Seismic Acceleration Response Research Articles

Shake table tests on the traditional column-and-tie timber structures

In order to study the seismic performance of Chinese traditional column-and-tie timber structure, two 1:2 scaled model structures, one without infilled wallboard and the other with infilled wallboard, were fabricated and tested on shaking table in Key Laboratory of Structural Engineering and Earthquake Resistant at Xi'an University of architecture and technology. In the test, the maximum responses of acceleration and displacement were measured and evaluated, as well as the dynamic characteristics, global hysteresis response and torsion effect. Test results indicate that the column-and-tie timber structure has large flexibility and deformability, and the energy dissipation capacity of the structure increases with the increasing magnitude of earthquake excitation. Meanwhile, the structure incorporating wallboard exhibited a substantial increase in its lateral stiffness and a dramatic reduction in its seismic displacement response. Furthermore, the seismic acceleration response of the structure was moderately increased by the presence of wallboard. It is suggested that the wallboard should be taken into consideration on the lateral stiffness of the whole structure. Such a comprehensive analysis helps enhance understanding of the seismic-resistant behavior of this type of construction, which is certainly important for historic preservation efforts.

Practical seismic analysis of large underground structures: Theory and application

Due to the conceptual clarity and calculational simplicity, practical methods for seismic analysis have been widely used in seismic design and calculation of underground structures. All of the commonly adopted practical methods assume that the earthquake inertia force of the analysis model equals that of free-field. However, this assumption neglects the influence of underground structures on their surrounding soil layers, and may lead to significant errors in both conceptual and computational terms when the size of a structure increases. This article focuses on the practical seismic analysis of large underground structures. Theoretical derivation is demonstrated on the basis of the establishment of mechanical models of the soil-structure system and free-field, and consequently, the quantitative relation between the seismic acceleration response of the soil-structure system and that of free-field is obtained. This relation can be used to revise the earthquake inertia force applied to the analysis model so that the calculation accuracy is effectively improved. By doing so, a revised pushover analysis method, which combines the traditional pushover analysis and theoretical derivation, is proposed in order to be appropriate to seismic analysis of large underground structures. Moreover, an example of application of the proposed method is given, in which a selected large underground structure is analyzed. The results show that this revised method has higher efficiency than the traditional method thanks to the revision of the earthquake inertia force.

Seismic Isolation of Reactor Assembly for a Fixed Base Accelerator Driven System Reactor Building

In the SILER (Seismic-Initiated events risk mitigation in LEad-cooled Reactors) Project, it is interesting to apply seismic isolation technology for the reactor assembly of the fixed base reactor building for ADS (Acceleration Driven System) heavy liquid reactor MYRRHA (Multipurpose Hybrid Research Reactor for High-Tech Application) which contains the most critical safety related components, such as reactor vessel, safe shutdown and control rod mechanisms, primary heat exchangers, primary pumps, spallation target assembly and fuel assemblies, etc. The purpose of this paper is to investigate the possibility of an application of a partial seismic isolation to the safety critical components only, here, the reactor assembly. This paper presents the preliminary analysis results of the isolated reactor assembly and compares these with those of seismic isolated ADS reactor building. The analysis results show the reduction of the seismic acceleration response but the increase of the relative displacement for the reactor assembly. Some safety issues, especially, coolant's incapable covering the reactor core make difficult to apply for the partial seismic isolation of the ADS reactor assembly due to large relative displacement occurring the partial isolation system. Further study on the partial seismic isolation application of the critical safety components are also discussed.

Seasonal differences in seismic responses of embankment on a sloping ground in permafrost regions

Because of its direct influence on the amount of unfrozen water and on the strength of intergranular ice in a frozen soil, temperature has a significant effect on all aspects of the mechanical behavior of the active layer in which temperature fluctuates above and below 0°C. Hence seismic responses of engineering structures such as embankment on a sloping ground in permafrost regions exhibit obvious differences with seasonal alternation. To explore the distinctive seismic characteristics of a railway embankment on the sloping ground in permafrost regions, a coupled water-heat-dynamics model is built based on theories of heat transfer, soil moisture dynamics, frozen soil mechanics, soil dynamics, and so on. A well-monitored railway embankment on a sloping ground in Qinghai–Tibet Plateau is taken as an example to simulate seismic responses in four typical seasons in the 25th service year. The numerical results show that seismic acceleration, velocity and displacement responses are significantly different in four typical seasons, and the responses on October 15 are much higher among the four seasons. When the earthquake is over, there are still permanent differential deformations in the embankment and even severe damages on the left slope on October 15. Therefore, this position should be monitored closely and repaired timely to ensure safe operation. In addition, the numerical model and results may be a reference for maintenance, design and study on other embankments in permafrost regions.

