Seismic Acceleration Research Articles

Analytical Computation of Sandy Slope Stability under the Groundwater Seepage and Earthquake Conditions

Groundwater and earthquake are two of the factors behind the occurrence of slope instability. This paper focuses on the computation of the safety factor acting on a sandy slope when subjected to groundwater seepage and earthquake load. Based on the theory of limit equilibrium and a pseudodynamic method of analysis, a general solution for the dynamic factor of sandy slope containing two load conditions is proposed. In the solution, the effects of parameters such as water level, seismic acceleration coefficients, slope angle, and soil internal friction angle on the slope stability have been discussed. In order to evaluate the validity of the present formulation, the dynamic factors of safety computed by the present method are compared with those given by other cases. It is found that the results of the present method are in good agreement with those of the previous method. The results indicate that the dynamic of safety factor increases linearly with an increase in the soil internal friction angle but decreases with the slope angle and groundwater level and that the effects of direction and magnitude of the seismic inertia forces on the dynamic safety factor of sandy slope are different at different times.

Seismic acceleration amplification factor for pin supported moment resisting RC frame structures for Chi-Chi earthquake

The Seismic forces, acting on the non-structural component, are different with respect to the lateral force observed by the different design codes. For remarking the behavior of the structural components during dynamic action, large numbers of research were done as compared to the secondary or non-structural components of the structures. The behavior of inertia force acting on the non-structural components changes along with the altitude of the structure. The inertia force existing on nonstructural components depends on the acceleration amplification factor. In this paper, five different RC moment-resisting frame models as 2,4,6,8 and 10 stories, with pin support conditions are considered. The linear time history method is used for the analysis of all RC frame models with different range (0.01g to 0.32g) of ground motion data. Determine the acceleration amplification factor for all these models and compared with the previously models. It is observed that no previous model performed satisfactory results. Therefore, to proposed the amplification model which not only depends on the height of the building, natural period of the building but also depends on the range of the Peak Ground Acceleration (PGA).The proposed model is compared with the previous renowned models, It is detected that the proposed model performs better results with respect to other models.

Extending Mononobe-Okabe theory to account for arbitrary backfill topography and variable density of surcharge

Coulomb proposed a formula for the static earth pressure acting on a rigid gravity retaining wall supporting a soil. Many researchers have generalized this theory and several analytical studies were achieved regarding the evaluation of seismic action. Following the work of Mononobe and Okabe, investigations have considered cohesive backfill, and with some restrictions the topography of the backfill and the pattern of surcharge acting on its surface. In this work an extension of the Mononobe-Okabe theory was proposed to deal with the most general case of backfill having an arbitrary shape and also vertical surcharge acting with variable density at the ground level. Equilibrium of Coulomb wedge was applied to express the active earth pressure coefficient related to a given orientation of the failure plane. Then, numerical optimization was performed to fix the critical angle providing its maximum value. Parametric studies were conducted after that. It was found that both the upward and downward vertical seismic acceleration should be considered. The obtained results indicate that the backfill surface shape and surcharge density have a significant effect on seismic action. The maximum relative variation of the pressure coefficient with regards to the reference case is however limited to 20%.

Internal stability analysis of geocell-reinforced slopes subjected to seismic loading based on pseudo-static approach

Seismic stability analysis of geocell-reinforced slopes (GRSs), considering shear and moment strength in addition to tensile resistance for geocells, is a novel topic for which scarce studies are found in the literature. Despite few available studies, an analytical approach is presented in this study to investigate the seismic internal stability of GRSs, employing the pseudo-static method based on a limit state approach. Results are given in terms of conventional design charts representing the required total strength and critical length of geocells. The results show that with increasing the horizontal seismic acceleration (kh), the internal stability degenerates since the required strength and critical length of geocells increase. For GRSs subjected to greater kh, the effect of increasing the vertical seismic component (kv) on increasing the required strength and length of geocells is more considerable than those subjected to lower kh values. Parametric analyses are conducted, under various seismic conditions, to investigate the effect of increasing the geocell height and raising the number of geocell layers, leading to the reduction in the required strength and length of geocells. Such effects are found to be dependent on the parameters such as the intensity of seismic excitation, material properties and geometry of slope.

