Deep water gravity core from the Marsili Basin (Tyrrhenian Sea) records Pleistocenic–Holocenic explosive events and instability of the Aeolian Archipelago, (Italy)     

A. Di Roberto  M. Rosi  A. Bertagnini  M.P. Marani  F. Gamberi  A. Del Principe 《Journal of Volcanology and Geothermal Research》2008

A 4.8 m long gravity core was recovered on a relative topographic high in the northern part of the Marsili Basin (southern Tyrrhenian Sea) at a water depth of 3200 m. The core was taken in order to decipher the sedimentary record of the past volcanic events of the nearby Aeolian arc. A succession of thin (2 cm to 5 cm thick) fine-grained turbidites, mainly of volcaniclastic origin, topped by hemipelagic mud layers and a number of primary tephra layers were recovered by the core. The most prominent turbidite occurs in the lower part of the core at 385 cm. It consists of a 20 cm-thick, thinning-upward, pebble to sand-sized bed.  相似文献   

Quantification of modelling uncertainty in existing Italian RC frames     

《地震工程与结构动力学》2018,47(4):1054-1074

Assessment of the seismic performance of existing structures requires due consideration of both aleatory and epistemic sources of uncertainty; the former being typically associated with the randomness in ground motion records and the latter with the uncertainty in numerical modelling. Using a numerical modelling approach calibrated to available experimental test data collected from the literature, the uncertainty associated with different modelling parameters for existing reinforced concrete frames in Italy was quantified via an extensive numerical study. This was done to quantify the propagation of modelling parameter type uncertainty to the overall dispersion of the demand parameters typically used in seismic assessment, namely peak storey drift and peak floor accelerations. In addition, the impact of such modelling uncertainty on the median intensity and dispersion of the collapse fragility function was also examined. From the results of this study, empirical values of modelling parameter uncertainty were quantified with a view to being used in the assessment of existing reinforced concrete frames with masonry infill designed prior to the introduction of seismic design provisions in Italy during the 1970s. Comparing these empirical values to those available in the literature, it is seen how the fundamental behaviour of the frames differs from more modern frames with ductile detailing to the extent that values available in guidelines such as FEMA P58 cannot be reasonably adopted for these structural typologies.  相似文献   

THE DISPLACEMENT AND STRESS FIELD GENERATED BY THE COLLAPSE IN PINGYI COUNTY,SHANGDONG PROVINCE,ON DECEMBER 25, 2015          下载免费PDF全文

WAN Yong-ge  JIN Zhi-tong  CUI Hua-wei  HUANG Ji-chao  SHENG Shu-zhong  ZHANG Shan-shan  LI Cui-qin 《地震地质》2017,39(1):81-91

A collapse happened in Pingyi County, Shandong Province, on December 25, 2015. The displacement field, stress field and Coulomb failure stress change on the Mengshan frontal fault generated by the collapse are calculated by using point collapse model in isotropic medium. The result shows that: (1) The maximum horizontal displacement is located at the center of the collapse with value of~18mm. The horizontal displacements are greater than 1mm within~5km of the collapse with its direction pointing to the collapse center. The maximum subsidence is located at the center of the collapse with the value of 4mm. The subsidence is greater than 1mm within ~3km of the collapse. The displacement field decays so rapidly that can be ignored at far away from the collapse for the shallow source, which caused local displacement field. (2) Influenced by the free surface, the contraction area stress within ~5km of the collapse with the order of 1000Pa and expansion area stress in farther away areas at depth of 2km are estimated. the expansion area stress of 1000Pa is estimated at the~5km from the collapse center. Then the expansion area stress decays to 100Pa at the distance of ~10km from the collapse. The maximum compressive and extensional principal stresses are estimated as 10000Pa at the depth of 2km. The compressive stress axes present radical direction pointing to the collapse within ~5km of the center. In farther away from the collapse, The extensional principal stress axes present radical direction pointing to the center of the collapse. With farther distance to the collapse, the compressive and extensional stress decay rapidly to the order of 100Pa. (3) The Coulomb failure stress on the northwestern part of the Mengshan frontal fault, which is known as active segment of the Mengshan frontal fault, is decreased by the collapse with maximum value of 2500Pa. Whereas, the Coulomb failure stress on the southeastern part of the Mengshan frontal fault, which is known as left-lateral normal slip fault segment in Quaternary period, is increased by the collapse with maximum of 2400Pa, to which attention would be paid in seismic hazard analysis.  相似文献   

