Seismic Mitigation Research Articles

Experimental Study of Seismic Isolated Structures with Sliding Implant-Magnetic Bearings

ABSTRACT Sliding implant-magnetic bearing (IMB) is a new type of seismic isolators that benefits from its adaptive energy-dissipation behavior. In order to assess the performance of the sliding IMB for seismic protection, a complete shaking table test on the base-isolated structure is reported in the present paper. Tri-directional-recorded earthquake ground motions and mono-directional artificial earthquake ground motions pertaining to both site classes II and III are employed to drive structural vibration in the laboratory experiment, respectively. Seismic mitigation of the base-isolated structure with respect to dynamic characteristics, story accelerations, inter-story drifts, horizontal torsions, and local strains is addressed. Experimental study shows expected results that the base-isolated structure with sliding IMBs attains more profitable mitigations on story accelerations and inter-story drifts under earthquake ground motions pertaining to the stiff soil site than those pertaining to the soft soil site. Significant mitigations on horizontal torsion of the structure and on local strain at the column bottom are attained as well. In addition, seismic performance of sliding IMBs during the shaking table test is assessed. It is revealed that the isolators exhibit satisfactory energy-dissipation capacity and excellent frictional behavior, and maintain good working state during the entire experimental test.

Nonlinear dynamic analysis of the bridge bearing and genetic algorithm–based optimization for seismic mitigation

Seismic mitigation for bridges by the specific bearing with highly elastoplastic dissipaters is very important to ensure safety of superstructures exposed to earthquakes. To study the lateral vibration of the bridge bearing, a nonlinear dynamic model is developed while thoroughly considering highly nonlinear mechanical properties of the bearing in this article. The generalized- α method is specifically adapted to solve the nonlinear equations. Moreover, nonlinear behavior of the bearing is fully incorporated through direct path-following of the practical experimental hysteresis curve. The proposed method is validated through careful comparison between the dynamic simulation and the quasi-static experimental results. Mechanical responses of the bridge-pier system under earthquake excitations can be calculated in a more reliable manner. On this basis, a parametric optimization model involving several key parameters of the bearing-pier system is developed. The optimization problem is solved by the genetic algorithm as the searching tool. Numerical examples show that mechanical responses of the bridge-pier system subjected to the earthquake excitations can be effectively mitigated after parametric optimization. The extensive applicability of the proposed method is validated through finding the optimized parameters for the bearing when multiple different earthquakes are considered. Moreover, the accumulative energy absorption of the bearing is also considered to enhance the seismic performance of the bearing. This work provides a reliable way of dynamic performance prediction and seismic mitigation study of nonlinear bridge bearing under earthquake excitations given any complex experimental hysteresis curve.

3DGIS representation for supporting seismic mitigation policies at urban scale: The case study of Lisbon

Abstract The structural capacity of buildings to guarantee acceptable safety levels during and after earthquakes has significant influence on community and urban resilience. The paper presents the implementation in the Geographic Information System (GIS) of the data related to the expected seismic damage scenarios for some existing residential mixed masonry-reinforced concrete buildings located in Lisbon area. At city scale, such kind of representation can effectively support the seismic risk management including the design of mitigation policies. In fact, the spatial representation of results provides clear and global overview of the area under analysis, understandable not only to scientist and engineers, but also to the city councils and population. Damage scenario are defined on basis on fragility curves computed analytically through a nonlinear static approach by focusing the attention only to the in-plane global response and considering also the aggregate effect. The application to Lisbon city shows that the expected level of the damage consequent to the code action is high for the structural typology under investigation.

