Search Results (20)

Objective: The research on turbid current deposition in shallow Marine shelf environments is relatively weak. Method: Based on three-dimensional seismic, drilling and logging data, etc., the spatio-temporal characterization of the shallow sea turbidity current sedimentary system was carried out by using seismic geomorphology and sedimentary numerical simulation techniques. Results and Conclusions: (1) A set of standards for identifying sedimentary units in the X Gas Field was established, identifying four sedimentary units: channel, mound body, channel-side accumulation body, and shelf mud; (2) The vertical evolution and planar distribution of the sedimentary units in the painting were precisely engraved. Along with the weakly–strongly–weak succession of turbidity current energy, the lithological combination of argillaceous siltstone–siltstone–mudstone developed vertically. On the plane, the clusters showed an evolution of isolation–connection–superposition. The scale of the river channel continued to expand, and the phenomena of oscillation and lateral accumulation occurred. (3) Three factors were analyzed: sea level, material sources, and sedimentary substrates (paleo landforms), and a shallow Marine turbidity current sedimentary system was established in the Honghe area in the northwest direction under the background of Marine receding, which is controlled by sedimentary slope folds and blocked by the high part of the diapause during the downward accumulation process of material sources along the shelf. (4) The numerical simulation results reconstructed the process of lateral migration of waterways, evolution of branch waterways into clusters, expansion of the scale of isolated clusters, and connection and superposition to form cluster complexes on a three-dimensional scale. The simulation results are in high agreement with the actual geological data. Full article

This paper proposes a method to investigate the design properties of geotechnical seismic isolation (GSI). This technique has been the object of many research contributions, both experimental and numerical. However, methods that may be used by practitioners for design procedures are still unavailable. The formulation presented herein may be used for preliminary assessments of two important properties: the thickness and the shear wave velocity. Three-dimensional advanced numerical simulations were performed with the state-of-the-art platform OpenSees in order to verify the analytical formulation on a benchmark case study. The elongation ratio has been taken as the relevant parameter to discuss the efficiency of GSI in decoupling the soil from the structure. The main findings consist of assessing the dependency of the elongation ratio on two parameters: the thickness and the shear velocity of the GSI layer. In this regard, a novel formulation was proposed in order to make preliminary design assessments that can be used by practitioners for practical applications. Full article

(1) Background: In most cases, passive isolation control methods are commonly used for the seismic isolation design in bridge engineering. However, passive seismic isolation devices, due to their non-adjustable performance parameters, struggle to achieve effective seismic isolation across a wide frequency range of 0 Hz to 20 Hz in response to random and varying seismic loads. (2) Methods: The sensitivity of the design parameters of the seismic isolation bearing was analyzed using the optimization center gradient method, and an improved genetic algorithm was employed to quickly optimize and obtain the optimal design parameters. (3) Results: The effectiveness of the three-dimensional seismic isolation bearing was validated through experiments. (4) Conclusions: The multi-factor sensitivity analysis approach used in this study for designing novel isolation bearings is applicable not only to seismic design in bridges but also serves as a reference for parameter design in isolation bearings requiring medium to high precision in seismic performance. Full article

A novel three-dimensional isolation system consisting of thick rubber bearing (TNRB), disc spring bearing (DSB), and laminated rubber bearing (LRB) in series combination was designed, and its composition, principle, and isolation effect were comprehensively analyzed. By combining numerical examples, the whole structure method is used to compare and analyze the dynamic characteristics, dynamic response, and structural damage of large-span isolation structures containing new three-dimensional systems, large-span horizontal isolation structures based on LRB, and corresponding non-isolation structures under multi-dimensional seismic excitation. The results show that compared with the horizontal isolation structure based on LRB, the structure of the new three-dimensional isolation system has a 33% longer vertical natural vibration period, a 17.85% attenuation in the overall damage index, and a 36.86% increase in vertical energy dissipation capacity. It can achieve good isolation effects in both horizontal and vertical directions, which can form a favorable complement to the horizontal isolation structure based on LRB in terms of vertical isolation and energy dissipation. Full article