AP1000 Shield Building Dynamic Response for Different Water Levels of PCCWST Subjected to Seismic Loading considering FSI

Huge water storage tank on the top of many buildings may affect the safety of the structure caused by fluid-structure interaction (FSI) under the earthquake. AP1000 passive containment cooling system water storage tank (PCCWST) placed at the top of shield building is a key component to ensure the safety of nuclear facilities. Under seismic loading, water will impact the wall of PCCWST, which may pose a threat to the integrity of the shield building. In the present study, an FE model of AP1000 shield building is built for the modal and transient seismic analysis considering the FSI. Six different water levels in PCCWST were discussed by comparing the modal frequency, seismic acceleration response, and von Mises stress distribution. The results show the maximum von Mises stress emerges at the joint of shield building roof and water around the air inlet. However, the maximum von Mises stress is below the yield strength of reinforced concrete. The results may provide a reference for design of the AP1000 and CAP1400 in the future.

Nonlinear Seismic Analysis of a Three-dimensionalUnsymmetrical Reinforced Concrete Structure

Abstract This paper presents the seismic performance of a geometrically unsymmetrical reinforced concrete building considering torsional effect and material nonlinearity of concrete and steel. The reinforced concrete building is a structure for seismic performance evaluation in the SMART-2013 international benchmark program. Nonlinear constitutive models for concrete and steel were constructed, and their numerical performance was demonstrated by various local tests. Modal analysis showed that the first three natural frequencies and mode shapes were close to the experimental results from the SMART-2013 program. In the time history analysis for low-intensity seismic loadings, displacement and acceleration responses at sampling points were similar to the experimental results. In the end, nonlinear time history analysis was conducted for Northridge earthquake to predict the behavior of the reinforced concrete structure under high-intensity seismic loadings. Keywords :reinforced concrete structure, seismic response, time history analysis, SMART-2013 international benchmark program

A MODEL SHAKING TABLE TEST INVESTIGATION ON AN ASSEMBLY FRAME

A shaking table test on a two-story aluminum alloy space frame model with mortise and tenon joints were carried out. The natural frequency and the damping ratio of the model in two directions were obtained by vibration frequency sweep. Inputting EL-Centro (N-S) 0.1g, 0.2g and 0.4g seismic motion, the strain, displacement and acceleration response of the model structure were investigated. It shows that the mortise and tenon joint frame has lower natural vibration frequency, higher damping ratio, better ductility, and better seismic performance than the corresponding rigid connecting structure.

지진규모를 고려한 방파제 특성에 관한 연구

부산지역은 낙동강 하구에 위치하여 퇴적층, 매립층 등이 매우 잘 발달되어 있어 지진이 발생한다면 이러한 지층 등에서 증폭현상이 나타나 모래층과 성토층 및 매립지반에 액상화 발생 가능성이 매우 커진다. 만약 액상화가 발생한다면 지진에 의한 피해는 크게 가중되어 막대한 피해를 야기 시키게 된다. 그러므로 본 연구는 지진 발생 시 항만시설의 1차 보호구조물인 부산항 신항 방파제의 안정성을 검토하기 위하여, 국내 내진설계기준과 항만 및 어항 설계기준을 바탕으로 인공지진과 국내에 널리 사용되는 장주기 지진파와 단주기 지진파인 포함하여 지진규모 5.6~7.9 수준의 지진 13개 등을 사용하여 첫 번째로 여러 제시된 액상화 평가방법을 이용하여 방파제 하부 치환모래층의 액상화 발생 가능성을 검토하여 안정성을 평가하고, 두 번째 지진규모에 따른 지진에너지와 가속도 응답스펙트럼에 대한 특성분석을 수행하여 설계기준에 근접하는 지진파 제시하며, 세 번째 제시된 지진파를 이용하여 방파제의 동적 안정성을 검토하기 위해 유한요소해석을 실시하여 구조물의 안정성을 확인하고, Geotextile에 발생하는 변위 및 인장력의 변화에 대하여 확인하였다. 따라서 본 연구결과 방파제 하부 치환모래층에 대한 액상화 발생가능성과 방파제의 동적수평변위 및 Geotextile의 변화는 하부지반(치환모래층)에 의해 매우 큰 영향을 받는 것으로 나타났다. Busan is located at the mouth of Nakdong River and if an earthquake occurs, it is very likely that the damage by the earthquake will be worse as liquefaction can happen in the sand layer, builtup soil, and landfill ground due to amplification in the lower sedimentary layer that is well developed in the river mouth. Therefore, this study first examined the possibility of liquefaction in the replaced sand layer under breakwater using 14 earthquakes in 5.6-7.9 scale and artificial earthquakes including the seismic wave suggested in the standard specifications for seismic design of ports and fishing port facilities to evaluate the stability of breakwater which is the primary protective structure for port facilities against earthquakes. Second, analysis on characteristics of the seismic energy and acceleration response spectrum by size of earthquake was performed to suggest the most appropriate size of seismic wave for the condition in Korea. Third, finite element analysis was performed using the suggested seismic wave to study the characteristics of earthquake by finding the dynamic lateral displacement of breakwater and verifying the stability of structure and the displacement and forces occurring at geotextile. Results of the study showed that the possibility of liquefaction in the landfill and replaced sand layer, the dynamic lateral displacement of breakwater, and changes of geotextile are greatly affected by the subsurface ground (replaced sand layer).