Seismic stability of vibration-insulated turbine foundations depending on the frequency composition of seismic impact

The seismic resistance of vibration-insulated turbine foundations is a complex and multifaceted problem that includes many aspects. The turbine foundation is a special building structure that unites parts of the turbine and generator unit into a single machine and it is used for static and dynamic loads accommodation. The number of designed and constructed power plants in high seismic level areas is large and steadily growing. In addition, engineers and designers deal with the issue of the frequency composition of the seismic impact influence on the seismic resistance of vibration-insulated turbine foundations. Dynamic calculations were performed in Nastran software using time history analysis and the finite element method. The main criteria for the seismic resistance of a vibration-insulated turbine foundation are the values of the maximum seismic accelerations in the axial direction at the level of the turbine installation and the values of vibration-insulated foundation maximum seismic displacements (deformations of vibration isolators). The results of the calculation experiments proved a significant effect of seismic action frequency composition on the behavior of the vibration-insulated turbine foundations. Calculations of foundations, taking into account earthquakes of the same intensity, but with different values of the prevailing frequencies of the impact, lead to the differing by several times values of the maximum seismic accelerations at the turbine level and seismic displacements.

Displacement Estimation for Nonlinear Structures Using Seismic Acceleration Response Data

ABSTRACT The displacements estimated using seismic accelerations are useful for post-earthquake inspection of structural damage. In previous studies, displacements were usually obtained through non-trivial measurement or double integration of the measured acceleration response and then an additional correction process. However, from the signal processing perspective, double integration induces substantial numerical errors. In this study, a displacement estimation approach is developed based on the extended Kalman filter (EKF) with an embedded Bayesian noise-parameters updating technique. The displacement is estimated by EKF with updated time-varying noise parameters based on a Bouc–Wen model. Numerical simulations and a shaking‐table test are presented to demonstrate the proposed method.

Modelling and simulation of earthquake‐induced changes in methane emission from the working face in an underground coal mine

Evidence demonstrates that unusual methane emissions in coal mines may happen after earthquakes or mine tremors. Here, a seismicity-induced permeability change model is constructed and validated using field data from the Laohutai coalmine. The validated model is employed to explore the extent to which different peak ground velocities (PGVs), seismic acceleration coefficients, remnant coal seam methane pressures, and initial coal seam permeabilities affect earthquake-induced methane emissions. Detailed simulation results suggest that the permeability of a coal seam subjected to earthquakes is both controlled by the dual competing mechanism of earthquake-imposed strain and excess pore pressure. A higher PGV leads to a rapid increase in the coal seam permeability and the maximum of methane concentration in the airflow, while higher seismic acceleration coefficients could somewhat reduce them. Meanwhile, increasing the remnant methane pressure and initial permeability in a coal seam subjected to an earthquake increases the maximum of methane concentration in the airflow at working faces. These results have provided reliable guidance for how to adopt emergent measures to prevent earthquake-triggered methane accidents in underground coal mines.

Estimation of the Critical Seismic Acceleration for Three-Dimensional Rock Slopes

An analytical approach for the estimating of critical seismic acceleration of rock slopes was proposed in this study. Based on the 3D horn failure model, the critical seismic acceleration coefficient of rock slopes was conducted with the modified Hoek–Brown (MHB) failure criterion in the framework of upper-bound theory for the first time. The nonlinear Hoek–Brown failure criterion is incorporated into the three-dimensional rotational failure mechanism, and a generalized tangent technique is introduced and employed to convert the nonlinear Hoek–Brown failure criterion into a linear criterion. The critical seismic acceleration coefficients obtained from this study were validated by the numerical simulation results based on finite element limit analysis. The agreement showed that the proposed method is effective. Finally, design charts were provided for exceptional cases for practical use in rock engineering.

