Far-field Earthquakes Research Articles

Evaluation of pounding effects between reinforced concrete frames subjected to far-field earthquakes in terms of damage index

In this paper, three different damage indexes were used to detect nonlinear damages in two adjacent Reinforced Concrete (RC) structures considering pounding effects. 2-, 4- and 8-story benchmark RC Moment Resisting Frames (MRFs) were selected for this purpose with 60%, 75%, and 100% of minimum separation distance and also without any in-between separation gap. These structures were analyzed using the incremental dynamic analysis method under 44 far-field ground motion records. Comparison of the results between the MRFs with and without considering pounding effects show that collisions lead to a decrease in the values of coefficient of determination and the nonlinear damage occurs in lower seismic intensity. As a result, using the damage indexes, nonlinear damages can be detected during a specific seismic intensity. Moreover, considering a minimum separation distance leads to an increase in the coefficient of determination between the damage index and the maximum story drift ratio. Furthermore, due to pounding, shorter MRFs are damaged more significantly than the taller structures.

Loading protocols for seismic performance evaluation of buckling-restrained braces in RC frames

The selection of a proper loading protocol for seismic performance evaluation of structural dampers poses quite a challenge at the very first step of quasi-static cyclic tests. Existing loading protocols for buckling-restrained braces (BRBs) are mainly developed on the basis of the seismic responses of BRB-steel frame systems. However, the behavior of a BRB in reinforced concrete frames (RCFs) differs markedly from that in the steel frames. In this study, a set of loading protocols were constructed to provide a reference for seismic performance assessment of BRBs in RCFs. The methodology for the development of loading protocols was illustrated and a series of BRB-RCFs varying in building heights and story shear resisted by BRBs were designed. An extensive analytical investigation of seismic responses of BRBs under far-field, near-fault, and long-duration earthquakes was systematically evaluated and quantified. Based on the rainflow counting method, the control parameters in terms of numbers of cycles, amplitudes, and residual core strains were determined to construct loading sequences. The effectiveness of the proposed loading protocols was discussed and verified through comparisons with existing loading sequences and time-history analysis results of a validated BRB-RCF model. It is indicated that the proposed loading protocols can conservatively reflect the actual seismic damage demands with a reasonable agreement.

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.

Distribution of Seismic Damage in Steel Buildings Component Equipped by Viscoelastic Dampers against Far-Field Earthquake

Damage to structures with the concept of inelastic behavior and consequently hysteresis energy is very close. Therefore, it can be said that hysteresis energy at these levels can be a significant criterion for designing or controlling the structure. In this research, the first three steel frames of 4, 8, and 12 floors with the medium bending frame system have been designed with the statically equivalent method according to valid international regulations; then, all frames have been subjected to nonlinear dynamic analysis by seven accelerometers. The purpose of this study is to investigate the distribution of damage, energy, relative displacement, roof displacement, and base shear in the studied frames. In the following, the necessity of using the retrofitting method to reduce the relative displacement is described based on the regulations. Then, viscoelastic dampers are used to strengthen and reduce damage in the studied frames in the face of distant field records. The obtained results indicate that despite the uniform distribution of resistance in the height of the floors, the hysteresis energy distribution and damage diagrams do not follow this distribution and other parameters such as hysteresis energy, which play a major role in structural members’ damage, should be included in the design process. In this research, viscoelastic dampers have been used for retrofitting. The results show that this type of damper shows good performance in reducing damage under earthquakes in the remote area.

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.

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.

GPS Derived Seismic Signals for Far Field Earthquake Epicenter Location Estimation

A reliable epicenter estimation method is proposed for Global Positioning System (GPS) derived seismic signal for far-field regional earthquake. The main contribution is the use of time-frequency analysis to estimate the time of arrival (TOA) using multilateration technique. The data from the 2004 Sumatra Andaman earthquake captured from four GPS continuously operating reference stations (GPS CORS) were used in the analysis. To validate the accuracy of the proposed method, the estimated epicenter location was compared with the data released by the United States Geological Survey (USGS). The estimated location shows an error of about 0.0572 degrees in latitude and 0.2848 degrees in longitude. The proposed analysis method could complement existing seismometer measurements, improve in understanding of geo-seismic phenomena, and plan future infrastructure development.

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%.

