Near-field Earthquakes Research Articles

Seismic control of damaged structure by pole assignment and intermittent wavelet-based identification

Calculation of the control forces by control algorithms, such as the pole assignment, proportional-integral-derivative, and linear quadratic regulator, is usually based on initial dynamic characteristics of the intact and undamaged structure, which is considered to be in the ideal conditions. However, because of the effect of natural loads and damage due to aging, these features can change during the structure’s life span, eventually leading to incorrect control forces. In this research, to overcome this problem and to get closer to the actual dynamic characteristics and on the other hand, in order to elude the adverse effects of real-time identification, such as elapsed time of detection, induced to the controller, the intermitted wavelet-based identification technique besides the pole assignment control is introduced. Performance of the proposed controller on three- and five-story with different cases of stiffness and two failure scenarios, under far and near-field earthquakes, are examined and compared by non-updated wavelet-based pole assignment, proportional-integral-derivative and linear quadratic regulator controllers. Results show that damaged structure response controlled by the suggested adapted pole assignment method is significantly reduced compared to ones controlled by other control methods.

2D seismic response of shallow sandy basins subjected to obliquely incident waves

Under the effects of the near-field earthquakes, the change in the incident angle of the incoming wave changes the symmetric response of basins to asymmetric. This paper investigates the 2D response of shallow trapezoidal sandy basins to incident plane SV waves. To attain this goal, a trapezoidal basin with 100 m depth, as the representative of shallow sedimentary basins, with an inclined bedrock angle of 10° was selected. These values fall inside of the ranges of the shallow basin depth and bedrock angle of several real basins. To make the results useful in engineering affairs, three different sand types belonging to the different class of soils, with respect to the soil classification codes, were selected. The constructed models were subjected to the collection of 24 earthquakes with different PGA's of 0.1, 0.2, 0.3 and 0.4 g using a fully nonlinear method. The results showed that the change in the incident angle of the motions not only affects the response at two basin edges but also influences the response of the central part. Among different sandy basins, the behavior of the basin with medium dense sand is less affected by the change in the wave incident angle. For basin with loose sand, while greater maximum spectral amplifications happen at the backward direction of the basin, the forward direction is less affected by the change in the wave incident angle. A different pattern was seen for basin with dense sand. Greater maximum spectral amplifications were seen at the forward direction of the basin. Regarding the effect of motion incident angle on the amplification frequency of shallow basins, it was seen that in case of the obliquely incident waves the spectral amplification curves of the points close to the edges have more than one (generally two) maximum points. Besides, unlike the vertical incident wave case that the SAF curves tend to almost one curve at the distant points from edges, no convergence among the SAF curves of the surface points was seen for the obliquely incident wave condition.

Direct displacement-based design approach for isolated structures equipped with supplemental fluid viscous damper

In this paper, direct displacement-based design (DDBD) approach is extended for the isolated structures equipped with supplemental fluid viscous damper (FVD) while this method can be also implemented for the isolated structures without supplemental FVD. The design process has been developed based on a non-iterative manner whereas a complexity from preliminary design to iterative design process can be found in previous DDBD approaches. To validate the proposed method, three steel moment-resisting frames with four, eight and twelve stories are designed using this method. Nonlinear time-history analysis has been performed under a far-field record set including twenty-two earthquakes and a near-field record set including fourteen earthquakes. The results show that the isolated frames without supplemental FVD have effective performance under far-field earthquakes. Therefore, the proposed design method can be employed as effective design approach for isolated structures. However, their performance is not very reliable under near-field earthquakes because base isolation system originally does not have effective performance under near-field earthquakes. Seismic performance of isolated frames equipped with FVD shows that their peak response is less than target drift under both far-field and near-field earthquakes and these frames have effectively achieved the desired performance levels related to both superstructure and base isolation levels. Therefore, the developed DDBD approach can be introduced as an effective design method for isolated structures equipped with supplemental FVD.