Numerical verification of variable friction cladding connection for multihazard mitigation

The motion of cladding systems can be leveraged to mitigate natural and man-made hazards. The literature counts various examples of connections enhanced with passive energy dissipation capabilities at connections. However, because such devices are passive, their mitigation performance is typically limited to specific excitations. The authors have recently proposed a novel variable friction cladding connection capable of mitigating hazards semi-actively. The variable friction cladding connection is engineered to transfer lateral forces from the cladding element to the structural system. Its variation in friction force is generated by a toggle-actuated variable normal force applied onto sliding friction plates. In this study, a multiobjective motion-based design methodology integrating results from the previous work is proposed to leverage the variable friction cladding connection for nonsimultaneous wind, seismic, and blast hazard mitigation. The procedure starts with the quantification of each hazard and performance objectives. It is followed by the selection of dynamic parameters enabling prescribed performance under wind and seismic loads, after which an impact rubber bumper is designed to satisfy motion requirements under blast. Last, the peak building responses are computed and iterations conducted on the design parameters on the satisfaction of the motion objectives. The motion-based design procedure is verified through numerical simulations on two example buildings subjected to the three nonsimultaneous hazards. The performance of the variable friction cladding connection is also assessed and compared against different control cases. Results show that the motion-based design procedure yields a conservative design approach in meeting all of the motion requirements and that the variable friction cladding connection performs significantly well at mitigating vibrations.

Seismic response mitigation of building structures with a novel vibro-impact dual-mass damper

This paper presents a comprehensive study on seismic response mitigation of building structures enabled by a novel vibro-impact dual-mass damper (VIDM). VIDMs consist of a linear oscillator and a nonlinear oscillator with impact surfaces between these two oscillators. The working principle of VIDMs is first presented via the equations of motion and the impact model of the device-attached system. The experimental studies of VIDM are subsequently carried out on a three-story steel frame structure with different column layouts. Test results show that the VIDM can exhibit strong robustness against structural frequency change and does not cause the adverse effect of excessively large structural acceleration as conventional vibro-impact-type devices do. Based on the validated numerical model, additional comparative studies under impulsive and seismic excitations are performed. Compared with tuned mass damper and cubic nonlinear energy sink, dual-mass damper and VIDM both show energy robustness and frequency robustness but the latter is preferred with a much smaller stroke demand. Therefore, the VIDM demonstrates great potential as an effective control strategy for seismic response mitigation of building structures.

Predicting Stability of a Prototype Unbonded Fiber-Reinforced Elastomeric Isolator by Finite Element Analysis

Unbonded fiber-reinforced elastomeric isolator (U-FREI) is an improved device for seismic mitigation of low-rise buildings. The horizontal force — displacement behavior of U-FREI is nonlinear due to rollover deformation and the horizontal stiffness is a function of both vertical load and horizontal displacement. In this paper, stability of a prototype U-FREI is studied based on the dynamic response utilizing finite element (FE) analysis. Furthermore, the horizontal response of the isolator is also evaluated under the design vertical load and increasing horizontal displacement up to [Formula: see text] [Formula: see text] is the total thickness of rubber layers) to observe the rollout instability.

Vibration Attenuation and Amplification of One-Dimensional Uncoupled and Coupled Systems with Optimal Metafoundations

Finite locally resonant metafoundations represent an innovative solution for structural seismic response mitigation based on their filtering capabilities at selected frequency ranges. They inherit the filtering properties of periodic foundations and bands in which response amplitudes are reduced, the so-called attenuation zones. Nonetheless, other bands of vibration-induced resonances amplify the components of superstructure response and are generally named nonattenuation zones. Both frequency bandwidths and amplification depend on the dynamic properties of metafoundations and superstructures as well as their coupling. Thus, in order to shed light on the mechanisms of seismic mitigation of coupled systems endowed with optimal metafoundations, this paper explores both elastic uncoupled and coupled unit-cell chains in the frequency domain based on the analysis of various transfer functions. Moreover, to address uncertainty at the excitation level, time history analyses are performed with a set of natural accelerograms that characterize operating basis earthquakes; thus, response contributions from both attenuation zones and nonattenuation zones can be distinguished by relating response variances to peak responses. Eventually, the attenuation effects of optimal metafoundations, frequency shift of superstructures due to unit cells of metafoundations, and coupling of both attenuation zones and nonattenuation zones are analyzed in depth.

