Seismic safety assessment with non-Gaussian random processes for train-bridge coupled systems

Extensive high-speed railway(HSR)network resembled the intricate vascular system of the human body,crisscrossing mainlands.Seismic events,known for their unpredictability,pose a significant threat to both trains and bridges,given the HSR’s extended operational duration.Therefore,ensuring the running safety of train-bridge coupled(TBC)system,primarily composed of simply supported beam bridges,is paramount.Traditional methods like the Monte Carlo method fall short in analyzing this intricate system efficiently.Instead,efficient algorithm like the new point estimate method combined with moment expansion approximation(NPEM-MEA)is applied to study random responses of numerical simulation TBC systems.Validation of the NPEM-MEA’s feasibility is conducted using the Monte Carlo method.Comparative analysis confirms the accuracy and efficiency of the method,with a recommended truncation order of four to six for the NPEM-MEA.Additionally,the influences of seismic magnitude and epicentral distance are discussed based on the random dynamic responses in the TBC system.This methodology not only facilitates seismic safety assessments for TBC systems but also contributes to standard-setting for these systems under earthquake conditions.

Seismic safety of high concrete dams

China is a country of high seismicity with many hydropower resources. Recently,a series of high arch dams have either been completed or are being constructed in seismic regions,of which most are concrete dams. The evaluation of seismic safety often becomes a critical problem in dam design. In this paper,a brief introduction to major progress in the research on seismic aspects of large concrete dams,conducted mainly at the Institute of Water Resources and Hydropower Research(IWHR) during the past 60 years,is presented. The dam site-specific ground motion input,improved response analysis,dynamic model test verification,field experiment investigations,dynamic behavior of dam concrete,and seismic monitoring and observation are described. Methods to prevent collapse of high concrete dams under maximum credible earthquakes are discussed.

Seismic failure modes and seismic safety of Hardfill dam

Based on microscopic damage theory and the finite element method, and using the Weibull distribution to characterize the random distribution of the mechanical properties of materials, the seismic response of a typical Hardfill dam was analyzed through numerical simulation during the earthquakes with intensities of 8 degrees and even greater. The seismic failure modes and failure mechanism of the dam were explored as well. Numerical results show that the Hardfill dam remains at a low stress level and undamaged or slightly damaged during an earthquake with an intensity of 8 degrees. During overload earthquakes, tensile cracks occur at the dam surfaces and extend to inside the dam body, and the upstream dam body experiences more serious damage than the downstream dam body. Therefore, under the seismic conditions, the failure pattern of the Hardfill dam is the tensile fracture of the upstream regions and the dam toe. Compared with traditional gravity dams, Hardfill dams have better seismic performance and ~reater seismic safety.

Research on the effect estimation of seismic safety evaluation

Seismic safety evaluation is a basic work for determining the seismic resistance requirements of major construc-tion projects. The effect, especially the economic effect of the seismic safety evaluation has been generally con-cerned. The paper gives a model for estimating the effect of seismic safety evaluation and calculates roughly the economic effect of seismic safety evaluation with some examples.

Active Tectonic Research for Seismic Safety Evaluation of Long-Line Engineering Sites in China

Long-line engineering sites usually have to pass through active tectonics, so the research of active tectonics is of great importance to seismic safety evaluation of this sort of site. In the paper, basing on the summarization and analysis of the requirements for seismic safety evaluation of long-line engineering site and the status quo of active tectonics research, we propose the focal points of active tectonics research for seismic safety evaluation of long-line engineering sites, including the research contents, technical targets and routes, and the submission of the achievements, etc. Finally, we make a preliminary analysis and discussion about the problems existing in the present-day active tectonics research for seismic safety evaluation of long-line engineering sites.

Seismic safety of arch dams with aging effects

Arch dams suffer time-varying external loadings and harsh environment that harm their physical properties. With the aging of such dams, damage accumulates and concrete degradation inevitably appears. In this paper, a model is proposed for simulating concrete degradation with aging because of chemo-mechanical damage. The seismic response of an arch dam with aging effects is analyzed using the proposed model. The results show that the damage caused by the aging of arch dams may result in an increase in tensile cantilever stresses during earthquakes. Meanwhile, the dynamic displacement and joint opening also clearly increase in comparison with those without damage. Thus, the seismic safety of arch dams is reduced by aging effects.