Analysis of Ignitions Following 2011 Tohoku Earthquake Using Kawasumi Model

Ignitions following the Tohoku earthquake (2011) can be divided either into earthquake-generated ignitions or tsunami-generated ignitions. This study analyzed the behavior of the earthquake-generated ignitions. Ignition records of 698 municipalities of eastern Japan was collected by a questionnaire survey and found that 191 ignitions were either directly or indirectly caused by seismic motion. These records of earthquake- generated ignition were analyzed using the statistical model proposed by Kawasumi (Kawasumi model). Kawasumi model is a simple one-parameter model which formulates the relationship between the ignition probability p and the scale of seismic intensity Θ. Seismic indices Θ used in this analysis were (a) collapse ratio of houses, (b) JMA (Japan Meteorological Association) seismic intensity, (c) PGA (peak ground acceleration), (d) PGV (peak ground velocity), (e) PGD (peak ground displacement), (f) acceleration response and (g) SI (Spectral Intensity). Obtained adjusted determination coefficients were higher than 0.7 for most of the seismic indices Θ except for (a) collapse ratio of houses and (e) PGD. After normalization with regard to time and season of its occurrence, the results were further compared with that of various earthquakes (1927-1968), and the Kobe earthquake (1995). Ignition probability ρ of the Tohoku earthquake (2011) was substantially lower than that of the various earthquakes (1927-1968). On the other hand, the difference of ignition probability ρ between the Tohoku earthquake (2011) and Kobe earthquake (1995) was relatively small.

Probabilistic method to select calculation accelerograms based on uniform seismic hazard acceleration response spectra

A dynamic analysis of a structure requires the previous definition of the accelerograms and the structure characteristics. The response of a structure subject to a seismic movement can be determined by two methods: either using the accelerograms recorded near the site, or using visco-elastic response spectra. The first method should only be used for locations where many accelerograms have been recorded, and needs a probabilistic calculation to ascertain the design accelerograms. The use of visco-elastic response spectra is based upon the fact that the response spectrum is the soil movement parameter better related to the structural response and is more adequate to obtain accelerograms in regions where the number of records is insufficient. This is the most commonly used method as the response of structures, in the elastic linear range, can be obtained as the superposition of a few modes of vibration. A probabilistic method for selecting calculation accelerograms is presented in this paper. First, the probabilistic hazard equation is solved. Based on the hazard curves obtained, the uniform seismic hazard acceleration response spectrum (USHARS) is constructed for the location, according to the type of soil and the required hazard level (exposure time and exceedance probability). Then, calculation accelerograms are selected. Based on this methodology, real accelerograms, for a return period of 975 years, have been obtained for San Pedro Cliff (Spain) at the Alhambra in Granada.