Reliability of Seismic Signal Analysis for Earthquake Epicenter Location Estimation Using 1 Hz GPS Kinematic Solution

This paper proposed a reliable analysis method of Global Positioning System (GPS) derived seismic signal to locate the epicenter of a far-field regional earthquake. The surface wave of the seismic signal is utilized due to the attenuation in the body wave which is conventionally used in seismometer. The main contribution is the identification of time-frequency representation (TFR) as a signal analysis method to derive the time of arrival (TOA) for epicenter location estimation using multilateration technique. The comparison was made with other methods such as directly from the time representation, the instantaneous energy, and the power spectrum estimation. The data from the 2004 Sumatra Andaman earthquake captured from four GPS continuously operating reference stations (GPS CORS) were used in the analysis. To validate the accuracy of the proposed method, the estimated epicenter location was compared with the data released by the United States Geological Survey (USGS). The estimated location shows an error of about 0.0572 degrees (6.3 km) in latitude and 0.2848 degrees (31.33 km) in longitude. This is comparable to previous studies using seismometer with an average error of 25 km for far field earthquakes and 20 km for recent work on GPS derived seismic signals for near field earthquakes.

Various far-field hydrological responses during 2015 Gorkha earthquake at two distant wells

Aquifer hydraulic parameter can change during earthquakes. Continuous monitoring of the response of water level to seismic waves or solid Earth tides provides an opportunity to document how earthquakes influence hydrological properties. Here, we use data of two groundwater wells, Dian-22 (D22) and Lijiang (LJ) well, in southeast Tibet Plateau in response to the 2015 Mw 7.8 Gorkha earthquake to illustrate hydrological implications. The coherences of water level and seismic wave before and after the far-field earthquake show systematic variations, which may confirm the coseismic dynamic shaking influence at high frequencies (f > 8 cpd). The tidal response of water levels in these wells shows abrupt coseismic changes of both phase shift and amplitude ratio after the earthquake, which may be interpreted as an occurrence in the vertical permeability of a switched semiconfined aquifer in the D22 well, or an enhancement unconfined aquifer in the LJ well. Using the continuous short-term transmissivity monitoring, we show that the possible coseismic response for about 10 days and instant healing after 10 days to the causal earthquake impact. Thus, the dynamic shaking during the Gorkha earthquake may have caused the short-term aquifer responses by reopening of preexisting vertical fractures and later healing at epicentral distances about 1500 km.

Velocity pulse effects of near-fault earthquakes on a high-speed railway vehicle-ballastless track-benchmark bridge system

The near fault (NF) line waves send out signal envelopes that oscillate over lengthy periods of time with periodic impulses. Like train bridges, train tracks demonstrate comparable track-bridge (TB) motion dynamics. Using these coupling dynamics, are the high-speed train-track-bridge (HSTTB) system designs sensitive to those parameters? This research incorporates a Finite Element Analysis (FEA) technique developed for simulating the dynamic reactions of the coupled TB system when faced with simultaneous NF lateral and vertical ground motions (GMs). For the first time, data from the pre-commissioning field testing of the Beijing-Shanghai high-speed train are utilized to validate the Train-Track-Bridge Dynamic Analysis (TTBDA) test. As a matter of fact, the current research has concentrated on the running safety of the high-speed train's operations, as well as the possible derailment mechanism of the high-speed train, in light of the far-field (FF) earthquakes. This analysis reveals that the NF GMs in the bridge structure's seismic reactivity are considerable. Many high-speed train derailments are due to frequent wheel displacement, elevated wheels, and significant lateral motion. The data discovered in the field may give engineers vital information for calculating relevant situations and railroad engineering projects.

Health Monitoring of Storage Tanks Subject to Near-Field and Far-Field Earthquakes

Structural Health Monitoring (SHM) is a method to conserve the structures and monitor their stress and strain situation. Natural disasters, significantly earthquake could damage the water supply systems, including water tanks. The earthquake could conclude cavitation and water sloshing inside the underground water tank. On the other hand, it can cause human tragedy economically, socially, and ecologically. Therefore, useful and essential measures for repairing and utilizing the underground water tanks after the earthquake should be considered. This research aims to monitor the underground storage tanks subject to near-field and far-field earthquakes, considering the cavitation effect. In this article, the effect of earthquakes on the underground water tanks, considering the seismic behavior and cavitation effect of the underground tank, will be considered. For considering seismic behavior on the storage tanks and their reaction, the ANSYS software has been used to simulate and model them via the finite element method. After that, the prone places to the cavitation wherever the pressures are minus will be detected by the Monte Carlo method. The cavitation effect statistics were examined, and their placement is compared with the results obtained from the Monte Carlo method. The MATLAB codes have been used to make decisions for optimal smart sensor placement via the Monte-Carlo method. Moreover, to decrease the analysis time, the comparison method is taken into account. Finally, underground water tanks were loaded subjected to near-field and far-field earthquakes. The finite element result will be analyzed via the Monte Carlo method, and the best places for installing the smart sensors will be proposed.

