Subsequent Aftershocks Research Articles

Pseudo-dynamic tests of steel frame with disc spring self-centering energy dissipation braces under doublet earthquake and mainshock-aftershock sequence

To provide valuable insights into the seismic performance and self-centering behavior of self-centering braced systems, a 1/2-scale 3-story 1-bay steel frame equipped with disc spring self-centering energy dissipation braces (DS-SCBs) was designed, fabricated, and subjected to pseudo-dynamic testing. This testing encompassed various earthquake hazard levels, a doublet earthquake, and a mainshock-aftershock sequence. The experimental findings revealed the stable hysteretic response of the DS-SCB, with no observed degradation in stiffness or activation forces. Additionally, the test frame exhibited outstanding seismic performance, sustaining only confined damage under very rare earthquakes. Due to the presence of the DS-SCBs, the test frame performed commendable self-centering behavior, characterized by minimal residual deformations. Peak story drifts and floor accelerations under two earthquakes of the same hazard level were regarded as equivalent. Furthermore, the subsequent aftershocks exhibited no discernible impact on the seismic performance of the test frame. Floor acceleration spikes were observed at locations where the brace stiffness underwent changes or where adjacent stories moved in opposite directions. The steel frame equipped with DS-SCBs proved to be an attractive, low-damage alternative to conventional steel systems for the development of resilient urban areas.

Investigation of Liquefaction in Balaroa, Petobo, and Jonooge (Central Sulawesi, Indonesia) Caused by the 2018 Palu Earthquake Sequence

The liquefaction that occurred in the city of Palu on September 28, 2018, was caused by a series of significant earthquakes that took place in a relatively short time around 25 minutes after the main earthquake of magnitude 7.5. This event was followed by aftershocks of magnitudes 6.4, 6.2, and 6.1. The magnitude 6.2 aftershock occurred at 10.16 UTC, while the magnitude 6.1 aftershock occurred at 10.25 UTC. These were both located very close to the liquefaction locations in Balaroa, Petobo, and Jono Oge. We investigated the mainshock and the three aftershocks using the NCEER method based on Vs30 measurements and data from the drill liquefaction locations at Balaroa, Petobo, and Jono Oge. We found that the liquefaction was not only caused by the main earthquake but also by the subsequent aftershocks that occurred within 25 minutes after the mainshock.

Numerical Simulation on Aftershock Fragility of Low-Ductility RC Frames under Different Mainshock-Induced Damage Conditions

Aftershocks typically occur multiple times following major earthquakes, potentially inflicting enhanced damage. It is crucial to quantify the impact of aftershocks on the seismic performance of low-ductility reinforced concrete (RC) frames with different mainshock-induced damage states. For this purpose, this study investigated the aftershock fragility of low-ductility RC frames with different damage states induced by mainshocks via the case study of a six-story RC frame without a seismic design. The models of the low-ductility RC frames with different damage states were established via OpenSees software 2.5.0. Incremental dynamic analysis (IDA) was carried out to establish damage states induced by a mainshock. Then sixty-five real aftershocks were inputted to analyze the structures with different main-induced damage states. Aftershock fragility curves of low-ductility RC frame structures with different damage states were obtained. The results show that the exceedance probability of the low-ductility RC frame with mainshock-induced damage is higher than that of the intact low-ductility structure, corresponding to each limit state. The severity of the mainshock-induced damage directly amplifies the demand for a low-ductility RC frame in the subsequent aftershocks. As the mainshock-induced damage increases, the exceedance probability of the low-ductility RC frame undergoing more severe damage under aftershocks significantly increases.

Midcrustal moderate-size earthquake occurrence in paleovolcanic structures off Jeju Island, South Korea

A series of midcrustal moderate-size earthquakes occurred in the Korean Peninsula recently. A midcrustal ML4.9 strike-slip earthquake with a fault-plane strike in N-S occurred on December 14, 2021 at the southwestern offshore region of Jeju Island, South Korea. The fault plane orientation and slip sense (faulting mechanism) hardly conform with the regional stress field. The deep focal depth and N-S directional strike-slip motion require transient changes in the medium properties and stress field. Strong ground motions of the midcrustal earthquake induce preferential dynamic stress changes in NE-SW direction, triggering subsequent aftershocks in NE-SW-directional adjacent faults. Both the static and dynamic stress changes caused by the mainshock contribute to the aftershock sequence. The number and focal depths of aftershocks decrease with distance from the mainshock. The different fault-plane orientations between the mainshock and aftershocks suggest earthquake nucleations in independent fault structures. The mainshock occurred in aseismic midcrustal paleovolcanic structure on the outskirt of a high seismicity region. The ML4.9 earthquake suggests possible nucleation of earthquake in seismically-inactive paleotectonic structures, successively incurring aftershocks conforming to the ambient stress. The mainshock and aftershocks suggest that paleotectonic structures may behave as source structures to spawn earthquakes.