Analysis of seismic disaster failure mechanism and dam-break simulation of high arch dam

Based on a Chinese national high arch dam located in a meizoseismal region, a nonlinear numerical analysis model of the damage and failure process of a dam-foundation system is established by employing a 3-D deformable distinct element code(3DEC) and its re-development functions. The proposed analysis model considers the dam-foundation-reservoir coupling effect, infl uence of nonlinear contact in the opening and closing of the dam seam surface and abutment rock joints during strong earthquakes, and radiation damping of far fi eld energy dissipation according to the actual workability state of an arch dam. A safety assessment method and safety evaluation criteria is developed to better understand the arch dam system disaster process from local damage to ultimate failure. The dynamic characteristics, disaster mechanism, limit bearing capacity and the entire failure process of a high arch dam under a strong earthquake are then analyzed. Further, the seismic safety of the arch dam is evaluated according to the proposed evaluation criteria and safety assessment method. As a result, some useful conclusions are obtained for some aspects of the disaster mechanism and failure process of an arch dam. The analysis method and conclusions may be useful in engineering practice.

Large, moderate, small earthquakes and seismic fortification criterion

This paper discusses the relation between two-step seismic design and the standard of probability of exceedance, and the relation of three-levels seismic ground motion parameters given by probability method and comprehensive probability method. The relative size relations of the ground motions with 2%, 10%, 63% probability of exceedance in 50 years, namely large earthquake, moderate earthquake, and small earthquake, are discussed through a practical example of seismic hazard analysis. The methods to determine seismic fortification criterion are discussed.

Seismic hazard mitigation for nuclear power plant

The seismic safety of nuclear power plan(tNPP)has always been a major consideration in the site selection,design,operation,and more recently recertification of existing installations. In addition to the actual NPP and all their operational and safety related support systems,the storage of spent fuel in temporary or permanent storage facilities also poses a seismic risk. This seismic risk is typically assessed with state-of-the-art modeling and analytical tools that capture everything from the ground rupture or source of the earthquake to the site specific ground shaking,taking geotechnical parameters and soilfoundationstructureinteraction (SFSI) into account to the non-linear structural response of the reactor core,the containment structure,the core cooling system and the emergency cooling system(s),to support systems,piping systems and non-structural components,and finally the performance of spent fuel storage in the probabilistically determined operational basis earthquake (OBE) or the safe shutdown earthquake (SSE) scenario. The best and most meaningful validation and verification of these advanced analytical tools is in the form of full or very large scale experimental testing,designed and conducted in direct support of model and analysis tool calibration. This paper outlines the principles under which such calibration testing should be conducted and illustrates with examples the kind of testing and parameter evaluation required.

Dynamic Properties of Long Large Cross-section Underground Structures in Dynamic Seismic Analysis

Seismic safety of underground structures is one of the main concerns in underground space exploitation. As the first step for dynamic seismic response analysis, the free vibration of long large cross-section underground structures is studied in the present paper. The general free transverse vibration motion equation of long large cross-section underground structure is derived with the comprehensive consideration of internal and external damping, effects of shear, cross-sectional rotational inertia and axial force, and a twoparameter soil model. In this way, Timoshenko＇s beam theory is extended. Two limit cases of free transverse vibration of underground structures are discussed. Parameter study shows that in general wave propagation velocities in structures increase with soil elastic parameters. However the influence of Winkler＇s parameter k is significant while the effect of the second soil elastic parameter gp is insignificant. The free vibration frequency of underground structures increases with relative wave number and soil elastic parameters. Unlike the influence of soil elastic parameters on wave propagation velocities, the influence of soil elastic parameters k and gp on the vibration frequency of underground structures have the same order; therefore the influence of the second soil parameter gp on the free vibration of underground structures should not be neglected in dynamic seismic analysis of underground structures