Non-isolated structures have strong destructive effects and poor isolation effects when encountering earthquakes. Setting isolation bearings can prolong the natural vibration period of the structure, reduce the horizontal seismic response of the structure under the influence of variables such as acceleration, base reaction, and inter story displacement, and enhance the overall seismic performance of the structure. The new material—epoxy plate thick layer rubber isolation bearing—has unique advantages compared to other bearings, such as effective energy absorption, simple construction, and low cost. This study establishes a three-dimensional isolated nuclear power plant containment structure based on the principle of similarity ratio, and compares and analyzes the acceleration, base reaction, and displacement responses of non-isolated and isolated structures. At the same time, the incremental dynamic analysis method (IDA) is used to analyze the seismic vulnerability of the structure, and the isolation performance of the nuclear containment structure using epoxy plate thick layer rubber isolation bearings is comprehensively and deeply explored. The results show that the epoxy plate thick layer rubber isolation bearing effectively prolongs the natural vibration period of the structure, reduces the horizontal seismic response of the structure, reduces the dome acceleration response by 66.55%, and reduces the base horizontal shear force by 55.51%. Therefore, setting epoxy plate thick layer rubber isolation bearings in the isolation layer can effectively enhance the seismic performance of the structure, thereby improving the redundancy of the nuclear power plant containment structure. Full article

This article discusses the foundations of a conical shape directed with their apex downwards to increase the cross-sectional area and, accordingly, the bearing capacity during settlement and under the influence of horizontal tensile strains in undermined areas. To simulate the deformability of undermined and seismically exposed foundations, a three-dimensional expandable box was manufactured and assembled. Models of a conical foundation with an aperture angle of the cones at 90° and 80° were buried into the soil at 0.75 of its height, in order to provide a safety margin for further loading due to an increase in the bearing area when the cone is immersed deeper into the ground. Laboratory and field tests were performed on the vertical loading of single cones before and after horizontal soil displacement. Numerical modeling of the interaction between soil and foundation was carried out for conical foundation models that were considered for laboratory and field testing using the Plaxis 2D (Version 8.2) program. To compare the bearing capacity, isolated shallow foundations with a diameter equal to the cross section of the conical foundation at the intersection with the ground surface were tested. The isolated shallow foundations lost their bearing capacity after 0.15 kN in laboratory tests and after 75 kN in the field tests, while the ultimate bearing capacity of conical foundations with the similar cross section at the soil surface was not achieved, even after 0.2 kN during laboratory tests with horizontal soil displacement and at a load of 100 kN in field tests. Full article

Potential damage caused by earthquakes combined with reduced comfort due to traffic has become a big challenge when designing modern buildings, and base-isolation is one of the most effective solutions to such a problem. However, most isolation bearings cannot provide sufficient mitigation for both earthquakes and traffic-induced vibrations simultaneously. To this end, this research proposes a new type of three-dimensional isolation bearing for the mitigation of both earthquake effects and traffic-induced vibrations, which is composited by a thick rubber bearing, an auto-reset flat sliding bearing, and a double concave friction pendulum bearing. In this study, the analytical hysteresis model of the proposed isolation bearing was derived and experimentally validated. In addition, the fatigue performance and vertical compression performance of the proposed isolation bearing was tested and analyzed. Finally, the mitigation effect for traffic-induced vibrations of the proposed isolation bearing was validated through a field test. Full article

