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1.
Determination of the seismic performance factors for post‐tensioned rocking timber wall systems 
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下载免费PDF全文 Post‐tensioned technologies for concrete seismic resistant buildings were first developed in the 1990s during the PREcast Seismic Structural Systems program. Among different solutions, the hybrid system proved to be the most resilient solution providing a combination of re‐centering and energy dissipative contributions respectively by using post‐tensioned tendons and mild steel reinforcement. The system, while providing significant strength and energy dissipation, reduces structural element damage and limits post‐earthquake residual displacements. More recently, the technology was extended to laminated veneer lumber (LVL) structural members, and extensive experimental and numerical work was carried out and allowed the development of reliable analytical and numerical models as well as design guidelines. On the basis of the experimental and numerical outcomes, this paper presents the evaluation of the seismic performance factors for post‐tensioned rocking LVL walls using the FEMA P‐695 procedure. Several archetype buildings were designed considering different parameters such as the building and story height, the type of seismic resistant system, the magnitude of gravity loads and the seismic design category. Lumped plasticity models were developed for each index archetype to simulate the behavioral aspects and collapse mechanisms. Non‐linear quasi‐static analyses were carried out to evaluate the system over‐strength factor; moreover, non‐linear time history analyses were performed using the incremental dynamic analysis concept to assess the collapse of each building. From the results of quasi‐static and dynamic analyses the response modification factor, R, system over‐strength factor, Ω0, and deflection amplification factor, Cd, values of, respectively, 7, 3.5 and 7.5 are recommended. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
2.
This article explores the impacts of floods on the economy, environment, and society and tries to clarify the rural community’s
coping mechanism to flood disasters in Central Viet Nam. It focuses on the social aspects of flood risk perception that shapes
the responses to floods. The research findings revealed that flooding is an essential element for a coastal population, whose
livelihood depend on productive functions of cyclical floods. The findings also revealed that floods, causing losses and damages,
often inhibited economic development. The surveyed communities appeared to have evolved coping mechanisms to reduce the negative
impacts of the floods, yet these coping mechanisms are under pressure due to environmental degradation. Integrated flood risk
management is considered as a suitable paradigm for coping with flood disasters.
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| Phong TranEmail: |
3.
The 64-m Sardinia Radio Telescope (SRT) is currently under construction in Sardinia (Italy). To ensure future surveying and
monitoring operations at an utmost level of accuracy, we aim at selecting the optimal design and the most cost-effective solution
for the establishment of the local ground control network (LGCN). We simulate and test 45 data sets corresponding to 5 different
network configurations. We investigate the influence of 2 LGCN geometries (14 or 8 ground markers) and 3 terrestrial observation
schemes (based on redundant forward intersections or side shots) on the precision and accuracy of the conventional reference
point (CRP) of SRT and the simulated tie vector with a global navigation satellite system (GNSS) station. In addition, thermal
and gravitational deformations of the radio telescope structure are simulated as systematic errors introduced into the observations
and their effects on the CRP estimates are quantified. The state-of-the-art of CRP surveying and computation, based on terrestrial
indirect methods, is applied. We show how terrestrial indirect methods can estimate the position of the radio telescope CRP
to the millimeter precision level. With our simulations, we prove that limiting the LGCN to a 8-point configuration ensures
the same precision on the CRP obtained with a 14-point network. Furthermore, we demonstrate that in the absence of telescope
deformations, side shots, despite the lower redundancy, preserve a precision similar to that of redundant forward intersections.
We show that the deformations due to gravitational flexure and thermal expansion of the radio telescope cannot be neglected
in the tie vector computation, since they may bias the CRP estimate by several millimeters degrading its accuracy but not
impacting on its formal precision. We highlight the dependency of the correlation matrices of the solutions on the geometry
of the network and the observation schemes. Similarly, varying the extent of telescope deformations, we show that the CRP
estimate again depends on the combination of the network geometry and the observation schemes. 相似文献
4.
Gravity-dependent signal path variation in a large VLBI telescope modelled with a combination of surveying methods 总被引：4，自引：3，他引：1
The very long baseline interferometry (VLBI) antenna in Medicina (Italy) is a 32-m AZ-EL mount that was surveyed several times,
adopting an indirect method, for the purpose of estimating the eccentricity vector between the co-located VLBI and Global
Positioning System instruments. In order to fulfill this task, targets were located in different parts of the telescope’s
structure. Triangulation and trilateration on the targets highlight a consistent amount of deformation that biases the estimate
of the instrument’s reference point up to 1 cm, depending on the targets’ locations. Therefore, whenever the estimation of
accurate local ties is needed, it is critical to take into consideration the action of gravity on the structure. Furthermore,
deformations induced by gravity on VLBI telescopes may modify the length of the path travelled by the incoming radio signal
to a non-negligible extent. As a consequence, differently from what it is usually assumed, the relative distance of the feed
horn’s phase centre with respect to the elevation axis may vary, depending on the telescope’s pointing elevation. The Medicina
telescope’s signal path variation ΔL increases by a magnitude of approximately 2 cm, as the pointing elevation changes from horizon to zenith; it is described
by an elevation-dependent second-order polynomial function computed as, according to Clark and Thomsen (Techical report, 100696,
NASA, Greenbelt, 1988), a linear combination of three terms: receiver displacement ΔR, primary reflector’s vertex displacement ΔV and focal length variations ΔF. ΔL was investigated with a combination of terrestrial triangulation and trilateration, laser scanning and a finite element model
of the antenna. The antenna gain (or auto-focus curve) ΔG is routinely determined through astronomical observations. A surprisingly accurate reproduction of ΔG can be obtained with a combination of ΔV, ΔF and ΔR. 相似文献
5.
