Infinite Foundation Research Articles

Seismic damage characteristics of high arch dams under oblique incidence of SV waves

This study investigates the seismic damage characteristics of high arch dams considering the oblique incidence of seismic waves. Based on the dynamic implicit finite element method, a viscous-spring artificial boundary is applied to consider radiation damping of the infinite foundation, the seismic wave input is converted into an equivalent nodal force of the artificial boundary, and the equivalent nodal loads of the wave input under oblique incidence of the SV wave is deduced. Taking JP Ⅰ arch dam as an example, combined with the concrete damaged plasticity (CDP) model, the nonlinear dynamic response of the dam under 25° oblique incidence of the SV wave is conducted considering the geometrical nonlinearity of contraction joints and the dynamic mechanical properties of concrete materials. Based on the incremental dynamic analysis (IDA) method, the relative displacement and transverse joint opening are selected as the damage measures for fragility analysis of the arch dam. According to the damage distribution from the analysis of a large number of seismic time-history responses, the damage levels of the arch dam are classified. Three limit states of slight damage, moderate damage and severe damage are proposed for the arch dam. The average responses of the 10 earthquakes are considered as the limit values to quantitatively describe the damage of the arch dam. By fitting the results of incremental dynamic analysis, the seismic probabilistic demand model and seismic fragility curves for the two damage measures to predict the probability of the arch dam reaching damage levels under different seismic actions have been established. The fragility curve shows that the probability of severe damage is almost zero under the maximum design earthquake (PGA = 0.1971 g) and less than 5% under the maximum credible earthquake (PGA = 0.2299 g). It is concluded that JP Ⅰ arch dam has a high degree of safety redundancy and fully satisfies the “two levels” design requirements.

Seismic analysis of post-tensioned concrete gravity dams using scaled boundary finite elements implemented as ABAQUS UEL

This paper presents an efficient numerical framework for the seismic analysis of post-tensioned concrete gravity dams, which automatically inserts anchors into the structure. The proposed approach is implemented in the commercial finite element software ABAQUS by introducing a polygonal user element (UEL) derived by the scaled boundary finite element method (SBFEM). By inserting nodes in the polygonal structural mesh along the anchor layouts, duplicating the inserted nodes representing anchors, and generating cohesive elements on the node pairs, post-tensioned anchors are naturally embedded into the structure, and the bond–slip interactions are considered. Furthermore, an unbounded UEL derived by the SBFEM is implemented to simulate the unbounded foundation in the dam–reservoir–foundation interaction systems. The unbounded UEL only requires a small truncation area around the region of interest to rigorously capture the dynamic properties of the infinite foundation in terms of a displacement unit-impulse response. This ABAQUS implementation allows the use of built-in capabilities of ABAQUS for nonlinear dynamic analysis, including contact modeling and cohesive fracture. Weak structural interfaces existing in a concrete gravity dam (dam–foundation interface and construction joints) are modeled by a cohesive–frictional contact scheme. In the end, sophisticated numerical models dams featuring post-tensioned gravity dams with weak interfaces and anchors can be generated in a fully automatic manner, requiring no special treatments for mesh generation such as partitioning. The accuracy of the proposed technique is verified through a numerical example of the Manly dam strengthened by a vertical anchor. The efficiency of this approach is demonstrated through a dam with three construction joints anchored by multiple inclined anchors. The input files of the numerical examples are available from the authors upon request.

Comparison of the Seismic Responses of an Arch Dam under Excitation from the Design Response Spectrum in the New and Old Chinese National Standards

The new Chinese national standard, Standard for the seismic design of hydraulic structures (GB51247-2018), has been published. Compared with the Specifications for the seismic design of hydraulic structures (SL203-1997), the standard design response spectrum curve was revised in the new national standard. In order to compare the seismic responses of an arch dam under excitation from the design response spectrum in the new and old standards, the dynamic calculation of a 240 m high arch dam is carried out by a three-dimensional finite element method. In the dynamic calculation, the B-differentiable equation is used to simulate the tension motion of arch dam contraction joints, and the multi-transmitting boundary method and the Westergaard added mass method are used to simulate the dam–infinite foundation and dam–reservoir interactions, respectively. The results show that the dynamic stress responses of the arch dam under excitation from the design response spectrum in the new standard are increased compared with those of the old standard. The seismic safety of an arch dam may decrease under excitation from the design response spectrum in the new standard. Thus, the seismic validation on built arch dams should be carried out by using the new standard when it is possible.