Seismic stability analysis of two-stage slopes reinforced with one row of piles

Seismic stability of a two-stage soil slope reinforced by one row of piles is analyzed using the upper bound theorem combined with pseudo-static method considering the pile axial force. For a specified safety factor of the piled slope, explicit expression of the required pile shear resistance is derived, in which the effect of axial force of the piles on the potential slide mass omitted in most of previous studies is reasonably introduced. Analysis results of examples show that the pile shear resistance and potential slip surface by the proposed method are in good agreement with those by numerical simulation. The pile reinforcement effect on the slope is operational under smaller seismic conditions, whereas it is limited and not significant with the increase of the seismic excitations. The pile shear resistance and range of the critical slide mass increase with the horizontal seismic acceleration coefficient. Compared with the existing results omitting the pile axial force, more conservative upper bound solutions of the pile shear resistance are obtained by the proposed method, especially under higher design safety factor and seismic loads. Widening the bench and constructing the pile row near the slope crest are conducive to practicably optimize the reinforcement effect on the two-stage slope under seismic excitations.

Study on instability and damage of a loess slope under strong ground motion by numerical simulation

The instability and damage of loess slopes under strong ground motion can be a complicated process, involving sliding, translation, and rotation, which makes the discrete element method as a suitable theory to simulate such a process. Therefore, in this study, the particle flow code (PFC) is developed to simulate the instability and damage process of the loess landslide under strong motion. Based on field investigations and laboratory tests, the detailed identification of mesoscopic parameter was calibrated, and a 2D model was established. The results show that the slope surface tends to amplify the ground motion, resulting in the strong vibration of the soil on the slope surface. The slope shoulder is the position with the largest amplification coefficient of seismic acceleration, which is the key to the instability and failure of the slope. And, under the seismic force, the tensile failure firstly occurs in the slope upper part, and then the accumulation failure occurs in the lower part, finally a shear outlet is formed. Accordingly, high-frequency component of the Fourier spectrum increases with the slope failure. This study highlights the gradual increase in the difference between the first principal stress and the third principal stress, which destroys the inherent cohesive cements between particles, which is the main cause of slope failure under strong motion.

The AD 1755 Lisbon Earthquake-Tsunami: Seismic source modelling from the analysis of ESI-07 environmental data

This work presents a macroseismic analysis of the AD 1755 Lisbon Earthquake-Tsunami event by means of the combination of intensity data derived from the EMS-98 scale and the ESI-07 scale (Environmental damage). About 600 records of secondary earthquake environmental effects (EEEs) for the whole Spain have been used to define intensities, focused on the SW portion of the Iberian Peninsula. The Spanish data have been complemented with 308 EEEs records from Portugal. The analyses indicate maximum intensities of X EMS-ESI along the Atlantic margin of the Iberian Peninsula with 76 records of Tsunami environmental effects (TEEs). An important amplification (VIII – VII) occurred all along the Guadalquivir basin and the adjacent Betic front at epicentral distances of 300–700 km. In these zones 55 records of ground effects (ground cracks, Liquefactions and slope movements) are catalogued. In the rest of the territory of the Peninsula the most widespread effects were hydrogeological changes with 505 records in Spain and 196 in Portugal (total 701 records) covering all the intensity levels. Increase of flow discharges in springs and elevation of water level in wells was the common groundwater response to seismic shacking, especially in SW Iberia. In this zone water elevation in wells was between 5 and 3 m and persistent increases of discharges long-lasting (several days to two months). Persistent discharges on springs were linked in 143 cases to important SW-NE crustal faults (e.g., Alentejo-Plasencia Fault). From the Intensity distribution the historic seismic scenarios are explored by means of the development of empirical ShakeMaps. These consider the three classical seismic sources proposed for this earthquake: Gorringe Bank (G); Marques de Pombal Fault (M) and Atlantic delamination beneath the Gulf of Cadiz (C). However, individually these seismic sources are too small and unable to generate the resulting seismic scenario depicted by the intensity map developed in this work, with onshore seismic accelerations (PGA) up to 0.82 g. These acceleration values and the great amplification experienced throughout the Guadalquivir basin (0.34–0.52 g) are only possible considering a combination of the three seismic sources (GMC Source) probably related to shallow subduction or lithospheric delamination beneath SW Iberia and the Gulf of Cadiz. This will suggest an NNE-SSW offshore rupture length of 350–360 km with an overall rupture area of c. 84,500 km2 resulting in an event magnitude 8.6 Mw calculated from empirical relationships. The results demonstrate the efficacy of these kind of approaches for better identifying and modelling seismic sources for historical events.

