Long-period Structures Research Articles

Post-earthquake regional structural damage evaluation based on artificial neural networks considering variant structural properties

The application of artificial neural networks (ANN) to regional seismic damage evaluation is still challenging due to variant structural properties and high computing requirements. This study aims to develop an ANN-based approach of regional seismic damage evaluation and investigate the ANN performance when structural properties like the fundamental period T and ductility factor μ change. By utilizing the Single-Degree-of-Freedom (SDOF) structures, ANN seismic classifiers, whose inputs are multiple intensity measures (IMs) and outputs are damage states, are trained for a structure portfolio with T from 0.3 to 3 s and μ from 1.5 to 6. The importance ranking of the multiple input IMs for classification indicates that the most important IMs for the correct classification of damage states vary when the structural properties change. Acceleration-related IMs play the most important role for short-period structures (e.g., less than 0.5 s), velocity-related IMs are most important for intermediate structures (e.g., 0.5 to 2.0 s), and displacement-related IMs are most important for long-period structures (e.g., larger than 2.0 s). This importance variation of IMs validates the necessity and advantage of ANN seismic classifiers with multiple IMs as input for the regional seismic damage evaluation. Further comparison of two different damage indices shows that the ANN performance will not be compromised by changing the damage index. Overall, the classification accuracy higher than 92% on the structure portfolio shows that the ANN-based regional seismic damage evaluation could be a robust and accurate approach with some limitations to be addressed in future studies.

Shaking table test of multiple-type isolation control strategies for high-rise structure based on friction pendulum

Given the difficulties associated with deploying isolation technique in high-rise structures, this article conducts a comprehensive comparison of three operating systems: friction pendulum system (FPS) base isolation form: FPS-B, FPS inter-story isolation form: FPS-I, and FPS hybrid isolation form: FPS-H. A 9-layer scaled test model is constructed by using third generation benchmark model, and the accompanying FPS model is created and fabricated using the geometric similarity criterion. Considering four typical ground motions and four peak ground acceleration (PGA), the structural seismic responses of the three control systems were analyzed. The result demonstrates that FPS-H technology greatly decreases the superstructure’ top floor acceleration and even the substructure's acceleration impact in both mild and major earthquakes. The working mechanism of FPS-H technology in terms of vibration reduction is similar to the conjunction of tuned mass damper (TMD) and FPS-B structure. The inertia force of superstructure suppresses the substructure since superstructure has FPS inter-story isolation form, and even the substructure is an FPS-B form that can extend the structural period and segregate earthquake energy. The FPS-H technology, which reduces the acceleration response of the structure's 1st -order mode and restrains the dynamic reaction of the high-order mode by changes the dynamic characteristics of whole structure, is primarily responsible for the long-period structure's effective damping.

A novel tuned inerter eddy current damper: modeling, optimization, and evaluation

This study proposes a novel tuned inerter eddy current damper using a rack and gear mechanism (TIECD), in which the configuration and mechanical model are introduced in detail. The TIECD design procedure for the seismic control of primary structures is established based on the effective damping ratio enhancement (EDRE) effect. A closed-form solution for TIECD optimal design under white noise excitation is presented using stochastic linearization techniques (SLT) with force-based and energy-based equivalence criteria. The control performance of the TIECD obtained by the closed-form solution, including the EDRE effect and effective damping ratio, is in good agreement with the numerical results obtained from the Monte Carlo simulation when a suitable TIECD critical velocity is selected; a large critical velocity is conducive to improving the accuracy of the closed-form solution. Note that the effect of a low structural damping level on the optimal design of TIECD can be ignored, which is beneficial in practical engineering applications because structural damping cannot be precisely known in most cases. Furthermore, several numerical studies have been conducted to investigate the availability of TIECD under real seismic excitations. The results indicate that the effectiveness of TIECD in mitigating the seismic response of primary structures is approximately the same as that of a tuned viscous mass damper (TVMD) and much greater than that of the viscous and eddy current dampers with the same damping parameters. It can be considered that the maximum damping force and maximum deformation of TIECD and TVMD are the key design factors for short-period and long-period structures, respectively, and the advantages of TIECD over TVMD are owing to the damping force limiting characteristics and small deformation.

