Seismic Coefficient Research Articles

Enhancing Seismic Resistance of G+10 MSB by Introducing FVD System

Lateral load resisting systems (LLRS) play a key role in reducing or eliminating the damage of the structure due to the earthquake. The damping system is one of the LLRS which controls the vibrations when an earthquake occurs. Fluid Viscous damping decreases tension and deflection because due to flexing the columns, the energy from the damping is totally out of phase with stresses. This is valid only for viscous fluid damping, where the damping force varies with the velocity of the stroke. Other types of damping do not vary their performance with velocities, such as yielding components, friction devices, plastic hinges, and visco-elastic elastomers; hence, they can increase column stress while reducing deflection, and typically do so. While coming to this work, under the seismic coefficient method for seismic zone-5, G+10 multistoried buildings were modelled and analyzed in ETABS along with limit state of collapse and limit state of serviceability load combinations. The response of the building was examined by introducing viscous dampers to the structure by varying the position of FVD in the building (S-1, S-2, and S-3), which are regular and irregular in plan, and by altering the width of the bay, by inserting the dampers at the four corners of the building in the first stage, by inserting the dampers at the four edges of the building in the second stage (S-2), and by inserting the dampers at the centre of the building in the third stage (S-3). Dampers are introduced from top to bottom storey of the building. Placement of FVD device system plays a key role against earthquake forces which are acting on the structure during the event of an earthquake. After the comparison in between above-defined stages and various parameters, when dampers are inserted at the edges of the building (S-3), the entire building is displaced identically with lesser values of displacement and inter-storey drifts, which are significant parameters in the event of an earthquake.

Code Compliance in Reinforce Concrete Design: A Comparative Study of USA Code (ACI) and Chinese Code (GB)

The structural engineering codes dictate the design criteria of the facility. Given that different countries use different parameters to design a facility, different codes are followed. Current code comparison focus on the clauses analysis in the code gives theoretical guideline. When the US facility design team needs to make a decision to follow which code to in China, the current study cannot provide a business decision input. This study evaluates the design process to illustrate when and where the codes will be applied and calculated through a design process where the loading and coefficient factors of different codes are analyzed. Software programs built‐in codes are then used to design the structure to obtain the structure result in terms of volume of the concrete and weight of the rebar being calculated. The study also presents a case study and calculates that the United States code uses 8–10% more rebar compared to the Chinese code. The study result can be a reference for the project management team who has to make a business decision over which code to be followed at what cost. The paper also identifies the choice of the seismic coefficient factor has a significant impact on the usage of the rebar and might be justified for the future study.

Concept of Design Seismic Coefficient of Final Disposal Site

Concept of Design Seismic Coefficient of Final Disposal Site

Dynamic behaviour of drystone retaining walls: shaking table scaled-down tests

In this paper, an experimental study aiming at understanding the seismic behaviour of dry stone retaining walls is presented. Harmonic shaking table tests have been carried out on scaled-down dry-joint retaining walls involving parallelepiped bricks. It is found that a thicker wall is more resistant and that a given retaining wall is less sensitive to higher frequencies. For those higher frequencies, the walls accept larger displacements before collapsing. The displacements start to occur from a given threshold, which depends on the wall geometry but not on the frequency of the base motion. The typical toppling failure is observed for slender wall and/or low frequency inputs. For less slender walls or higher frequency inputs, walls experience local sliding failures until the complete collapse of the system. The acceleration at failure reported during the dynamic tests has been compared to the corresponding pseudo-static resistance, enabling a conservative estimate of the seismic behaviour coefficient for pseudo-static analysis of this class of retaining walls. This novel experimental dataset is aimed to serve as a validating framework for future numerical or analytical tools in the field.

Seismic Bearing Capacity for Strip Footings on Undrained Clay with Voids

ABSTRACT This paper investigates the seismic bearing capacity of strip footings on undrained clay with single continuous square voids. Numerical studies for a wide range of geometric parameters and material properties are performed using adaptive finite element limit analysis (AFELA). Based on the pseudo-static approach, rigorous upper and lower bounds of the seismic bearing capacity for the strip footing are obtained, with relative errors of 4% or better. The calculated results are presented in the form of design tables and charts, and the effects of different governing parameters on the seismic bearing capacity are evaluated, including the size and location of the voids, the dimensionless strength ratio and the horizontal seismic coefficient. In addition, typical failure mechanisms are examined, and comparisons with previous studies are also conducted.

Undrained Seismic Stability of Dual Unsupported Circular Tunnels Subjected to Surcharge Loading

Undrained seismic stability of dual unsupported circular tunnels was investigated in this work using a self-developed code for adaptive finite element limit analysis. The so-called pseudo-static method was used to simulate the seismic effects during an earthquake. Accurate upper and lower bounds of seismic stability factor [Formula: see text] were obtained by using an adaptive remeshing technique incorporated in the code. Comprehensive parametric studies of the problem variables, including the horizontal seismic coefficient [Formula: see text], the relative spacing ratio [Formula: see text]/[Formula: see text], the relative depth ratio [Formula: see text]/[Formula: see text] and the strength ratio [Formula: see text]/[Formula: see text] were performed to provide dimensionless design tables for practical uses. In addition, visualized results from AFELA were summarized to reveal how the failure mechanism of dual tunnels would evolve with varying problems variables. Numerical results showed that both the stability and failure mechanism of dual tunnels can be much affected by seismic effects which should be carefully considered for a reasonable design in earthquake zones.

A method for seismic stability analysis of jointed rock slopes using Barton-Bandis failure criterion

Earthquakes are the main cause of slope failure in seismic active regions. In this study, we present a method for analyzing the seismic stability of a plane jointed rock slope with two blocks. In this analysis, the Barton-Bandis failure criterion is applied, considering the nonlinear characteristics of rock joints. Based on the limit equilibrium principle, we derived the safety factor of a jointed rock slope subjected to the modified pseudo-dynamic seismic forces. In addition, the analytical method developed in this study explains the interaction force between two blocks. Hence, it can effectively analyze the stability of a jointed rock slope and distinguish the failure modes. Further, a parametric study was conducted to investigate the effects of geometric and material properties on the safety factor of a hypothetical slope. The results show that the slope stability is significantly influenced by the geometry of the slope and the parameters including the joint roughness coefficient JRC, the horizontal seismic acceleration coefficient kh, the joint compressive strength JCS, and the basic friction angle of the structural plane ϕb. Moreover, the accuracy of the derivation is verified by the universal distinct element code UDEC 6.0. A parametric sensitivity analysis is used to determine the key parameters affecting slope stability. Finally, a set of seismic stability design charts is produced for preliminary design.

Probabilistic evaluation of three-dimensional seismic active earth pressures using sparse polynomial chaos expansions

This work presents a probabilistic analysis of three-dimensional (3D) seismic active earth pressures acting on rigid retaining walls that are designed to support cohesive-frictional soil masses. The analysis is implemented using sparse polynomial chaos expansions (SPCE) to represent the physical model responses. The deterministic evaluation of 3D seismic active earth pressures is conducted with the application of the kinematic approach of limit analysis combined with a pseudo-static method. All of the input parameters are deemed as random variables. After the SPCE metamodels are determined, the method of Monte Carle simulations is applied to perform the probabilistic analysis of 3D seismic active earth pressures. The effects of uncertainty levels and correlation relationships of input parameters are investigated. Several illustrative examples of the reliability-based design of retaining walls are shown. Results indicate that uncertainties in input parameters possess a notable effect on 3D seismic active earth pressures, suggesting the need to investigate the problem from a stochastic perspective. In most cases, the soil cohesion, internal friction angle, and seismic coefficient are found to be three of the parameters that affect the final response the most significantly. It is also indicated that considering 3D effects and soil cohesion has a favorable effect on increasing the stability of retained slopes.

Pseudostatic analysis of soil nailed vertical wall for composite failure

ABSTRACT In the present study, pseudostatic method is used to analyse the stability of soil-nailed vertical wall under seismic conditions. This approach includes an additional inertial force equivalent to the dynamic load caused by earthquake. The soil surface which undergoes failure due to the static and dynamic condition is assumed to be a realistic composite failure surface rather than the conventional planar, circular or log-spiral surfaces. This study investigates the effect of various parameters such as vertical and horizontal seismic acceleration coefficients, friction angle of soil, shear wave velocity, primary wave velocity, amplification factor, nail length, spacing of the nails, and nail inclination on the stability of the vertical soil-nailed wall. A comparison study is made between the results obtained from the present analysis and the values reported in the literature. It is observed the present study with composite failure surface gives higher values of Factor of Safety compared to planar failure surface. Composite failure surface is more realistic and hence more accurate compared to a planar failure surface which gives a conservative value of Factor of Safety.

Improved performance-based seismic coefficient for gravity-type quay walls based on centrifuge test results

Verifying the seismic performance of port structures when the force balance limit is exceeded is important for the performance-based seismic design of gravity-type quay walls. Over the last three decades, performance verification methods have been developed that consider the effects of the design earthquake motion, geotechnical conditions, and structural details on the deformation of a quay wall to accurately predict earthquake-induced damage. In this study, representative performance verification methods (i.e., simplified dynamic analysis methods extending from the Newmark sliding block method and performance-based seismic coefficients developed in Japan) were quantitatively assessed with actual cases of earthquake-damaged quay walls and the results of dynamic centrifuge tests previously conducted under various conditions (i.e., different wall heights, earthquake motions and the thickness of subsoil). The dynamic centrifuge test results suggested directions for improving the performance-based seismic coefficients of the representative methods, while their field applicability and reliability were confirmed according to the actual earthquake records.

