to short-duration earthquakes.

Failure behavior and mechanism of a slope under the action of earthquake after rainfall

Failure behavior and mechanism of a slope under the action of earthquake after rainfall

Seismic fragility analysis of self-centering segmental piers with mortise-tenon shear keys

To comprehensively consider and study the seismic performance of the self-center mortise-tenon segmental pier, its vulnerability under earthquake is evaluated. The reliability of the model is verified by comparing the cyclic pseudo-static test results with the finite element models. The model is used as the basis for vulnerability analysis. Taking the maximum displacement of the pier top as a damage index. Different damage states are described. The damage index limits μcy1, μcy, μc2, and μcmax of different damage levels are determined. The time history analysis of cast-in-place pier and mortise-tenon segmental piers under different earthquake actions is carried out by using finite element software. The probabilistic seismic demand model is established through IDA curves. And the seismic vulnerability analysis is carried out. The influence of various parameters on the seismic vulnerability of mortise-tenon segmental pier is studied by changing the longitudinal reinforcement ratio, axial compression ratio, and aspect ratio. The results show that the seismic vulnerability of the two types of piers designed according to the principle of equivalence is similar under different damage states. It can be considered that it has better seismic performance. The longitudinal reinforcement ratio, axial compression ratio, and aspect ratio have a great impact on the vulnerability of piers.

Seismic Performance and Parametric Study of a Winding Rope Fluid Viscous Damper (WRFVD) for Continuous Girder Bridges

ABSTRACT To decrease the seismic response of continuous girder bridges, the seismic performance of a novel winding rope fluid viscous damper (WRFVD) was investigated. This device was installed between the sliding piers and superstructure, and connected to the superstructure by winding ropes. WRFVD can accommodate the thermal deformation of superstructure under service condition, and make the fixed pier and sliding piers bear the seismic loads together by establishing the friction connection between the sliding piers and superstructure under earthquake action. In this study, the theoretical mechanism of WRFVD is derived, and verified by a dynamic performance test. A shaking table test was conducted on a scaled three-span continuous girder bridge employing WRFVD. The test results showed that WRFVD can effectively reduce the seismic response of continuous girder bridges. The parametric study of WRFVD on a five-span continuous girder bridge was investigated. The parametric study shows that the seismic response of multi-span continuous girder bridge equipped with WRFVD decrease with the increasing damping coefficient and friction coefficient, and the decreasing damping index.

Dynamic Response Analysis of Coastal Piled Bridge Pier Subjected to Current, Wave and Earthquake Actions with Different Structure Orientations

The goal of the experiment described in this paper was to examine the effects of structure orientation (0°–90°) and fluid–structure interaction (FSI) under combined water loads, represented by water current and waves, and earthquake actions, on the dynamic response of a reduced-scale bridge pier specimen with pile foundation. The peak relative displacement and peak acceleration of the specimen are measured using the first time innovative in Iraq, Reality Water–Structure–Earthquake Interaction Test (RWSEIT). The findings are given and analyzed concerning water depths, current speed, wave characteristics, earthquake amplitudes, and structural orientations. A numerical model of the examined specimen with three dimensions (3D) was constructed, and the findings were successfully confirmed using the data from the experiments. A pile foundation bridge pier's 3D structural response under orientations that cannot be tested in a lab was computed using the constructed numerical model. The complicated dynamically produced FSI effects on the response of coastal pile foundation bridges may be better understood according to the research's experimental and numerical findings.

Dynamic responses of long-span road–rail cable-stayed bridge under combined seismic and wave action

Cross-sea–cable-stayed bridges located in earthquake-prone areas can be subjected to earthquakes, wave action, and other dynamic loads of potential threats during their construction and service periods. The dynamic response of a cable-stayed bridge was studied under the combined effects of earthquakes and wave flow. In this study, a cross-sea–cable-stayed bridge is investigated as a prototype. ANSYS software was used to establish a spatial finite-element model, and CFD software was used to simulate the wave loads and calculate the fluid-structure coupling. The peak displacement at each location was determined under different loading conditions during the combined action of earthquakes and waves. The displacement at the top of the tower was the largest, followed by that at the main span. However, when the wave action was severe, the peak displacements of the tower top and main span were comparable, and these two peak displacements occurred simultaneously. The internal-force-response law at the bottom of the tower tended to be consistent, and only the peak values differed. The peak change in the shear force was smaller than that in the bending moment. Earthquakes and waves had a negative effect on bridges; however, they played a dominant role. Nevertheless, the presence of waves alters the dynamic response during joint action; therefore, the effect of waves on the bridge cannot be ignored. The root-mean-square (RMS) under the joint action of earthquakes and waves was evaluated using the RMS of superimposed independent earthquakes and independent waves. However, it can be observed that the joint effect is not a simple superposition effect. Complex interactions exist between the earthquakes and waves.