A seismological method for estimating the long-period transition period TL in the seismic building code

Many changes have been made to the design response spectrum used in the ASCE 7 Standard in recent years. One parameter that has not been investigated or revisited since its first appearance in FEMA 450-1/2003 is the long-period transition period parameter, TL. The long-period transition period parameter was introduced and defined as the corner period that marks the transition from the constant velocity to the constant displacement segments of the design response spectrum. The long-period transition period parameter is primarily important for long-period structures such as high-rise buildings and bridges. The most current estimation of TL used in engineering design standards is loosely based on a correlation between modal magnitude Mw and TL that does not account for stress drop Δ σ or the crustal velocity in the source region β. This study aims to include both Δ σ and β in its estimation of TL. Modal magnitude is obtained from disaggregation data from the 2018 National Seismic Hazard Model (NSHM) for the conterminous United States (CONUS) and from the 2021 NSHM for Hawaii (HI). The parameter β is determined from previous literature. Then, inversion of ground motion models for Central and Eastern United States (CEUS) is used to determine Δ σ for CEUS events, and published information is used to determine Δ σ for Western United States (WUS) events and HI events. Then, the definition of the corner period is used to determine TL. The results yield a generally more conservative (or longer) estimation of TL than the estimation that is currently used in engineering design standards.

Microstructure and Mechanical Properties of Mg-Gd-Dy-Zn-Zr Alloy with Long-Period Stacking-Ordered Structure

Microstructure and Mechanical Properties of Mg-Gd-Dy-Zn-Zr Alloy with Long-Period Stacking-Ordered Structure

On energy dissipation or harvesting of tuned viscous mass dampers for SDOF structures under seismic excitations

In the past decade, tuned viscous mass dampers (TVMD) have been demonstrated as effective seismic resistant dampers. However, theoretical study on energy dissipation or energy harvesting of the TVMD has rarely been investigated, particularly, whether or not its optimal passive vibration control and energy dissipation maximization are consistent remains questionable. Here, from the theoretical perspective, we present an analysis of energy dissipation or energy harvesting of the TVMD in terms of damping power or output power, respectively. We derive the closed-form solutions of the average damping power of a single-degree-of-freedom (SDOF) structure-TVMD system under white-noise base excitations or seismic excitations modeled by the Kanai-Tajimi spectra, which is verified against the Monte Carlo simulations. Based on the closed-form solutions, the influences of the TVMD parameters, site conditions, and structural dynamic characteristics on the average damping power are analyzed via a parametric study. Theoretical results indicate that structural damping, site condition, structural period, frequency ratio, and inertance-to-mass ratio have a significant impact on the damping power or dissipated energy. In addition, the TVMD dissipates much more energy at a soft-soil site than at a stiff-soil site. At a stiff-soil site, the TVMD dissipates more energy for a short-period structure than for a long-period structure, however, at a soft-soil site, the law is the opposite. The study also presents the theoretical upper bound of the output power of an energy-harvesting TVMD. Particularly, results also illustrate that the maximization of TVMD energy dissipation is not consistent with the optimal passive vibration control. This study may shed light on the TVMD studies for seismic response control or energy harvesting purposes in the years to come.

In-Fiber Breathing Monitoring Sensor by Micro-Tapered Long-Period Grating Structure

A simple in-fiber breathing monitoring sensor based on a micro-tapered long-period fiber grating (MT-LPFG) structure was proposed and demonstrated. The MT-LPFG structure was manufactured through the periodical tapering of an optical fiber utilizing a CO2 laser fusion splicer. Without the use of a humidity sensitive film, the MT-LPFG structure can directly and dynamically monitoring relative humidity with a fast response, based on which, the breathing process can be monitored in real time through the monitoring of its transmission affected by the humidity. Experiments show that breathing rate and breathing status during respiration were successfully monitored by placing the sensor structure nearby the nose in a breathing mask. A rise time of 0.237 s and a fall time of 0.299 s were realized in the breathing process monitoring. For its advantages of simple fabrication, miniature size, and fast response, the proposed sensor may found applications in visual observation of the patient’s breathing condition.