Seismic vulnerability of offshore wind turbines to pulse and non-pulse records     

Ahmer Ali  Raffaele De Risi  Anastasios Sextos  Katsuichiro Goda  Zhiwang Chang 《地震工程与结构动力学》2020,49(1):24-50

The increasing number of wind turbines in active tectonic regions has attracted scientific interest to evaluate the seismic vulnerability of offshore wind turbines (OWTs). This study aims at assessing the deformation and collapse susceptibility of 2MW and 5MW OWTs subjected to shallow-crustal pulse-like ground motions, which has not been particularly addressed to date. A cloud-based fragility assessment is performed to quantify the seismic response for a given intensity measure and to assess the failure probabilities for pulse-like and non-pulse-like ground motions. The first-mode spectral acceleration S_a(T₁) is found to be an efficient response predictor for OWTs, exhibiting prominent higher-mode behavior, at the serviceability and ultimate conditions. Regardless of earthquake type, it is shown that records with strong vertical components may induce nonlinearity in the supporting tower, leading to potential failure by buckling in three different patterns: (i) at tower base near platform level, (ii) close to tower top, and (iii) between the upper half of the main tower and its top. Type and extent of the damage are related to the coupled excitation of vertical and lateral higher modes, for which tower top acceleration response spectra S_a,i(Top) is an effective identifier. It is also observed that tower's slenderness ratio (l/d), the diameter-to-thickness ratio (d/t), and the rotor-nacelle-assembly mass (m_RNA) are precursors for evaluating the damage mode and vulnerability of OWTs under both pulse-like and non-pulse-like ground motion records.  相似文献   

Earthquake‐induced loss assessment of steel frame buildings with special moment frames designed in highly seismic regions          下载免费PDF全文

Seong‐Hoon Hwang  Dimitrios G. Lignos 《地震工程与结构动力学》2017,46(13):2141-2162

This paper discusses an analytical study that quantifies the expected earthquake‐induced losses in typical office steel frame buildings designed with perimeter special moment frames in highly seismic regions. It is shown that for seismic events associated with low probabilities of occurrence, losses due to demolition and collapse may be significantly overestimated when the expected loss computations are based on analytical models that ignore the composite beam effects and the interior gravity framing system of a steel frame building. For frequently occurring seismic events building losses are dominated by non‐structural content repairs. In this case, the choice of the analytical model representation of the steel frame building becomes less important. Losses due to demolition and collapse in steel frame buildings with special moment frames designed with strong‐column/weak‐beam ratio larger than 2.0 are reduced by a factor of two compared with those in the same frames designed with a strong‐column/weak‐beam ratio larger than 1.0 as recommended in ANSI/AISC‐341‐10. The expected annual losses (EALs) of steel frame buildings with SMFs vary from 0.38% to 0.74% over the building life expectancy. The EALs are dominated by repairs of acceleration‐sensitive non‐structural content followed by repairs of drift‐sensitive non‐structural components. It is found that the effect of strong‐column/weak‐beam ratio on EALs is negligible. This is not the case when the present value of life‐cycle costs is selected as a loss‐metric. It is advisable to employ a combination of loss‐metrics to assess the earthquake‐induced losses in steel frame buildings with special moment frames depending on the seismic performance level of interest. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Effect of ground motion selection methods on seismic collapse fragility of RC frame buildings   总被引：1，自引：0，他引：1       下载免费PDF全文

Mohammad E. Koopaee  Rajesh P. Dhakal  Gregory MacRae 《地震工程与结构动力学》2017,46(11):1875-1892

