Dynamic Characteristic Analysis of Two Adjacent Multi-grid Composite Wall Structures with a Seismic Joint by a Bayesian Approach

Field ambient vibration tests and modal identification using a Bayesian approach are conducted for a building made of multi-grid composite wall structure and divided into two adjacent parts by a seismic joint, to investigate the dynamic characteristics of the special structural type and the effects of the infilled seismic joint. It is found that dynamic interactions between the two structural parts exist possibly induced by the infill of the building separation. Natural frequencies obtained from other two modal parameter identification methods and modal analysis results of finite element models considering dynamic interactions agree with those identified by the Bayesian approach.     

FUZZY PATTERN CLASSIFICATION OF STRONG GROUND MOTION RECORDS

Classification of earthquake strong ground motion (SGM) records is performed using fuzzy pattern recognition to exploit knowledge in the data that is utilised in a genetic algorithm (GA) search and scaling program. SGM records are historically treated as “fingerprints” of certain event magnitude and mechanism of faulting systems recorded at different distances on different soil types. Therefore, databases of SGM records of today present data of complex nature in high dimensions (many of the dimensions—or SGM parameters in time and frequency domain—are presently available from different archives). In this study, simple ground motion parameters were used but were combined and scaled nonlinearly such that the physical properties of the data could be preserved while reducing its dimensionality. The processed data was then analysed using fuzzy c-means (FCM) clustering method to explore the possibility of meaningfully representing earthquake SGM data in lower dimensions through finding subsets of mathematically similar vectors in a benchmark database. This representation can be used in practical applications and has a direct influence on the processes of synthesising ground motion records, identifying unknown ground motion parameters (e.g. soil type in this study), improving the quality of matching SGM records to design target spectra, and in rule generalisation for response. The results showed that the stochastic behaviour of earthquake ground motion records can be accurately simplified by having only a few of motion parameters. The very same parameters may also be utilised to derive unknown characteristics of the motion when the classification task on “training” records is performed carefully. The clusters are valid and stable in time and frequency domain and are meaningful even with respect to seismological features that were not included in the classification task.     

Ground Motion Parameters for the 2011 Great Japan Tohoku Earthquake

The 2011 great Japan Tohoku earthquake is not only the most devastating but also, one of the best recorded earthquakes in the history of seismology. A thorough study of strong motion characteristics of this earthquake is conducted using 20 well established ground motion parameters (GMPs). The behaviour of these parameters with fault distance and average shear wave velocity is examined and attenuation relationships are developed using the 1172 surface level strong motion records. In addition, all GMPs are categorized on a statistical basis using principal component analysis, which is further used to rate the damage potential of ground motion records.     

Transient and Long-Term Changes in Seismic Response of the Natural Resources Building,Olympia, Washington,due to Earthquake Shaking

The Natural Resources Building (NRB) in Olympia, Washington, was shaken by three earthquakes (Mw = 5.8, 6.8, and 5.0) between 1999 and 2001. Building motions were recorded on digital accelerographs, providing important digital recordings of repeated strong shaking in a building. The NRB has 5-stories above grade with 3 sub-grade levels and a ductile steel-frame elongated in the E-W direction. The upper two floors extend significantly beyond the lower 3 on the southern and eastern sides. N-S motions dominate the fundamental modal vibrations of the building system. In the 1999 Satsop M5.8 earthquake, the frequency of this fundamental system mode was 1.3 Hz during motions of 10% g. The frequency dropped to 0.7 Hz during the 2001 M6.8 Nisqually strong motions. Moreover, the Nisqually recordings reveal both numerous high-frequency transients of up to 0.18 g, several of which are visible on widely spaced sensors, and long-term tilts of some of the sensors. The weaker 2001 M5.0 Satsop earthquake motions showed the frequency remained depressed at less than 1 Hz for the eastern side of the structure, although the western side had recovered to 1.3 Hz. An ambient noise survey in 2008 showed the fundamental frequency of N/S vibrations remains about 1.0 Hz for the eastern side of the building and 1.3 Hz for the western side. These results suggest that in the Nisqually earthquake, the east side of the NRB suffered a permanent reduction in fundamental mode frequency of 37% due to loss of system stiffness by undetermined mechanism.     

Assessing Seismic Behavior of a Masonry Historic Building considering Soil-Foundation-Structure Interaction (Case Study of Arge-Tabriz)

ABSTRACT

Historic heritage buildings are a part of historic basis of each society and an economic resource. Therefore, preserving and maintenance of these buildings are cultural, economic and social demand. This research investigates the seismic performance of a historical building named Arg of Tabriz (Arge Alishah) that dates back to 14th century and is located at the city center of Tabriz (NW of Iran). Static, modal, and finally nonlinear dynamic (time history) analysis were performed by both “Considering Soil-Structure Interaction (SSI)” and “fixed base (ignoring SSI)” Cases.