On the Influence of the Vertical Earthquake Component on Structural Responses of High-Rise Buildings Isolated with Double Friction Pendulum Bearings

The double friction pendulum (DFP) bearing is adapted from the well-known single friction pendulum (SFP) bearing. This type of bearings has been widely used for structural vibration controls. The main advantage of the DFP is its capacity to accommodate larger displacements as compared with the SFP one. This paper aims to assess the effect of the vertical earthquake component on the seismic behaviour of a base-isolated high-rise building. In this respect, the mathematical model of the building subjected to earthquake excitations with an implementation of a DFP bearing system is established. The model presented herein considers earthquake excitations in horizontal (X and Y) and vertical (Z) directions. A series model of two friction elements is presented for the bearing, where the friction load of the bearing surface is governed by a modified Bouc-Wen model, which is dependent on the sliding velocity and the contact pressure. The numerical results of an example of a base-isolated 9-story steel building subjected to near-source and far-field earthquakes show the high effectiveness of the bearing system in reduction of the seismic response of the building, especially in the near-source region, as well as exhibit considerable effectiveness of the vertical earthquake component on the bearing and structural behaviour.

Structural analyses of self-centring-beam moment-frames under near-fault and far-field earthquakes

A self-centring-beam (SCB) is a new structural member with a capacity for recentring and deformation compatibility for moment-frames (MFs). This paper examines the lateral drift responses of SCB-MFs when subjected to the far-field (FF) record set, near-field pulse (NF) record set, and near-field no pulse (NP) record set. A series of 3-, 6-, 9-, and 12-storey SCB-MFs were modelled and analysed using centralized spring models in OpenSees software. Based on the observed differences in the experiments, a parametric analysis of the effect of the three design factors was conducted. The three design factors were initial stiffness, gap-opening moment, and maximum self-centring rotation at the beam ends. The analyses indicated that all of the SCB-MFs, except for 3-storey SCB-MFs, experienced an obvious increase in the inter-storey drift demand as the excitation was changed from the FF and NP to the NF records.

A study on effect of soil-structure interaction on performance of strong-back structural system subjected to near and far-field earthquakes

During the past years, researchers have developed ideas to thoroughly investigate the behavior of structural bracing systems. Accordingly, one of these emerging systems is the Strong Back Bracing System by which the inter-story drifts are maintained constant to prevent the occurrence of failure. Hence, due to the importance of the soil-structure interaction (SSI) and the type of soil underlying the structure, the SSI needs to be taken into account for seismic-resistant design. Accordingly, this paper deals with the seismic behavior of the structures equipped with the Strong Back Bracing System considering the soil-structure interaction (SSI) under near and far-field earthquakes. In this respect, 3, 6 and 12-story structures resting on stiff and soft soil (soil type II and IV) have been analyzed. The results indicate that the ratio of the inter-story drift in the case of soft soil for all structures has increased by 11.67% under near-field records and subjected to the far-field motions, this ratio has raised by 7.7% for the 12-story building. Moreover, the ratio of the residual drift of the 3, 6, and 12-story structures under the average of near-field earthquakes, has decreased and increased by 8.52 and 36.02 in the case of stiff and soft soils, respectively.

Simulation of the MW = 7.9 Gulf of Alaska earthquake on January 23, 2018, by the stochastic finite fault model

