Tectonic significance of Late Neoproterozoic granites from the Tibesti massif in southern Libya inferred from Sr and Nd isotopes and U–Pb zircon data   总被引：1，自引：0，他引：1  

Ismail B. Suayah  Jonathan S. Miller  Brent V. Miller  Tovah M. Bayer  John J.W. Rogers   《Journal of African Earth Sciences》2006,44(4-5):561

The Neoproterozoic crust of the Tibesti massif was stabilized by magmatism that included subduction-generated batholithic suites and post-orogenic granite plutons. All of the magmatism occurred in a period of about 20 million years centered around 550 Ma, and nearly all of the granites have initial ⁸⁷Sr/⁸⁶Sr ratios of about 0.706. The Wadi Yebigue pluton has U–Pb zircon ages of 563 Ma and 558 Ma on two different phases and ε_Nd at 550 Ma from −0.5 to −2.2. These isotopic data and the geologic history of the massif suggest that granites in the Tibesti massif developed during and shortly after closure of a short-lived ocean basin that developed by fragmentation of pre-existing continental crust of the Saharan region.  相似文献   

砌体结构并联复合隔震建筑有限元分析     

赵士永  李旭光 《华北地震科学》2011,29(2):23-26

本文以某六层砌体橡胶隔震支座与摩擦滑移支座的并联复合隔震结构为例,运用有限元分析程序,对该建筑的一般抗震结构和并联复合隔震结构分别进行了地震作用下的有限元时程分析,结果显示:并联复合隔震结构能够降低上部结构的地震反应,提高建筑物的抗震能力,有明显的隔震、减震效果.  相似文献   

Assessment indices for the seismic vulnerability of existing R.C. buildings     

G. E. Thermou  S. J. Pantazopoulou 《地震工程与结构动力学》2011,40(3):293-313

The seismic vulnerability of old multi‐storey reinforced concrete (R.C.) buildings reinforced with substandard details is assessed as a function of interstorey drift demand imposed by the design earthquake while considering brittle termination of elastic response of the critical members of the structure due to a premature shear failure. Interstorey drift demand is related to column and wall translational stiffnesses which are expressed through analytical derivations in terms of the floor area ratios of gravity and lateral load bearing members in the critical floor. Interstorey drift capacity is related to the available transverse reinforcement and the axial load ratio of the vertical members. The significance of the area ratio of vertical members in the typical floor as an index of vulnerability is explored with reference to the limitations in the value of axial load ratio used in R.C. design in order to secure ductile flexural behavior, and also with reference to the stability index of gravity load bearing members. Interstorey Drift Spectra are derived for the existing R.C. buildings suitable for rapid seismic vulnerability screening but also as a guide for rehabilitation of the existing structures. Lightly reinforced or substandard reinforced concrete buildings that reportedly collapsed during previous earthquakes are used as example case studies in order to calibrate the proposed methodology. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Shaking‐table tests of a full‐scale single‐story masonry veneer wood‐frame structure     

Hussein O. Okail  P. Benson Shing  William M. McGinley  Richard E. Klingner  Seongwoo Jo  David I. McLean 《地震工程与结构动力学》2011,40(5):509-530

This paper presents the findings of shaking‐table experiments conducted to examine the seismic performance of a full‐scale, one‐story, wood‐framed structure with masonry veneer. The structure was designed and constructed in accordance with current U.S. code provisions. The veneer was attached to the wood backing with two kinds of metal anchors, corrugated ties fastened with 8d nails and rigid ties fastened with #8 screws. The tests have shown that the use of nails to fasten veneer anchors to the wood studs is highly unreliable due to the high variation of the nail extraction capacity, which can be influenced by the moisture content of the wood. Other than this, both the wood frame and the masonry veneer performed well under severe ground motions far exceeding a design level earthquake for Seismic Design Category D. Good performance was observed for the rigid veneer ties, which were attached to the wood studs with screws. The results have shown that the veneer walls parallel to the direction of shaking helped to restrain the motion of the wood structure and therefore should not be simply treated as added mass. The detailing of wood roof diaphragms requires special attention in consideration of the out‐of‐plane inertia force of the veneer that can be transmitted through the top plate of the wood‐stud wall to the rim joist. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