It is found from the results that, SSI extremely affects mode shapes and their frequencies and depending on the frequency content of the records, can has an incremental or decremental effect on structural responses. As expected, the building of Arg could carry gravity loads easily and despite its stability against earthquake loading in fixed base case, showed a weakness (especially in eastern and western walls direction) and overturned when it was analyzed in SSI case because of yielding of the surrounding soil.     

SYSTEM IDENTIFICATION OF FEI-TSUI ARCH DAM FROM FORCED VIBRATION AND SEISMIC RESPONSE DATA

This paper presents the experimental investigation of the Fei-Tsui arch dam using the forced vibration test and its seismic response data. A forced vibration test was conducted on Fei-Tsui dam, this study presents the identified dynamic properties of the dam from these test data. For the identification of dam properties from seismic response data, in order to consider the nonuniform excitation of the seismic input and to describe the global behavior of the dam, the multiple input/multiple output discrete-time ARX model with least square estimation is applied to identify the dynamic characteristics of the dam. The system modal frequency, damping ratio and frequency response function are identified from both the forced vibration and seismic response data. To verify the accuracy of the identification result, comparison between discrete-time ARX model and a frequency domain conditioned spectral analysis was made. Finally, the spatial variation of ground motion across the free-field canyon surface is also studied.     

博物馆文物的防震保护研究（二）——设防地震动输入及结构地震动反应

通过对上海及邻近地区地震危害性分析,结合地震研究工作结果,根据上海博物馆文物防震保护的具体要求,研究确定了该博物馆文物防震保护的设防水准及地震动参数。场地地震动输入峰值加速度水准确定为50年超越概率3％,地震动反应谱采用上海市标准《建筑抗震设计规范》(DGJ08-9-92)中给出的地震影响系数曲线(阻尼比0.05),并将输入峰值加速度调整为180gal。研究采用了目前通用的拟合反应谱的方法,通过拟合选定的地震动反应标准谱,合成了6条人造地震波时程曲线,拟合精度控制在相对误差不大于5％;同时结合上海市《建筑抗震设计规范》(DGJ08-9-92)中所附的一条强震记录,共同作为上海博物馆结构地震反应分析的输入地震动。又根据上海博物馆建筑的结构特征分析,结合建筑结沟动力特征的实测结果,通过采用层模型结构时程分析计算方法,计算并获得了在遭遇设防地震时,上海博物馆建筑物每一层的地震动反应,表明上海博物馆建筑各楼层的地震动反应具有明显的楼层放大作用。对各楼层地震动反应的统计分析,给出了上海博物馆建筑物每一层的地震动参数,以此可作为今后文物地震危害性分析,及研究设计隔震装置等防震措施的依据。     

Estimating the Higher-Mode Response of Ductile Structures

While the importance of higher-mode actions is appreciated within the engineering community, the affect that ductile nonlinear response has on higher-mode characteristics and the subsequent implications this has for design has received little attention. In this article, the manner in which the higher-mode response of frame-wall structures is affected by inelastic behavior is closely examined and a means of accounting for this in design is proposed. The work focuses firstly on the characteristics of the higher modes present at the development of peak response and then considers how these characteristics would affect the total forces in the building. The study utilizes a series of nonlinear time-history analyses of two different groups of RC frame-wall structures subject to a suite of real records. It is shown that a new modal analysis approach that incorporates transitory inelastic modal characteristics gives significantly improved predictions of peak base shear in frame-wall structures than more traditional modal analysis methods which use elastic higher-mode characteristics. The issues associated with the use of transitory inelastic modal characteristics are discussed and various challenges that would need addressing for the prediction of other response parameters and structural types are identified.     

Correlations Between Frequency Content Indicators of Strong Ground Motions and PGV

The frequency content of ground motions seems to be one of the most important parameters to explain the structural damage experienced during worldwide strong earthquakes. The frequency content of ground motions can be characterized by various stochastic and/or deterministic indicators: the frequency bandwidth indicator ? (Cartwright & Longuet-Higgins) related to the power spectral density function and, respectively, the control (corner) period T_c of the structural response spectra or the mean period T_M . Peak ground velocity (PGV) and the ratio PGA/PGV can be used as either damage potential parameters or frequency content indicators. A comparative analysis of stochastic and deterministic frequency content indicators and of PGV is applied to a set of 30 strong ground motion records having peak ground acceleration (PGA) from 0.2–0.8 g and recorded on 4 continents during the last 70 years.     