On the premise of constraining the seismogenic fault structure of a future large earthquake, we proposed using empirical equations to determine the length, width, seismic moment and slip distribution of a large seismogenic fault plane and using the stochastic finite fault model to predict future large earthquakes. The ground motion time histories and response spectra recorded by 12 seismic stations on bedrock during the MW = 7.9 Gulf of Alaska earthquake on January 23, 2018, were simulated. The simulation error determined by the average ratio of the simulated spectrum amplitude to the recorded spectrum amplitude varied between 1.08 and 0.92 in the period range of 0–10 s, and the standard deviation of the simulation error at different frequencies did not exceed 1; the 95% confidence interval also did not change significantly with the period. The above analyses show that our simulation results reflect the mean ground motion. To further discuss the reliability of predicting future large earthquakes by the stochastic finite fault model, we redistributed the initial rupture point and slip distribution on the seismogenic fault plane by the quasi-random method, and the simulation errors and simulation results of the redistribution model were similar to those of the previous model. Further research confirmed that our method for obtaining the seismic source parameters is viable and that the stochastic finite fault model for the prediction of future large earthquakes is reliable, especially for large far-field earthquakes. The seismic stations that we used are all situated on bedrock on one side of the fault and do not involve rupture directivity, i.e., the seismic wave pathways may be similar, so the simulation results are ideal. However, if the rupture directivity, different site conditions, surface topography and basin effects are considered, it will be necessary to amend the proposed method.

Seismic Response of RC Frames with a Soft First Story Retrofitted with Hysteretic Dampers under Near-Fault Earthquakes

Reinforced concrete (RC) frame structures with open first stories and masonry infill walls at the upper stories are very common in seismic areas. Under strong earthquakes, most of the energy dissipation demand imposed by the earthquake concentrates in the first story, and this eventually leads the building to collapse. A very efficient and cost-effective solution for the seismic upgrading of this type of structure consists of installing hysteretic dampers in the first story. This paper investigates the response of RC soft-story frames retrofitted with hysteretic dampers subjected to near-fault ground motions in terms of maximum displacements and lateral seismic forces and compares them with those obtained by far-field earthquakes. It is found that for similar levels of total seismic input energy, the maximum displacements in the first story caused by near-fault earthquakes are about 1.3 times larger than those under far-field earthquakes, while the maximum inter-story drift in the upper stories and the distribution and values of the lateral forces are scarcely affected. It is concluded that the maximum displacements can be easily predicted from the energy balance of the structure by using appropriate values for the parameter that reflects the influence of the impulsivity of the ground motion: the so-called equivalent number of cycles.

Increment of material usage in construction of four storey reinforced concrete building due to seismic design

Malaysia is fortunate because it is located outside the Pacific Ring-Fire region which is seismically active. However, it still exposes to earthquake hazard from Far-Field earthquake from neighbouring countries. In Peninsular, it is exposes to Sumatra-Andaman earthquake from Indonesia. In East Malaysia, to states namely as Sabah and Sarawak are expose to Philippines earthquake. Besides, Malaysia also experienced earthquakes from local faults such as Bukit Tinggi in 2007. On 5th June 2015, a moderate earthquake with Mw6.1 occurred in Ranau, Sabah which caused 18 fatalities. The same event also caused damage to 61 buildings around Ranau and Kundasang. For the sake of safety, construction of new buildings in Malaysia has to consider seismic design. This paper presents a study to evaluate the increment of construction materials used due to consideration of seismic design. A typical four-storey generic reinforced concrete school building had been used as model. This study adjusted the value of reference peak ground acceleration, α gR in modelling, analysis, and design process. The concrete grade was fixed as C30. Four soil types had been considered for all models with seismic design consideration. Findings from this study demonstrate that the consideration of seismic design caused the increment of steel reinforcement around 16% to 32% for beam and 1% to 14% for column. In term of cost of structural work, consideration of seismic design increases the cost in range of 2% to 5% compared to the nonseismic design. Therefore, it is worth for Malaysia to fully implement the seismic design in new development.

Seismic Analysis of Single Unit Tunnel Form Building Subjected to In-Plane Lateral Cyclic Loading Using Ruaumoko 2D Programme

Seismic effect to the tunnel form building (TFB) will vary depending on the location of the epicentre, magnitude and frequency of the seismic event. This effect can be mitigated by implementing a seismic analysis using the Ruaumoko 2D programme. The seismic analysis was conducted to examine the safety level of the TFB when it was subjected to 10 previous seismic events. The analysis emphasized the in-plane direction of lateral cyclic loading. The 10 selected seismic excitations were Pacoima Dam, El Centro North-South and East-West, Mexico City, Ranau, Lahad Datu, Kunak, Batu Niah, Manjung and Bukit Tinggi. The analysis results of tunnel form building (TFB) in terms of spectral displacements, earthquake excitations, pseudo-spectral acceleration and deformed shape of single unit tunnel form building obtained in this study. Based on these analyses, tunnel form building (TFB) can only withstand low seismic loading with far-field earthquakes. When subjected to a seismic load greater than 5 Richter Scale and near field excitation, tunnel form building will not safe to be occupied.