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71.
72.
Jorge M. Proença António S. Gago Filipa Chaves 《Bulletin of Earthquake Engineering》2018,16(1):377-395
The present paper aims to contribute to the knowledge concerning the seismic assessment of load bearing masonry buildings with reinforced concrete slabs. The final goal of the present research was to propose a simple, yet accurate, methodology to assess the seismic safety of existing masonry buildings. The methodology here presented was based on the so-called ICIST/ACSS methodology with major improvements such as the extension to load bearing masonry wall buildings and the consideration of the effects of one of the most common strengthening solutions for masonry walls, here referred to as reinforced plastering mortar, as well as the possibility of considering four levels of increasing refinement: global, by alignment, by wall panel and by wall element. An extended research was performed on the existing methodologies to evaluate the seismic structural risk of load bearing masonry buildings, briefly describing methodologies similar to the one proposed, namely all of those that have in common the fact that they are based in the physical comparison between the resisting and acting shear forces at all storeys and along the two orthogonal horizontal directions. A case study is presented to check the applicability of the proposed methodology. The case study showed that the proposed methodology is relatively simple to apply and has a sufficiently good accuracy when compared with alternative methodologies. The degree of refinement of the analysis (global, by alignment, by wall panel and by wall element) must be taken into consideration and successively more complex analyses may be required when the results of simpler analyses are inconclusive. 相似文献
73.
Alexandre Raphael Cabral Nikola Koglin Ant?nio Augusto Seabra Gomes Bernd Lehmann 《International Journal of Earth Sciences》2012,101(1):377-383
Dissolution cavities in weathered pebbly quartzite of the ~2.5-Ga Moeda Formation at Capanema, Quadrilátero Ferrífero of Minas
Gerais, Brazil, are decorated with suspended filaments of opaline silica. The filaments sustain xenotime–hematite aggregates
in the open space. Xenotime occurs as inclusions in buds and botryoidal aggregates of hematite. The filamentous structures
consist of strand-forming buds, hypha-like extensions, and thin strands that compose mat-like arrangements. They resemble
microbial filaments that were replaced by opaline silica and fossilized. The occurrence of spherical hematite as protuberances
on hematite-free opaline hyphae is interpreted as accretion of dissolved iron onto extracellular polymers. Phosphate sites
in polymeric substances expelled from the microbial filaments might have adsorbed yttrium and heavy rare-earth elements from
groundwater to the iron-accreting polymers. These would have resulted in botryoidal aggregates of hematite with xenotime inclusions.
The presence of authigenic xenotime in the weathering zone opens a new possibility to constrain the evolution of lateritic
profiles by xenotime geochronology. 相似文献
74.
Miguel Cortés Sánchez Francisco J. Jiménez Espejo María D. Simón Vallejo Juan F. Gibaja Bao António Faustino Carvalho Francisca Martinez-Ruiz Marta Rodrigo Gamiz José-Abel Flores Adina Paytan José A. López Sáez Leonor Peña-Chocarro José S. Carrión Arturo Morales Muñiz Eufrasia Roselló Izquierdo José A. Riquelme Cantal Rebecca M. Dean Emília Salgueiro Rafael M. Martínez Sánchez Nuno F. Bicho 《Quaternary Research》2012,77(2):221-234
New data and a review of historiographic information from Neolithic sites of the Malaga and Algarve coasts (southern Iberian Peninsula) and from the Maghreb (North Africa) reveal the existence of a Neolithic settlement at least from 7.5 cal ka BP. The agricultural and pastoralist food producing economy of that population rapidly replaced the coastal economies of the Mesolithic populations. The timing of this population and economic turnover coincided with major changes in the continental and marine ecosystems, including upwelling intensity, sea-level changes and increased aridity in the Sahara and along the Iberian coast. These changes likely impacted the subsistence strategies of the Mesolithic populations along the Iberian seascapes and resulted in abandonments manifested as sedimentary hiatuses in some areas during the Mesolithic–Neolithic transition. The rapid expansion and area of dispersal of the early Neolithic traits suggest the use of marine technology. Different evidences for a Maghrebian origin for the first colonists have been summarized. The recognition of an early North-African Neolithic influence in Southern Iberia and the Maghreb is vital for understanding the appearance and development of the Neolithic in Western Europe. Our review suggests links between climate change, resource allocation, and population turnover. 相似文献
75.
The cyclic behaviour of reinforced concrete columns has been the subject of many experimental studies in recent years. However, most of these studies have focused on the unidirectional loading of columns with square cross‐sections under constant axial loading conditions. In the present study, four types of full‐scale quadrangular building columns were tested under different types of loading, including uniaxial and biaxial loading conditions. The first two specimens of each column type were independently cyclically tested in the strong and weak directions. Bidirectional tests using different loading paths were performed on the other column specimens. All columns were tested under constant axial loading conditions. In this paper, the experimental results are presented, and the global behaviour of tested columns is discussed, particularly focusing on the stiffness and strength degradation because of the increasing cyclic demand. Finally, the deformation‐based performance limits proposed in Part 3 of Eurocode 8 were calculated and compared with the experimental results. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
76.