Seismic vulnerability evaluation of educational buildings of Mymensingh city, Bangladesh using rapid visual screening and index based approach

Purpose Seismic vulnerability evaluation of various public structures, especially school buildings, is very crucial for designing hazard mitigation initiatives in seismic prone areas. The city of Mymensingh is at great risk of earthquake because of its geographical location, geological structure and proximity to active faults. The city is famous for its ancient and renowned educational institutes that need to be evaluated for understanding the seismic performance of the building during an earthquake. This study aims to evaluate the seismic vulnerability of educational buildings of Mymensingh city using rapid visual screening (RVS) and index based approach. Design/methodology/approach RVS procedure includes field survey and secondary source assessment for evaluating structural vulnerability attributes. Analytical hierarchy process is applied to develop an index focusing on systematic attributes of vulnerability based on expert opinions. Then, a composite vulnerability map is developed combining both structural and systematic vulnerability score providing an equal weight. Findings This study evaluates the seismic vulnerability of 458 educational buildings of Mymensingh city and the result shows that 23.14% educational building has high, 46.29% has moderate and 26.86% has moderately low and only 3.71% buildings has the low seismic vulnerability. This study expected to be helpful in resource targeting and prioritizing seismic hazard mitigation activities for education buildings of Mymensingh city. Originality/value This study endeavors to present a comprehensive vulnerability assessment method by integrating RVS and index based approach that incorporates both structural and systematic dimensions of vulnerability. The result is expected to be helpful in the formulation of disaster prevention policy for vulnerable educational buildings and development of the earthquake-resistant building codes for the new building construction in Mymensingh city.

Effect of rigid connection to an asymmetric building on the random seismic response

Connection of adjacent buildings with stiff links is an efficient approach for seismic pounding mitigation. However, use of highly rigid links might alter the torsional response in asymmetric plans and although this was mentioned in the literature, no quantitative study has been done before to investigate the condition numerically. In this paper, the effect of rigid coupling on the elastic lateral-torsional response of two adjacent one-story column-type buildings has been studied by comparison to uncoupled structures. Three cases are considered, including two similar asymmetric structures, two adjacent asymmetric structures with different dynamic properties and a symmetric system adjacent to an adjacent asymmetric one. After an acceptable validation against the actual earthquake, the traditional random vibration method has been utilized for dynamic analysis under Ideal white noise input. Results demonstrate that rigid coupling may increase or decrease the rotational response, depending on eccentricities, torsional-to-lateral stiffness ratios and relative uncoupled lateral stiffness of adjacent buildings. Results are also discussed for the case of using identical cross section for all columns supporting each plan. In contrast to symmetric systems, base shear increase in the stiffer building may be avoided when the buildings lateral stiffness ratio is less than 2. However, the eccentricity increases the rotation of the plans for high rotational stiffness of the buildings.

Ships and air guns reduce social interactions in humpback whales at greater ranges than other behavioral impacts

Understanding the interactions between human activity in the ocean and marine mammals is a fundamental step to developing responsible mitigation measures and informing policy. Here, the response of migrating humpback whales to vessels towing seismic air gun arrays (on or off) was quantified as a reduction in their likelihood of socially interacting (joining together). Groups were significantly less likely to participate in a joining interaction in the presence of a vessel, regardless of whether or not the air guns were active. This reduction was especially pronounced in groups within a social environment that favored joining, that is, when singing whales or other groups were nearby. Seismic survey mitigation practices are designed primarily to prevent damage to whales' hearing from close-by sources. Here, we found potentially detrimental behavioral changes at much greater ranges, and much lower received levels, than those used for current mitigation recommendations.

Effectiveness of Exhibits Fixed by Nylon Gut in the Museum for Seismic Disaster Mitigation

Effectiveness of Exhibits Fixed by Nylon Gut in the Museum for Seismic Disaster Mitigation