Selection and modification of ground motion records using Newmark-Hall spectrum as target spectrum for long-period structures

Selection and modification of ground motion records using Newmark-Hall spectrum as target spectrum for long-period structures

Mechanical properties of curvature-consistent frictional pendulum bearings and isolation performance of spherical reticulated shells

With the increasing demand for isolated long-span spatial structures, the seismic performance of structures during rare earthquakes should be improved. In this study, we proposed a type of curvature-consistent frictional pendulum bearing (CC-FPB) that may induce notable seismic isolation effects in long-period and long-span spatial structures during rare earthquakes. Hysteresis tests were performed on the structure with the CC-FPB, and a refined numerical simulation method was established to analyse the isolation performance of the CC-FPB was established. The accuracy of the simulation method was verified by comparing the simulation results with experimental results. Based on the refined numerical simulation method, the CC-FPB was applied to a single-layer spherical reticulated shell structure, and the dynamic time history response of the structure was analysed. Furthermore, the seismic isolation effect was compared with that of the classical friction pendulum bearing (C-FPB). Parametric analysis was performed for structures with different roof qualities and input ground motions. We also analysed the seismic isolation effect and isolation influence mechanism of the structure with the CC-FPB. The results indicated that the CC-FPB had high isolation performance and energy dissipation capacity. Although the isolation performance had negligible influence on the loading frequency, the energy dissipation capacity and isolation performance increased with the increase in the loading frequency and loading displacement. The isolation efficiency of the isolation structure with the CC-FPB improved in comparison with that of the structure with the C-FPB. The isolation performance and energy dissipation capacity of the isolation structure increased with the increase in the seismic amplitude. The energy dissipation and damping capacity of the CC-FPB improved under high-frequency excitation.

Enhancing tunability of liquid storage tanks to function as deep tuned liquid dampers by use of a submerged stretched membrane

This is a study on a deep, liquid-containing tank, such as an overhead water tank on a building, with a vertically submerged stretched membrane (SSM). Here, instead of the sloshing mode, which can become detuned and also affords a low damper mass ratio, the impulsive liquid–membrane interacting system is designed to serve as a dynamic vibration absorber. The requirement of tuning the frequency of the impulsive liquid–membrane interacting system to the structural frequency can be achieved without any imposition on the tank dimensions, which are generally fixed from the tank's functional requirements. The system frequency would remain unchanged so long the membrane would remain submerged below a minimum liquid depth, thereby allowing fluctuation of liquid level within a prescribed range of the tank depth. The formulation for obtaining the frequency of the impulsive liquid–membrane interacting system is derived, using the sub-domain partition approach. It is seen that through suitable adjustment of the design parameters of the membrane, the proposed tank damper can be tuned to both short-period and to long-period structures. Further, the impulsive liquid mass, which otherwise has no role to play in the damping mechanism of a tuned liquid damper (TLD), is here utilized to absorb and dissipate the vibrational energy. Through a time-domain study considering recorded seismic accelerograms, the significant control effectiveness of the proposed damper system is illustrated. Further, the results obtained from the equivalent mechanical model of the structure–damper system are compared with those from a finite element analysis of the fluid–structure system in the ANSYS Workbench environment.

Seismic Signal-Based Investigation on the Disaster Differences between 2021 Yangbi Ms 6.4 Earthquake and 2014 Ms 6.5 Ludian Earthquake in Yunnan Province, China

