Input Ground Motion Characteristics Research Articles

Stochastic assessment of 3‐D tunnels in near‐fault ground motion using modified domain reduction method

AbstractA robust assessment of tunnels due to uncertainties present in soil and ground motion properties can affect the dynamic response of these structures. In this paper, a stochastic analysis considering an aleatory variability in shear velocity Vs by performing Monte Carlo simulations and assessing its influence on underground tunnels. To numerically assess the response of the soil‐tunnel system to near‐fault earthquake ground motion, the required computational domain usually spans multiple kilometers including both earthquake fault and the structure. Thus, these simulations are computationally expensive. An efficient alternative method, that is, the Domain Reduction Method (DRM), in which a modular two‐step methodology for reducing the computational costs in the large domain analysis is employed. A 3‐D soil‐tunnel structure interaction is modeled to simulate the response of tunnel subjected to an inclined earthquake fault. The numerical simulation of the soil‐tunnel‐fault system is conducted in an open‐source FE package called Multi‐hazard Analysis for STOchastic time DOmaiN phenomena (MASTODON) based on MOOSE framework. The interactive analyses are carried out for three distinct types of soils based on National Earthquake Hazards Reduction Program (NEHRP) provision, that is, soft, medium, and hard, by generating 130 realizations. The results provide many insights into the influence of local site effects, that is, frequency shift for the peak response and the importance of input ground motion characteristics that govern the response of underground structures. The dynamic response of the structure is very sensitive to the uncertainty in rock material properties, especially, the stiffness of the rock sample and the shear wave velocity.

Statistical numerical method for determining seismic performance and fragility of shallow-buried underground structure

Currently, research on the underground structures seismic fragility is still in its infancy state. In this study, we carried out numerical simulation on soil-underground structure system (SUSI) by taking the Daikai metro station damaged in the Kobe earthquake as analysis object. Considering input ground motion characteristics, based on incremental dynamic analysis (IDA method), a statistical numerical modeling method was established to classify underground structure seismic damage status and its seismic performance level. The analysis results showed that the input ground motions had a significant effect on the IDA curves. The rationality and randomness of the selected ground motions were important influencing factors to ensure the underground structures seismic fragility curves. In relation to the damage that occurred to the Daikai station in 1995, the peak ground acceleration (PGA) and peak relative lateral displacement (PRLD) of the site were suitable for estimating the seismic performance of the shallow buried structure constructed. Finally, the seismic fragility curves were compared with the existing research results, and a seismic damage assessment was carried out, which verified the effectiveness of the statistical numerical modeling method developed in this study.

Effect of Characteristics of Ground Motion on Seismically Induced Sliding Surface of Slopes

The seismic performance of slopes is typically evaluated with a pseudo-static method using equivalent horizontal load or with Newmark sliding block analysis. In both procedures, the definition of the potential sliding surface is a required input. The sliding surface has been reported to be marginally influenced by the input ground motion and, therefore, is most often assumed from a pseudo-static procedure. In this study, extensive series of two-dimensional dynamic nonlinear finite element analyses are performed to evaluate the sensitivity of the sliding surface on the slope geometry, soil strength parameters, and input ground motion characteristics. It is demonstrated that the sliding surface may vary with the intensity and frequency characteristics of the input motion. Slopes with inclination angle equal or less than 35° are shown to be marginally influenced by motion intensity if the mean period (Tm) < 0.3 s. However, slopes inclined at 45° are revealed to be more sensitive to the motion intensity and Tm. For motions with Tm > 0.3 s, the sliding surface is demonstrated to widen with an increase in the intensity of the input ground motions. The degree of widening increases proportionally with an increase in Tm. It is, therefore, recommended to derive sliding surfaces from a dynamic analysis for steep slopes.

Transmitting Characteristics of Seismic Motion in Super-Deep Overburden Layer Ground

Dynamic response characteristics and antiseismic performance of the structures which were constructed on the super-deep overburden layer are affected obviously by the seismic motion characteristics of the super-deep overburden layer foundation. In this paper, the seismic motion characteristics of horizontally stratified super-deep overburdenIn this paper, the seismic motion characteristics of horizontally stratified super-deep overburden based on the research results of on-site in situ tests and indoor material property tests, the horizontal shear layer method that can consider the nonlinear characteristics of dynamic soil deformation and the characteristics of seismic wave propagation in the soil is used to study the characteristics of ground motions of super-deep and thick overburden level of an earth-rock dam in China. The influence law of input ground motion characteristics and input ground motion position on seismic response analysis results of overburden ground is studied. Taking the uniform overburden layer model as an example, the coupling influence analysis of soil layer thickness and shear velocity on ground motion response are carried out, and the coupling influence law is proposed. The study shows that the seismic motion propagating characteristics of the earthquake in super-deep overburden layer is involved, inputting location of the seismic motion affects the results of ground seismic response greatly; super-deep overburden layer thickness and the soil shear wave velocity on influence law of ground motion characteristics have coupling. When the shear wave velocity of the soil layer is constant, the surface acceleration response has an inflection point with the change of the soil layer thickness; when the thickness of overburden is constant, the surface acceleration response also has an inflection point with the change of shear wave velocity of the soil layer; these inflexion values are influenced by both soil thickness and shear wave velocity.