A probabilistic seismic hazard assessment of southern Peru and Northern Chile

Southern Peru and northern Chile (17–30°S, 67–74°W) make up a seismically active region due to the convergence of the Nazca Plate and the South American Plate. The region has experienced a number of destructive earthquakes and tsunamis over the past few centuries, which have caused loss of human life and significant damage to infrastructure, highlighting the importance of seismic hazard assessment in the region. In fact, a reliable seismic hazard assessment is critical for developing policies for seismic hazard mitigation and risk reduction. In this study, we performed a probabilistic seismic hazard assessment (PSHA) of the study area based on an earthquake catalog that was very carefully analyzed. In earlier studies, we demonstrated that inappropriate treatment of the earthquake catalog can result in a serious bias in evaluations of seismicity parameters (e.g., a bias of up to 42% in the “b” parameter of the Gutenberg–Richter law). To address this issue, we compiled a homogenous earthquake catalog consisting of 39,977 events during the 1513–2016 period and accounted for site-specific local effects by developing site-specific scaling relationships between different measures of magnitude (e.g., mb, Ms, MD) and moment magnitude (Mw). The study area was subdivided into 15 seismogenic zones, accounting for site-specific seismicity patterns. The parameters “a” and “b” of the Gutenberg–Richter law were estimated for each zone based on independent earthquake events. The PSHA was performed using a standard logic tree approach, which allowed us to systematically take into account the model-based uncertainty and its influence on the estimated ground motion parameters. Uniform hazard spectra for return periods of 475 and 2475 years were estimated for peak ground accelerations and spectral accelerations at 0.2 s and 1.0 s to meet the definitions of seismic hazards provided by the International Building Code (IBC, International Code Council [ICC], 2009). This study is expected to provide a basis for design maps for building codes and emergency planning.

Quantification of seismic mitigation performance of periodic foundations with soil-structure interaction

This paper investigates the influence of soil-structure interaction (SSI) on the seismic mitigation performance of a periodic foundation (PF) on vertically propagating shear waves. Two different mechanical models are employed to compare seismic responses of controlled and uncontrolled superstructures: i) the first one for the PF-controlled system, which is based on the Winkler approach and where the PF is treated as a shear frame; ii) the second one for the uncontrolled superstructure, which is based on the cone model. These two models are verified by comparison against the results of two-dimensional finite element models. Based on the mechanical models, the PF is optimized considering SSI. Then, the impact of SSI is investigated by comparing responses of the controlled and uncontrolled superstructures in both the frequency and time domains in two different soil types, respectively. Relevant results show that the PFs' performance can benefit from SSI. The robustness of PFs is improved and less damping is needed in resonators, both of which improve PFs’ feasibility.

Two Earthquake Sequences Nearly a Century Apart Reveal a Conjugate Seismogenic System in Central Taiwan

Abstract Seismically active central Taiwan is considered part of an orogenic wedge with low-angle east-dipping active faults above a detachment surface and an active mountain-building process later. In 2013, two moderate reverse-faulting earthquakes of magnitudes ML 6.2 and 6.5 occurred in Nantou. They brought to mind the historically damaging sequence of four earthquakes in the same area that claimed a total of 71 lives in 1916. The 2013 earthquake sequence provides a good opportunity to study the 1916 sequence. We compared the historical Omori record of the main event in the 1916 sequence, discovered in the Seismogram Archives at the Earthquake Research Institute, University of Tokyo, and the corresponding simulated Omori records of the 2013 events. Our comparison shows significant similarity among the earthquakes, although they are separated by nearly 100 yr. To understand the seismogenic structure associated with these earthquake sequences, we further studied the source rupture properties of earthquakes in this region since 1999 using local broadband records to determine the rupture fault planes. Results show that all events have similar focal mechanisms with one low-angle east-dipping and another high-angle west-dipping nodal planes. Rupture plane determination indicates that whereas events at shallow depths (<20 km) ruptured on the low-angle east-dipping plane, events at greater depths (>20 km) slipped on the high-angle west-dipping plane in a conjugate fault system. The comparison also suggests that the 1916 sequence occurred on the low-angle east-dipping plane of this conjugate fault system in the orogenic wedge as part of a mountain-building process. Given the active mountain-building process in central Taiwan, occurrences of this type of earthquake must be addressed in seismic hazard mitigation efforts.