VERTICAL EARTHQUAKE GROUND MOTION RECORDS: AN OVERVIEW

Recent research clearly shows the importance of including the vertical component of earthquake ground motion in seismic analysis and design. In addition, pioneering studies [e.g., Elnashai and Papazoglou (1997)] have explored and documented the characteristics of available near-field vertical ground motion records. As a follow-up, this paper complements earlier studies, and investigates additional far-field records and available downhole array vertical motion records. A total of 111 free-field strong motion records (from California) and available downhole array records are employed. Compared to near-field records, far-field records generally contain more energy at longer periods. Based on the available data, response spectra are presented for near-field and far-field records respectively. The currently scarce downhole-array vertical motion records show that significant amplification may occur within the top 10-20 m soil layers. A simple one-dimensional (ID) vertical wave propagation model did not appear adequate for modelling the observed downhole array response. In using such a simplified model, very high viscous damping in the range of 15-25% was needed to match the recorded downhole vertical response, even for small tremors. Additional data and research are required [Beresnev et al., 2002] towards the development of a rational vertical motion site response analysis procedure.     

Seismic Analysis of Non Proportionally Damped Two-Way Asymmetric Elastic Buildings Under Bi-Directional Seismic Ground Motions

This study investigates the effectiveness of the modal analysis using three-degree-of freedom (3DOF) modal equations of motion to deal with the seismic analysis of two-way asymmetric elastic systems with supplemental damping. The 3DOF modal equations of motion possessing the non proportional damping property enable the two modal translations and one modal rotation to be non proportional in an elastic state. The simple approximation method is to use the single degree-of-freedom (SDOF) modal equations of motion, which are obtained by neglecting the off-diagonal elements of the transformed damping matrix. One, one-story and one, three-story non proportionally damped two-way asymmetric buildings under the excitation of bi-directional seismic ground motions are analyzed. The analytical results are obtained by using the proposed method, noted simple approximation method, and direct integration of the equation of motion. It is seen that the proposed method can significantly improve the accuracy of the analytical results compared with those obtained by using the simple approximation method. Moreover, the proposed method does not substantially increase the computational efforts.     

Dynamic Response of Saturated Soil - Foundation System Acted upon by Vibration

In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. In order to investigate the response of soil and footing to steady state dynamic loading, a physical model was manufactured to simulate steady state harmonic load at different operating frequencies. Total of 84 physical models were performed. The footing parameters are related to the size of the rectangular footing and depth of embedment. Two sizes of rectangular steel model footing were tested at the surface and at 50 mm depth below model surface. Meanwhile the investigated parameters of the soil condition include dry and saturated sand for two relative densities 30% and 80%. The response of the footing was elaborated by measuring the amplitude of displacement by the vibration meter. The response of the soil to dynamic loading includes measuring the stresses inside the soil using piezoelectric sensors as well as measuring the excess pore water pressure using pore water pressure transducers. It was concluded that the maximum displacement amplitude response of the foundation resting on dry sand models is more than that on the saturated sand by about 5.0–10%. The maximum displacement amplitude of footing is reduced to half when the size of footing is doubled for dry and saturated sand. The final settlement (St) of the foundation increases with increasing the amplitude of dynamic force, operating frequency and degree of saturation. Meanwhile, it is reduced with increasing the relative density of sand, modulus of elasticity, and embedding inside soils. The excess pore water pressure increases with increasing the relative density of the sand, the amplitude of dynamic loading and the operating frequency. In contrast, the rate of dissipation of the excess pore water pressure during dynamic loading is more in the case of loose sand.     

A PROCEDURE FOR COMBINING VERTICAL AND HORIZONTAL SEISMIC ACTION EFFECTS

The vertical component of earthquake ground motion has generally been neglected in the earthquake-resistant design of structures. This is gradually changing due to the increase in near-source records obtained recently, coupled with field observations confirming the possible destructive effect of high vertical vibrations.

In this paper, simple procedures are suggested for assessing the significance of vertical ground motion, indicating when it should be included in the determination of seismic actions on buildings. Proposals are made for the calculation of elastic and inelastic vertical periods of vibration incorporating the effects of vertical and horizontal motion amplitude and the cross-coupling between the two vibration periods. Simplified analysis may then be used to evaluate realistic vertical forces by employing the vertical period of vibration with pertinent spectra without resorting to inelastic dynamic analysis.

Finally, a procedure is suggested for combining vertical and horizontal seismic action effects which accounts for the likelihood of coincidence, or otherwise, of peak response in the two directions.     