Study on attenuation coefficient characteristics of the in-seam seismic wave in fault and collapse column

Various types of geological structures exist in the working face of coal mine stope. Failure to identify the structural development in advance could defer the timely implementation of reasonable management measures, which may eventually affect production safety and connectivity. As a matter of fact, fine detection and interpretation problems of in-seam seismic wave caused by different types of geological anomalies such as faults and collapse columns can exist simultaneously in the working face of mining. In view of these problems, forward modeling research of three-dimensional seismic wave fields on geological models with fault and collapse column are carried out in this study. Meanwhile, in combination with the imaging results of in-seam seismic wave attenuation coefficient of the exposed fault and collapse column, the characteristics of in-seam seismic wave were analyzed. Following comparative analysis, we found the attenuation coefficient anomaly of the fault is generally banded and weakens at both ends of the fault. The attenuation coefficient of the collapse column presents as an irregular ellipse. The energy of the smaller collapse column has a relatively small attenuation, while the energy of the larger collapse column shows a significantly obvious attenuation.

An Investigation of Building Seismic Design Parameters in Mataram City Using Lombok Earthquake 2018 Ground Motion

Mataram City is the capital of West Nusa Tenggara Province. West Nusa Tenggara consists of two islands namely Lombok and Sumbawa islands. Major earthquakes which have occurred in Lombok in 2018 are definitely making a difference in spectral acceleration. This becomes an important factor to be addressed in structural building design. Spectral acceleration in the short period, S S increases by 18,323% compared to the value listed in existing seismic code, SNI 1976:2012 corresponding to a return period of 2475 years. However, even though the S S value increases, the building design category has not changed, which remains in the D category. In general, the acceleration value in this study is found relatively greater than that of the existing code for periods of less than 0.462 s for site class D, and in periods of less than 0.830 s in site class E. Furthermore, the seismic response coefficient, C S increases by 10.782% compared to C S calculated using current code for medium soil. This impact is more severe in soft soil areas, where the increase reaches 13.168%. Improving of the existing code with the new building seismic design parameters affected by recent strong earthquake ground motion, leads to be more preparedness and becomes an important part of disaster risk reduction for the region.

Seismic Reflection Coefficient Inversion Using Basis Pursuit Denoising in the Joint Time-Frequency Domain

Seismic reflection coefficient inversion in the joint time-frequency domain is a method for inverting reflection coefficients using time domain and frequency domain information simultaneously. It can effectively improve the time-frequency resolution of seismic data. However, existing research lacks an analysis of the factors that affect the resolution of inversion results. In this paper, we analyze the influence of parameters, such as the length of the time window, the size of the sliding step, the dominant frequency band, and the regularization factor of the objective function on inversion results. The SPGL1 algorithm for basis pursuit denoising was used to solve our proposed objective function. The applied geological model and experimental field results show that our method can obtain a high-resolution seismic reflection coefficient section, thus providing a potential avenue for high-resolution seismic data processing and seismic inversion, especially for thin reservoir inversion and prediction.

Undrained seismic bearing capacity of strip footings horizontally embedded in two-layered slopes

This study investigated the undrained seismic bearing capacity of strip footings embedded in two-layered slopes by finite element limit analysis (FELA); in particular, a pseudostatic method was specified to seismic loads. Lower bound theory (LB), upper bound theory (UB), and adaptive meshing technique are employed for exploring the effect of the shear strength ratio of top layer and bottom layer, cu1/ cu2; the horizontal embedment depth of footings, b/ B; the footing locations (in bottom layer or top layer); seismic coefficient kh; and the slope gradient β on seismic bearing capacity. Results indicated that the seismic bearing capacity would increase with the growth of horizontal embedment depth of footings. The comparison between the predictions obtained from the proposed method and the existing method was presented, and the failure mechanisms are further summarized.

Caissons in Cohesionless Soils Considering 3D Wedge under Earthquake Loading

Ultimate soil resistance that acts on a seismically induced caisson foundation and its distribution along the caisson height have been formulated by considering passive wedge failure analysis for both dry and submerged conditions. The method for limiting the equilibrium of forces acting on a three-dimensional idealized passive wedge developed due to seismicity has been adapted in this study. Using this process, seismic inertia forces will be computed by considering the surrounding soil as a viscoelastic material that overlays a rigid stratum subjected to a harmonic shaking. For a very large value of caisson width, the comparison of this analysis with a 2D seismic earth pressure problem illustrates the compatibility of this methodology in the plane strain condition. Variation in earth pressure coefficients and their distribution for different seismic acceleration coefficients, soil properties, excess pore pressure ratios, and caisson aspect ratios will be discussed in this analysis. The reasonable agreement of the distribution of total passive pressure along the wedge height under the submerged condition with the experimental results shows the applicability of the proposed formulations as a design approach for caissons in sandy soil.