Damage Localization of Frame Structures Using Seismic Acceleration Response Data

In this study, damage localization of frame structures from seismic acceleration responses is explored using the DLV technique and ARX model for system identification. The concept of the DLV method is to identify the members with zero stress under some specific loading patterns derived by interrogating the changes in flexibility matrix of the structure before and after the damage state. Success of the DLV method for damage localization lies on the ability to identify the flexibility matrix. The ARX model, a discrete-time non-parametric auto-regressive system identification technique is adopted to identify the modal parameters (natural frequencies, transfer functions and mode shapes) from which the flexibility matrices of the intact and damaged structures are constructed. To explore the effectiveness of the DLV method, a five-storey steel model frame with diagonal bracings was considered for seismic shaking table tests. The damage conditions of the structure were simulated by partially removing some of the diagonals. With the flexibility matrices of both the intact and damaged structures synthesized on a truncated modal basis, the damage locations have been successfully identified by the DLV method for either single or multiple damage conditions, regardless of the damage locations. This study confirms the potential of the DLV method in the detection of local damages from global seismic response data for frame structures.

Damage Localization of Frame Structures Using Seismic Acceleration Response Data

In this study, damage localization of frame structures from seismic acceleration responses is explored using the DLV technique and ARX model for system identification. The concept of the DLV method is to identify the members with zero stress under some specific loading patterns derived by interrogating the changes in flexibility matrix of the structure before and after the damage state. Success of the DLV method for damage localization lies on the ability to identify the flexibility matrix. The ARX model, a discrete-time non-parametric auto-regressive system identification technique is adopted to identify the modal parameters (natural frequencies, transfer functions and mode shapes) from which the flexibility matrices of the intact and damaged structures are constructed. To explore the effectiveness of the DLV method, a five-storey steel model frame with diagonal bracings was considered for seismic shaking table tests. The damage conditions of the structure were simulated by partially removing some of the diagonals. With the flexibility matrices of both the intact and damaged structures synthesized on a truncated modal basis, the damage locations have been successfully identified by the DLV method for either single or multiple damage conditions, regardless of the damage locations. This study confirms the potential of the DLV method in the detection of local damages from global seismic response data for frame structures.

The Characteristic of the Seismic Response Spectrum of Slope Reinforced with Piles under the Different Diameters

In order to study the characteristic of seismic response of the reinforced slope subjected to earthquake, the seismic response spectrum of slope reinforced with piles under the two different diameters were compared and analyzed. The seismic acceleration response shows a steady amplification with the increase of height without water in substratum, and the maximal seismic response occurs near the crest of slope. The dominant frequency of the amplification of seismic response spectrum of the slope reinforced with piles under the smaller diameter obviously shifts to the medium and low frequency. In addition, because of the liquefaction of substratum and the resulting dynamic failure of the pile, the response components of the medium and low frequency also are strengthened further. The results show that the global stiffness of the reinforced slope is obviously affected by the diameter of the pile and the liquefaction in substratum, which thereby affects the seismic acceleration response and the distribution of spectral amplification factor.

Seismic Response Analyses of the Folded Cantilever Shear Structure: Analytical and Experimental Studies

The seismic acceleration response of the multistory buildings can be decreased by extending their natural period. In this study a new seismic isolation approach, a folded cantilever shear structure, is proposed to get more seismic performance than the ordinary multistory buildings by extending its natural period and increasing damping ratio with attaching additional viscous dampers which mitigates the seismic response of the structure. The proposed folded cantilever shear structure is designed consisting of mainly two parts, fixed shear sub-structure and movable shear sub-structure. These sub-structures are interconnected by a rigid connection beam at the top of the sub-structures. Besides, additional viscous dampers are supplemented to connect fixed and movable shear sub-structures with each other horizontally on the base of stories. In order to investigate the seismic behavior of the proposed structure, analytical and experimental studies are carried out, respectively. At first, 15 stories of folded cantilever shear structure model and ordinary cantilever shear structure model are analyzed analytically due to four exemplary earthquake wave data as El Centro, Miyagi, Hachinohe and Taft earthquakes. Then the experimental vibration test model of the proposed structure is performed through shaking table for the same earthquake waves and seismic response diagrams are obtained. The agreeable results between the experimental analysis and analytical analysis are obtained. According to the results of these studies, it is clarified that the proposed folded cantilever shear structure has substantial improvement in terms of seismic responses with long natural period and high damping ratio in contrast with the ordinary cantilever shear structure.