In situ cyclic tests on existing stone masonry walls and strengthening solutions     

Alexandre A. Costa  António Arêde  Aníbal Costa  Carlos Sousa Oliveira 《地震工程与结构动力学》2011,40(4):449-471

The present work reports on an in situ experimental test campaign carried out on abandoned traditional masonry houses after the 9th July 1998 earthquake that seriously hit the Faial island of Azores. For the testing purposes, an experimental test setup was developed based on a self‐equilibrated scheme, which is herein described reporting on the advantages and drawbacks of this in situ test setup. Five specimens were tested aiming at characterizing the out‐of‐plane behavior of stone masonry walls and strengthening solutions recommended for post‐earthquake interventions. A detailed comparison between solutions' efficiency is presented including a cost vs benefit analysis. In order to assess the efficiency of the developed test setup for other applications on stone masonry walls, an in‐plane test on an existing URM panel is also presented. Several related issues are discussed, namely the advantages of dealing with the real boundary conditions and the capacity of providing valuable information of the response, as well as a detailed analysis of the obtained results. The authors believe that this work provides an increase in knowledge on the seismic behavior of the existing masonry constructions, resulting from the development of an in situ test setup and the efficiency quantification of strengthening solutions. Therefore, the work is thought to positively contribute for the preservation of architectural heritage and for its seismic vulnerability reduction. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Nonlinear analysis of out‐of‐plane masonry façades: full dynamic versus pushover methods by rigid body and spring model     

Siro Casolo  Giuseppina Uva 《地震工程与结构动力学》2013,42(4):499-521

The paper proposes a systematic comparison between two methods of analysis that are well established in the field of earthquake engineering: nonlinear dynamic analysis and nonlinear static procedure (NSP), applied to the out‐of‐plane seismic response of two masonry façades representative of many ancient Italian churches. The comparison is based on extensive numerical analyses, which focus on the flexural and torsional mechanisms, while the in‐plane damage mechanisms and the possible detachment between the façade and the lateral walls because of a poor connection have been presently disregarded. The computations, both in the static and in the dynamic field, are based on a rigid body and spring model specifically implemented for this issue, computationally efficient and equipped with a realistic model of damage and hysteresis at the mesoscale. An innovative aspect of this study is the heuristic modelling of three‐wythe masonry, to include some typical texture effects on the macroscale nonlinear response. For each façade, two different masonry textures were considered, performing extensive dynamic analyses that offered a detailed overview about the performance under earthquakes of different intensities. In parallel, NSP and the classical N2‐based seismic assessment were applied. A critical discussion and comparison of the results of the two methods is presented to rationally appraise limits and opportunities. In particular, flexural and twisting out‐of‐plane mechanisms were clearly appraised in the dynamic field, whereas NSPs were not always able to describe the collapse, because they missed the partial failures determined by higher vibration modes, as could be expected. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Free rocking response of a regular stone masonry wall with equivalent block approach: experimental and analytical evaluation     

Alexandre A. Costa  António Arêde  Aníbal Costa 《地震工程与结构动力学》2013,42(15):2297-2319

The evaluation of the dynamic behaviour of rocking elements is directly correlated to the energy dissipated because of the impacts at the base interface, which can be represented by means of a coefficient of restitution. This schematization is commonly accepted as representative of the out‐of‐plane response of stone masonry walls. An experimental campaign (in a lab environment) aiming at assessing the value of this coefficient for a sacco granite masonry wall is presented in this work. The rocking motion at a predefined bed joint level was induced in the tested specimens in order to validate a novel test setup designed to assess the coefficient of restitution value by means of a realistic reproduction of the rocking behaviour of a single element, under the hypothesis of an infinitely stiff system above the bed joint level. As the main objective of the work was to assess the rocking behaviour of a masonry wall that looses energy at the impacts at a certain joint level, the flexural behaviour was not desirable and had to be avoided. For this purpose, a test setup based on the equivalent block approach was developed. In the final section of this work, comparisons between experimental and numerical results are presented together with some preliminary conclusions on the appropriate modelling strategy and the values of the coefficient of restitution to be used for the seismic assessment of the out‐of‐plane rocking behaviour of this type of sacco stone masonry walls. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Discovery of an outcropping Mass Transport Deposit (MTD) in the Palaeogene subalpine synclines of southeastern France: Implications on flexural sub-basin deformation     