Variation in the seismic collapse fragility of reinforced concrete frame buildings predicted using different ground motion (GM) selection methods is investigated in this paper. To simulate the structural collapse, a fiber‐element modelling approach with path‐dependent cyclic nonlinear material models that account for concrete confinement and crushing, reinforcement buckling as well as low cycle fatigue is used. The adopted fiber analysis approach has been found to reliably predict the loss in vertical load carrying capacity of structural components in addition to the sidesway mode of collapse due to destabilizing P–Δ moments at large inelastic deflections. Multiple stripe analysis is performed by conducting response history analyses at various hazard levels to generate the collapse fragility curves. To select GMs at various hazard levels, two alternatives of uniform hazard spectrum (UHS), conditional mean spectrum (CMS) and generalized conditional intensity measure (GCIM) are used. Collapse analyses are repeated based on structural periods corresponding to initial un‐cracked stiffness and cracked stiffness of the frame members. A return period‐based intensity measure is then introduced and applied in estimating collapse fragility of frame buildings. In line with the results of previous research, it is shown that the choice of structural period significantly affects the collapse fragility predictions. Among the GM selection methods used in this study, GCIM and CMS methods predict similar collapse fragilities for the case study building investigated herein, and UHS provides the most conservative prediction of the collapse capacity, with approximately 40% smaller median collapse capacity compared to the CMS method. The results confirm that collapse probability prediction of buildings using UHS offers a higher level of conservatism in comparison to the other selection methods. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

实验室造波条件对内孤立波发展影响的直接数值模拟     

叶潇潇  游景皓  宋金宝 《海洋与湖沼》2021,52(3):573-583

内孤立波具有振幅尺度大、能量集中的特点,其引起流场和密度场的迅速变化可能对海洋工程结构物以及水下潜体造成严重威胁。因此研究不同造波条件下生成的内孤立波运动的流场特征具有重要的学术意义和实际应用价值。采用直接数值模拟方法和给定的初始密度场密度跃迁函数,对重力塌陷激发内孤立波的运动过程进行研究,探讨了不同造波条件下,激发产生的内孤立波波型、涡度、振幅和水平速度等流场特征。结果表明:(1)直接模拟数值方法能够模拟内孤立波传播过程中的密度界面波型反转现象;(2)从定性和定量的角度,证实了不稳定内孤立波传播过程中存在能量的向后传递;(3)对于相同的台阶深度(水闸两侧初始密度界面的高度差),初始涡流保持相同,但是随着上下层水深比的减小,其强度下降显著;(4)台阶深度对初始涡流的垂直结构的影响要大于上下层水深比,且台阶深度对内孤立波的振幅、水平速度的影响显著。  相似文献   

岩溶塌陷临界土洞的极限平衡高度公式   总被引：9，自引：1，他引：8  

王滨  贺可强 《岩土力学》2006,27(3):458-462

土洞的产生和发展是岩溶塌陷的基础,临界土洞是土洞发展的最终阶段,以临界土洞为界,岩溶塌陷在时间和空间上划分为内部塌陷阶段和地表塌陷阶段。内部塌陷阶段是土洞在覆盖层土体内部的发育扩展阶段,土洞顶板土体的破坏形式类似于地下洞室洞顶围岩的破坏。根据地下洞室普氏平衡拱理论,建立覆盖层土体的天然平衡拱高度,即临界土洞的极限平衡高度公式,并以唐山市体育场岩溶塌陷为例,对该公式进行验证评价,计算所得塌陷的临界土洞高度与实际情况相符合,误差仅为4.3 %。  相似文献   

小陷落柱异常波提取及其特征的模型研究   总被引：1，自引：0，他引：1  

周国兴  杨文钦  杨文强 《煤田地质与勘探》2006,34(5):63-65

通常情况下,较小规模陷落柱的地震响应特征不明显。运用矩阵的奇异值分解(SVD)方法,通过对三维模型数据的处理,把煤层反射波作为被压制的对象,突出断陷点所产生的绕射波,以达到提高对较小规模陷落柱地震解释的目的。实际运用效果较好。   相似文献   

华北煤田岩溶陷落柱分类及其特征   总被引：7，自引：0，他引：7  

李永军  彭苏萍 《煤田地质与勘探》2006,34(4):53-57

在总结华北煤田多起陷落柱突水事例及对徐淮煤田40多个矿区调研的基础上,依据陷落柱不同发育阶段的水文地质工程地质特征等,将其分为4个发育阶段:前期发育阶段、强烈发育阶段、衰退阶段和死亡阶段。通过分析陷落柱发育的不同层位,将其划分为3类,即奥灰层位之上可溶岩组、奥陶纪可溶岩组及寒武纪可溶岩组。继而,将陷落柱综合划分为12类,并总结分析了各类型陷落柱的地质特征。   相似文献