An Ms 6.4 earthquake occurred in Yangbi County, Yunnan Province, on May 21, 2021. The magnitude is only 0.1 difference when compared with the 2014 Ms 6.5 earthquake in Ludian County, Yunnan Province, but the disasters show a big difference. Seismic signal includes the comprehensive information of source, propagation path, and site effect, which directly reflect the effect of the earthquake on the ground. The study mainly investigated the difference between seismic signals of two events in time domain and time-frequency-energy space based on variational mode decomposition and Hilbert transform to clarify the reasons for disaster differences. Most damaged buildings are column-and-tie timber structures with Earth walls with local collapse or vertical crack at the corner of the Earth wall in the Yangbi earthquake. Multistorey buildings are intact, and a few small landslides are triggered, whereas, in the Ludian earthquake, multistorey buildings with the frame structure and masonry structure occurred with serious X-type cracking, large interlayer displacement, and even complete collapse, and large landslides with length about 165 m are triggered. 53LLT and 53YBX are two strong motion stations in the Ludian earthquake and Yangbi earthquake, respectively, and are near the disaster investigation points. Peak ground acceleration in 53LLT is up to 949.2 cm/s2, which is larger than 720.3 cm/s2 in 53YBX, and the duration in 53LLT is longer than 53YBX. The instantaneous energy of 53YBX is concentrated within 0–10 Hz and 10–20 Hz, respectively; however, the instantaneous energy of 53LLT is concentrated at 5 Hz. Cumulative energy of 53YBX is mainly distributed at 0–5 Hz and 10–20 Hz, which is around the natural frequency of column-and-tie timber structure, while the energy of 53LLT is concentrated at 1.6 Hz and is much greater than other stations. Thus, large energy in high frequency caused the instantaneous and cumulative damage to short-period structures in Yangbi County and may cause the resonance of column-and-tie timber structure, and large energy in low frequency caused the instantaneous and cumulative damage to long-period structures of Longtou Village in Ludian earthquake. The result is meaningful to understanding the seismic disasters from the characteristics of seismic signals and can provide a reference for the seismic design of structures.

Modal Pushover Analysis for Seismic Performance Assessment of Underground Structures

ABSTRACT Pushover analysis as an efficient nonlinear static analysis method has been widely applied to the seismic inelastic performance evaluation of above-ground structures. Although it has the main advantage of high computational efficiency compared to nonlinear dynamic time-history analysis (THA), the assumption that the fundamental mode dominates structural response limits its application to long-period structures. Improved pushover analysis has been developed to consider the higher mode effect, named modal pushover analysis (MPA), but all research mainly focused on buildings and bridges. Since the mechanical behaviors of the underground structures and above-ground structures under seismic exaction are not exactly the same, so far, MPA suitable for seismic performance assessment of underground structures still has not been developed. Therefore, the aim of this investigation is to develop MPA for the seismic performance assessment of underground structures. A prototype subway station structure and a soft site are used to study the applicability of the developed MPA and compare it with the traditional pushover analysis procedure and nonlinear THA. Numerical analysis results of the subway station illustrate the applicability and potential of the developed MPA for underground structures.

New Metastable Baro- and Deformation-Induced Phases in Ferromagnetic Shape Memory Ni2MnGa-Based Alloys.

Structural and phase transformations in the microstructure and new metastable baro- and deformation-induced phases of the Ni50Mn28.5Ga21.5 alloy, typical of the unique class of ferromagnetic shape memory Heusler alloys, have been systematically studied for the first time. Phase X-ray diffraction analysis, transmission and scanning electron microscopy, and temperature measurements of electrical resistivity and magnetic characteristics in strong magnetic fields were used. It was found that in the course of increasing the pressure from 3 to 12 GPa, the metastable long-period structure of martensite modulated according to the 10M-type experienced transformation into a final non-modulated 2M structure. It is proved that severe shear deformation by high pressure torsion (HPT) entails grainsize refinement to a nanocrystalline and partially amorphized state in the polycrystalline structure of the martensitic alloy. In this case, an HPT shear of five revolutions under pressure of 3 GPa provided total atomic disordering and a stepwise structural-phase transformation (SPT) according to the scheme 10M → 2M → B2 + A2, whereas under pressure of 5 GPa the SPT took place according to the scheme 10M → 2M → B2 → A1. It is shown that low-temperature annealing at a temperature of 573 K caused the amorphous phase to undergo devitrification, and annealing at 623–773 K entailed recrystallization with the restoration of the L21 superstructure in the final ultrafine-grained state. The size effect of suppression of the martensitic transformation in an austenitic alloy with a critical grain size of less than 100 nm at cooling to 120 K was determined. It was established that after annealing at 773 K, a narrow-hysteresis thermoelastic martensitic transformation was restored in a plastic ultrafine-grained alloy with the formation of 10M and 14M martensite at temperatures close to those characteristic of the cast prototype of the alloy.

Weighted Average Conditional Mean Spectrum (WACMS): A bridge between common CMS and Uniform Hazard Spectrum (UHS)

In order to accurately predict structural response subject to ground motion excitation in the hazard level of interest, it is necessary to determine appropriate target spectrum. Conditional Mean Spectrum (CMS) conditioned on occurrence of a target spectral acceleration (Sa) at a single period is an alternative of the overly conservative Uniform Hazard Spectrum (UHS). The first-mode period is usually advised as conditioned period to create CMS, but it is not always appropriate. A Weighted Average Conditional Mean Spectrum (WACMS) is newly introduced as a more suitable target spectrum to long-period structures and practical guidelines for use are presented. WACMS is the weighted average of CMS suite conditioned on occurrence of target Sa at first several periods, the sum of whose mass participation factors exceeding 90%. The significant advantage is that it can consider hazard levels at multiple periods and use mass participation factor as the weight. CMS and UHS can be integrated with WACMS. WACMS is equivalent to CMS when one period is considered while almost overlaps UHS when all periods are considered. That is, WACMS bridges the gap between CMS and UHS. In this paper, three different structures designed by Chinese code are utilized as examples to verify this method. Results show that WACMS is more appropriate as a target spectrum to predict mean inter-storey drift ratio (IDR) consistent with Chinese code, compared to CMS conditioned on occurrence of Sa at the first-mode period. Meanwhile, WACMS increases the rate of exceeding IDR limit and IDR dispersion.

Relationship Between Asperities and Velocity Pulse Generation Mechanism

Near-fault ground motion records often capture instances of pulse-like behavior, where a burst of energy is expressed as large wave amplitude that occur over short time. The pulse-like ground motion can cause serious damage to long-period structures. Using numerical simulations of near-fault ground motions, we analyze the mechanisms involved in the generation of velocity pulses in the 1994 Northridge Earthquake and the 1979 Imperial Valley Earthquake. The degree to which the asperities affect the pulse generation process is investigated by identifying individual velocity pulses from the superposition process of sub-fault ground motions. Pulse indicators Ep and PGVp represent pulse characteristics in the ground motions at the stations located near the epicenter (near-epicenter stations) and the stations located along the forward rupture propagation direction of the asperity (rupture-direction stations), respectively. To observe the effects of the asperities and the spatial relationship between the pulse-like ground motion stations and the asperities, we determine the contribution of the sub-fault motions to the pulse amplitude. Furthermore, we analyze the pulse indicators and the frequency components using simulated ground motions from two different slip distributions. The near-epicenter station ground motions, produced by homogeneous slip distribution, exhibit higher pulse amplitude and more concentrated low-frequency energy than those generated by the inhomogeneous slip distribution. The rupture-direction station ground motions, produced by inhomogeneous slip distribution, present higher pulse amplitude and more concentrated low-frequency energy than those generated by the homogeneous slip distribution. Our analysis reveals that during the fault rupture process, the pulse energy and the pulse amplitude are influenced by both the slip distribution on the fault plane and the spatial relationship between the seismic station and the asperity.

Characteristics of Ground Vibrations Induced by Teleseismic Earthquakes and Their Impact on Vibration-Sensitive Facilities

ABSTRACT The ground vibrations observed in Taiwan during three teleseismic earthquakes in 2011 by broadband seismometers near major science parks were investigated. Their frequency content was exhibited via spectral analysis, and their effect on structures was examined by response spectra. To assess their possible impact on vibration-sensitive facilities, three vibration criteria in terms of velocity or displacement were utilized. Their predominant frequencies were between 0.04– and 0.16 Hz and somewhat dependent on focal depth and site geology, and they were therefore only influential to very long-period structures. However, the vibration levels exceeded the adopted criteria to some extent, especially at the softer site.