At many North Atlantic continental margins, the early Neocomian is characterized by a major stratigraphic turning point from Late Jurassic-Berriasian carbonate bank/pelagic carbonate deposition to Valanginian-Barremian hemipelagic sedimentation with thick Wealden-type deltaic to deep-sea fan sequences. The stratigraphy and structure of the very old, starved passive margin of the Mazagan Plateau and adjacent steep escarpment off Morocco was studied during the French-German CYAMAZ deep diving campaign. The drowning of the Late Jurassic-early Berriasian carbonate platform was strongly influenced by a global late Berriasian sea level fall which was followed by a rapid late Valanginian sea level rise and/or by a major regional blockfaul ting event with accelerated subsidence rates. Upper Berriasian to (?) Hauterivian quartz-bearing bioclastic wackestones document the transition from the carbonate platform to the hemipelagic deposition on the drowned platform margin. Seawards, these deposits are correlated with a deep sea fan sequence. We discuss also an example from the Tarfaya Basin-Fuerteventura area further south. A 300 m thick succession of organic-rich claystone and sandstone turbidites (including m-thick debris flow units) of Hauterivian to Barremian age was an unexpected discovery at DSDP Site 603 off North Carolina (Leg 93). We discuss a tectonically confined fan model with laterally migrating channels, influenced by sea level fluctuations and varying terrigenous supply. During the Valanginian to Barremian time of high-standing (or rising) sea level, shelf construction (Wealden-type deltas) coincided with subdued, resedimentation-starved turbiditic system on the continental rise. Extensive unconsolidated sands, however, reflect sudden input of shelfal material into the basin during a mid-Aptian sea level lowstand (shelf destruction). The following global late Aptian transgression terminated the clastic fan deposition, raised the CCD and started the deposition of organic-rich shales. 相似文献
6.
Río Fardes剖面位于西班牙南部Granada东北,构造上属于深水环境的Subbetic中带。该剖面主要由白垩纪Fardes组第Ⅱ段和第Ⅲ段(半)远洋沉积构成,并出现浊流沉积和混杂沉积。本次研究在Fardes组浊流层序内首次发现两段红色沉积。钙质超微化石表明红层的时间从Turonian早期(UC7 带)到Coniacian中期—晚期界线(UC10/?UC11带)。红层由mm级红色泥岩夹灰色、杂色、偶尔黑色泥岩和钙质泥岩组成。沉积学研究表明新发现的Turonian Coniacian远洋红色泥岩沉积形成于CCD面之下深水盆地环境,浊流和碎屑流沉积强烈地影响着(半)远洋环境的背景泥岩相,并成为红色沉积结束的原因。 相似文献
7.
On the displacement of marked pebbles on two coarse-clastic beaches during short fair-weather periods (Marina di Pisa and Portonovo, Italy) 总被引：1，自引：1，他引：0
Duccio Bertoni Edoardo Grottoli Paolo Ciavola Giovanni Sarti Giuliano Benelli Alessandro Pozzebon 《Geo-Marine Letters》2013,33(6):463-476
The aim of the investigation was to define the mechanisms of sediment transport in the swash zone of microtidal coarse-clastic beaches in the very short term by evaluating the displacement rates of marked pebbles under low-energy wave conditions. Tests were performed at two sites (Marina di Pisa, Ligurian Sea, and Portonovo, central Adriatic Sea) to check the consistency of the data over a range of different grain sizes. Two recovery campaigns were carried out at both sites, one 6 h and the other 24 h after the injection. During the experiments wave action was at a minimum (wave heights never exceeded 0.3 m). The results show that 20% of pebbles ranging in diameter from 30–90 mm moved significantly (more than 0.5 m) already 6 h after the injection, with some tracers being lost (3%). After 24 h, 40% of the pebbles were significantly displaced and 10% were lost. The preferential downslope movement of tracers, which suggests that coarse sediment movement under low-energy conditions is mainly controlled by gravity processes enhanced by steep beachface slopes, represents the novelty of the results reported here. It would appear that swash processes on low-energy beaches cause a significant rate of pebble displacement through the destabilization induced by wave uprush and backwash. Despite the microtidal range, the position of the mean water level plays a major role in changing the beach level at which swash processes can actually trigger pebble movement. The results of this study show that considerable, and mostly seaward-directed, coarse sediment transport takes place even during short fair-weather periods. 相似文献
8.
