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11.
Shear effects on hollow section piers under seismic actions: experimental and numerical analysis 总被引：1，自引：0，他引：1
Raimundo Delgado Pedro Delgado Nelson Vila Pouca António Arêde Patrício Rocha Aníbal Costa 《Bulletin of Earthquake Engineering》2009,7(2):377-389
Shear effects are often a very important issue on the seismic behaviour of piers, particularly for hollow section bridge piers.
In fact, for this type of piers the cyclic response is similar to that of a structural wall in which both the transverse reinforcement
ratio and the detailing can play an important role on its performance, even likely to be determinant in terms of the failure
mechanism. On the other hand, codes and design guidelines are usually very conservative concerning shear capacity in order
to avoid any shear failure mechanism likely to trigger well known catastrophic consequences. Therefore, research studies on
this topic are still needed for a better understanding of pier cyclic shear response and also for improvement of the performance
under seismic actions. Pursuing this general objective, this paper partially reports on an experimental/numerical campaign
carried out on 1:4 reduced scale bridge piers in order to highlight and investigate shear-type problems. Within the scope
of this paper, two specimens types were selected having equal rectangular hollow section (900 × 450 mm2, 75 mm thick) but different transverse reinforcement detailing, namely one with a single stirrup per wall (representative
of typical bridge construction without seismic design requirements) and another with multiple stirrups, according to Eurocode
8 provisions. Numerical simulations of the experimental results were also conducted aiming at contributing for complete and
consistent interpretations of experimental results. Detailed modelling was performed allowing for realistic simulations of
the non linear behaviour, particularly suitable when a significant shear component is involved. Therefore, the numerical strategy
was based on a detailed 3D FEM discretization using a two-scalar variable damage model for the concrete constitutive law and
a suitable cyclic behaviour law for steel bars represented by truss elements. Results have shown that shear deformation and
failure modes are well simulated, while providing detailed insight concerning concrete damage pattern and distribution of
yielding on the transverse and longitudinal reinforcement. 相似文献
12.
Raimundo Delgado Aníbal Costa António Arêde Nelson Vila Pouca João Guedes Xavier Romão Pedro Delgado Patrício Rocha 《Bulletin of Earthquake Engineering》2010,8(1):181-199
Research on seismic safety assessment has been the centre of great interest among the scientific community in recent years.
Although the devastating impact of earthquakes on current society should be incentive enough to increase research, the development
of more realistic mechanical behaviour models and the continuous enhancement of computation capabilities are paramount factors
contributing a great deal to the increase of such interest. In this context, three research areas can be identified as currently
leading to important developments: code related research, especially in Europe where new design codes are in the implementation
process; risk analysis, namely concerning the definition of methodologies for safety assessment that involve the evaluation
of the failure probability and could be included in future generations of codes; and experimental characterization of constitutive
laws which provides support for the development and calibration of accurate and realistic numerical models for seismic analysis
and for the adequate characterization of limit state capacities. The paper will present some of the current scientific research
trends on these three seismic safety assessment related topics. Studies addressing the seismic safety assessment of structures,
either probabilistically or based on code provisions, and that consider realistic nonlinear mechanical behaviour models will
be focussed. Reference will also be made to experimental research on the seismic behaviour of structural elements, emphasizing
its crucial role to support the development of numerical models simulating the effects of different seismic strengthening
techniques. Finally, given the development of studies leading to new trends and perspectives for performance based earthquake
engineering, a possible scenario for seismic design in the future is presented, emphasizing the key issues for its implementation. 相似文献
13.
Are taxonomic distinctness measures compliant to other ecological indicators in assessing ecological status? 总被引：1，自引：0，他引：1
Salas F Patrício J Marcos C Pardal MA Pérez-Ruzafa A Marques JC 《Marine pollution bulletin》2006,52(2):162-174
Assessing the ecological status, a concept implemented in the European Water Framework Directive [Directive of the European Parliament and of the Council 2000/60/EC establishing a framework for community action in the field of water policy PE-CONS 3639/1/00, 72 p.], requires the application of methods capable of distinguishing different levels of ecological quality. Somerfield and Clarke [Marine Environmental Research 43 (2003) 145-156] proposed Average Taxonomic Distinctness to be used as tool in this context. We tested the robustness of Taxonomic Distinctness measures applying it in different scenarios (estuarine eutrophication, organic pollution, and re-colonisation after physical disturbance), analysing simultaneously its compliance to other types of ecological indicators. Results show that, in most of the case studies, only Total Taxonomic Distinctness was relatively satisfactory in discriminating between disturbed situations. Other Taxonomic Distinctness measures have not proved to be more sensitive than other ecological indicators (Shannon-Wiener, Margalef, and Eco-Exergy indices). Therefore, this approach does not seem to be particularly helpful in assessing systems' ecological status with regard to the WFD implementation. 相似文献
14.