Comparative study of floor response spectra for regular and irregular buildings subjected to earthquake

Past earthquakes have resulted in structural collapse and failure of non-structural components. In the nuclear, chemical, and hazardous industry, working on no-failure conditions of non-structural components after an earthquake is sensible. It has been observed that to minimize financial loss and to avoid fears of life safety, non-structural components should be designed for proper seismic forces. This design has been based on a maximum inertia force, which is interrelated to the floor response spectra. Therefore, the primary objective of the current study is to recognize and quantify the acceleration floor amplification of the low-rise building models. This paper aims to obtain the elastic and inelastic acceleration response of regular building and buildings having irregularity such as mass and stiffness irregularity located at the lower and higher storey, and vertical geometric irregular buildings. It perceived that input ground motion characteristics govern the response of lower storey. Also, floor response spectra are indicating distinct peaks analogous to contributing modes due to the dynamic characteristics of the building. Due to the dynamic filtering effect, the floor accelerogram intensified concerning the base and has an enormous frequency content for the periods, near to the modal time periods of the elastic model.

Seismic performance and design of bridge piers with rocking isolation

Seismic isolation technology has a wide application to protect bridges from earthquake damage, a new designed bridge pier with seismic isolation are provided for railways in seismic regions of China. The pier with rocking isolation is a self-centering system under small and moderate earthquakes, and the unbonded prestressed tendons are used to prevent overturning under strong earthquakes. A numerical model based on pseudo-static testing results is presented to evaluate the seismic performance of isolation bridge piers, and is validated by the shaking table test. It is found that the rocking response and the loss of prestressing for the bridge pier increase with the increase of earthquake intensity. Besides, the intensity and spectral characteristics of input ground motion have great influence on displacement of the top and bottom of the bridge pier, while have less influence on the bending moment of the pier bottom. Experimental and numerical results show that the rocking-isolated piers presented in this study have good seismic performance, and it provides an alternative way for the railway bridge in the regions with high occurrence of earthquakes. Therefore, we provide the detailed procedures for seismic design of the rocking-isolated bridge pier, and a case study of the seismic isolation design with rocking piers is carried out to popularize the seismic isolation methods.

Behavior of shallow tunnel in soft soil under seismic conditions

In tunneling practices, it is vital to have an accurate estimate of the depth of embedment of the tunnel; lining thickness and shape of the tunnel, which enables resisting of stresses; and deformation generated by the surrounding soil under seismic loading conditions. The present study highlights the behavior of shallow tunnel in soft soil under seismic conditions by using the finite element (FE) analysis. The developed numerical model is compared with available analytical solutions. Thereafter, a series of parametric studies are carried out by varying the tunnel embedment ratio, soil-tunnel interface conditions, lining thickness, shape of the tunnel, and input ground motion. It has been observed that distortion in the tunnel lining is dependent on the depth of embedment and the flexibility ratio of the tunnel. Ovaling (in a circular tunnel) and racking (in a rectangular tunnel) are found to decrease significantly when embedment ratio is greater than 2. Nearly 6–18% of greater distortion and 20% of greater bending moment are obtained in the full-slip interface condition when compared to the no-slip interface condition. The maximum induced bending moment in the tunnel lining is directly proportional to its flexural rigidity. An unconventional square tunnel with rounded corners, yields 55% lesser bending moment than the square tunnel under the same seismic loading condition. This study also highlights the importance of the input ground motion characteristics that govern the development of the maximum dynamic earth pressure around the lining of the tunnel, and the heaving of the ground surface just above the crown. The outcomes of the present study will be useful in design through understanding the effects of various influencing parameters that control the stability of the tunnel in soft soil under seismic loading conditions.