Influence of clay content on repeated liquefaction resistance of sand using element test

Soil liquefaction is a major concern because of its potential to cause building collapse, roadbed settlement, and sand eruptions. Field investigations have shown that clayey sand, when liquefied during mainshock, may undergo multiple liquefaction events during the subsequent aftershocks. Although previous research has primarily focused on the initial liquefaction event in clayey sand, research on the mechanism responsible for repeated liquefaction is limited. Consequently, a series of cyclic triaxial experiments are conducted on sand with varying clay contents, and these samples are subjected to various earthquake sequences. The primary objective of this study is to evaluate the cyclic behavior of sandy soil with clay content and analyze its repeated liquefaction resistance under different load sequences. A comprehensive assessment is conducted to understand the evolution of the repeated liquefaction resistance. The test results indicate that clayey sand exhibits the lowest liquefaction resistance during the second liquefaction event. Repeated liquefaction is dominated by stress-induced anisotropy at earlier events and relative density at the final events.

Robustness of remediation measures against liquefaction induced manhole uplift under mainshock-aftershock sequence

Earthquakes generally consist of one mainshock and subsequent aftershocks. Although effects of aftershocks following the mainshock on surface structures has been studied extensively, similar studies on underground structures are rarely reported in the literature. With the fast advances in underground space development, robustness of remediation measures against underground structures uplift induced by soil liquefaction shall be examined to ensure their functioning subject to not only the mainshock but also the subsequent aftershocks. This paper studies the uplift behaviour of a conventional manhole subjected to the mainshock-aftershock sequence. It was found that, in the ground that becomes liquefied during the mainshock, manholes become more vulnerable when faced with aftershocks. Due to this reason, some of the previously proposed remediation measures, such as increasing the manholes’ self-weight, roughening the sidewalls, were examined using centrifuge modeling in this study. It was found that such measures had little effect in the aftershocks despite their effectiveness in the precedent mainshock. In contrast, the methods that mitigates manhole uplift by enhancing the manhole’s base permeability, demonstrated better performance in the aftershock than in the mainshock, indicating its promising application potential in future mitigation design.

Exposure to earthquakes and development of ischemic heart disease

BackgroundThe evidence regarding the effect of earthquake exposure on the development of cardiovascular diseases is limited. This study evaluated the association between the 2016 Gyeongju earthquake, which had a magnitude of 5.8, and over 600 subsequent aftershocks occurring within a year in Korea, with the development of ischemic heart disease (IHD) among residents of Gyeongju.MethodsTen years (2010–2019) of medical records from a randomly selected cohort of residents (n = 540,858) in Gyeongju and 3 control cities were acquired from the national health insurance service. Employing difference-in-difference and meta-analyses, the risks of IHD development of Gyeongju residents before (reference: Sep 2014 to Aug 2015; period 1: Sep 2015 to Aug 2016) and after (period 2: Sep 2016 to Aug 2017; period 3: Sep 2017 to Aug 2018; period 4: Sep 2018 to Aug 2019) the earthquake were estimated.ResultsThe monthly average incidence of IHD in Gyeongju was 39.5 persons (per 1,000,000) for reference period and 38.4 persons for period 1. However, the number increased to 58.5 persons in period 2, and 49.8 persons in period 3, following the earthquake. The relative risk (RR) [with a 95% confidence interval] of developing IHD among Gyeongju residents increased by 1.58 times (1.43, 1.73) in period 2, 1.33 times (1.21, 1.46) in period 3, and 1.15 times (1.04, 1.27) in period 4, in comparison to both the control cities and the pre-earthquake reference period. The increase in RR was particularly noticeable among women, adults aged 25–44, and individuals with lower incomes.ConclusionsThe major earthquake in Korea was associated with an increase in the development of IHD among local residents. Individuals exposed to earthquakes may benefit from cardiovascular health surveillance.

Deep-Seated Fluids in Thermal Waters Before and After the 2016 Kumamoto Earthquakes.