The INSIEME seismic network: a research infrastructure for studying induced seismicity in the High Agri Valley (southern Italy)

Abstract. The High Agri Valley is a tectonically active area in southern Italy characterized by high seismic hazard related to fault systems capable of generating up to M=7 earthquakes (i.e. the 1857 Mw=7 Basilicata earthquake). In addition to the natural seismicity, two different clusters of induced microseismicity were recognized to be caused by industrial operations carried out in the area: (1) the water loading and unloading operations in the Pertusillo artificial reservoir and (2) the wastewater disposal at the Costa Molina 2 injection well. The twofold nature of the recorded seismicity in the High Agri Valley makes it an ideal study area to deepen the understanding of driving processes of both natural and anthropogenic earthquakes and to improve the current methodologies for the discrimination between natural and induced seismic events by collecting high-quality seismic data. Here we present the dataset gathered by the INSIEME seismic network that was installed in the High Agri Valley within the SIR-MIUR research project INSIEME (INduced Seismicity in Italy: Estimation, Monitoring, and sEismic risk mitigation). The seismic network was planned with the aim to study the two induced seismicity clusters and to collect a full range of open-access data to be shared with the whole scientific community. The seismic network is composed of eight stations deployed in an area of 17 km×11 km around the two clusters of induced microearthquakes, and it is equipped with triaxial weak-motion broadband sensors placed at different depths down to 50 m. It allows us to detect induced microearthquakes, local and regional earthquakes, and teleseismic events from continuous data streams transmitted in real time to the CNR-IMAA Data Centre. The network has been registered at the International Federation of Digital Seismograph Networks (FDSN) with code 3F. Data collected until the end of the INSIEME project (23 March 2019) are already released with open-access policy through the FDSN web services and are available from IRIS DMC (https://doi.org/10.7914/SN/3F_2016; Stabile and INSIEME Team, 2016). Data collected after the project will be available with the permanent network code VD (https://doi.org/10.7914/SN/VD, CNR IMAA Consiglio Nazionale delle Ricerche, 2019) as part of the High Agri Valley geophysical Observatory (HAVO), a multi-parametric network managed by the CNR-IMAA research institute.

A Database of Digitized and Analog Seismograms of Historical Earthquakes in Japan

AbstractSeismic and tsunami instrumental observations by seismographs and tide gauges began in Japan in 1875; hence, many analog records of earthquakes and tsunamis are stored at various universities and institutions throughout the country. Re-examination of historical records using modern waveform analysis methods, high-performance computing, and current knowledge on seismic velocity structure is expected to produce new results and interpretations of the mechanism of large earthquakes and tsunamis, leading to improved seismic disaster mitigation practices. However, such work requires extensive effort and skills for the digitization of the analog waveforms recorded on papers. To conveniently use the analog seismograms, we currently construct a database of digitized historical records and seismogram image copies of major earthquakes that occurred in Japan (e.g., the 1923 Kanto, 1944 Tonankai, and 1946 Nankai earthquakes). The data can be searched in this database by event, station, and seismograph names. Users can obtain the instrumental response and station information, if available, in addition to the digitized data. We plan to open this database to the public in a few years via the National Museum of Nature and Science and the Earthquake Research Institute of the University of Tokyo. The database on the museum website will be fundamental for outreach activity of seismology for the general public, and the information contained in the database will be useful in various fields such as seismology or earthquake engineering.

Seismic Response Mitigation of Base-Isolated Buildings

Earthquake response mitigation of a base-isolated (BI) building equipped with (i) a single tuned mass damper at the top of the building, (ii) multiple tuned mass dampers (MTMDs) at the top of the building, and (iii) MTMDs distributed on different floors of the building (d-MTMDs) is studied. The shear-type buildings are modeled by considering only one lateral degree of freedom (DOF) at the floor level. Numerical approach of Newmark’s integration is adopted for solving the coupled, governing differential equations of motion of 5- and 10-story BI buildings with and without TMD schemes. A set of 40 earthquake ground motions, scaled 80 times to get 3200 ground motions, is used to develop simplified fragility curves in terms of the isolator maximum displacement. Incremental dynamic analysis (IDA) is used to develop simplified fragility curves for the maximum target isolator displacement. It is found that TMDs are efficient in reducing the bearing displacement, top floor acceleration, and base shear of the BI buildings. In addition, it was noticed that TMDs are efficient in reducing the probability of failure of BI building. Further, it is found that the MTMDs placed at the top floor and d-MTMDs on different floors of BI buildings are more efficient in decreasing the probability of failure of the BI building when compared with STMD.