Energy flow and performance evaluation of inerter-based vibration isolators mounted on finite and infinite flexible foundation structures

This study investigates the vibration power flow behavior and performance of inerter-based vibration isolators mounted on finite and infinite flexible beam structures. Two configurations of vibration isolators with spring, damper, and inerter as well as different rigidities of finite and infinite foundation structures are considered. Both the time-averaged power flow transmission and the force transmissibility are studied and used as indices to evaluate the isolation performance. Comparisons are made between the two proposed configurations of inerter-based isolators and the conventional spring-damper isolators to show potential performance benefits of including inerter for effective vibration isolation. It is shown that by configuring the inerter, spring, and damper in parallel in the isolator, anti-peaks are introduced in the time-averaged transmitted power and force transmissibility at specific frequencies such that the vibration transmission to the foundation can be greatly suppressed. When the inerter is connected in series with a spring-damper unit and then in-parallel with a spring, considerable improvement in vibration isolation can be achieved near the original peak frequency while maintaining good high-frequency isolation performance. The study provides better understanding of the effects of adding inerters to vibration isolators mounted on a flexible foundation, and benefits enhanced designs of inerter-based vibration suppression systems.

Three-dimensional linear seismic analysis of normal concrete gravity dam

The three-dimensional linear finite element model is established for the bottom outlet dam section of concrete gravity dam. Mode-superposition response spectrum method and the massless foundation time history method are adopted to analyze the static and dynamic comprehensive stress response and displacement response of the dam under the action of the standard response spectrum of the design earthquake or the corresponding artificial wave under the action of design earthquake and check earthquake. The results show that the dam works well in seismic condition. In addition, the influence of radiation damping of infinite foundation on the dynamic response of the dam section under different seismic waves is analysed. By comparing the dynamic and static comprehensive stress changes of the dam, it shows that after considering the radiation damping effect of the infinite foundation, the dynamic response of the dam body is significantly reduced.

Seismic Damage Indexes of a High Arch Dam Based on the Monolith

To assess safety of a dam in an earthquake, establishing the performance evaluation index of the arch dam is significant. The finite-element model based on the 289 m-high Baihetan Dam in Southwest China is taken as a case for seismic response analysis, in which the radiation damping of infinite foundation and opening of contraction joints are taken into consideration. Using the incremental dynamic analysis (IDA) approach, a three-component earthquake scaled to 12 increasing intensity levels is applied to the model, and the seismic response of the model is analysed. In this paper, it is proposed to study the damage based on the monolith, so the monolith damage volume ratio and monolith damage area ratio are suggested to determine the most severe part of the dam. Meanwhile, to help identifying the damage of the dam, the response results of contraction joints are extracted to analyse the potential relationship between the proposed indexes, providing a reference for exploring new detection indexes and damage evaluation indexes. In order to explore the possibility of the simplified layout of dam damage monitoring, the dam body is partitioned according to the results of monolith damage development.

Dynamic Response of Rock Slopes under Obliquely Incident Seismic Waves

In this study, the seismic input model of slope is proposed to investigate the dynamic response of the rock slope under obliquely incident seismic wave on the basis of the time‐domain wave analysis method. The model includes viscoelastic boundary considering the infinite foundation radiation damping and the seismic obliquely incident method. The semi‐infinite space numerical example is simulated to verify the validity and accuracy of the model. Based on the established model, the effects of the variation of the seismic wave incident angles and slope angles on the dynamic response of a rock slope are analyzed. The results demonstrate that the changes of the incident angle and the slope angle have no discernible effect on the dynamic response of the rock slope when the P wave is obliquely incident. As the SV wave is obliquely incident, the peak ground acceleration amplification coefficient along the slope surface gradually increases with the increase of the incident angle; when the slope angle gradually increases, the peak ground acceleration amplification coefficient along the slope surface will also gradually increase at the upper part of the slope. The research results can provide some basis for the pseudostatic method to determine the seismic action coefficient.