Parameter Analysis and Optimization of Friction Pendulum Bearings in Underground Stations Based on Genetic Algorithm

ABSTRACT This paper analyses the influence of friction coefficient and equivalent radius on the seismic reduction effect of friction pendulum bearings in the underground station under far-field and near-field earthquakes with different strength. It is found that the parameters of the friction pendulum bearings will obviously influence seismic reduction effectiveness. By combining genetic algorithm with finite element method, the parameters of friction pendulum bearings in the station can be optimized. By using this method, the optimal parameters range can be obtained, which can provide reference for parameter design of friction pendulum bearings in underground stations.

Seismic Damage Probability Assessment of Isolated Girder Bridges Based on Performance under Near-Field Earthquakes

This paper presents a copula technique for developing seismic fragility curves for an RC (reinforced concrete) isolated continuous girder bridge, by considering earthquake damage indicators such as bridge piers, isolated bearing components, and the main girder of collision damage. The results of this method are compared with those of the limit method of the first-order reliability theory. Meanwhile, the incremental dynamic analysis of the bridge structure under different failure conditions is carried out, and the randomness of the near-fault ground motion and the structural parameters are accounted. Based on the damage index of the isolated bridge under different damage conditions, the seismic fragility curves of each component and the whole isolated bridge are obtained. The research shows that the safety control of the isolated continuous girder bridge structure is mainly affected by the seismic fragility of the isolated bearing, the influence of bridge pier seismic fragility is relatively small, and the probability of beam collision in an isolated bridge is lower than that of a general bridge without isolation bearing. By applying the isolation scheme, the probability of different damage state of the bridge structure is greatly reduced, thus the seismic performance is improved. It also verifies the efficiency and superiority of copula technology. The results will provide a reference for future seismic damage prediction.

Multiple mechanisms of coseismic water level changes at the Rongchang well in a seismically active area in China

We examined water level data at the Rongchang (RC) well in the Rongchang natural gas field in China's Sichuan Basin from November 2007 through 2019, where injection-induced seismicity with a magnitude of up to 5.2 has been reported. Coseismic water level changes caused by earthquakes from 3 km to 3500 km away, as well as changes in water temperature, provide a good opportunity to systematically study the mechanisms underlying the response of water level to earthquakes. Among 41 ML ≥ 3.0 local earthquakes, 20 events exceeded the magnitude-distance threshold for the water level to change. Eleven events caused water levels to rise, and only one earthquake led to a decrease in water level. For the 22 distant earthquakes with a seismic energy density greater than the threshold of 0.0017 J/m3, ten events caused rises in the water level and only the MW 7.9 Wenchuan Earthquake caused a temporary, but large, decrease in water level. In total, eight local events and 11 distant events, which were expected to cause coseismic water level changes, actually resulted in no changes. The findings imply that an earlier sizable earthquake may decrease the sensitivity of the well for a certain period of time (approximately two months). The dominant mechanisms of coseismic water level changes in response to near-, mid-, and far-field earthquakes are different. For near-field earthquakes, the drop in coseismic water level is governed by the combined effects of static strain changes and the release of trapped gas bubbles due to the strong vibration of seismic waves in the aquifer; however, only static strain changes are dominant after mid-field earthquakes. For far-field earthquakes, the dominant mechanism is aquifer softening due to growth of gas bubbles in the groundwater that is associated with weak and low frequency seismic shaking of passing surface waves.

Vulnerability analysis of pile-reinforced slope under the condition of near-fault impulse ground motions

In order to analyze the impact of the near-fault pulse ground motions on the slope, the method of seismic vulnerability analysis based on IDA is introduced into the stability evaluation. Taking the slope reinforced by stabilizing piles as an example, a typical analysis model is established. The seismic performance is divided into four stages: basically intact, partial damage, severe damage and overall instability. A large number of calculations are used to compare the instability probability of slopes with near-fault and far-field ground motions. The results show that: 1) The calculation model which combines the Newmark and the limit analysis method can reflect the difference between the near-fault and the far-field ground motions. 2) The IM-DM curve with indexs of PGA and displacement has a better fitting effect. The vulnerability analysis based on IDA can be used to evaluate the slope failure risk under seismic loads. 3) The IDA curve shows a monotonous increasing trend. When the seismic intensity is lower(GPA=0∼0.5), there is no obvious difference between the vulnerability curves of the near-fault and far-field. As the intensity increases(GPA=0.5∼1.2), the failure probability of near-fault is significantly higher than the far-field. Meanwhile, the failure mode changed from the partial failure to the complete failure. It is clear that near-fault ground motions have the characteristics of large energy and strong impact, which are more likely to cause slope instability. If the impact of the near-field earthquake is ignored, the disaster may be underestimated.