Effect of bidirectional ground shaking on structures in the elastic and post-elastic range: Adequacy of design provisions

During an earthquake, structures are generally excited to multiple ground motion components: two orthogonal horizontal components and one vertical component. However, the interaction of the deformations along two principal orthogonal directions in the presence of various levels of axial force in columns in post elastic range can be successfully captured if nonlinear dynamic analysis can be carried out using the bidirectional hysteresis model. On the other hand, the seismic codes prescribed simple combination rules to capture this effect in an equivalent sense even without consideration of axial force in columns. Though these rules may be valid in the elastic range, they may not be applicable in the post-elastic range as mentioned in a few seismic codes. Surprisingly, these codes did not specify any user-friendly provision needed by design offices. Hence, the applicability and efficacy of these rules in the post-elastic range is needed to be compared with that obtained from detailed nonlinear tine history analysis under orthogonal pair of bidirectional ground motions obtained from a number of chosen seismic acceleration data for performance-based design. In this study, idealized low-rise buildings with small, medium, and long periods were investigated, considering the presence of axial force in columns. Most of the current design codes and standards suggest that the addition of response of 30% of ground motion in other direction if added to the response of unidirectional ground motion in the considered direction of analysis or the resultant responses obtained by square root of sum of square from the unidirectional analyses carried out separately in both principal directions (referred as SRSS response) may predict the response with reasonable accuracy. The results obtained from the current study makes an attempt to exhibit the trends of post elastic range response for the structures. Further, it shows that seismic codes options significantly underestimate the post-elastic range seismic demand though they are proved to be adequate to predict elastic range response. This paper may prove helpful in improving code provisions.

Highly Efficient Piezoelectrets through Ultra-Soft Elastomeric Spacers.

Piezoelectrets are artificial ferroelectrics that are produced from non-polar air-filled porous polymers by symmetry breaking through high-voltage-induced Paschen breakdown in air. A new strategy for three-layer polymer sandwiches is introduced by separating the electrical from the mechanical response. A 3D-printed grid of periodically spaced thermoplastic polyurethane (TPU) spacers and air channels was sandwiched between two thin fluoroethylene propylene (FEP) films. After corona charging, the air-filled sections acted as electroactive elements, while the ultra-soft TPU sections determined the mechanical stiffness. Due to the ultra-soft TPU sections, very high quasi-static (22,000 pC N−1) and dynamic (7500 pC N−1) coefficients were achieved. The isothermal stability of the coefficients showed a strong dependence on poling temperature. Furthermore, the thermally stimulated discharge currents revealed well-known instability of positive charge carriers in FEP, thereby offering the possibility of stabilization by high-temperature poling. The dependences of the dynamic coefficient on seismic mass and acceleration showed high coefficients, even at accelerations approaching that of gravity. An advanced analytical model rationalizes the magnitude of the obtained quasi-static coefficients of the suggested structure indicating a potential for further optimization.

Fourteen‐Year Acceleration Along the Japan Trench

AbstractAn acceleration of the background seismicity and a shortening of the slow slip events recurrence intervals in the Boso peninsula (Japan) suggest a slow unlocking of the Philippine Sea‐North America (PHS‐NAM) subduction interface from 1990 to 2011. Motivated by these previous observations, we used GPS (Global Positioning System) time series to study the 1997–2011 evolution of interface locking offshore Honshu with a specific focus on the Kanto region. We newly processed the GPS data in double difference and analyzed them with a trajectory model that accounts for seismic and aseismic variations, and that includes an inter‐seismic acceleration term. We inverted the surface acceleration obtained, on both the Pacific‐North America (PAC‐NAM) and the PHS‐NAM interfaces. The inverted slip rate changes over time compare well with previous studies: we infer slip deceleration between –N and acceleration between –N (PAC‐NAM), with a maximum amplitude of 1.75 mm/ corresponding to an equivalent geodetic locking change of 0.3 over the 14 years. More notably, our analysis reveals a novel and robust slip acceleration South of N that we interpret as an unlocking of the PAC‐NAM interface. It is located noticeably far from the 2011 Tohoku earthquake rupture and is therefore unlikely connected to it. The slip acceleration inverted from the surface displacements is comparable to the changes observed in the seismicity rate. Our results further demonstrate that inter‐seismic slip rate can significantly evolve over years to decades, and suggest a simple relationship between the seismicity and the slip on the subduction interface.