Noble gases, oxygen-hydrogen isotope ratios, and ion compositions were measured at three sampling points (KUM, OTN, and ASO) from December 2013 to July 2021. The 3He/4He values at the three sampling points remained stable in the range of 3-4 Ra throughout the observation period, suggesting that the supply of deep-seated gases to the aquifer was stable. The 4He/20Ne values of KUM and OTN indicate that the supply of surface-source fluids to the aquifer decreased relative to that of deep-seated fluids at KUM and OTN. In contrast, in the ASO site, both the surface- and deep-seated fluids supplied to the aquifer were stable. The δD-δ18O relationship indicated the supply of deep-seated water to the KUM and OTN aquifers but not to the ASO aquifer. Nevertheless, the δD-δ18O relationship remained stable throughout the observation period, suggesting that the supply of deep-seated water to the three stations was stable. The Li/Cl and 1/Cl relationships for the three sampling points were plotted within a narrow range throughout the observation period, suggesting that the groundwater recharge was stable. Neither spikes nor step changes owing to the 2016 Kumamoto earthquake were observed in any of the data. These results indicate that the KUM and OTN aquifers are constantly supplied with deep fluids from the fluid-rich zone beneath the Kumamoto region, and that only deep-seated gas was supplied to the ASO aquifer. We also confirmed that these supply conditions were unaffected by the 2016 Kumamoto earthquake or the subsequent aftershock activity.

Caprock integrity at Çanakkale-Tuzla hydrothermal system inferred from magnetotelluric modeling using particle swarm optimization

The impermeable caprock within a geothermal system serves the purpose of effectively sealing the reservoir, resulting in the elevation of both pressure and temperature. This sealing mechanism plays a crucial role in the long-term preservation of the system, while also contributing to its overall sustainability. Caprock failure subsequent to seismic activity near a geothermal site can lead to the permeation of the caprock structure, resulting in diminished sealing capabilities and a decline in the reservoir temperature. Additionally, this process alters the geochemical composition of the water by creating a hydrothermal mixture zone that disrupts the resistivity structure of the caprock, which is typically characterized by low resistivity values due to its substantial clay content and mineral alteration. This study focuses on investigating the integrity of the caprock at ơnakkale-Tuzla geothermal field in Turkey, where the water temperature and conductivity were reported to have decreased after a moderate magnitude earthquake and subsequent aftershocks. For this purpose, we performed magnetotelluric (MT) measurements, a method known for its sensitivity to geochemical reactions. These measurements were conducted along two parallel profiles that encompassed a total of 32 stations. Particle swarm optimization (PSO) technique was employed to overcome subtle difficulties associated with conventional inversion methods when modeling the MT data of complex formations. This is the first study that overcomes the difficulties emanating from the caprock failure by modeling MT data using PSO. Our modeling approach produced resistivity images that we interpreted as the signature of the failed caprock following the earthquake at the study site. Our results appear to confirm the documented geochemical changes or hydrothermal mixture zone about caprock structure.

Probabilistic framework for seismic resilience assessment of transmission tower-line systems subjected to mainshock-aftershock sequences

Immediate damage to electricity transmission systems after strong earthquakes can significantly cause widespread power outages and impede maintenance activities. Whereas previous seismic resilience assessments have investigated comprehensively the recovery capability of structures under isolated mainshocks, the effect of aftershocks has received less attention. This paper introduces a probabilistic framework for resilience assessment incorporating the effect of aftershocks and utilizes it to investigate the seismic performance of a transmission tower-line system (TTLS) under mainshock-aftershock (MSAS) sequences. Exceedance probabilities for different damage states of the TTLS are analyzed using fragility curves. Multiple decision variables (including functionality loss, recovery time, recovery function and resilience indicator) are subsequently calculated to quantify the effect of aftershocks. Meanwhile, the seismic resilience of the TTLS is further assessed by considering the uncertainties associated with those decision variables. The results reveal that aftershocks exert a significant influence on the seismic resilience of the TTLS, particularly when it experiences minor or moderate damage following the mainshocks. However, as the damage to the TTLS worsens due to larger mainshocks, the role of subsequent aftershocks becomes comparatively less influential. The proposed framework provides valuable insights for infrastructure systems before and after earthquake, effectively mitigating the adverse effects of sequential earthquakes.

