固定和浮放条件下文物展柜动力响应分析与试验研究

目前对文物保护的研究主要以试验为主,本研究试图用数值方法分析文物展柜的动力学特性,以解决试验分析方法所导致的缺陷。为此,对固定和浮放两种不同边界条件的文物展柜进行地震作用和简谐激励下的动力响应分析,给出了展柜展台面处的加速度动力放大系数(简称放大系数)上限值。以某博物馆展柜为原型,按1∶1/0.39进行缩尺振动试验,得出两种边界条件下展柜展台面处的放大系数。对试验展柜建立有限元模型,通过与试验对比,验证模型及分析方法的正确性。然后,建立展柜模型的有限元模型,对5种尺寸的展柜进行了动力响应分析,并考虑激励幅值、激励频率等对放大系数的影响。分析结果有助于指导文物的防震保护工作。     

Numerical Evaluation of Topographic Effects at the Nicastro Ridge in Southern Italy

Numerical site response analyses were carried out on the Nicastro ridge in Southern Italy in order to investigate topographic effects. First, the analyses were carried out on a simplified model by employing simple artificial signals, in order to get preliminary physical insights into the two-dimensional phenomena involved. Then, numerical analyses were carried out on a more realistic heterogeneous subsoil model developed on the basis of geotechnical and geophysical investigations. Real accelerograms were selected for these analyses. Particular attention was devoted to separating topographic from stratigraphic amplification. Finally, the topographic amplification factors were compared with literature data and Eurocode 8 recommendations.     

Spectral Attenuation Relations at Soft Sites Based on Existing Attenuation Relations for Rock Sites

A simple and general method based on well-known random vibration theory is used to compute spectral attenuation relations at soft sites based on existing spectral attenuation relations at rock sites. The method consists of: (1) computation, for given magnitude and distance, of the expected Fourier amplitude spectrum associated with the median rock response spectrum computed with the attenuation relation; (2) inclusion of site effects characterized by a frequency-dependent, linear, or nonlinear transfer function; and (3) computation of the response spectrum at the soft site.     

Experimental Study on Seismic Performance of Mechanical/Electrical Equipment with Vibration Isolation Systems

A prototype diesel generator equipped with a vibration isolation system consisting of restrained isolators (denoted as I/system) is quasi-statically and dynamically tested. Sequentially, the seismic simulation tests are conducted to further investigate the effectiveness of additional snubbers incorporated into the vibration isolation system (denoted as I/R system). Comparing the test results to the static design demands specified in ASCE 7-10, the recommended component amplification factor could represent the horizontal acceleration amplification phenomenon of the generator equipped with I/R system; however, the seismic force demands for static design of I/R system might not be appropriate and conservative enough.     

Seismic Site Response Modeling for Three Missouri River Highway Bridges

Three highway bridges spanning the Missouri River flood plain were selected for evaluation of seismic site response for moderate size earthquakes emanating from the New Madrid Seismic Zone (NMSZ) in the Midwestern United States. The NMSZ is known to be capable spawning earthquakes larger than magnitude (M) 7.0, four of which occurred in a three-month period between 1811 and 1812, and the M_w 6.0 earthquake of October 1895 centered near Charleston, Missouri. This study evaluated the likely impacts of long period motion of these historic earthquakes on three long-span highway bridges using geotechnical data obtained from recent investigations. Our results suggest site amplification between 6× and 9×, depending on the magnitude and epicentral distance. We believe that threshold magnitude for serious foundation failure and damage to these bridges is between M_w 6.5 and 6.6. Above these magnitudes widespread liquefaction is predicted, which would effect the peak horizontal acceleration and spectral accelerations, causing the ground motions to be different than predicted. Increase in amplification of the response spectra also should be expected where the periods are higher than 1.0 sec. Therefore, M_w 6.5+ earthquakes at ranges 210–260 km could be expected to engender resonant frequency problems for multiple span bridges and tall buildings (10 to 25 stories) in channel corridors containing 20 to 46 m of unconsolidated sediment.     

Effect of Irregular Seabed on Seismic Motions

Several studies indicate that marine seismic activity is vast. Actually, about 90% of all natural earthquakes have epicenters in o_shore areas and may cause damage to subsea and floating structures. In this numerical study the indirect boundary element method is used to analyze the influence that some parameters, involved in this kind of problems, have on the dynamic response of marine waters under the incidence of theoretical seismic events. According with the results, the seismic amplifications depend on the seabed configuration and produce displacements which can be a serious concern.     

Seismic Response of the Central Part of Indo-Gangetic Plain

In spite of high seismic risk, there is no numerical model of Indo-Gangetic Plain. In this paper, seismic response of the central part of Indo-Gangetic Plain, i.e., Ganga Plain is studied using a two-dimensional plane strain finite element model. Seismic source is assumed to be located beneath the Himalayas near Himalayan Frontal Thrust. Basin response is simulated for a hypothetical M_w 8.0 Himalayan earthquake. Ground motion amplification and sensitive frequency band of the basin, obtained from the numerical simulation, show that the sediment depth and epicentral distance at a site play significant role in the seismic response of the site.     

Seismic Microzonation and Damage Assessment of Bam City,Southeastern Iran

This article aims to study the dynamic characteristics of soil in Bam, southeastern Iran. Fundamental frequency and amplification factor of soil sediment were estimated by microtremor measurement. This procedure was performed at 49 sites in the city. Two 120-second data were recorded at each site. Segmental cross spectra were applied to calculate spectrum, Nakamura's method (H/V) was used for analyzing data and fundamental frequency and amplification factor values were derived. Iso-frequency and iso-amplification maps of the city were prepared. Results show that soil type in Bam city is mainly stiff, although amplification factor is relatively large. There is a short period zone in northwest to southeast direction. Sediment depth was estimated using a correlation between fundamental frequency and sediment thickness. Results obtained from microtremors were compared to the geotechnical boreholes and it was shown that microtremors can be used for a rough estimation of sediment thickness. Damage distribution map of Bam due to the Bam earthquake on December 26, 2003 was prepared by both field and aerial investigation. Quality of buildings in Bam was evaluated, as a result a crude zoning map on the building quality was prepared. Finally, it was concluded that several factors have contributed to damage intensity variation; earthquake characteristics, local site effect, and buildings' quality. All mentioned parameters affected the damage variation.     

Site Classification System and Site Coefficients for Shallow Bedrock Sites in Korea

Recent studies have shown that the site coefficients obtained from site response analyses of Korean soil sites are significantly different from those specified in the current Korean seismic code, especially in the short-period portion of site response. This difference is mainly attributed to the shallow bedrock conditions (bedrock depth usually less than 30 m) in Korea. This study proposes a new site classification system and site coefficients for shallow bedrock sites based on site response analyses of more than 300 sites. The proposed site classification scheme and site coefficients proposed in this study are an improvement over the current seismic code and previous studies.     

Floor Spectra of Inelastic RC Frame Buildings Considering Ground Motion Characteristics

A range of reinforced concrete frame buildings with different levels of inelasticity as well as periods of vibration is analyzed to study the floor response. The derived floor acceleration response spectra are normalized by peak ground acceleration, peak floor acceleration, and ground response spectrum. The normalization with respect to ground response spectrum leads to the lowest coefficients of variation. Based on this observation as well as previous studies, an amplification function is proposed that can be used to develop design floor spectra from the ground motion spectrum, considering the building’s dynamic characteristics and level of inelasticity.