Hugo Rodrigues António Arêde Humberto Varum Aníbal Costa 《Bulletin of Earthquake Engineering》2013,11(5):1517-1540
An analysis of the damage observed in 24 reinforced concrete (RC) columns tested under uniaxial and biaxial horizontal loading is presented. The test results show that for biaxial loading conditions specific damage occurs for lower drift demands when compared with the corresponding uniaxial demand (a reduction of 50–75 % was found). The damage distribution observed in each column is also analysed. No significant differences are found in the plastic hinge length for uniaxial and biaxial loading. The drift demands associated with each damage state are compared with reference values proposed in international guidelines. Finally, and based on the philosophy of the Park and Ang uniaxial damage index, two new expressions are proposed for the evaluation of damage in RC elements under biaxial loading. The results of the application of these expressions to the experimental results are discussed. 相似文献
77.
78.
Maurício Dambros Melati Fernando Mainardi Fan Gustavo Barbosa Athayde Pedro Antônio Roehe Reginato Walter Collischonn Camila de Vasconcelos Muller Athayde 《水文研究》2021,35(10):e14388
The anomalous entrance of water into groundwater systems can affect storage throughout long periods and normally relies on infrequent and irregular pulses of groundwater recharge defined by the term episodic recharge. Recently there was a groundwater recharge of large magnitude with unknown circumstances in the Caiuá aquifer. This unique event was explored in detail here and allowed to better understand the occurrence of such events in humid subtropical climates in South America. For this study, groundwater monitoring daily data from the Integrated Groundwater Monitoring Network was used combined with a specific yield obtained from geophysical wireline logging to obtain groundwater recharge rates. To improve the investigation, we also used a baseflow separation method to obtain the groundwater contribution into local rivers. The groundwater storage variations were also assessed by remote sensing with the GRACE data. Results showed the importance of high soil moisture storage on the occurrence of large episodic recharge events. We estimated that the groundwater recharger volumes derived from 1 year that included the unique episodic recharge observed (total of 866 mm for April 2015–March 2016) were comparable with the sum of 7 years of groundwater recharge (total of 867 mm). Atypical rainfall in winter periods were responsible for the increase in soil moisture that explained that unique event. GRACE-based GWS showed concordance detecting the occurrence of the unique episodic recharge. However, the variation in terms of volumes obtained by GRACE does not represent the behaviour observed in the aquifer by the WTF method. The results also indicated that changes in aquifer storage caused by episodic recharge events directly affect low flows in rivers over long periods. The main knowledge gap addressed here relates to exploring a unique episodic recharge event quite rare to observe with its long-term impacts on hydroclimatic variability over a humid subtropical portion of the Caiuá aquifer. 相似文献
79.
Eutrophication and hypoxia in four streams discharging in Guanabara Bay, RJ, Brazil, a case study 总被引:1,自引:0,他引:1
Four streams in the city of São Gonçalo, were sampled to evaluate their potential as sources of nutrients to Guanabara Bay aiming to contribute with the government program to decrease the levels of pollution in this area. Imbuaçu, Guaxindiba, Marimbondo and Brandoas streams were sampled in 2007, 2008 and 2009. The streams revealed to be hipereutrophic with severe limitation of primary production by nitrogen, as shown by the N/P molar ratio. Phosphate levels were abnormally high varying between 4.35 and 130.82 μM, whereas nitrate and nitrite ranged from 0.06 to 54.05 μM and from 0.28 to 19.23 μM, respectively. The streams also presented severe hypoxia and anoxia, with oxygen values varying from non-detected to 3.72 ml l−1. Heavy loads of particulate suspended material were recorded in the studied streams, ranging between 6.00 and 400.00 mg l−1. The streams were considered inexorable sources of nutrients, enhancing the severe eutrophication process in Guanabara Bay. 相似文献
80.
Ana L. Santos Isabel Henriques Newton C. M. Gomes Adelaide Almeida António Correia Angela Cunha 《Aquatic Sciences - Research Across Boundaries》2011,73(1):63-77
The effects of ultraviolet-B (0.4 W m−2) radiation on the abundance, diversity and heterotrophic metabolism of bacterioneuston and bacterioplankton communities from
Ria de Aveiro (Portugal) were assessed and compared to those of freshwater communities from Lake Vela (Portugal) in microcosm
experiments. Exposure to 9 h of artificial ultraviolet radiation (UVR) led to 24–33% reduction in bacterial abundance and
up to a 70% decrease in bacterial diversity. Maximum extracellular enzyme activity and monomer incorporation rates were reduced
by 16–90% and 80–100%, respectively. Recovery of bacterial activity during post-UV dark incubations ranged from 10 to 100%
for extracellular enzyme activity and 40% for monomer incorporation rates. In general, the heterotrophic activity of bacterioneuston
was more inhibited by UVR than that of bacterioplankton. However, DGGE profiles revealed greater UVR-induced reductions in
the diversity of bacterioplankton compared to bacterioneuston. The similarity between bacterioneuston and bacterioplankton
communities in samples collected at early morning was lower than at noon (pre-exposed communities) and increased upon experimental
irradiation, possibly indicating selection for UV-resistant bacteria. The observation that UV exposure resulted in enhanced
reduction of bacterioneuston activity, but a lower reduction in bacterial diversity accompanied by enhanced dark recovery
potential compared to bacterioplankton, indicates re-directioning of bacterioneuston metabolism towards stress defence/recovery
strategies rather than the sustained heterotrophic metabolism. Our results indicate that UVR can significantly decrease the
abundance, diversity and activity of bacteria inhabiting the surface and sub-surface layers of freshwater and estuarine systems
with potentially important impacts on the biogeochemical cycles in these environments. 相似文献