Image-based preliminary emergency assessment of damaged buildings after earthquake: Taiwan case studies

Structural collapses that occur during earthquake disasters and subsequent aftershock periods often result in high numbers of fatalities. Rapid preliminary building evaluations are necessary to determine whether buildings are safe for continued occupation. Currently, structural damage is evaluated manually in on-site, expert inspections that are time-intensive, uncertain, inconsistent, and heavily reliant on the experience of the expert team. Therefore, TL-EfficientNet, which combines EfficientNet and Transfer Learning, was used in this research to create an image recognition system for use in an Emergency Assessment Damaged Building Model (EADBM). The integration of hybrid models and building safety assessments presents a pioneering approach to replace manual damage assessments. This system classifies images of structural members into four damage levels based on Taiwan's emergency assessment code, then calculates a structural damage index (SDI) based on the assessed level of damage to columns and structural walls. The accuracy and overall F1 score obtained by the proposed model were both high, with the accuracy of validation results reaching 97% and 91% for columns and structural walls, respectively. Furthermore, the model was applied to two actual damaged building case studies, with the highest accuracy and overall F1 score for columns reaching 90% and 95%, respectively. The SDI value indicates that the first case study was correctly classified as dangerous, while the second case study was categorized as restricted. This model has been proven to overcome subjective and inconsistent results associated with manual assessment, achieving rapid and accurate preliminary assessment in post-earthquake building inspections and safety evaluations.

Understanding fabric evolution and multiple liquefaction resistance of sands in the presence of initial static shear stress

Recent field observations have shown that mainshock and subsequent aftershock events can induce multiple-liquefaction events, in which soil liquefies several times at the same site. However, the fundamental mechanism of multiple liquefaction in most previous studies is under level ground conditions, and the cyclic loading condition is symmetric under such conditions. In this study, we conduct 3D DEM simulations of multiple-liquefaction processes considering initial static shear stress. 14-sphere clumped models are used to reconstruct the realistic grain shape of Toyoura sand particles. Cyclic liquefaction and reconsolidation tests are carried out alternately five times. The soil samples with various initial static shear stresses are sheared up to different maximum shear strains in each liquefaction stage. We investigate the liquefaction behavior and volumetric compression during multiple-liquefaction stages considering initial static shear stress. In addition, the evolution of contact-based fabrics, including coordination number (Z) and degree of fabric anisotropy (ac), are analyzed during the whole liquefaction and reconsolidation tests. Furthermore, we establish the relations among contact-based fabrics (Z and ac), volumetric compression and liquefaction resistance. The results reveal that in stress reversal cases, the maximum shear strain is the governing factor that influences the multiple-liquefaction resistance. Conversely, the static shear stress becomes the dominant factor affecting the multiple-liquefaction resistance in non-stress reversal cases. Moreover, changes in multiple-liquefaction resistance are attributed to the microstructure of soils represented by Z after reconsolidation.

Stochastic dynamic and reliability analysis of AP1000 nuclear power plants via DPIM subjected to mainshock-aftershock sequences

Earthquakes usually consist of a mainshock and a series of aftershocks, both of which are random. The mainshock can damage structures, and the subsequent aftershocks may cause further damage. However, no studies have considered the effects of stochastic seismic sequences on nuclear power plants (NPPs). We propose a new framework to analyze the stochastic dynamic response and dynamic reliability of AP1000 NPPs. First, stochastic mainshock-aftershock sequences are generated by combining a physical random function model, the narrowband harmonic group superposition method and the copula function. Then, the effects of aftershocks on NPPs are highlighted using acceleration and displacement as response indices and the tensile damage ratio (TDR) and plastic strain as damage indicators. Finally, probabilistic information and reliability of NPPs are obtained based on the direct probability integration method (DPIM) and the absorbing condition method (ACM). The results show that the dynamic response is larger for seismic sequences than a single mainshock, and seismic sequences cause more damage to the NPPs. When the peak ground acceleration (PGA) increases, the effect of the aftershock becomes more pronounced, and the response of the NPP becomes more random. Moreover, aftershocks reduce the reliability of NPPs, and the degree of reduction is related to the thresholds.

Evaluating structural failure probability during aftershocks based on spatiotemporal simulation of the regional earthquake sequence

Engineering structures damaged in a mainshock become much more vulnerable to the subsequent aftershocks. Estimating the aftershock hazard and the subsequent structural fragility is of significant interest for post-mainshock decision-making. This study introduced the spatiotemporal epidemic-type aftershock sequence (ETAS) model to simulate the regional aftershock sequence and developed a framework for evaluating the aftershock-induced failure probability of structures. The procedure includes: aftershock sequence modeling, aftershock hazard estimation, aftershock ground motion generation, fragility analysis, and structural damage probability estimation. The procedure can quantitatively estimate the failure probability of a mainshock-damaged structure during aftershocks considering the influence of spatial location of aftershock and time interval between the mainshock and aftershock. As an example, the 2021 Yangbi earthquake sequence was fitted by the ETAS model, and the failure probability of a local 5-story concrete frame structure was analyzed. The variation of the failure probability of the structure with the increase of time was investigated.