Behaviour of the integral bridge under multi-component earthquakes

The performance of integral bridges subjected to a multi-component earthquake has not been thoroughly investigated. Here, the responses of an integral bridge subjected to three-component far- and near-field earthquakes are determined to evaluate its relative structural advantages and disadvantages over a conventional bridge. Further, the effect of the interaction between the internal forces in the three directions on the total responses or yielding due to simultaneous application of the three components of an earthquake is investigated. For this purpose, two geometrically comparable bridges, one integral and other conventional, are analysed under far- and near-field earthquakes using SAP2000. The parameters varied are the type of ground motion, peak ground acceleration and orientation of the major horizontal component of the ground motion. Seismic demand parameters include the maximum bending moment in the girders, maximum moments at the top and bottom of piers, displacements in three directions and the plastic hinges formed. The results of the analysis show that the deck of the integral bridge has smaller displacements when compared with the conventional bridge. A greater number of plastic hinges are formed in the integral bridge, but the degree of damage shown by the hinge rotations in the conventional bridge is greater.

Mitigation of Earthquake Responses Using SMA Supplemented Base-Isolation Devices for Benchmark Building

The efficiency of traditional isolation bearings is doubted for near-field earthquakes because these bearings undergo large displacement. A comparative study of different base isolation systems of base-isolated benchmark building is carried out in the present study. The study is based on assumption that buildings are bi-directionally acted upon by near-field earthquakes for assessing their relative performance in seismic control of the benchmark building. The time history variations of important response parameters and evaluation criteria of the benchmark building has been studied for assessing the effectiveness of the isolation systems. The Shape Memory Alloy (SMA) is utilized with elastomeric bearings and friction bearings to study the effectiveness of SMA wires with different isolators. The benchmark building is modelled as a discrete linear elastic shear structure having three degrees of- freedom at each floor level. Time domain dynamic analysis of this building has been carried out with the help of constant average acceleration Newmark’s method and equilibrium of non-linear forces has been taken care by fourth order Runge-Kutta method. The comparative performance of various isolation systems has been studied with uniform and hybrid combinations. The hybrid combination of SMA supplemented bearings works out the better isolation system keeping in view of the percentage reduction in evaluation criteria for smart base-isolated benchmark building. Furthermore, it is shown that, the functionality of SMA wire is not efficient with Lead Rubber Bearing system, as it is able to control displacement but increases the acceleration, base shear, story drift and isolation forces.

Evaluation of nonlinear static and dynamic analysis of steel braced frame buildings subjected to near-field earthquakes using FBD and DBD

Near-field earthquake is one of the primary sources of ground motions that significantly affecting the structure's seismic response in its surrounding area containing pulse-long periods. The two popular and reliable approaches for the seismic investigation of structures are known as the force and displacement-based seismic design (FBD and DBD), extensively developed in the literature. In the present study, three types of steel buildings were defined for the seismic analysis, including five, eight, and fifteen-story steel buildings as the representatives of the multi-story, middle-rise, and small high-rise buildings, respectively. Steel structure designs and nonlinear analysis were done by implementing SAP2000 and Opensees software, respectively. The designed buildings were analyzed statistically and dynamically by performing the criteria determined in the FEMA-P750, Standard Code 2800, FEMA 356, and FEMA-P695, and then, FBD and DBD results were compared. The nonlinear static analysis results showed the acceptable displacements corresponding to the displacement criteria suggested by FEMA 356, showing the desirable performance of the designed structures. Also, the dynamic analysis results confirmed the reliability of the FEMA 356′s design criteria for the five and 8-story steel structures. However, the small high-rise building design has not met the regulations suggested by FEMA 356.