In order to investigate the seismic performance of a rubber-modified soil isolation layer, a three-dimensional finite element model was constructed using finite element analysis software, utilizing a two-story frame structure as the engineering background. Nonlinear dynamic time history analysis and comparisons were performed against the seismic performance of the structure. The evaluation was based on several parameters, including the contact area of the base, the thickness of the rubber-particle-modified soil isolation layer, ground motion records with varying amplitudes, and seismic frequency spectrum characteristics. The research findings indicate that the implementation of a rubber-modified soil isolation layer effectively mitigates the peak acceleration, horizontal displacement, and shear stress of the frame structure. This not only enhances the seismic performance of the structure but also enlarges the contact area of the base. Increasing the thickness of the rubber-modified soil isolation layer will effectively decrease the peak acceleration, horizontal displacement, and shear stress of the structure during seismic events. The effectiveness of the isolation provided by the rubber-modified soil layer improves as the intensity of the ground motion record increases. Full article

Spherical reticulated shell structure is an important structural form of large-span space buildings. It is of great significance to monitor three-dimensional (3D) dynamic responses of spherical reticulated shell structure to better understand its seismic performances, which will be helpful in the future to ensure the healthy condition of large-span space buildings during their lifespan. In this study, with the advantages of non-contact and high accuracy, a high-speed videogrammetric measurement method is proposed for monitoring the 3D dynamic responses of the seismically isolated, spherical, reticulated shell structural model. Two issues—the high-speed videogrammetric acquisition system and network configuration, as well as image sequence target tracking and positioning—are emphasized to achieve a cache of high-speed images and to improve the accuracy of tracking and positioning target points. The experimental results on the shaking table from the proposed method have been compared with those from traditional Optotrak Certus and accelerometers. The results prove that the proposed method is capable and useful for analyzing the seismic performance of spherical reticulated shell structures, as the dynamic responses monitoring accuracy of the method can reach the submillimeter level, with root mean square error values of 0.32 mm, 0.7 mm and 0.06 mm in the X, Y and Z directions, respectively. Full article

In this study, the seismic behavior of isolated- and fixed-base regular and irregular reinforced concrete structures was investigated. For this purpose, a three-dimensional, eight-story reference building model without any irregularity was designed in accordance with the Turkish Building Earthquake Code (TBEC-2018). Later, the building models with irregularities were created using the reference building model. In the building models with seismic isolators and fixed supports, fiber hinges were used for columns and beams to model nonlinear behavior. Moreover, nonlinear behavior at the isolation level was taken into account in building models with seismic isolators. Eleven different earthquake records were scaled using the geometric scaling method. Bi-directional nonlinear response history analysis (NRHA) was performed simultaneously for both horizontal components of the earthquake records in all building models. In addition to boundary analyses (Lower Bound and Upper Bound), which do not take into account the strength loss defined by the codes, analyses considering the strength loss as a result of heating in the lead core due to cyclical motion (Temperature Including) were carried out for building models with seismic isolators. In the analyses, displacement, acceleration, story drift ratio, base shear ratio, and damage mechanisms in the columns and beams obtained from the fixed-base and isolated-base structures were compared. In addition, the results of the analysis, in which the loss of strength due to temperature increase due to cyclical motion in the lead core is taken into account, were compared with the results obtained from the boundary analysis. As a result of the study, it was deduced that significant improvements were observed in the structural behavior of all regular and irregular models with seismic isolators under earthquake effects. Full article

Three-dimensional (3D) seismic data and well log data were used to investigate the sandstone architecture of the Middle Jurassic deltaic reservoirs of the Zhetybay Oilfield, Mangeshrak Basin, Kazakhstan. The base-level cycles of different scales were identified and divided using well log and 3D seismic data. Five types of sedimentary boundaries were identified in the mouth bar sandstones. The boundaries divide single mouth bars. Vertically, the spatial distribution of sand bodies can be divided into superposed, spliced, and isolation modes. Laterally, contact modes can be divided into superposition, lateral, and isolation modes. We found that the base-level cycle controls the evolution of the delta front sand body architecture. In the early decline or late rise of the base-level cycle, the superimposed or spliced modes dominate the sand body. By contrast, the lateral or isolation modes dominate the sand body in the late decline or early rise of the base-level cycle. This paper proposes an architecture model of the delta front sand bodies controlled by the base-level cycle. The spatial distribution and morphological variation of deltaic sand bodies could be linked to the base-level cycles. Full article