A New Proposed Passive Mega-Sub Controlled Structure and Response Control

It is still a serious challenge for structural engineers to effectively reduce the seismic responses of tall and super tall buildings to further improve these structural safeties. In order to solve this problem, in this article a new kind of structural configuration, named passive mega-sub controlled structure (PMSCS), is presented, which is constructed by applying the structural control principle into structural configuration itself, to form a new structure with obvious response self-control ability, instead of employing the conventional method. In the analysis of PMSCS the equations of motion of the seismically excited system are developed, based on a realistic analytical model of the complete mega-structural system. Expressions of the displacement and acceleration response of the structure, resulting from simulated earthquake ground motions represented by stationary and nonstationary random processes, are derived. These responses are then determined for both the PMSCS and its conventional mega-sub structure (MSS) counterpart, whose configuration was modeled after the traditional mega-frame that was used in the construction of the Tokyo City Hall. A parametric study of the structural characteristics that influence the response control effectiveness of the PMSCS is presented and discussed. The region over which these structural characteristics yield the optimum seismic response control of the PMSCS is identified and serves as a very useful design tool for practitioners. The study illustrates that the proposed PMSCS offers an effective means of controlling the seismic displacement and acceleration response of tall/super-tall mega-systems. It also overcomes shortcomings exhibited in earlier proposed mega-sub controlled structural configurations.

A method of calculating the non‐linear seismic response of a building braced with viscoelastic dampers

AbstractBuildings are continually subject to dynamic loads, such as wind load, seismic ground motion, and even the load from internal utility machines. The recent trend of constructing more flexible high‐rise buildings underscores the importance of including viscoelastic dampers in building designs. Viscoelastic dampers are used to control the dynamic response of a building. If the seismic design is based only on the linear response spectrum, considerable error may occur when calculating the seismic response of a building; rubber viscoelastic dampers show non‐linear hysteretic damping that is quite different from viscous damping.This study generated a non‐linear response spectrum using a non‐linear oscillator model to simulate a building with viscoelastic dampers installed. The parameters used in the non‐linear damper model were obtained experimentally from dynamic loading tests. The results show that viscoelastic dampers effectively reduce the seismic displacement response of a structure, but transmit more seismic force to the structure, which essentially increases its seismic acceleration response. Copyright © 2003 John Wiley & Sons, Ltd.

A rooftop tuned mass damper frame

AbstractThis article documents the analytical study and feasibility of placing a tuned mass damper in the form of a limber rooftop moment frame atop relatively stiff structures to reduce seismic acceleration response. Six existing structures were analytically studied using a suite of time history and response spectra records. The analyses indicate that adding mass in conjunction with a limber frame results in an increase in the fundamental period of each structure. The fundamental period increase generally results in a decrease in seismic acceleration response for the same time history and response spectra records. Owing to the limber nature of the rooftop frames, non‐linear analysis methods were required to evaluate the stability of the rooftop tuned mass damper frame. The results indicate the addition of a rooftop tuned mass damper frame reduces the seismic acceleration response for most cases although acceleration response can increase if the rooftop frame is not tuned to accommodate the specific structure's dynamic behaviour and localized soil conditions. Appropriate design of the rooftop tuned mass damper frame can result in decreased seismic acceleration response. This translates to safer structures if used as a retrofit measure or a more economical design if used for new construction. Copyright © 2003 John Wiley & Sons, Ltd.

Seismic Testing of Two-Story Woodframe House: Influence of Wall Finish Materials

A two-story, single-family woodframe house, designed according to current engineered code seismic design requirements, was tested on a uniaxial shake table. The main objectives of this experimental study were to determine the dynamic characteristics and the seismic performance of the test structure under various base input intensities representative of both ordinary and near-field ground motions in southern California. The structure was tested with and without interior (gypsum wall board) and exterior (stucco) wall finish materials. The test results revealed good performance of the engineered woodframe structure. Wall finish materials are usually considered in design as nonstructural elements. However, the structure incorporating wall finish materials exhibited a substantial increase in its lateral stiffness and a dramatic reduction in its seismic displacement response. Furthermore, the seismic acceleration response of the structure was only moderately increased by the presence of wall finish materials. These shake table test results provide the motivation for further studies on the evaluation of the long-term effectiveness of wall finish materials as potential structural components of lateral load-resisting systems of woodframe structures.

Vulnerability Function of Wooden Houses Based on Seismic Performance Indices and Acceleration Response Spectrum

Vulnerability Function of Wooden Houses Based on Seismic Performance Indices and Acceleration Response Spectrum