458 research outputs found
Indagine sperimentale e numerica sul comportamento ciclico di telai in c.a. tamponati
No full textUnder seismic loads the interaction between masonry panels and the concrete structure of infilled frames (a very diffuse structural type in Italy) may generate stress and strain concentrations in r.c. elements (particularly in columns) and brittle failure behaviour can be detected due to these mechanisms.
The non-linear constitutive models for masonry, currently available, are calibrated to predict accurately the global response in terms of forces in masonry panels, and not to analyze local and global failure interaction mechanisms of panels and r.c. frames.
Through an experimental investigation information about the real behaviour of masonry infilled frames under seismic action have been gathered; with special attention on stresses and forces, but also on global and local failure mechanisms. Experimental tests performed at the Laboratory of experiments on materials and structures of the University Roma Tre, on bricks, mortar, single and double infill walls and finally on bare and infilled r.c. portals, are described and discussed.
In parallel with the experimental activity non linear fiber structural models representative of the considered structures by means of triple strut nonlinear cyclic models for masonry panels have been set up.
The accuracy of the models has been assessed through comparison with experimental results obtained form cyclic tests of frames
Seismic Response of an Existing RC Frame Building Struck by 2016 Central Italy Earthquakes
No full textA large number of research studies have been devoted to the modelling and analysis of infilled Reinforced Concrete (RC) framed buildings under seismic actions; it is well known that infills play a significant role in the overall structural performance. The present work reports the results of the nonlinear static assessment performed on a masonry infilled RC frame building retrofitted with dissipative braces, located in the area struck by the 2016 Central Italy seismic sequence. The building is an interesting case study because it is equipped with dissipative braces and with a monitoring system; the monitoring system recorded the building response to the seismic sequence and consequently the evolution of the structural response with the progressive deterioration of the infill. Numerical analyses were performed by using nonlinear 3D models, considering both the bare and the infilled frame, in order to appraise the interaction of the infills with the RC elements and the dissipative contribution offered by the dissipative bracing system; an alternative retrofitting approach, finalized to prevent non-structural damage, according to the Bergami-Nuti procedure is finally proposed
UCP 600 rules – changing letter of credit business for international traders?
No full textA letter of credit (L/C), in international trade may be described as an instrument of finance carrying a conditional guarantee of payment from the overseas (buyer’s) bank to the seller. Consequently, a L/C is desirable in high value and/or high risk transactions. The guarantee is conditional upon the seller complying 100% with the documentary requirements of the L/C, an issue of
particular concern to exporters, as the International Chamber of Commerce (ICC) estimates worldwide documentary discrepancy rates of 70%. L/C transactions are governed by ICC rules, and whilst these provide an international standardised process, the differing interpretations of what
constitutes documentary compliance create difficulties for sellers in particular. The new rules: UCP 600, supposedly have simpler and clearer wording, to reduce ambiguity and differences in interpretation, and hopefully reduce
documentary discrepancy rates and the associated financial risks. This article examines the major changes introduced by the UCP 600 and comments on their likely impact on future L/C business. Whilst acknowledging some improvements were introduced in the UCP 600, the article concludes that a number of issues have been ignored to the detriment of traders
Plastics counteract the ability of Antarctic krill to promote the blue carbon pathway in the deep ocean
No full textThe Antarctic krill (Euphausia superba) play a critical role in promoting the so-called "blue carbon pathway" by producing a large amount of fast-sinking faecal pellets (FPs) which facilitate the transport of CO2 through the water column. Here we assess how exposure to negatively (PS-COOH) and positively (PS-NH2) charged polystyrene nanoparticles, impacts degradation of krill FPs (i.e. change in peritrophic membrane state, Carbon concentration and Carbon/Nitrogen ratio). Our findings suggest that exposure of nanoplastics, particularly negatively charged particles, increases krill FP degradation. This can result in a potential loss of FP-sequestrated C of up to 27 %, equivalent to up 5.5 Mt. C per productive season (Spring-early Autumn). This study provides new insights into how increasing levels of plastic pollution could affect the natural capital provided by krill FPs. The effect of this emerging anthropogenic contaminant should be considered by international policies focused on climate change mitigation and adaptation
Fenomenologia e rivelazione: istruttoria di una controversa questione
No full textil saggio propone una istruttoria della questione "fenomenologia e rivelazione" nella fenomenologia francese contemporanea
Interplay Between Nanoplastics and the Immune System of the Mediterranean Sea Urchin Paracentrotus lividus
No full textThe present study highlights for the first time the interplay between model nanoplastics, such as the carboxyl-modified polystyrene nanoparticles (PS-COOH, 60 nm) NPs and the coelomocytes of the sea urchin Paracentrotus lividus, a benthic grazer widely distributed in Mediterranean coastal area, upon acute in vitro exposure (4 h) (5 and 25 μg mL–1). Insight into PS-COOH trafficking (uptake and clearance) and effects on immune cell functions (i.e., cell viability, lysosomal membrane stability, and phagocytosis) are provided. Dynamic Light Scattering analysis reveals that PS NP suspensions in CF undergo a quick agglomeration, more pronounced for PS-COOH (608.3 ± 43 nm) compared to PS-NH2 (329.2 ± 5 nm). However, both PS NPs are still found as nano-scale agglomerates in CF after 4 h of exposure, as shown by the polydispersity index > 0.3 associated with the presence of different PS NP size populations in the CF. The observed changes in ζ-potential upon suspension in CF (–11.1 ± 3 mV and –12.1 ± 4 mV for PS-COOH and PS-NH2, respectively) confirm the formation of a bio-corona on both PS NPs. Optical fluorescence microscopy and fluorimetric analyses using fluorescently labeled PS-COOH (60 nm) reveal a fast uptake of PS-COOH primarily by phagocytes within 1 h of exposure. Upon transfer to PS NP-free CF, a significant decrease in fluorescence signal is observed, suggesting a fast cell clearance. No effect on cell viability is observed after 4 h of exposure to PS-COOH, however a significant decrease in lysosomal membrane stability (23.7 ± 4.8%) and phagocytic capacity (63.43 ± 3.4%) is observed at the highest concentration tested. Similarly, a significant reduction in cell viability, lysosomal membrane stability and phagocytosis is found upon exposure to PS-NH2 (25 μg mL–1), which confirms the important role of surface charges in triggering immunotoxicity. