Seismic Acceleration Response Research Articles

Dynamic responses of reinforced concrete silo considering pile–soil‐structure–granular solid interaction

SummaryThe columned‐supported reinforced concrete silo models with different filling conditions considering soil‐structure dynamic interaction (SSI) are established based on the finite element program ANSYS to thoroughly investigate the complex interaction mechanism of the soil–pile–silo structure with granular solid. The dynamic characteristics and seismic responses of the SSI system and fixed‐base condition are analyzed and compared when the filling conditions are empty‐filled state, half‐filled state and full‐filled state. The numerical results reveal that the SSI effect reduces the seismic acceleration response of columned‐supported silos effectively. However, in terms of displacement, the SSI effect often amplifies the relative deformation of the supporting column and the cylindrical silos. Furthermore, the SSI effect often increases the relative dynamic lateral pressure of the storage material in the half‐filled silo condition. In the full‐filled silo condition, the relative dynamic lateral pressure at the top and bottom of the storage material is increased by the SSI effect; while it is decreased in the middle part of the granular solid, demonstrating that the SSI effect could change and increase the seismic responses of the silo structure in certain areas. Therefore, the investigation provides a comprehensive insight into the interaction mechanism of the pile–soil–silo structure with different filling conditions.

Shaking-Table Tests for Seismic Response of Arch Foot of a Long-Span Arch Bridge on Sand-Gravel Soil Sites Considering SSI Effect

ABSTRACT The seismic performance of arch bridges is dependent on the strength of bridges and the built-on soil site types. To investigate the influence of soil-structure interaction (SSI) on the seismic response of an arch-foot arch bridge with a sand-gravel soil site, several shaking-table tests for a 1/90 downscaled arch-foot model placed on sand-gravel soil were conducted based on the engineering prototype of the third Pingnan Bridge with a long-span concrete-filled steel-tube (CFST) arch bridge. The test results showed the following: (1) The seismic acceleration response of both the sand-gravel soil site and arch foot were amplified, which is related to both the non-linear dynamic behavior of sand-gravel soil and frequency-spectrum characteristics of the input seismic waves. (2) The sliding displacement of the arch foot under strong ground motions increased accompanied with a settlement of the soil surface. However, the safety risk of the arch foot may be underestimated in seismic design. (3) The dynamic shear stress-strain loops of sand-gravel soil exhibited a high-energy dissipation capacity, and the energy-transfer mechanism at the interface between the model soil and arch foot was integrated. The results obtained are expected to provide insights into the dynamic interaction behavior of the gravel soil and arch bridge systems and the seismic design of arch bridges built on sand-gravel soil sites in practical engineering.

Influence of frozen soil site conditions on ground motion characteristics in cold regions

It is necessary to understand the site seismic response for seismic design and post-earthquake damage assessment of structures in seismically active regions. In cold regions, the presence of layered frozen soil not only affects the ground motion characteristics but also influences the seismic response of structures on these sites. This study aims to investigate the effect of frozen soil site conditions on ground motion characteristics in cold regions through shaking table tests using a laminar shear box equipped with a soil freezing system. The seismic acceleration response, displacement response, and dynamic shear stress-strain relation were analyzed for both unfrozen and frozen soil sites under various seismic waves with different intensities. The existence of the frozen soil layer has been observed to mitigate ground motion during earthquakes, resulting in a reduced peak ground acceleration compared with the unfrozen soil site. If an earthquake occurs, the high-frequency waves will be attenuated by the frozen soil layer, which possesses a dominant frequency lower than that of the unfrozen soil site. Moreover, the energy dissipation capacity of the frozen soil site is larger than that of the unfrozen soil site during earthquakes. By combining the Fourier spectral ratio curves, it can be inferred that different input ground motions have varying effects on the seismic response of both unfrozen and frozen sites. These findings serve as valuable references for seismic design of structures in cold regions.

Reduction of the seismic absolute acceleration response with supplemental viscous damping

The relationship between the seismic absolute acceleration response of single- and multi-degree-of freedom building models and the amount of supplemental viscous damping is analyzed. Possible influence of the fundamental period, the number of stories, and the frequency content of the excitation is evaluated. It was found that, qualitatively, the relationship between the absolute acceleration response and the amount of supplemental viscous damping is different from that between the displacement response and the amount of supplemental viscous damping. The implications of the findings of this study for the design of supplemental viscous damping systems aimed at reducing the absolute acceleration response of buildings are discussed.

Normalized energy index-based signal analysis through acceleration trendlines for structural damage detection

Utilizing the Trend line-based Signal decomposing Algorithm (TSA), this paper develops an innovative Structural Health Monitoring (SHM) method to locate damages in structures on the basis of vibration signature analysis. Firstly, a suitable vibration mode of the structure should be selected. The TSA is then used to determine special trend lines of the structural response according to the selected vibration mode. The damage is located through a normalized energy-based damage index calculated for these special trend lines. The accuracy of the developed method is examined using two examples: an experimental five floor laboratory building model, and a numerical arch-tied bridge, both subjected to seismic excitations. For the building model, the seismic excitation was exerted to the building model using a shaking table and the seismic acceleration responses were recorded using a set of wireless accelerometers installed at the center of each floor. For the arch-tied bridge, the numerical simulation was performed in ABAQUS software and the seismic acceleration responses were recorded on the deck near the cables. For the building model, damages were modeled as loss of stiffness in columns on different floors. For the arch-tied bridge, damages were modeled as loss of stiffness in cables. The results show that, provided that the response records and reflects damage-induced changes in the monitored structure, the developed method can accurately locate the damaged floor or damaged cable in both examples. Additionally, using the normalized energy-based method to locate the loss of stiffness in a structure makes the developed method a good candidate for rapid and simple assessment of a structure’s health state.

Prediction of seismic acceleration response of precast segmental self-centering concrete filled steel tube single-span bridges based on machine learning method

The precast segmental self-centering concrete-filled steel tube (PSCFST) bridge is not only the ideal choice for fast and environmentally friendly construction but also has good seismic and resilience properties. Our research group has carried out shaking table test research on the PSCFST bridge, but due to the limitation of test equipment and site, no damage test has been carried out. To further study the seismic performance of PSCFST bridges when subjected to larger ground motions, machine learning (ML) models are developed to predict the seismic performance of PSCFST. A novel combined prediction model based on Conv1D-LSTM was proposed to predict the PSCFST bridge acceleration response. Two other commonly used ML methods including XGBoost and Random forest regression (RFR) are also used for comparison purposes. A database of ML prediction models is established based on 116 sets of input ground motion (GM) and superstructure acceleration response from shaking table tests. Then, the data of RSN292 60% GM were selected as the prediction test data. Furthermore, based on the Opensees platform, the PSCFST fiber finite element (FFE) model was established and validated by the shaking table test results, then the dynamic time history analysis of the ground motion with larger amplitude (greater than the input ground motion assignment of the shaking table test) was carried out. The superstructure acceleration response of 70%–120% of the RSN 292 GM is obtained by the FFE model and used as the data set for the ML prediction model. After that, the superstructure acceleration response is obtained through three prediction models. Comparing the simulation and prediction results shows that all the Conv1D-LSTM, XGBoost, and RFR models can reliably predict the acceleration response of the PSCFST bridge. In all cases, the Conv1D-LSTM model performed outperforms the XGBoost and RFR models. The determination coefficients (R2) of Conv1D-LSTM, XGBoost, and RFR model for the prediction of superstructure response are 0.9643, 0.8780, and 0.9623, respectively.

Analysis on Dynamic Characteristics and Seismic Response of Wooden Structure of South Gate Building in Jiangzhang Town

In order to study the seismic performance of ancient wooden structures with single eaves and beam lifting in China, the finite element model of the upper floor of the south gate of Jiangzhang town in Shanxi Province was established by using ANSYS. Through modal analysis, the main frequencies and modes of the south gate of Jiangduan were obtained. Through the seismic response analysis of the south gate tower model, the displacement and acceleration response curves of the top nodes of the outer eaves column, golden column and through column under various working conditions of the South gate tower are obtained. The results show that the first and second order frequencies of the South Gate tower model are 1.830Hz and 1.855Hz, and the first two order modes are mainly transitional. With the increase of seismic excitation, the displacement and acceleration response of the top joints of the outer eave column, golden column and through column increase.

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.

Assessment of the Lattice Discrete Element Method in the simulation of wave propagation in inhomogeneous linearly elastic geologic materials

Attenuation equations for seismic peak ground acceleration, ground velocity or seismic response spectra, in terms of distance to the source and magnitude of the causative event are typically based on results of the theory of linearly elastic wave propagation in homogenous solids. The latter also furnishes the fundaments for both the study of vibrations induced by surface loadings on the ground and for the design of isolation systems. In engineering applications, the propagation of seismic waves through inhomogeneous materials acquires unquestionable relevance. At the same time, analytical solutions impose increasing difficulties, requiring resort to numerical approaches. In the paper, a version of the Discrete Element Method, herein designated as Lattice Element Method (LDEM), is employed to study propagation of body waves in linearly elastic homogeneous and inhomogeneous media, with or without viscous linear material damping, with the objective of assessing bounds for solutions based on the assumption of linear elastic material models.

Interface friction effects on scaling a vertical spring-viscous damper isolation system in a shaking table test

A vertical spring had a changeable horizontal stiffness to avoid resonance under a seismic displacement, and a viscous damper had a perfect energy dissipation function to reduce the seismic displacement. They were joined together to achieve a seismic isolation system considerably reducing the seismic acceleration response, however, their displacement should be paid more attentions under an earthquake or in a shaking table test. Because the interface friction in the system affected the scaling process of the system in the shaking table test and the corresponding displacement responses, the system was numerically scaled before a real shaking table test. The comparison between the displacement responses of scaled models and prototype models shows that the spatial friction variation and the gravity distortion are the error sources of the relative and residual displacements of scaled models. The error of scaled relative displacement is reduced by the means of increasing PGA, damping constant, spring constant or reducing vertical spring length with zero stress, however, the error of scaled residual displacement is still chaotic under these means. Only if the error sources above are eliminated fundamentally will the error of scaled models be avoided. The conclusions are validated correct by a real shaking table test.

Study on Dynamic Amplification Factor of UHV Pillar Equipment

In the research of UHV pillar equipment, the dynamic amplification factor of bracket is a key parameter. This paper mainly focuses on the relationship between the dynamic amplification factor of ceramic equipment under the condition of seismic acceleration response spectrum when the structural parameters of the bracket are the same. In this paper, the stiffness of the bracket is changed by altering the elastic modulus of the steel. The dynamic amplification factors of the speed, displacement, stress and acceleration of the bracket in the two kinds of overall structures are compared and analyzed by numerical simulation. At the same time, the relationship between the bracket frequency and the steel consumption is compared by calculating the steel consumption of different bracket structures. Based on the results of simulation analysis and considering the seismic design of porcelain electrical equipment in UHV substations and converter stations, it is suggested that the dynamic amplification factor, the envelope of displacement and stress amplification factor of 1.40 should be adopted, thus providing a theoretical basis for the design of UHV bracket equipment.

Experimental investigation on the performance of multi-tiered geogrid mechanically stabilized earth (MSE) walls with wrap-around facing subjected to earthquake loading

Construction of mechanically stabilized earth (MSE) walls in multi-tiered configurations is a promising solution for increasing the height of such walls. The good performance of this type of walls after recent major earthquakes was reported in a number of technical studies. In the present study, an experimental approach was adopted to compare the seismic performance of single-tiered and multi-tiered MSE walls using physical modeling and through conducting a series of uniaxial shaking table tests. To do so, several geogrid-reinforced soil walls with wrap-around facing (i.e., three-, two-, and single-tiered) with a total height of 10 m were designed in the form of prototypes of 1-m-height wall models. The step-wise intensified sinusoidal waves were applied to the models in 14 typical forms. Comparing the shaking table test results confirmed the post-earthquake advantages of multi-tiered MSE walls. The results revealed that tiered walls exhibited better behaviors under earthquake loading in terms of the seismic stability of the wall, displacement of the wall crest, horizontal displacement of the wall facing, deformation mode and failure mechanism of the wall, settlement of backfill surface, and seismic acceleration responses.