Liquefaction analysis and damage evaluation of embankment-type structures

The increasing importance of performance-based earthquake engineering analysis points out the necessity to assess quantitatively the risk of liquefaction of embankment-type structures. In this extreme scenario of soil liquefaction, devastating consequences are observed, e.g., excessive settlements, lateral spreading and slope instability. The present work discusses the global dynamic response and interaction of an earth structure-foundation system, so as to determine quantitatively the collapse mechanism due to foundation’s soil liquefaction. A levee-foundation system is simulated, and the influence of characteristics of input ground motion, as well as of the position of liquefied layer on the liquefaction-induced failure, is evaluated. For the current levee model, its induced damage level (i.e., induced crest settlements) is strongly related to both liquefaction apparition and dissipation of excess pore water pressure on the foundation. The respective role of input ground motion characteristics is a key component for soil liquefaction apparition, as long duration of mainshock can lead to important nonlinearity and extended soil liquefaction. A circular collapse surface is generated inside the liquefied region and extends toward the crest in both sides of the levee. Even so, when the liquefied layer is situated in depth, no significant effect on the levee response is found. This research work provides a reference case study for seismic assessment of embankment-type structures subjected to earthquake and proposes a high-performance computational framework accessible to engineers.

Spatial Variation of Seismic Ground Motions and Foundation Ground Stability of Inhomogeneous Layered Ground Considering Nonlinearity - Due to the Difference of Ground Inhomogeneous Distribution Property and Input Ground-Motion Characteristics

Spatial Variation of Seismic Ground Motions and Foundation Ground Stability of Inhomogeneous Layered Ground Considering Nonlinearity - Due to the Difference of Ground Inhomogeneous Distribution Property and Input Ground-Motion Characteristics

Dimensional Analysis of Inelastic Structures with Negative Stiffness and Supplemental Damping Devices

A negative stiffness device (NSD) has been proposed as an innovative way for seismic protection of structures. It was shown both numerically and experimentally to improve the performance of inelastic structures when it is appropriately designed for the given application. In order to systematically evaluate the effects of a NSD, dimensional analysis is used in this study to quantify the structural responses as the function of input ground motion characteristics, model parameters of structure and NSD, as well as supplemental damping. To facilitate this, a simplified yet parameterized numerical model is first proposed to mimic the observed responses of the tested prototype NSD. The dimensional analysis is then conducted on a single degree of freedom (SDOF) system equipped with both a NSD and a nonlinear damper. By comparing the dimensionless structural responses for the cases of (1) inelastic structure only, (2) inelastic structure with nonlinear damper, and (3) inelastic structure with both nonlinear damper and NSD when subject to various pulse type motions, the effectiveness of a NSD is investigated thoroughly. Finally, the optimal ranges of NSD model parameters are also identified.

Dimensional analysis of the slotted bolted connections against impulsive earthquake ground motions

The slotted bolted connections (SBCs) are modified bolted connections designed to dissipate input energy through friction slippages during static and dynamic cyclic loadings. Over the recent years, SBCs have received more implementations in buildings with steel moment resisting frames as their ductile behaviors are highly compatible with other connection details against earthquakes, such as the self-centering post-tensioned (PT) steel beam-to-column connections. Hence, it becomes necessary to properly characterize and grasp their dynamic responses. In order to systematically evaluate the effectiveness of SBCs, the dimensional analysis is used in this study to quantify the connection responses as the function of input ground motion characteristics and SBC model parameters. To facilitate this, a simplified yet parameterized numerical model is first proposed to mimic the observed responses of the tested prototype steel SBC. By comparing the dimensionless structural responses of the regular bolted welded connection with that of the SBCs when subject to various pulse type motions, the effectiveness of the presented SBCs is investigated thoroughly. Then, a parametric study is presented based on the nonlinear dimensional spectra, where each of the variables that contribute to the SBC effects was studied in details. Finally, some design recommendations are provided based on the observed results.

Seismic optimum design of triple friction pendulum bearing subjected to near-fault pulse-like ground motions

Triple Friction Pendulum Bearing (TFPB) as a novel seismic isolator, provides different combinations of stiffness and damping during its course of motion. The adaptive behavior of TFPBs is one of the practical solutions for unsuitable performance of seismic isolation systems under near-fault ground motions. Selecting the TFPB's design variables (curvature radii, friction coefficients and displacement capacity of sliding surfaces) is complicated process while finding the optimized combination of these variables depends on input ground motion characteristics and seismic performance objectives of the superstructure. Here first, comprehensive nonlinear dynamic analyses are performed to identify influence of the design variables on superstructure response (roof acceleration and displacement of isolated level). Next, a specific numerical optimization method based on Genetic Algorithms (GA) is applied to determine the optimum values of the design variables that minimize superstructure demands. In this process, near-fault ground motions are employed with ranges of pulse periods and hazard levels as input excitations. According to GA results, the derived optimum design variables of TFPB have significantly distinct intervals for different target responses such as story drift and TFPB displacement. Therefore response targets (single objective functions) are combined to make a new fitness function. The proposed optimization method for determining design variables and design intervals can be used for investigating many other types of superstructures with similar behaviors.