Modified pseudo-dynamic analysis of slope considering logarithmic spiral failure surface with numerical solution

ABSTRACT A methodology for the analysis of soil slope made up of c-ϕ soil using a modified pseudo-dynamic approach is tried to develop here. In this study, the slope is divided into a number of vertical slices and the failure surface of the slope is assumed to be logarithmic spiral. The suggested modified pseudo-dynamic approach satisfies the zero-stress boundary condition at the free ground surface and considers the damping properties of the materials. Results of the present analysis are presented in tabular form. The effects of the variation of different parameters like horizontal and vertical seismic acceleration, slope angle, soil friction angle, damping ratio, frequency ratio, cohesion and surcharge on the FOS are shown graphically. Consequently, required reinforcement strength is evaluated to ensure the safety of the slope under seismic loading conditions. The results obtained from the present method are compared with the results of the available literature and also a numerical validation of the model is given using PLAXIS 2D.

Seismic loads estimation on the storage tanks for toxic and flammable liquids

There are about 1 million earthquakes of varying intensity every year in the world. Further more increase in the technogenic objects number and the necessity to create environmentally safety conditions for their operation leads to improved scientific substantiation of seismic hazard parameters of technogenic objects that could adversely effect on the environment. Therefore, the research of seismic loads on the important technogenic objects still remains the urgent issue both globally and regionally. The aim of the paper is to prevent emergencies and negative impact on the environment in case of damage, destruction and leakage of storage tanks for toxic and flammable liquids due to seismic loads of different strength. There have been treated the peak amplitudes of seismic acceleration simulation during an earthquake from 1 to 9 points at the distance to the epicenter from 10 to 1000 m, the dominant excitation frequencies at the earthquake from 1 to 9 points at the distance to the epicenter from 10 to 1000 m, the earthquake average duration with the magnitude of 1 to 9 points at the distance to the epicenter from 10 to 1000 m and the issue of fluid oscillations in the arbitrary shell of rotation has been solved. The results of the research will allow to select the storage tanks parameters from the influence of resonant frequencies, to prevent their destruction and to extend the service life, to minimize the ecologically hazardous impact on the environment and prevent emergencies. For the increasing the ecological safety level of the adjacent to the storage tanks territories, it has been proposed to control the effects of natural and technogenic factors on the storage tanks taking into account the forecast models of seismic changes and fluctuations in storage tanks using the algorithm for monitoring seismic loads on storage tanks.

Seismic acceleration demand and fragility assessment of storage tanks installed in industrial steel moment-resisting frame structures

Recent seismic events highlighted the importance of non-structural elements in seismic assessment and performance-based earthquake engineering. When referring to industrial facilities, storage tanks represent one of the most critical components for the continuous functionality of industrial and building plants after seismic events. At the same time, the dispersion of dangerous or inflammable materials, due to their collapse, could become a safety issue in terms of both human life and environmental impact. This study focuses on the seismic performance assessment of a liquid-storage tank installed in an industrial steel moment-resisting frame building. The performance is assessed in terms of fragility curves, that are provided for the meaningful limit states that affect the liquid-storage tank and considering several intensity measures. The results related to the structural performance are also discussed in detail in terms of fragility functions and floor response. The assessment is performed through nonlinear dynamic analyses using two different modelling approaches to evaluate the structural and non-structural performance. The first modelling approach explicitly accounts for the tank-structure interaction, while in the second one the tank is only modelled considering its seismic mass. The results show the importance of the modelling assumptions to accurately estimate the seismic demand on liquid-storage tanks and corresponding fragility, which is calculated in terms of different intensity measures (IM): average ground spectral acceleration, peak floor acceleration, and floor spectral accelerations. Peak floor acceleration, drift profiles, and absolute acceleration and relative displacement floor response spectra are instead scrutinised for what concerns demand. The comparison with the code formulations available in the literature for estimating the seismic demand to non-structural elements pointed out their inaccuracy for the analysed liquid-storage tank and the need for further efforts to develop more accurate procedures. Furthermore, the outcomes indicate that the IM adopted for secondary components, i.e. peak floor acceleration, may not always be the optimal one hence additional attention should also be paid to the definition of updated fragility curves for non-structural elements, identifying and adopting more suitable IMs.