Analysis of Multistorey RCC Frame subjected to Mainshock and Aftershock Earthquake

Abstract: Structure analysis and design are significantly influenced by earthquake. It is believed that seismic evaluation is required for the viability and serviceability of both present and future building structures. When a structure's base is subjected to a certain type of ground motion, a time history analysis is performed to examine the dynamic reaction of the structure at each time interval. The near-field earthquake ground motion verification may have specific impacts for both forward and backward directivity. The initial's velocity and displacement motions, respectively, exhibit pulse and fling-step characteristics. Therefore, it is crucial to assess how well structures built solely to withstand the primary shock would work through future aftershocks. Using modern seismic protection systems, such as base isolations or / and supplemental dampening devices, that significantly reduce building damages during main shocks and their related aftershocks is one of the appropriate solutions to this issue. Due to changes in both static and dynamic stress that take place during the earthquake process, aftershock events are set off by the primary shock. In order to better understand the ground motion features of a sizable collection of mainshock and subsequent aftershock ground motion data recorded in accelerograph stations around the region, this study reviews pertinent literature in the field. The G+9 RCC building will be used in this study to conduct a time history analysis of the mainshock and aftershock data of the Chamoli earthquake provided by the Centre for Engineering Strong Motion Research Ground Motion Database. For designing purposes, the IS 456-2000 code is taken into consideration. Live loads are measured in accordance with IS 875-part 1, and seismic zone IV is selected for analysis in accordance with IS 1893-2016. Storey drift, base shear, joint reactions, and storey displacement are just a few of the variables that can have an impact on how well a building performs. Since each of these variables has a significant impact on how a structure responds to seismic loads, they are also taken into account when evaluating the results.

Toppling of a Trona Pinnacles Spire following the Mw 5.5 Ridgecrest Aftershock of June 2020

AbstractThe 2019 Mw 7.1 Ridgecrest California earthquake rupture passed within 4 km of the Trona Pinnacles, a large group of tufa rock pillars. Reconnaissance following the Ridgecrest mainshock documented fresh damage to several of the Pinnacles. Repeated aerial photogrammetric surveys also documented damage during subsequent aftershocks. Here, we describe the photogrammetric data with emphasis on a specific rock spire that toppled during an Mw 5.5 aftershock. We calculate the volumes of the intact spire and of its subsequent debris. To explore the utility of the pinnacles as fragile geologic features for constraining past earthquake shaking intensity, we calculate the quasi static, horizontal acceleration required to break the spire at its base. We also examine the response of this feature to observed shaking using a dynamic model of the spire. In this case, we find that the quasi-static estimate provides a conservative maximum constraint on fragility. The dynamic model of the spire suggests that shaking during the Mw 7.1 mainshock likely generated tensile stresses in excess of the spire’s bulk strength, thereby making it vulnerable to collapse in subsequent aftershocks.

The role of interplate locking on the seismic reactivation of upper plate faults on the subduction margin of northern Chile

Quaternary deformation in the northern Chile forearc is controlled by trench parallel shortening along reactivated Mesozoic faults. Dextral strikes-slip is expressed in NW–SE striking faults of the Atacama Fault System, and reverse displacement dominates in E–W faults. This deformation results of the convergence in a concave-seaward continental margin. On September 11th, 2020, a Mw 6.3 earthquake and its subsequent aftershocks took place in the coastal region of northern Chile, revealing the reactivation of the deepest segment of a WNW–ESE striking upper plate fault. The reactivation of this fault occurred after the Mw 8.1 Iquique earthquake, and it seems to be connected to a N–S interplate locking segmentation of the plate margin, which is clearly shown by the locking pattern before the Iquique earthquake. This poses the question of how heterogeneous locking influences upper plate seismicity and how it relates to trench-parallel shortening.