Experimental investigation on the seismic performance of low-level corroded and retrofitted reinforced concrete bridge columns with CFRP fabric

Seismic damage mitigation of corroded reinforced concrete (RC) bridge columns in marine environment will be an impending problem in many countries in which a mass of bridges have been constructed for 20 or more years. In this paper, cyclic pseudo-static tests were conducted on three 1/4-scaled RC column specimens with and without retrofit by carbon fiber reinforced polymer (CFRP) fabric in order to investigate seismic performance of low-level corroded columns and the efficiency of CFRP as a retrofit measure. The first specimen was designed with normal design details of Chinese specifications, which worked as a reference. The second and third columns were both corroded with a target of low-level corrosion in the plastic hinge zone using an electrochemical method. Meanwhile, the third column was retrofitted by CFRP jackets in the plastic hinge region. The experimental results were then employed to evaluate the damage process, failure mode, displacement ductility, energy dissipation, lateral resistance strength, and residual displacement of each specimen. The results show that although low level of corrosion in the tested columns, the displacement ductility was significantly reduced due to weakened confinement of the corroded transverse rebars and reduced area of the corroded longitudinal bars. In addition, retrofitting the column using CFRP fabric jackets could significantly increase the displacement ductility and reduce the residual displacement to some extent. It is worth noting that retrofitting of corroded column using CFRP jackets did not improve the lateral strength.

Analysis of the Site Effects in the North East Region of India Using the Recorded Strong Ground Motions from Moderate Earthquakes

ABSTRACT Site effect estimation using recorded ground motion is an effective approach to assess the seismic hazard of a region. Keeping the same thing in mind, an endeavor is being made to study the local site effects at different locations in the North East region of India through analysis of recorded strong ground motion data provided by Indian strong motion network. The data recorded at 25 sites from 37 earthquakes with a magnitude range 4.0–6.9 have been utilized. The estimated predominant frequencies ( using horizontal to the vertical spectral ratio (HVSR) is well observed for various sites placed in various geological formations like the Precambrian, Tertiary and Quaternary Consequently, the pseudo velocity response (PSV) for 5% critical damping is estimated and compared with the regional geological formations, especially in the Brahmaputra Valley region. It is further noticed that the HVSR, as well as PSV, show a noticeable correlation according to the geological set up of the region for most of the sites, giving a clear idea about the site effect evaluation. Analyzed strong motion data also show the effect of non-linearity, which is an important parameter as it explains the inelastic behavior of the soil causing a reduced or non-linear amplification. Since some of the sites used in present work do not correlate with geology, the sites used for HVSR estimation are used to classify them according to the classical approach employing . All the sites are classified in four different classes namely A, B, C, and D based on shear wave velocity in the upper 30 m. The outcome of the present study is being shown in the form of contour maps for and site amplification for various types of buildings in order to assess the seismic hazard and risk mitigation.

Seismic structural responses reduction of double-layered containment nuclear power plant via BIS-TMD

Purpose In recent years, a new type of double-layered containment structure of nuclear power plant has been built in China, named ACP1000 NNP. This paper aims to propose a new method to mitigate the seismic responses of this type of the structure. Design/methodology/approach The new base isolation structure (BIS)- tuned mass damper (TMD) structure was proposed and implemented only by modifying the connection between various components of NPPs, and the application of this concept design in ACP1000 was skillfully realized. Findings The new structure adopts the combination of structural form and function, adopts appropriate amplification of the seismic response of the secondary component, possesses advantages in explicit damping mechanism, good damping effect, robustness of seismic structures, simple implementation process, etc., and meets the special seismic safety requirements of the NPPs. Originality/value This seismic and hazard mitigation and BIS-TMD structure can avoid the risk of ACP1000 accidents caused by horizontal earthquakes.