The Investigation of Traffic and Near-Field Earthquake Loads Effects on the Nailed and Braced Excavations

Considering the statistical and probabilistic characteristics of construction conditions, the investigation of dynamic overloads' effects on the urban excavation wall is of great importance. In the present study, the performance of nailed and braced excavations under two vibrational dynamic excitations, traffic and near-field earthquake loads, have been investigated in four regions of Ahvaz. Critical boreholes with the lowest static bearing capacity have been selected by analyzing the layers' strength parameters in each region. Numerical models have been designed to limit the seismic waves' reflection at the excavation boundaries with 20 x 100 meters and with absorbing walls. Also, the damping ratio was assumed to be 2%. A harmonic wave at different speeds has simulated the excitation caused by the traffic passage. Resonant frequencies due to traffic induced vibration have been recorded in the speed range of 56 to 72 km/hr. Due to the traffic load, the bracing and the nailing systems showed less vertical and lateral displacements, respectively. Moreover, the excavations have been analyzed under ten acceleration with compatible near field characteristics of the Ahwaz plan acceleration (0.25g). The Kiyanpars region showed the highest vertical displacement difference between the two systems in the range of 0.032 m to 0.006 m. Due to earthquake loads, the bracing system showed less vertical displacement. The error of the analytical models' results in vertical displacement was 10% and 26% and in lateral displacement was 5% and 20% less than a nailed excavation located in the Kiyanpars region under traffic passage.

A holistic seismotectonic model of Delhi region

Delhi region in northern India experiences frequent shaking due to both far-field and near-field earthquakes from the Himalayan and local sources, respectively. The recent M3.5 and M3.4 earthquakes of 12th April 2020 and 10th May 2020 respectively in northeast Delhi and M4.4 earthquake of 29th May 2020 near Rohtak (~ 50 km west of Delhi), followed by more than a dozen aftershocks, created panic in this densely populated habitat. The past seismic history and the current activity emphasize the need to revisit the subsurface structural setting and its association with the seismicity of the region. Fault plane solutions are determined using data collected from a dense network in Delhi region. The strain energy released in the last two decades is also estimated to understand the subsurface structural environment. Based on fault plane solutions, together with information obtained from strain energy estimates and the available geophysical and geological studies, it is inferred that the Delhi region is sitting on two contrasting structural environments: reverse faulting in the west and normal faulting in the east, separated by the NE-SW trending Delhi Hardwar Ridge/Mahendragarh-Dehradun Fault (DHR-MDF). The WNW-ESE trending Delhi Sargoda Ridge (DSR), which intersects DHR-MDF in the west, is inferred as a thrust fault. The transfer of stress from the interaction zone of DHR-MDF and DSR to nearby smaller faults could further contribute to the scattered shallow seismicity in Delhi region.

Effects of Stick-Slip in Behavior of Structures with Friction Damper under Near-Field Earthquakes

The present study is an attempt to investigate structures equipped with friction dampers under the influence of near-field earthquakes based on Stribeck friction behavior of velocity function. At present, the cyclic behavior of friction dampers in structural design engineering software is simple and based on the Coulomb friction force that is independent of velocity, which should be estimated and considered in terms of Stribeck velocity-dependent friction. Their sliding and vibration methods, including displacement, velocity, and acceleration, are calculated using numerical analysis and differential equation. For this purpose, the representative of the near-field records affects the structure with Stribeck frictional behavior of velocity function as a pulse of Ricker wavelet stimulation. The response of the structure is evaluated in the transition phase from impending motion with a friction coefficient of μs to kinetic motion with μk and vice versa, which makes the poor results of previous simplifications more accurate. Due to the nonlinear behavior of the damping force, programming has been used to perform nonlinear analytical dynamics. Also, behavioral models in OpenSees software are used to investigate the behavior of Stribeck friction for friction damper and to compare its results with the results obtained from accurate analysis.