Macroalgae communities constitute one of the ecological quality elements for the evaluation of the ecological quality status (EQS) of coastal and transitional waters, required to implement the WFD. While these algae are natural components of estuarine systems and play important roles in several estuarine processes, macroalgal blooms are of ecological concern because they can reduce the habitat quality. Several works are being carried out to set standard methods for monitoring macroalgae blooms, in order to develop tools to derive EQS based upon this biological quality element. The aim of this paper is to apply the methodology described by Scanlan et al. [Scanlan, C.M., Foden, J., Wells, E., Best, M.A., 2007. The monitoring of opportunistic macroalgal blooms for the water framework directive. Marine Pollution Bulletin 55, 162–171] to a series of data assembled in the south arm of the Mondego estuary (Atlantic coast of Portugal) considering two different ecological situations. Additionally, an alternative assessment method intended to be used when no biomass data are available was also tested. In general, both options captured the inter-annual variations in accordance with the system evolution. Option 2, less expensive and time-consuming, allowed an EQS evaluation with accurate results when biomass data were not available. The results suggest that sampling should be carried out from April to June. 相似文献
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Absorption and fluorescence properties of rainwater during the cold season at a town in Western Portugal 总被引：1，自引：0，他引：1
Patrícia S. M. Santos Regina M. B. O. Duarte Armando C. Duarte 《Journal of Atmospheric Chemistry》2009,62(1):45-57
This study aims at evaluating the variability of the optical properties of chromophoric dissolved organic matter (CDOM) of
rainwater during the cold season, specifically between Autumn and Winter periods. The spectroscopic characteristics of rainwater
samples collected at a town (Aveiro) in western Portugal were assessed by UV-Vis absorbance and three-dimensional excitation-emission
matrix (EEM) fluorescence spectroscopies. Rainwater samples showed similar characteristics to those of natural humic substances
when analysed by UV-Vis absorbance spectroscopy, but a significant difference was observed in the volume weight average (VWA)
of absorbances between Autumn and Winter. In general, the EEM fluorescence spectra of the Autumn and Winter samples disclosed
the presence of six fluorophores with different VWA specific fluorescence intensities: three humic-like (λ
excitation/λ
emission ≈ 230/415 nm; 290/415 nm; and 340/415 nm) and three protein-like (λ
excitation/λ
emission ≈ 230/350 nm; 280/340 nm; and 225/300 nm), but one of the humic-like peaks (≈340/415 nm) does not always appear in the EEM
fluorescence spectra of the Winter samples. During the cold season, chromophoric compounds are important constituents of rainwater
dissolved organic matter and the presence of these highly absorbing and fluorescing compounds may exert a determining effect
in atmospheric absorption of solar radiation. 相似文献
17.
The incidental capture in fisheries is probably the main conservation problem affecting seabirds. While the capture of albatrosses and petrels on longline hooks is well-known worldwide, the bycatch of diving seabirds in gillnets is an overlooked conservation problem. During a winter coastal fishing trip, the capture of Magellanic penguins (Spheniscus magellanicus) was recorded in driftnet and bottom setnet fisheries for the first time in southern Brazil. The highest captures rates were found in driftnets, from 146.5 to 545.5 penguins/km2 of net and a total of 56 dead penguins were recorded. In the bottom gillnet, a total of 12 birds were killed and the capture rates varied from 41.7 to 125.0 penguins/km2 of net. Although preliminary, the results presented in this paper were consistent between sets. If we consider the magnitude of driftnet and setnet fishing fleets, and that most dead penguins were adults, the impact upon Magellanic penguin populations is probably significant. 相似文献
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Ras is regarded as one of the most important genes involved in carcinogenesis. Such genes have been characterised in several fish species and the presence of ras mutations have already been described in fish populations from hydrocarbon contaminated areas and following experimental exposure to specific contaminants. The aims of this study were to evaluate the DNA integrity by comet assay, to isolate the normal ras gene of Anguilla anguilla and analyse for the presence of ras gene mutations or changes in gene expression levels induced after one month of benzo[a]pyrene (BaP) experimental exposure. The A. anguilla ras cDNA isolated revealed a 189 amino acid protein and alignment with other vertebrate ras proteins revealed conservation of functionally important regions. Following experimental exposure to BaP, an increase in DNA damage was found by comet assay. However, no point mutations or changes in ras gene expression levels were detected when compared to control samples. In contrast to the majority of fish ras gene sequences, a high degree of polymorphic variation was detected in the A. anguilla ras gene. 相似文献
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