Seismic input model of high slope and its test verification

The Seismic input model of high slope is proposed, in which the Lagrangian discontinuous deformation analysis (LDDA) is adopted to simulate faults, cracks and structural surfaces, and the viscoelastic boundary is used as the energy absorbing boundary to reflect the influence of infinite foundation radiation damping. Due to employing the wave analysis method, the propagation and amplification effect of seismic waves in the slope can also be included. In order to verify the rationality of this calculated model, a slope dynamic model test of a large earthquake simulation shaking table was also carried out. From the results of experiment and numerical calculation, it can be seen that the acceleration of seismic response and its amplification effect, the slope base frequency and the opening degree of the simulated faults are comparable. The calculation model presented in this paper provides a good tool for correctly evaluating the seismic stability of the high slope near dam.

Analysis of seismic damage process of high concrete dam-foundation system

In the anti-seismic analysis of concrete high dams, only the damage cracking of the dam concrete is usually considered, and the nonlinear characteristics of the dam foundation rock during the earthquake are not considered. Taking the Koyna gravity dam in India and Shapai arch dam in China as examples, this paper adopts the nonlinear time-history analysis method and takes into account the comprehensive influence of the radiation damping of infinite foundation, the hydrodynamic interaction between dam and reservoir, the nonlinear dynamic contact between various joints in the dam body and foundation, and the damage of dam concrete and foundation rock mass in the damage evolution process, analyzes damage evolution process of dam body-foundation system under earthquake action and the influence of foundation rock mass damage on seismic failure mode of concrete dam-foundation system, and compares the numerical simulation results with the actual earthquake situation. The calculation results show that after considering the damage of the dam foundation rock mass, the rock mass of the dam heel firstly appears to be damaged under the action of the earthquake and gradually expands into the interior of the foundation. The dam heel and the foundation surface are not damaged. The numerical simulation results are more in line with the actual situation of earthquake.

Effect of foundation models on seismic response of arch dams

Simulation of the infinite foundation is a key issue in the seismic response analysis of high dams. This paper studies how the major characteristics of foundation models influence the nonlinear dynamic response of arch dams when the radiation damping effect is taken into account. The nonlinear dynamic responses of the 217 m high Yebatan arch dam under construction in China is performed as a numerical example. Several key factors, including truncated size, material damping and non-uniformity of the foundation, are analyzed comprehensively. The results show that the material damping and the size of the foundation affect the dynamic response of the dam when the incident wave method is used. Neglect of the material damping of the foundation is proposed to solve this problem, and its rationality is verified. In addition, the results show that the realistic non-uniformity of the foundation should be considered in the earthquake response of arch dams.

Global concurrent cross-scale nonlinear analysis approach of complex CFRD systems considering dynamic impervious panel-rockfill material-foundation interactions

Evaluating the seismic security of enormous structures is extremely vital, and this concern has continually motivated the trends of refined numerical simulations for years. However, the ability to perform a concurrent global refinement analysis of large-scale projects with complex spatial geometries and spanning huge scales has remained a formidable challenge in settings such as high concrete-faced rockfill dams. In this paper, a global concurrent cross-scale nonlinear analysis approach (GCCNA) benefitting from an efficient hybrid octree-based discretization technique is presented. Significantly, a polygon interface is constructed to automatically connect the cross-scale element and solve the interactions between the concrete-faced rockfill and foundation. A viscoelasticity polygonal artificial boundary element is subsequently developed to render the influence of radiation damping on an infinite foundation so that the travelling wave effect on the dynamic response and stabilization can be captured. A high-efficiency and economically time-consuming solution strategy is adopted, wherein the scaled boundary finite element is introduced to manage the minority polyhedrons in the generated octree model, and the numerous hexahedrons are assigned to the isoparametric element. The features of rapid discretization, high flexibility, extraordinary grid reconstruction and coupling with the conventional finite element are contained perfectly, which are demonstrated via the comprehensive elasto-plastic dynamic simulation of an extremely complicated practical constructed highest rockfill dam. The proposed approach has attractive potential and practicability for the efficient refinement analysis of complicated enormous engineering structures and can be readily extended to subterranean structures, nuclear plants, and architectural and aviation structures.