Seismic response correlation coefficient for the structures, systems and components of the Korean nuclear power plant for seismic probabilistic safety assessment

The seismic probabilistic safety assessments of nuclear power plants (NPPs) conservatively assume that the correlation between the seismic failure to structures, systems, and components (SSCs) is independent or fully dependent. This, however, is an extreme assumption, and so a more appropriate seismic failure correlation should be considered for accurate safety assessments. Quantification of the correlation of seismic failure can be expressed with a correlation coefficient; to calculate this, correlation coefficients for both seismic response and seismic performance between SSCs are required. This study suggests a seismic response correlation coefficient for the OPR1000 Korean NPPs. To this end, a probabilistic seismic response analysis was performed considering the randomness and uncertainty of earthquakes and structures. Based on this in-structure spectrum, the seismic response correlation coefficient between the SSCs was derived and databased. Seismic response correlation coefficient values are also suggested that can easily be applied to auxiliary buildings of NPPs.

Seismic Bearing Capacity of Strip Foundations on Fiber-Reinforced Granular Soil

The present study investigated the bearing capacity of strip footings on a bed of granular fiber-reinforced soils. Analyses were performed by the stress characteristics method (SCM). The failure criterion considers anisotropic distribution of fiber orientation and ignores the rupture of reinforcements. Seismic effects were included in the stress equilibrium equations as the horizontal and vertical pseudo-static coefficients. Stress equilibrium equations were solved by the finite difference method. A computer code was provided to solve the problem. Using the soil and reinforcement input parameters, the code determines the characteristics network and calculates the bearing capacity. The bearing capacity was expressed as the bearing capacity factors of the soil unit weight and surcharge. Parametric analysis was performed to investigate the effect of soil and reinforcement parameters on the bearing capacity and the shape of the failure zone. The outcomes indicated that the SCM results lower ultimate bearing capacity as compared with the upper bound method. Also, the depth of the failure zone increases with an increase in the amount of reinforcement or decrease in the horizontal seismic coefficient. Considering the anisotropic distribution of fiber orientations leads to more bearing capacity than the isotropic distribution.

Numerical studies on two-tiered MSE walls under seismic loading

Mechanically Stabilized Earth (MSE) retaining walls, reinforced by the geogrids and using rigid segmental blocks as facing elements have extensively been used in recent past as an economic and sustainable solution for the earth retention. Nevertheless, in the case of a high retaining wall, tiered walls are preferred than a single-tier retaining wall due to their cost-effectiveness and more stability than single-tiered MSE walls. However, the behavior of tiered MSE retaining wall under dynamic loading is not yet studied thoroughly as the conventional design in practice is based on offset distance between the tiered walls and certain assumptions of surcharge loading imparted by the weight of tiered walls itself. Therefore, an attempt has been made to examine the behavior of tiered MSE retaining wall using finite element method, having a height of 12 m (H) under gravity and seismic loading to compare its stability with the conventional (single-tier) MSE retaining wall in terms of factor of safety (FOS) and to look into the possible modes of failure. The factor of safety shows a raise of 66% in two-tiered walls, when the horizontal seismic acceleration coefficient (kh) is 0.36 for both the walls, during the analysis of single-tiered and two-tiered wall systems. An optimum reinforcement length is evaluated for two-tiered wall system under seismic and static loading conditions. It is suggested that reinforcement 0.8H and 1.1H is suitable in two-tiered MSE walls, under static and dynamic loading respectively.

Seismic stability of obliquely loaded circular plate anchors

The vertical uplift resistance of obliquely loaded circular plate anchors buried in sand subjected to seismic loadings has been obtained in this paper. The pseudo-dynamic approach based on kinematic theorem of limit analysis has been applied for performing the analysis in which the nonlinear acceleration distributions are incorporated considering standing shear (S) and primary (P) wave propagations within the soil medium. Results are obtained in terms of seismic uplift factor (Fγs) due to soil self-weight component for a wide range of parameters. Through a parametric study, the effects of different parameters including normalized frequencies of Shear (S) and Primary (P) waves and damping ratio (ξ) of soil are highlighted. On account of amplified accelerations effects, the value of Fγs has been found to drastically reduce with an increase in load inclination (θ), horizontal and vertical seismic acceleration coefficients (kh and kv). The results show that the influence of damping ratio (ξ) of soil becomes more dominant particularly for frequencies close to the fundamental frequency of P wave.

Taylor's slope stability chart for combined effects of horizontal and vertical seismic coefficients

Taylor's slope stability chart for combined effects of horizontal and vertical seismic coefficients