Effect of Foundation Flexibility on the Seismic Performance of a High-Rise Structure under Far-Field and Near-Field Earthquakes

In this study, the seismic performance of a 20-storey steel structure with a mat foundation located on layered soil is investigated under an array of strong ground excitations, which includes 6 far-fault and 6 near-fault earthquakes. Eight different modes for soil layering have been considered in the numerical simulation. FLAC 2D nonlinear platform has been used to model the near-realistic behavior. To this end, hundred lines of codes and sub-routines have been developed in this platform to perform the analysis. The results of the analyzes include the absolute displacement of the floors, the ratio of the relative displacement of the floors, the shear force, the axial force, and the bending moment of the columns. It was concluded that for a 20-story structure on a mat foundation under both far-field and near-field earthquakes, the most reliable type of soil is the dense sandy soil and the most critical case is the soft clay soil. It was also observed that the near-field strong ground motions have imposed more critical structural responses compared to far-field records.

Corrigendum to “Health Monitoring of Storage Tanks Subject to Near-Field and Far-Field Earthquakes” [Engineering Science & Technology, Volume 2 Issue 2 (2021) 116-130

Corrigendum to “Health Monitoring of Storage Tanks Subject to Near-Field and Far-Field Earthquakes” [Engineering Science & Technology, Volume 2 Issue 2 (2021) 116-130]
 https://doi.org/10.37256/est.222021640
 Published online May 7, 2021.
 
 The authors regret they missed to one of the authors, Hamidreza Vosoughifar, whose contribution to this paper that could not be ignored.
 The correct authorship should be: Hossein Mirzaaghabeik, Rafael Holdorf Lopez, Marcos Souza Lenzi, Hamidreza Vosoughifar.
 
 The authors would like to apologize for the inconvenience caused.

Seismic assessment of linked-column frame structural system considering soil-structure effects

The Linked Column Frame (LCF) structural system is comprised of moment-resisting frames as the primary gravity load-carrying system and a combination of closely-spaced dual columns interconnected with link beams acting together with the moment-resisting frames as the lateral load resisting system. In this system, the link beams are designed to provide ductility and deform plastically. As the damages are concentrated to the links thus, the LCF rapidly returns to occupancy design performance while retaining architectural privileges of the non-braced steel frames. In this study, 3, 6, and 9-story frames equipped with LCF and resting on soil type II and IV are subjected to seven near and far-field earthquake records. These structures are designed based on the plan of SAC buildings using SAP2000, and then, nonlinear time-history analyses were carried. The results indicate that maximum roof drift of the structures on stiff soil (type II) has been insignificantly affected under both near and far-field earthquakes. In soft soils (type IV), drifts values increase by 6.85%, subject to both far and near-field earthquakes. Moreover, in contrast to the stiff soil, roof acceleration has decreased more when the structure is on soft soil, nearly 6.12%. The result of maximum inter-story drift ratios of the structures founded on soil type II illustrates that under an average of near-field earthquakes, drift ratios of 3 and 6-story structures have increased by 3.2%. On the other hand, the 9-story structure has encountered a decrease of 5.17%. Under an average of near-field earthquakes in soil type IV, a drift ratio of 3 and 6 and 9-story structures has grown to 5.11 and 11.2%, respectively, compared to the fixed-base models. In far-field earthquakes, drift values of 3 and 6-story LCF were reduced by 6.2%, and the 9-story structure has experienced an increase of 8.79%.

Microzonation of Ground Motion Parameters in Shangluo City

This paper studied the regional seismic tectonic characteristics, regional seismic activity characteristics, the near-field seismic tectonic characteristics, near-field earthquake activity characteristics about the site of Seismic Microzonation in Shangluo City, seismic belts and potential seismic source zone were divided, calculating the seismic risk analysis of the bedrock of the site, surveying engineering geological conditions in the site, carrying out the seismic response analysis of the site, and zoning the ground motion parameters of the site. The above results provide a basis for the seismic fortification of the proposed general engineering in the site.