Factors affecting seismic response of submarine slopes

Abstract. The response of submerged slopes on the continental shelf to seismic or storm loading has become an important element in the risk assessment for offshore structures and "local" tsunami hazards worldwide. The geological profile of these slopes typically includes normally consolidated to lightly overconsolidated soft cohesive soils with layer thickness ranging from a few meters to hundreds of meters. The factor of safety obtained from pseudo-static analyses is not always a useful measure for evaluating the slope response, since values less than one do not necessarily imply slope failure with large movements of the soil mass. This paper addresses the relative importance of different factors affecting the response of submerged slopes during seismic loading. The analyses use a dynamic finite element code which includes a constitutive law describing the anisotropic stress-strain-strength behavior of normally consolidated to lightly overconsolidated clays. The model also incorporates anisotropic hardening to describe the effect of different shear strain and stress histories as well as bounding surface principles to provide realistic descriptions of the accumulation of the plastic strains and excess pore pressure during successive loading cycles. The paper presents results from parametric site response analyses on slope geometry and layering, soil material parameters, and input ground motion characteristics. The predicted maximum shear strains, permanent deformations, displacement time histories and maximum excess pore pressure development provide insight of slope performance during a seismic event.

Estimate of input energy for elasto‐plastic SDOF systems during earthquakes based on discrete wavelet coefficients

AbstractThe response of an elasto‐plastic single degree of freedom (SDOF) system to ground motion is estimated based on wavelet coefficients calculated by discrete wavelet transform. Wavelet coefficients represent both the time and frequency characteristics of input ground motion, and thus can be considered to be directly related to the dynamic response of a non‐linear system. This relationship between the energy input into an elastic SDOF system and wavelet coefficients is derived based on the assumption that wavelets deliver energy to the structure instantaneously and the quantity of energy is constant regardless of yielding. These assumptions are shown to be valid when the natural period of the system is in the predominant period range of the wavelet, the most common scenario for real structures, through dynamic response analysis of a single wavelet. The wavelet‐based estimation of elastic and plastic energy transferred by earthquake ground motion is thus shown to be in good agreement with the dynamic response analysis when the natural period is in the predominant range of the input. Copyright © 2005 John Wiley & Sons, Ltd.

연속지진하중에 의한 철근콘크리트 교량 교각의 응답해석

In this paper, the effect of cumulative damage for reinforced concrete bridge piers subjected to both single and multiple earthquakes is investigated. For this purpose, selected are three set of accelerograms one of which represents the real successive input ground motions, recorded at the same station with three months time interval. The analytical predictions indicate that piers are in general subjected to a large number of inelastic cycles and increased ductility demand due to multiple earthquakes, and hence more damage in terms of stiffness degradation is expected to occur. In addition, displacement ductility demand demonstrates that inelastic seismic response of piers can significantly be affected by the applied input ground motion characteristics. Also evaluated is the effect of multiple earthquakes on the response with shear. Comparative studies between the cases with and without shear indicate that stiffness degradation and hence reduction in energy dissipation capacity of piers are pronounced due to the multiple earthquakes combined with shear. It is thus concluded that the effect of multiple earthquakes should be taken into account for the stability assessment of reinforced concrete bridge piers.

Seismic response of support-isolated secondary structures in a multistorey structure

The effectiveness of the isolation system installed on the supports of the secondary structures mounted on a multistorey structure is evaluated for reducing the seismic response to various earthquakes in this study. The responses of the support-isolated secondary structure in a fixed-base multistorey structure are compared with those of a fixed support secondary structure in fixed-base and base-isolated multistorey structures to investigate the reduction of the seismic response. Three analytical models are used to evaluate the effectiveness of the isolation system: a fixed-base multistorey structure with fixed-support secondary structure, a base-isolated multistorey structure with a fixed-support secondary structure, and a fixed-base multistorey structure with a support-isolated secondary structure. The seismic responses are analysed to identify their behaviour due to the characteristics of input ground motion with various peak acceleration and frequency content. The efficient stiffness of the base-isolator for reducing the seismic response is also evaluated for several earthquakes through the acceleration — displacement relationship.