Shaking table test on the characteristics of seismic acceleration responses at the portal section of the loess tunnel

A large-scale shaking table test was conducted to study the dynamic response at the portal section of a tunnel based on the loess tunnel of the Baoji–Lanzhou high-speed railway as an engineering background. A wavelet packet transform method was applied to analyze seismic acceleration responses. The pattern of changes in energy in the loess tunnel under the seismic load was obtained. Results reveal that (1) the acceleration amplification factor of the slope surface increases with elevation, but a turn exists at the inverted arch of the tunnel because the stiffness of the tunnel is greater than that of the slope soil. As such, the tunnel elicits a certain protective effect on the slope soil below it. (2) The amplification effect of the internal slope soil decreases gradually outward, and the tunnel portal is affected by the amplification effect of the slope surface. The peak ground acceleration (PGA) of the tunnel vault is greater than that of the inverted arch of the tunnel. Thus, the vicinity of the tunnel vault should be the key seismic fortification area. (3) The loess layer causes an amplification effect on low-frequency-band seismic waves (0–12.51 Hz) and a filtering effect on the high-frequency-band seismic waves. The changes in the energy of the slope surface and the inside tunnel gradually stabilize as the seismic load increases. This study can provide a reference for the seismic fortification of the tunnel portal section of the loess slope–tunnel system under a seismic action.

Influence of nuclear island on seismic acceleration response on soft rock sites

As the site resources of nuclear power plant are getting increasingly scarce day by day, soft rock sites will be gradually used for nuclear power plant construction. In this paper, a three-dimensional finite element model for the nuclear island structure on soft rock site (based on the horizontal layered soft rock site) was established using the ABAQUS finite element software by adopting the modified Davidenkov constitutive model with configuration of viscoelastic artificial boundary and consideration of the embedding effect. This model was used to simulate the nonlinear characteristics of the soft rock site and comparatively analyse the influence of the nuclear island on the seismic acceleration response of soft rock site. The results show that the nuclear island increases the peak acceleration of the soft rock site. As the input ground motion increases, the ground surface peak acceleration increases accordingly, but due to the nonlinear effect of the soft rock site, the acceleration amplification factor shows a decreasing trend. Under the far-field ground motion, the ground surface acceleration increases significantly and may cause a strong potential destruction to the nuclear island. A non-free field (with a nuclear island) moves the ground surface acceleration response spectrum slightly toward the long-period direction. Under the near-field ground motion enriched with high-frequency components, the ground surface peak acceleration response spectrum caused by the nuclear island shows an increasing trend. Our research conclusions can provide useful reference for both the site selection and aseismic design of nuclear power plants.

Analysis on influence of adjacent buildings on mutual seismic acceleration response

During an earthquake, the seismic response of adjacent buildings will be affected by each other, which is known as structure-soil-structure interaction (SSSI). In order to study the SSSI between neighboring buildings, the slab foundation frame structure on a typical type II site in Nanjing is used as the object. ABAQUS software is used to establish a nonlinear static-dynamic coupling two-dimensional finite element analysis model of a single building and multiple buildings with different spacing. The numerical analysis of the model shows that: Under the action of earthquakes, the increase of surrounding structures will increase its own acceleration response; when the building spacing ratio is 1/2 and 1/4, the existence of adjacent buildings will reduce its own acceleration response. When the spacing ratio is greater than or equal to 1, the impact tends to be unfavorable, and it is the most unfavorable when the spacing ratio is 2. When the spacing ratio is greater than or equal to 4, the impact of adjacent buildings on each other’s peak acceleration response can be ignored.

Localization of damaged cable in a tied‐arch bridge using Arias intensity of seismic acceleration response

It is well-known that a bridge may end up with severe damage under aftershocks, even if it resisted the main shock. As such, a quick assessment seems necessary when a bridge experiences an earthquake event. In this paper, an output-only energy-based method was developed to locate damaged cables in an tied-arch bridge under seismic excitation. For this purpose, seismic acceleration response signals were first subjected to simple band-pass filtering. Then, the energy levels, in terms of Arias intensity, were calculated and normalized to locate the damaged cables. The proposed method was validated through a realistic 3-D numerical model of a tied-arch bridge under 16 different ground motions. It was shown that the proposed method can accurately detect the damaged cables under the earthquakes. Moreover, the damage detection procedure is proved to be insensitive to noise and adequately robust against near- and far-field parameters of the earthquake.