Shaking table test of acceleration response of surrounding rock of the 3D cross tunnel under earthquake

Taking the 3D cross-engineering of Caomeigou No.1 Tunnel and Pandaoling Tunnel as an example, a shaking table test was carried out to study the effect of tunnel spatial position on seismic wave propagation characteristics and acceleration response of surrounding rock under earthquake seismic excitation. Based on the influence of the spatial position of the tunnel, the characteristic form of the surrounding rock between the cross section and non-cross section is divided, and the accelerometer layout scheme is designed. Based on statistical probability, the ratio of peak ground velocity to peak ground acceleration (PGA) was introduced to quantitatively characterize the characteristics of seismic wave propagation spectrum. Furthermore, the SPECTR calculation was used to obtain the regional difference in the seismic wave propagation potential damage potential displacement parameter (P d ). Under the influence of the spatial location of the 3D cross tunnel, the peak acceleration and motion duration of the seismic wave are mainly reflected in the variation of the section along the elevation direction. Low-frequency (≤20 Hz) seismic waves have a greater impact on the tunnel structure, and peak ground velocity/peak ground acceleration ratio has a positive correlation with the peak input energy of ground motion. The ultra-small net-spacing cross tunnel has a spatially distributed coupling deformation effect. The crown of the upper-span tunnel is highly sensitive to earthquakes and becomes a weak link in seismic design. These results help us provide a theoretical basis for the seismic design of the cross-tunnel.

Optimal design and performance evaluation of tuned mass damper inerter in building structures

This paper concerns the numerical performance evaluation of multi-degree-of-freedom systems equipped with Tuned Mass Dampers-Inerter (TMDIs); a passive control device used for the mitigation of mechanical vibrations induced by dynamic loads. The inerter device is commonly used to increase the apparent mass of classics tuned mass dampers (TMDs), improving its seismic performance. To evaluate the TMDI action, three case studies are employed, determined from three real buildings of Medellin city from low, medium to high rise (30 meters, 97 meters, and 144 meters, respectively). Optimum design parameters are found using a metaheuristic optimization based on the differential evolution method, first, for the minimization of the horizontal peak displacements, and then, for the minimization of the root mean square (RMS) response of displacements. Besides, the case studies are assessed using eight seismic accelerations records representative of the literature. Finally, the seismic performance is evaluated on each case study considering different levels of inertance induced by the inerter device: 5%, 20%, and 50% with respect to the total mass of the building, for which it is observed a better dynamic behavior when TMDIs with lower values of inertance are implemented.

Earthquake Dynamic Failure Mechanism of Dangerous Rock Based on Dynamics and PFC3D

The dynamic failure mechanism of horizontally layered dangerous rock during earthquakes is complex and only few studies have addressed the combination of particle flow code (PFC) meso-level failure mechanism and mechanical analysis. Based on fracture mechanics and material mechanics we establish a calculation method for the interlayer load and stability coefficient of horizontal layered dangerous rock during strong earthquakes. The method was applied for calculating the stability of a horizontally layered dangerous slope along a highway in the Sichuan Province (China) during earthquakes as a case study. Using a 3D particle flow simulation technology, a PFC3D model of horizontal layered dangerous rock was established. Its dynamic stability, failure mode and Hilbert-Huang 3D time-frequency characteristics are analyzed, and the results of the simulation are largely consistent with the time of the dangerous rock failure as estimated by our new calculation method. Our study documents that as the seismic acceleration gradually increases, the stability coefficient of the rock block fluctuates more violently and the stability coefficient gradually decreases. The stability coefficient of the rock block decreases fastest between 5 and 6 s and the reduction in the stability coefficient is between 0.12 and 0.25. Before the seismic acceleration reaches the maximum, the dangerous rock blocks on the two main controlling structures collapse and get destroyed. 25 s after the earthquake, the failure mode of the dangerous rock is collapse-slip-rotation. We show that earthquakes with frequencies of 0–10 and 250 Hz have the strongest destructive effect on the stability of the horizontally layered dangerous rocks.