In this study, the seismic response and damage behavior of an isolated bridge under near-fault ground motion are studied and compared with the non-isolated bridge. To consider the local damage of the bridge pier and its evolution process, the nonlinear behavior of the bridge pier in the analysis is simulated by the fiber beam-column element model combined with the damage constitutive model of steel and concrete materials. The mechanical behavior of the isolation bearing is simulated by the three-dimensional isolation bearing model that can consider the instability and failure of the bearing. It is found that the isolation bearings do not work, and even amplify the seismic response of the bridge (pier displacement and pier shear) under the near-fault ground motion. This amplification also leads to more severe damage to the piers of the isolated bridge. In the case of the analyzed concrete bridge type and near-fault earthquake data, it can be concluded that the used isolating lead rubber bearings should not be recommended. In general, it can be stated that the selection of the types of bridge bearings in near-fault areas should always be analyzed in detail by designers in order to avoid unintentional amplifying of the bridge’s seismic response. Full article

In order to improve the seismic performance of long-span double deck steel truss continuous girder bridge, taking Dao Qing Chau Bridge in Fuzhou as an engineering background, the isolation scheme of friction pendulum bearing (FPB) and friction pendulum bearing combined with viscous dampers is applied to study seismic performance. A three-dimensional dynamic model of the bridge is established using SAP2000. Taking three artificial seismic waves as seismic excitation, the seismic response of the seismic structure is calculated by nonlinear time history integration, and is then compared with the seismic response of the seismic reduction and isolation structure. The results show that the friction pendulum bearing (FPB) scheme and combined seismic dissipation and isolation (CSDI) scheme show a good seismic dissipation and isolation effect and ensure the safety of the bridge structure. However, for whole-bridge isolation, friction pendulum bearing (FPB) will produce certain residual deformations and additional stress of the bearing under the conditions of temperature and external load. For the purpose of protecting the bearing, it is recommended to use the combined seismic dissipation and isolation (CSDI) scheme. Full article

Nuclear power plants are required to maintain operation after an earthquake, leading to a safe shutdown if necessary. In the case of a loss of offsite power, the onsite emergency diesel generator is critical to ensure procedural operations of the nuclear power plant. As a means to reduce the overall seismic risk, a three-dimensional seismic protection system is proposed to enhance the seismic performance of the emergency diesel generator. The proposed seismic isolation system decouples the horizontal and vertical components of shaking and considers available hardware to achieve an effective isolation solution over the range of excitation frequencies considered. Numerical analysis of the proposed system demonstrates a reduction in seismic demands on the emergency diesel generator and provides a higher safety margin than conventional base installation procedures. Umbilical lines that cross the isolation plane are considered and impose additional constraints on the displacement capacity of the isolation system. However, increasing the displacement capacity of these components can significantly increase the safety margin against failure. The seismic protection system can be customized depending on the seismic hazard and application to different seismic regions. Full article

Base-isolated frames supported by stepped foundation in mountainous areas possess their own particularity, so its progressive collapse dynamic response performance and dynamic effect propagation path are very different from those of ordinary flat ground-isolated structural systems. In order to study the progressive collapse performance of the base-isolated frames supported by stepped foundation in mountainous areas under two-directional coupled dynamic excitation, a four-span three-story plane frame demolition column test was simulated to verify the reliability of the computing platform. The common ground motion and three types of long-period ground motions were selected, and the two-dimensional dynamic coupling of the ordinary flat ground isolation structure and the base-isolated frames supported by stepped foundation in mountainous areas was obtained based on the demolition method. First, the seismic isolation structure was subjected to the collapse dynamic response under the vertical unbalanced load, then the collapse dynamic response under the vertical unbalanced load and the horizontal seismic coupling excitation was made; the two were compared and analyzed. It can be used as a reference for the design of progressive collapse of the frame structure of the base-isolated frames supported by stepped foundation in mountainous areas. Full article