Seismic Response Analysis of Reservoir Water-Gravity Dam-Foundation System

The Scaled boundary finite element method and finite-infinite element method are used to model the system of reservoir water – gravity Dam - infinite foundation. The effect of the reservoir water and the infinite foundation on the seismic response of the dam system is analyzed. In the paper, taking the Koyna gravity dam as the research object, the dynamic water pressure on the upstream face of the dam is calculated by SBFEM. The finite-infinite element method is used to model the infinite foundation. Finally, the time history of seismic displacement and the response of the dam under different elastic modulus are evaluated. By comparing the displacement response of the infinite element model of different elastic modulus, the conclusion is drawn that the response of the dam is increased with the increase of the elastic modulus of the foundation. In addition, the calculated results are compared with those of the model with no-mass foundation. It shows that the results of the model considering the radiation damping of the foundation are less than that of the model with no mass foundation.

The Development of the Calculation Module of ANSYS and Its Engineering Application

The damping radiation effect of infinite foundation is considered by using the Damping Solvent Extraction Method (DSEM) based on the Finite Element Method, the nuclear plant and the infinite foundation is coupled based on solving the interaction force between interface and the displacement coordination assumption, the time domain seismic analysis model of nuclear plant foundation is established. In order to improve the practicability, the developed model is functionally embedded in the general finite element software ANSYS by using the secondary development function UPFs, APDL and UIDL. Finally, the influence of different frequency harmonic wave on the accuracy and efficiency is analyzed through numerical example, and the parameter range of the applicable engineering application is also put forward, and then, Seismic adaptability analysis of china’s one million kilowatt pressurized water reactor nuclear power plant foundation is carried out, the calculation results show good reliability and engineering practicability.

Considering Effects of Infinite Foundation Radiation Damping on The Dynamic Response of Nuclear Island Structure

The effective simulation of influence of infinite foundation radiation damping is a key technical problem for implement seismic response analysis of nuclear island. Basd on Super FLUSH software as a platform, the vicous boundary is imposed on the boundary of the ground to dissipate the energy and the effect of infinite foundation radiation damping is considered. By taking calculation model of a practical engineering as the object of study and the contrast with rigid foundation, conducting a research on the impact of foundation radiation damping for seismic response of nuclear island structure. In addition, by comparing the influence of different elastic modulus of foundation on the radiation damping is also studied and the findings suggest that influence of the radiation damping is obvious. The calculation results show that the influence of radiation damping is obvious under the condition of soft foundation. The model shows good accuracy and computational efficiency. The results have some reference values for similar projects.

Seismic damage analysis of the outlet piers of arch dams using the finite element sub-model method

This study aims to analyze seismic damage of reinforced outlet piers of arch dams by the nonlinear finite element (FE) sub-model method. First, the dam–foundation system is modeled and analyzed, in which the effects of infinite foundation, contraction joints, and nonlinear concrete are taken into account. The detailed structures of the outlet pier are then simulated with a refined FE model in the sub-model analysis. In this way the damage mechanism of the plain (unreinforced) outlet pier is analyzed, and the effects of two reinforcement measures (i.e., post-tensioned anchor cables and reinforcing bar) on the dynamic damage to the outlet pier are investigated comprehensively. Results show that the plain pier is damaged severely by strong earthquakes while implementation of post-tensioned anchor cables strengthens the pier effectively. In addition, radiation damping strongly alleviates seismic damage to the piers.

The edge waves on a Kirchhoff plate bilaterally supported by a two-parameter elastic foundation

In this paper, the bending waves propagating along the edge of a semi-infinite Kirchhoff plate resting on a two-parameter Pasternak elastic foundation are studied. Two geometries of the foundation are considered: either it is infinite or it is semi-infinite with the edges of the plate and of the foundation coinciding. Dispersion relations along with phase and group velocity expressions are obtained. It is shown that the semi-infinite foundation setup exhibits a cut-off frequency which is the same as for a Winkler foundation. The phase velocity possesses a minimum which corresponds to the critical velocity of a moving load. The infinite foundation exhibits a cut-off frequency which depends on its relative stiffness and occurs at a nonzero wavenumber, which is in fact hardly observed in elastodynamics. As a result, the associated phase velocity minimum is admissible only up to a limiting value of the stiffness. In the case of a foundation with small stiffness, asymptotic expansions are derived and beam-like one-dimensional equivalent models are deduced accordingly. It is demonstrated that for the infinite foundation the related nonclassical beam-like model comprises a pseudo-differential operator.