《Comptes Rendus Geoscience》2014,346(1-2):37-44

We document the sedimentary facies of a large Mass Transport Deposit (MTD) within the sand-rich sediment gravity flow-dominated deposits of the Eocene–Oligocene south-western Alpine forelands (Annot Sandstone system). The MTD with an approximated volume of several hundreds of cubic kilometres fills a sub-basin located in the Mont-Tournairet confined sub-basin. Autochthonous facies are very typical sediment gravity-flow deposits (thin-bedded classical turbidites and thick-bedded hyperconcentrated to concentrated flow deposits) that stratigraphically belong to the Annot Sandstone infill. Slumps and internal metre-large fold axes of the deformed stratigraphic intervals indicate a main transport direction towards the northwest. The seafloor instability that led to the mass-flow events within the Mont-Tournairet sub-basin could have been favoured by high sedimentation rates in a small, confined and tectonically active sub-basin, possibly enhanced by local structural deformation associated with the Triassic evaporites on the eastern side of the Mont-Tournairet confined basin. The presence of the MTD suggests that a period of increased flexural subsidence rate and basin deformation occurred in this portion of the subalpine foreland basin. Therefore, the MTD forms a stratigraphic marker of a period of tectonic activity.  相似文献   

Ichnodiversity and ichnoabundance: Revealing depositional trends in a confined turbidite system   总被引：1，自引：0，他引：1  

Dirk Knaust  Michał Warchoł  Ian A. Kane 《Sedimentology》2014,61(7):2218-2267

Ichnological studies are still in their infancy when it comes to the interpretation of deep‐marine deposits. The Eocene–Oligocene turbidite system of the Grès d'Annot Formation in south‐east France is well‐studied sedimentologically, but its trace‐fossil content is poorly known. Here, an integrated ichnological–sedimentological study is presented from the Annot sub‐basin for the first time, which demonstrates its value for interpreting proximal to distal and axial to marginal trends in confined turbidite systems. A comprehensive trace‐fossil data set was collected from seven outcrops situated in the southern part of the basin. These data are presented following a morphology‐based classification scheme to allow easy recognition and characterization of ichnotaxa. Ichnodiversity and the abundance of ichnotaxa are regarded as important parameters in such interpretations. Instead of simply counting ichnotaxa per outcrop or stratigraphic unit, an equation has been developed in which the ‘ichnoabundance’ (new term) of each counted ichnotaxon is calculated. An exponential growth factor is applied to the increase of the frequency of trace fossils, and is assumed in this equation to better reflect the population dynamics of benthic organisms. A comparison of the solution for pre‐turbidite and post‐turbidite trace‐fossil suites seems to be more suitable for revealing regional and stratigraphic trends compared with conventional approaches. Despite varying size and conditions of the studied outcrops, the results achieved from the Grès d'Annot Formation can help in the reconstruction of sedimentary processes acting in this confined turbidite basin.  相似文献   

云南漾濞6.4级地震公共建筑的震害特征          下载免费PDF全文

李昆  周煜  陶思宇  吕珏  曲哲 《世界地震工程》2021,(3):001-8

2021年5月21日云南漾濞发生6.4级地震,成为继2014年6.5级鲁甸地震和6.6级景谷地震之后云南省内时隔7年的又一次震级大于6级的破坏性地震。漾濞地震虽然与鲁甸地震在震级、震源深度和震源机制等方面均较相似,但漾濞地震震中附近的地面运动强度远不及鲁甸地震,且漾濞县的抗震设防烈度远高于鲁甸;相应地,漾濞地震对抗震设防建筑造成的破坏也远轻于后者。本文首先通过比较这三次地震震中附近的强震记录的反应谱,并结合公共建筑的震后应急评估结果,说明漾濞地震和鲁甸地震中公共建筑破坏程度的显著差异。进而以位于漾濞县城的两栋钢筋混凝土公共建筑为例,介绍此次地震中砌体填充墙和吊顶等典型非结构构件的震害。  相似文献