Dynamic analysis of three-directional vibration isolation and mitigation for long-span grid structure

With the rapid development of the long-span space structures, some seismic isolation methods of ordinary buildings are also gradually applied in these structures. The special feature of the long-span space structure is that the vertical seismic property cannot be ignored, in addition to considering the horizontal property under multi-dimensional earthquake action. This study proposes a novel multi-dimensional earthquake isolation and mitigation device (MEIMD) consisted of viscoelastic core bearing and viscoelastic damper. This device provides certain stiffness that can satisfy the load-bearing capacity requirement of the structure and strong energy dissipation ability in the horizontal and vertical seismic directions. A mathematical model is presented to characterize the mechanical behavior of the MEIMD. The device is installed at the top of the support column, which creates a seismic isolation layer between the column and the upper grid model. The shaking table tests of the long-span grid structure with and without MEIMD under horizontal seismic excitations of various intensities were carried out. The experimental results showed that the acceleration response peak value on the isolation structure was significantly reduced. The novel device has a good horizontal isolation effect on the grid structure. To determine the vertical and three-direction seismic isolation properties of the MEIMD on the grid structure, finite element models of the long-span grid structure with MIEMD and without MEIMD were established for dynamic time history analysis. The numerical results revealed that the dynamic responses of the isolation grid in horizontal and vertical directions have been decreased compared to the non-isolated structure.

Seismic behavior of steel plate and reinforced concrete composite wall coupled to steel side columns

The steel plate and reinforced concrete (SPRC) composite wall coupled to steel side columns is a new type of coupled system, which consists of a single SPRC composite wall coupled to steel side columns through steel coupling beams at all floors. One 1/4 scaled five-story SPRC composite wall coupled to steel side columns with a plastic coupling ratio (CR) of 0.45 was designed, constructed, and tested under simulated earthquake action. The test results exhibited great seismic performance of the proposed coupled system with the coupling mechanism fully developed. The average displacement ductility coefficient was 3.12. And the average values of the inter-story drift ratio of all stories at the yield, peak load, and ultimate conditions were 1.32%, 2.55%, and 3.70%, respectively, showing good inter-story deformation capacity. The average ultimate plastic shear rotations of steel coupling beams at the 2nd, 3rd, 4th, and 5th floors were 0.0211 rad, 0.0364 rad, 0.0556 rad, and 0.0913 rad, respectively, indicating great energy dissipation contributions of the steel coupling beams. The steel side columns remained elastic under shear forces transmitted from steel coupling beams through hinge joints and provided a stable overturning moment resistance to protect the SPRC wall. The accuracy of the test results was verified against the numerical analysis results. The parametric analyses were conducted to further the understanding on the influences of key design parameters on the seismic performance of the proposed coupled system. The peak lateral load can be enhanced by increasing the axial load or steel plate ratio. In order to obtain good energy dissipation capacity and ductility, a moderate value of 0.15 for the axial load ratio or 6.6% for the steel plate ratio can lead to excellent deformation capacity.

Seismic Response Characteristics of a Tunnel Portal Subjected to Topographical and Geological Asymmetsric Loading

The tunnel portal is the most seismically vulnerable section of the tunnel against earthquakes. Due to the combined effects of topographic and geological asymmetric loading, the mechanical characteristics of this type of portal are very complex. In this study, a three-dimensional numerical model was developed and calculated to investigate the seismic response characteristics of a tunnel portal subjected to topographic and geological asymmetric loading. The results show that the seismic weakness of the tunnel support structure is located at the tunnel arch shoulders and sidewalls; the time to reach the peak displacement around the tunnel is slightly delayed compared to the slope, and the time to reach the peak displacement shows a phased pattern. Compared to the tunnel structure, the slopes are more prone to landslides and other disasters due to terrain and geological factors under earthquake action. Therefore, more attention should be paid to the seismic and anti-seismic design of tunnel slopes.

SPRINGS OF VARIABLE STIFFNESS IN THE CONTROL OF SEISMIC ACTIONS IN BUILDINGS

Many regions in the world have experienced the presence of intensive geological events. Given this reality, the control of vibrations caused by earthquakes on buildings is one of the great challenges in seismic regions, as they can cause structural, material, and personal damage, and must be considered with special attention when carrying out a structural project. For this reason, it is necessary to minimize the deleterious effects caused by earthquakes on buildings. In this sense, the present study seeks to evaluate, through the theory of mechanical vibrations, the use of springs of variable stiffness in the control of accelerations induced by seismic action, because springs introduce restoring forces in the system. The evaluation is done through numerical-computational simulation using the finite element method. The frame structure of an idealized building is used in the modelling, where columns and beams are represented by linear elements and the floors by shell elements. In the simulation, springs of variable stiffness are inserted into the joints to control the vibrations produced by earthquakes. These devices are added to the structural system at different heights and directions, aiming to keep the structure's behaviour unchanged, neutralizing the effects of the earthquake. Based on the obtained results, it is possible to verify the required stiffness and the position in which the springs must be inserted to obtain the constancy of the structural frequency of vibration during the earthquake action.