Development of long-period ordered structures during crystallisation of amorphous Mg80Cu10Y10 and Mg83Ni9Y8

Abstract The different transformations occurring during the crystallisation of amorphous Mg80Cu10Y10 and Mg83Ni9Y8 alloys have been elucidated. The formation of several unknown metastable phases was observed. The present work confirms that such phases exhibit long-period structures originated by the periodic alignment of (Y, TM)-layers (TM: transition metal). The long-period stacking-ordered phase, identified in the crystallised Ni-containing alloy, is stable at higher temperatures than that in the Cu-containing alloy.

A special characteristic of an earthquake response spectrum detected in Turkey

This article highlights a special characteristic of response spectrum behavior associated with a devastating earthquake recorded in Turkey. The behavior poses a threat to long-period structures (mid-to high-rise buildings and special structures). For this paper, a group of seven accelerations records was used from different parts of the world to validate the analysis tools for the accelerations record of interest. In addition, records of the special event from two different stations were used to eliminate the possibility of malfunctioning of the recording device. These records were converted into response spectrums as the form usually used in earthquake engineering. Response spectrums resulting from this event had two high response areas: 1) one in the short domain of periods (as generally known in typical response spectrum plots) 2) another one that is effecting long domain periods (which typically does not cause high response from earthquakes due to low value of response spectrum typically plotted in this domain). This paper is expected to raise awareness of the importance of locally developed response spectrums to cope with the possibilities of irregular and uncaptured events in international codes. Furthermore, it aims to promote the analysis using time-history accelerations records of structures from local records as a better tool to interpret the expected behavior of the structures.

Spectrum characterization and assessment method of long-periodic ground movements

To reveal the failure mechanism of resonance effect on long-periodic structures, the spectrum characterization of nonlinear and non-stationary long-periodic ground movements are studied. Firstly, the period and energy characterizations about IMFs (intrinsic mode functions) of ground movements are analyzed. Then, an energy-weighted average period is proposed to indicate the long-periodic characterization on different types of ground movements. Lastly, the simplified method on the low-frequency time history for long-periodic ground movements is proposed and verified. The research conclusions show that, various Hilbert amplitude spectra analysis can expose all the inherent information of nonlinear and non-stationary long-periodic ground movement accurately and comprehensively. The proposed periodic parameter that characterizes different earthquake classifications can help to efficiently and conveniently filter out long-period ground movements, and it also can be used as a quantitative indicator to identify long-period ground movements. The suggested simplified method can facilitate in-depth and accurate analysis of the low-frequency components of long-periodic ground movements. Effective and accurate evaluation on the low-frequency components of long-periodic ground movements plays the key role to uncover the nonlinear dynamic behavior of long-periodic structures, and it is of great scientific research significance in the field of earthquake engineering and structural engineering.

Impacts of the 2020 Samos earthquake on the modeling of ancient seismic events

The 2020 Samos, M7.0 earthquake was characterized by an unusual bi-modal-type distribution of damage: limited damage in the nearfield (especially northern Samos coast) and serious localized damage in multi-story buildings in the far field (İzmir area). This pattern is not consistent with the typical distribution of isoseismal lines, and it seems not to represent an isolated effect; the 2014 Samothraki- Gökçeada M6.9 earthquake, for example, may in fact represent a parallel, though at smaller scale. For this reason, the damage pattern of the Samos earthquake may characterize historical earthquakes in the wider region, and perhaps explain, among others, some apparently large meizoseismal areas of historical earthquakes. Furthermore, the fact that damage in a part of the İzmir area occurred under moderate background acceleration has important implications for various ancient, long-period structures, especially monumental Greek and Roman multi-block columns and temples. These structures are highly resistant to seismic loads and difficult to fail under common earthquakes. However, evidence from the İzmir area indicates that, under certain conditions, common background accelerations can be highly amplified and leave their traces in such structures, for example in the Heraion temple at Samos.