The Principle and Method for Delineation of Potential Seismic Sources in Northwest Yunnan

Based on the collection and analysis of achievements of other scholars, and by consulting the results of seismic safety evaluation of engineering sites and field surveys of recent years, the seismotectonic indicators are determined for northwest Yunnan and its vicinity, and then potential seismic sources are further delineated. In practice, the following principles are applied: for areas with strong historical earthquakes, the recurrence principle is used to determine the upper bound magnitude; for areas with distinct seismogenic structure but no historical strong earthquake records, the tectonic analogy principle is used in the light of the size and activity behavior of the structure; for areas where the segmentation of the active fault is well studied, the potential sources will be demarcated more precisely; and for areas with buried fault, the seismicity pattern and geophysical abnormity are used to determine the direction of the major axis of the potential seismic source.

Key Technologies in the Design and Construction of 300 m Ultra-High Arch Dams

Starting with the Ertan arch dam （240 m high, 3300 MW） in 2000, China successfully built a total of seven ultra-high arch dams over 200 m tall by the end of 2014. Among these, the ]inping 1 （305 m）, Xiaowan （294.5m）, and Xiluodu （285.5 m） arch dams have reached the 300 m height level （i.e., near or over 300 m）, making them the tallest arch dams in the world. The design and construction of these 300 m ultra-high arch dams posed significant challenges, due to high water pressures, high seismic de- sign criteria, and complex geological conditions. The engineering team successfully tackled these chal- lenges and made critical breakthroughs, especially in the area of safety control. In this paper, the author summarizes various key technological aspects involved in the design and construction of 300 m ultra- high arch dams, including the strength and stability of foundation rock, excavation of the dam base and surface treatment, dam shape optimization, safety design guidelines, seismic analysis and design, treatment of a complex foundation, concrete temperature control, and crack prevention. The experience gained from these projects should be valuable for future practitioners.

Estimation of the behavior factor of existing RC-MRF buildings

In recent years, several research groups have studied a new generation of analysis methods for seismic response assessment of existing buildings. Nevertheless, many important developments are still needed in order to define more reliable and effective assessment procedures. Moreover, regarding existing buildings, it should be highlighted that due to the low knowledge level, the linear elastic analysis is the only analysis method allowed. The same codes（such as NTC2008, EC8） consider the linear dynamic analysis with behavior factor as the reference method for the evaluation of seismic demand. This type of analysis is based on a linear-elastic structural model subject to a design spectrum, obtained by reducing the elastic spectrum through a behavior factor. The behavior factor（reduction factor or q factor in some codes） is used to reduce the elastic spectrum ordinate or the forces obtained from a linear analysis in order to take into account the non-linear structural capacities. The behavior factors should be defined based on several parameters that influence the seismic nonlinear capacity, such as mechanical materials characteristics, structural system, irregularity and design procedures. In practical applications, there is still an evident lack of detailed rules and accurate behavior factor values adequate for existing buildings. In this work, some investigations of the seismic capacity of the main existing RC-MRF building types have been carried out. In order to make a correct evaluation of the seismic force demand, actual behavior factor values coherent with force based seismic safety assessment procedure have been proposed and compared with the values reported in the Italian seismic code, NTC08.

Seismic running safety of trains and a new type of seismic-isolation railway structure

Until now,seismic-isolation structures have not yet been applied in the railway field.The reason is that though a seismic-isolation structure can reduce the inertial force to the structure,the energy absorption causes big response displacement on the structure,which adversely effects the running safety of the trains supported by the structure.In this paper,a methodology for seismic running safety assessment is introduced,and a new type of seismic-isolation foundation is proposed,which can convert the seismic response displacement in the lateral direction of track to the longitudinal direction that has a less adverse effect on the running safety of the train.The isolation foundation is composed of FPS(Friction Pendulum System)slider,concave plate and guide ditch.Moreover,through model experiments and 3D numerical simulation,it is verified that the proposed foundation can keep both the effects of the seismic isolation and the running safety of the train during an earthquake.