Effect of Nonlinearity of Frame Buildings on Peak Horizontal Floor Acceleration

Using representative numerical models of eight code-designed steel moment-resisting frame buildings and several ground motions, time-history analyses are performed and a critical evaluation of Peak Horizontal Floor Acceleration (PHFA) demands is conducted. The frames are modeled alternatively as linear and nonlinear systems to isolate the effect of building nonlinearity on PHFA. In most cases, PHFA is reduced when nonlinear behavior of a building is considered; however, in some cases, significant amplification of PHFA is observed. Results from the numerical study provide insight into the trend of modal response modification factors presented taking ground motion spectral shape into account.     

Fragility-Based Performance Evaluation of Asymmetric Single-Story Buildings in Near Field and Far Field Earthquakes

Previous studies have shown that both distribution and intensity of response parameters in asymmetric buildings are dependent on their stiffnesses and strength distributions. The locations of centers of strength and rigidity relative to the center of mass provide suitable metrics for strength and stiffness distributions. In general, the proper locations of these centers are a function of earthquake ground motion characteristics and the level of building's nonlinear responses. In this article, using nonlinear response evaluation of single-story building models with a wide range of uncoupled torsional to lateral frequencies subjected to near field and far field earthquake excitations the proper location of building centers is studied . Diaphragm rotation, interstory drift, hinge plastic rotation, and ductility demand are selected as damage measure parameters. To compare the performance of models in each limit state, fragility representation of responses is used. It is concluded that proper configuration of building centers in a torsionally stiff building fundamentally depends on the chosen demand parameter. The proper configuration of centers in a torsionally stiff building for a specific demand parameter can converge the probability and distribution of related damages to those in the symmetric building counterpart. When the critical demand parameter for a case is identified, its corresponding arrangements of centers for a suitable seismic behavior may also be recognized. By rearranging the configuration of centers based on the attained configuration, the adverse effects of asymmetry can be avoided.     

A Ground Motion Record Selection Approach Based on Multiobjective Optimization

The evaluation of the seismic safety and reliability of buildings and building contents within a probabilistic framework often requires response history analyses using site-specific ground motion records. The ground motion selection method proposed in this paper addresses this issue by a stochastic search procedure in which record sets are selected such that first- and second-order statistics (median and dispersion) satisfy predefined ground motion spectrum targets over a wide period range. Once a ground motion record set is selected, it can be used for seismic assessment of a broad class of buildings within the target period range at the given location.     

省志编纂工作组织推进体系的探索与创新

组织实施省志编纂是省级地方志工作机构的一项重要职责和主要工作内容。随着第二轮省志编纂工作的全面展开,各省都在积极探索组织推进的方式、路径。江苏省地方志办公室的做法是：围绕政府主持做文章,抓住社会参与谋思路,借用市场运作出实招。依靠政府,建立坚强有力的组织推动体系;面向社会,建立精干多元的修志参与体系;借鉴市场,建立规范有效的运行监控体系;形成政府、社会、市场的良性互动,促进省志编纂工作的健康发展。     

SEISMIC RELIABILITY ASSESSMENT OF EXISTING REINFORCED CONCRETE BUILDINGS

Structures designed according to earlier codes with inadequate seismic provisions have not performed satisfactorily during recent earthquakes. The seismic performance of an existing three-storey reinforced concrete building designed according to the 1963 ACI 313-63 is evaluated and compared to the performance of a similar frame designed according to current code provisions. Non-linear static and dynamic analyses of the reinforced concrete frames are conducted. In this study, a probabilistic approach is adopted where a large number of artificially generated ground motion records is used as input motion to the structure. The results of the analysis indicated the probability of various degrees of damage to be expected when the existing frame is subjected to different ground motion levels. This information is useful in the design of the required rehabilitation scheme to provide an identified level of protection.     

The Baseline Stiffness Method for Damage Detection in Buildings Without Baseline Modal Parameters

A new method called the Baseline Stiffness Method (BSM), used to locate and quantify damage in buildings without baseline modal parameters (undamaged state), is presented. In order to determine this reference state, the BSM uses modal parameters from the damaged state of the building and the lateral stiffness matrix of the first story without damage. Afterwards, by means of an iterative process using singular value decomposition, location and severity of damage are obtained by comparing information about the damaged and non damaged states. Numerical and experimental examples are presented and discussed showing the advantages of the application of the proposed BSM.     

当代方志文化的构建及其意义

当代方志文化所包含的内容十分丰富,涉及面极其广泛。长期以来,我们对当代方志文化的构建关注不够。构建当代方志文化有助于促进地方志事业又好又快地发展,有助于促进地域文化的传承与发展,有助于物质文明、精神文明、政治文明、生态文明的建设和社会主义法治国家、文化强国、和谐社会的建设。构建当代方志文化必须立足于当代地方志事业,善于从传统方志文化中汲取养分,善于吸收其他文化门类之所长,借鉴国内外学术研究的最新成果。