Influence of construction interfaces on dynamic characteristics of roller compacted concrete dams

To study the influence of construction interfaces on dynamic characteristics of roller compacted concrete dams (RCCDs), mechanical properties of construction interfaces are firstly analyzed. Then, the viscous-spring artificial boundary (VSAB) is adopted to simulate the radiation damping of their infinite foundations, and based on the Marc software, a simplified seismic motion input method is presented by the equivalent nodal loads. Finally, based on the practical engineering of a RCC gravity dam, effects of radiation damping and construction interfaces on the dynamic characteristics of dams are investigated in detail. Analysis results show that dynamic response of the RCC gravity dam significantly reduces about 25% when the radiation damping of infinite foundation is considered. Hot interfaces and the normal cold interfaces have little influence on the dynamic response of the RCC gravity dam. However, nonlinear fracture along the cold interfaces at the dam heel will occur under the designed earthquake if the cold interfaces are combined poorly. Therefore, to avoid the fractures along the construction interfaces under the potential super earthquakes, combination quality of the RCC layers should be significantly ensured.

Seismic Analysis of an Intake Tunnel of Different Tunnellining Programs for a Nuclear Power Plant

Developing an analysis program and simulating the radiation damping effect in the infinite foundation and inputs ground motion rationally. The static and dynamic analysis of an intake tunnel for a nuclear power plant is performed with ANSYS based on some 2-D finite element models considering of structure-foundation interaction by Time-History Analysis. Aiming at different programs of two linings in tunnel, the stress and internal force distribution of the tunnel , the wall rocks and the lining is researched and analyzed, and the diagram of stress and internal force is drawn. The regularity obtained can provide the basis for the seismic response analysis and design of tunnels.

An Investigation into the Influence of Damping on the Earthquake Response Analysis of a High Arch Dam

Two input models of seismic excitation, the nonlinear contact characteristics of contraction joints, were presented. The influence of the damping ratio on the seismic response of a high arch dam was then investigated. A new element (the viscous-spring boundary element capable of reflecting the radiation damping effects of an infinite foundation), the external source wave input subroutine, and the dynamic contact models, including the characteristics of normal opening-closing and radial sliding, were developed in this paper. The nonlinear contact behavior of contraction joints was simulated using a nonlinear exponential dynamic contact model, and the radial nonlinear characteristic was simulated using the Mohr-Coulomb criterion. Linear elastic and nonlinear seismic response analyses for a 300-m high concrete arch dam under construction were performed. The results showed that the damping ratio greatly influenced the seismic response of a high arch dam using a massless foundation model, and the damping ratio between 3–5% resulted in a conservative seismic response. The results of the viscous-spring boundary input model were in good agreement with those given by the massless foundation model when a damping ratio of 10% was used, but the openings of joints near the crown cantilever varied significantly. The effects of radiation damping of the foundation on the seismic response could be simplified to some extent by increasing the material damping of the dam in this study.

Study on Ultimate Anti-Seismic Capacity of High Arch Dam

AbstractA three-dimensional numerical simulation model for the failure process caused by an earthquake is established based on the Shapai high roller-compacted concrete arch dam in the Wenchuan, China earthquake region. Several comprehensive influencing factors, including nonlinear behavior of concrete, infinite foundation radiation damping, dam-reservoir dynamic interaction, and the contact nonlinearity of the transverse joints and the induced joints, are taken into account to study their effects on the seismic safety of high arch dams. In the paper, an analytical method is proposed to evaluate the ultimate anti-seismic capacity of high arch dams, and failure modes of the arch dam resulting from earthquakes with different levels are studied. The seismic limit state of the arch dam is determined according to distribution of the concrete’s failure zone, divergence of finite-element calculation, and mutation of the time-dependent displacement curves of key points on the dam. The revealed mechanism of dynami...