Investigation the Sidesway Collapse and Seismic Fragility Analysis of Frames with BRB Equipped with SMAs

Although Buckling-Restrained Braces (BRBs) can dissipate a large amount of the seismic input energy. However, they need to be repaired or replaced due to large permanent deformation after a severe earthquake. To overcome this issue, the use of Shape Memory Alloys (SMAs) in the braces has recently received attention. These alloys are able to return to their original state after loading. The present study aims to analyze the fragility curves and to investigate the sidesway collapse of the BRB frames equipped with SMA during near-field earthquakes in comparison with those given for the case without SMA. For the purposes, two 5 and 15-story BRB and BRB-SMA frames subjected to 7-pair of near-fault earthquake records are studied. Nonlinear Incremental Dynamic Analyses (IDAs) are carried out using OpenSees software. On average, the simulation results showed that collapse capacity and collapse duration of the BRB-SMA frames are about 30% and 35% more than those given for the BRB frames, respectively. For an instance, a collapse probability of 38% for the 5-story BRB-SMA frame and a collapse probability of 60% for the BRB frame is given for 3g spectral acceleration. Furthermore, at the performance level of 50% for the 15-story frame, the collapse duration of the BRB-SMA frame is obtained 25.6 seconds, while it is given about 10 seconds for the BRB frame. In addition, the use of a memory alloy for spectral accelerations of 1 to 4 g resulted in a reduction of 50% to reach the collapse performance level of the frames.

Seismic Performance Assessment of Velocity Pulse-Like Ground Motions Under Near-Field Earthquakes

As a part of the earthquake ground motion, large velocity pulses are probably one of the important factors leading to serious rock structural damage and geological disasters. It is vitally important to identify the response characteristics of large-scale structures under near-field pulse-like ground motions for earthquake prevention and disaster reduction. In this study, the pulse parameters from the 1999 Chi-Chi and 2018 Hualien earthquakes are extracted using the wavelet transform method, and the potential consequences of velocity pulses on the seismic response of the buildings are assessed. Our results show that the near-field ground motions affected by the directivity effect contain some rich large pulse contents in the velocity time histories. The Chi-Chi earthquake presents a more obvious directivity effect than the Hualien earthquake, and the near-field velocity pulses are closely related to the severely damaged structures. The potential damage of both earthquakes to high-rise buildings can be evaluated by the relationship between the characteristic period of the velocity pulse and the fundamental natural period of the engineering structure. By comparing the periods, it can be revealed that some long-period spectral values in the range of 0.8–3.0 s exceed the seismic design values in the vicinity of the causative faults, and the vulnerability of high-rise buildings against pulse-like ground motions in the Chi-Chi earthquake is stronger than that in the Hualien earthquake. Interestingly, the ratio of peak ground velocity to acceleration (PGV/PGA) and maximum pseudo response velocity (PSV) are suitable as seismic intensity indicators of pulse-like ground motions, which can reflect the rupture direction of source characteristic and site amplification of near-surface soft deposition area around the causative fault. This study provides some references for seismic hazard assessment and post-earthquake structural design.

Seismic analysis of steel concentrically braced frames with consideration of fling-step effect

Near-field earthquakes with a fling-step effect cause a permanent displacement at the end of the displacement record, which can affect the response of structures. Fling step is induced by permanent static displacement of the ground that is noticeable in strike–slip faults. This effect is usually omitted from the main record using the standard processing methods and, thus, the fling-step effect cannot be considered to obtain seismic response of different structures. To investigate the effect of near-field earthquakes with the fling-step effect, 14 original (non-filtered) ground motions with different fling displacement are selected. The selected records are applied to special concentrically braced frame (SCBF) structures with 3, 6, 9 and 12 stories to cover most structural periods. To investigate seismic response of the structures, two main parameters including lateral displacement and story–drift ratio are selected. A nonlinear time history analysis is used to obtain the displacement and story–drift ratio responses. The results show that the fling-step effect has no significant impact on any of the considered structures, and its effect can be neglected in case of special concentrically braced frame structures.