Incorporation of post-earthquake fire (PEF) and subsequent aftershock for performance analysis of steel buildings

The advancements in analysis and design approaches considering the seismic loads have helped safeguard buildings against structural failure and collapse. However, design objectives should also consider the associated effects and performance evaluation incorporating the sequential effects. Improving the performance of buildings at both the asset and community levels is now of major interest in the field of structural engineering. This research addresses the advancement toward this goal by incorporating post-earthquake fire and aftershock to multi-hazard design methodology. A set of mid-rise buildings – 3-, 9-, and 20-story moment resisting steel frames, characteristic of those found in rapidly growing metropolitan areas of US, are selected for the study considering the relative vulnerability to post-earthquake fire. The analyses of the responses are based on advanced finite element simulation methods/techniques and corresponding approaches. ABAQUS/CAE is primarily employed for the simulation and analysis. The effects of fire are thoroughly studied from the literature and considered explicitly, and the analysis is performed for a complete cycle of main shock (full-intensity) –fire- aftershock (reduced intensity) earthquake. The research commences with the investigation of the effects of modeling approach-- using beam element and using solid element with slab, on Post Earthquake Fire (PEF) study of a single room model. At the end of a complete sequence, the model developed using 3D solid elements are found to underestimate the stiffness loss by around 15% compared to those developed using 2D beam elements. The behaviors of selected steel moment resisting frame buildings then simulated with PEF are investigated to quantify the overall performance behavior of the building system. Inter-story Drift Ratio (IDR) and Stiffness Degradation over the complete sequence of events are chosen as the damage measures. The same approach is applied to a real building in California and the performance behavior is studied. All the building systems studied show the significant damages and change in behavior after incorporating the fire and aftershock. In all building sets, the stiffness loss (global) due to mainshock alone (2% to 10% in the cases studied) is very less as compared to the stiffness loss due to fire alone (6% to 15%) and aftershock (10% to 25%) alone.

Seismic Reflection Images of Possible Mantle-Fluid Conduits and Basal Erosion in the 2011 Tohoku Earthquake Rupture Area

Multi-channel seismic reflection and sub-bottom profiling data reveal landward-dipping normal faults as potential conduits for mantle-derived fluids in the coseismic slip area of the 2011 Tohoku earthquake (Mw9.0). Normal faults below the helium isotope anomaly sites appear to develop through the forearc crust (i.e., the seafloor sedimentary section and Cretaceous basement) and to evolve to lower dip angles as extension progresses deeper, potentially extending down to the mantle wedge, despite their intermittently continuous reflections. The faults are characterized by high-amplitude, reverse-polarity reflections within the Cretaceous basement. Moreover, deep extension of the faults connecting to a low-velocity region spreading from the Cretaceous basement into the mantle wedge across the forearc Moho suggests that the faults are overpressured by local filling with mantle-derived fluids. The locations of the normal faults are roughly consistent with aftershocks of the 2011 Tohoku earthquake, which show normal-faulting focal mechanisms. The 2011 Tohoku mainshock and subsequent aftershocks can lead the pre-existing normal faults to be reactive and more permeable so that locally trapped mantle fluids can migrate up to the seafloor through fault fracture zones. The reactivated normal faults may be an indicator of shallow coseismic slip to the trench. Locally elevated fluid pressures can decrease the effective normal stress for the fault plane, facilitating easier slip along the fault and local tsunami. The landward-dipping normal faults developing from the seafloor down into the Cretaceous basement are predominant in the middle slope region of the forearc. A possible shear zone with high-amplitude, reverse-polarity reflections above the plate interface, which is almost localized to the middle slope region, suggests more intense basal erosion of the overlying plate in that region.

Effectiveness of damaged viscoelastic dampers in seismic protection of structures under main shocks and aftershocks

It has been demonstrated through uniaxial reversal loading tests that damaged viscoelastic dampers are to some extent still able to possess stiffness and energy dissipation capabilities. Based on past performance test results, some analytical models originating from the fractional derivative method have been provided to account for the design, beyond-design, and residual performances of viscoelastic dampers. In this study, these models are employed for modelling the actual dynamic behavior of supplemental viscoelastic dampers installed at different stages in the numerical model of a practical high-rise steel building. Scenarios of main shocks and subsequent aftershocks are assumed as seismic inputs. The numerical results indicate that, even though viscoelastic dampers suffer damage during main shocks, the damaged dampers are still effective in reducing the structural acceleration and displacement responses compared with the undamped structural responses. It is assumed in the analytical model of viscoelastic dampers that the shear force will be immediately reduced to the beyond-design performance without hardening behavior when suffering damage at the beginning half-cycle. Thus, the damped structural acceleration control performance at that instant, particularly of the floors installed with the damaged dampers, might not be satisfactory but still superior to the undamped structural performance. Although some doubts are clarified in this study, it is emphasized that damaged viscoelastic dampers must still be appropriately repaired or even replaced before the next major earthquake occurs.