Ping Yin Cathryn N. Mitchell Lucilla Alfonsi Mike Pinnock Paul Spencer Giorgiana De Franceschi Vincenzo Romano Patrick Newell Pierguido Sarti Monia Negusini Alessandro Capra 《Journal of Atmospheric and Solar》2009,71(17-18):1757-1765
Ground-based dual-frequency GPS observations can be used to create images of electron density. This is well established for the Arctic ionosphere; here one of the first results is presented for the Antarctic. In this study, the GPS receivers in the Antarctic are supplemented with another GPS receiver onboard CHAMP. The aim of the study is to demonstrate the technique for investigating geophysical events, for example, an ionospheric disturbance period on 11 February 2004. The images have been validated by in-situ measurements from DMSP and CHAMP satellites, as well as Super Dual Auroral Radar Network (SuperDARN) convection patterns, which are able to confirm the location, presence, and transportation of large-scale plasma patches. This study indicates that although the convection still dominates in the high-latitude ionosphere, soft precipitation within the polar cap may play a role in the evolution of the polar patches. It also illustrates the potential for future multi-instrument studies of the Antarctic. 相似文献
9.
A. Cerrina Feroni L. Leoni L. Martelli P. Martinelli G. Ottria G. Sarti 《Geological Journal》2001,36(1):39-54
The study of clast composition carried out on the alluvial gravels of the Romagna Apennines of northern Italy has provided evidence for an extensive covering of allochthonous units (Ligurian nappe and Epiligurian succession) above the Miocene foredeep deposits (Marnoso‐Arenacea Formation), which has been subsequently eroded during the Late Miocene–Pleistocene uplift. This result is confirmed by the burial history outlined in the Marnoso‐Arenacea Formation through vitrinite reflectance and apatite fission‐track analyses. The Romagna Apennines represent, therefore, a regional tectonic window where the thrust system that displaced the Marnoso‐Arenacea Formation crops out. The geometric relations between this thrust system and the basal thrust of the Ligurian nappe, exposed at the boundaries of the Romagna Apennines (Sillaro Zone and Val Marecchia klippe), are consistent with a duplex structure. Thus, the Romagna Apennines thrust system is an eroded duplex. The duplex roof‐thrust corresponds to the surface of the synsedimentary overthrust of the Ligurian nappe on the Marnoso‐Arenacea Formation; the floor‐thrust is located in the pelagic pre‐foredeep deposits (Schlier Formation). Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
10.
Late Quaternary multiple incised valley systems: An unusually well‐preserved stratigraphic record of two interglacial valley‐fill successions from the Arno Plain (northern Tuscany,Italy) 下载免费PDF全文
下载免费PDF全文 Un‐fragmented stratigraphic records of late Quaternary multiple incised valley systems are rarely preserved in the subsurface of alluvial‐delta plains due to older valley reoccupation. The identification of a well‐preserved incised valley fill succession beneath the southern interfluve of the Last Glacial Maximum Arno palaeovalley (northern Italy) represents an exceptional opportunity to examine in detail evolutionary trends of a Mediterranean system over multiple glacial–interglacial cycles. Through sedimentological and quantitative meiofauna (benthic foraminifera and ostracods) analyses of two reference cores (80 m and 100 m long) and stratigraphic correlations, a mid‐Pleistocene palaeovalley, 5 km wide and 50 m deep, was reconstructed. Whereas valley filling is chronologically constrained to the penultimate interglacial (Marine Isotope Stage 7) by four electron spin resonance ages on bivalve shells (Cerastoderma glaucum), its incision is tentatively correlated with the Marine Isotope Stage 8 sea‐level fall. Above basal fluvial‐channel gravels, the incised valley fill is formed by a mud‐prone succession, up to 44 m thick, formed by a lower floodplain unit and an upper unit with brackish meiofauna that reflects the development of a wave‐dominated estuary. Subtle meiofauna changes towards less confined conditions record two marine flooding episodes, chronologically linked to the internal Marine Isotope Stage 7 climate‐eustatic variability. After the maximum transgressive phase, recorded by coastal sands, the interfluves were flooded around 200 ka (latest Marine Isotope Stage 7). The subsequent shift in river incision patterns, possibly driven by neotectonic activity, prevented valley reoccupation guiding the northward formation of the Last Glacial Maximum palaeovalley. The applied multivariate approach allowed the sedimentological characterization of the Marine Isotope Stage 7 and Marine Isotope Stage 1 palaeovalley fills, including shape, size and facies architecture, which revealed a consistent river‐coastal system response over two non‐consecutive glacial–interglacial cycles (Marine Isotope Stages 8 to 7 and Marine Isotope Stages 2 to 1). The recurring stacking pattern of facies documents a predominant control exerted on stratigraphy by Milankovitch and sub‐Milankovitch glacio‐eustatic oscillations across the late Quaternary period. 相似文献