Influence of pile spacing on seismic response of piled raft in soft clay: centrifuge modeling

In order to study the influence of pile spacing on the seismic response of piled raft in soft clay, a series of shaking table tests were conducted by using a geotechnical centrifuge. The dynamic behavior of acceleration, displacement and internal forces was examined. The test results indicate that the seismic acceleration responses of models are generally greater than the surrounding soil surface in the period ranges of 2–10 seconds. Foundation instant settlements for 4×4 and 3×3 piled raft (with pile spacing equal to 4 and 6 times pile diameter) are somewhat close to each other at the end of the earthquake, but reconsolidation settlements are greater for 3×3 piled raft. The seismic acceleration of superstructure, the uneven settlement of the foundation and the maximum bending moment of pile are relatively lower for 3×3 piled raft. Successive earthquakes lead to the softening behavior of soft clay, which causes a reduction of the pile bearing capacity and thus loads are transferred from the pile group to the raft. For the case of a 3×3 piled raft, there is relatively smaller change of the load sharing ratio of the pile group and raft after the earthquake and the distribution of maximum bending moments at the pile head is more uniform.

Stability evaluation of the acceleration and energy response spectra

Seismic design codes commonly use the acceleration response spectrum to determine the seismic force. It is based on the maximum elastic response at a specific time according to the equation of motion for a single-degree-of-freedom system. The seismic effect is evaluated as the load effect by the response spectrum. However, there is no close correlation between the seismic input energy and acceleration response spectrum. Structural damage is not necessarily proportional to the maximum response of acceleration/displacement and is also significantly affected by the accumulative inelastic deformation during an earthquake. In addition, real structures have multiple stories with various distributions of the strength, stiffness and mass alongside P-Delta and torsional effects, so the current acceleration spectrum is very different from real behavior. In this study, the stability of the acceleration response spectrum according to structural characteristics mentioned above was verified by numerical analysis and compared to the stability of the energy response spectrum. The adequacy of the current design spectrum was evaluated to develop suggestions for improving the accuracy of seismic design for the ground motions with the predominant period of less than 1.00 s.

Effects of Uncertainty of Dynamic Shear Modulus Ratio on Design Ground Motion

Based on numerical simulation and the statistics of fine sand layers in the Wuhan area (China), the effects of uncertainty of dynamic shear modulus (due to the limited range of current instruments) ratio on design ground motion were explored. Its effects on design seismic acceleration response spectrum, platform value of response spectrum, and characteristic period of response spectrum were analyzed quantitatively. This study could provide a guideline for the analysis of seismic response as well as theoretical study of nonlinear dynamics on geotechnical earthquake engineering.

Shake table tests on the traditional column-and-tie timber structures

In order to study the seismic performance of Chinese traditional column-and-tie timber structure, two 1:2 scaled model structures, one without infilled wallboard and the other with infilled wallboard, were fabricated and tested on shaking table in Key Laboratory of Structural Engineering and Earthquake Resistant at Xi'an University of architecture and technology. In the test, the maximum responses of acceleration and displacement were measured and evaluated, as well as the dynamic characteristics, global hysteresis response and torsion effect. Test results indicate that the column-and-tie timber structure has large flexibility and deformability, and the energy dissipation capacity of the structure increases with the increasing magnitude of earthquake excitation. Meanwhile, the structure incorporating wallboard exhibited a substantial increase in its lateral stiffness and a dramatic reduction in its seismic displacement response. Furthermore, the seismic acceleration response of the structure was moderately increased by the presence of wallboard. It is suggested that the wallboard should be taken into consideration on the lateral stiffness of the whole structure. Such a comprehensive analysis helps enhance understanding of the seismic-resistant behavior of this type of construction, which is certainly important for historic preservation efforts.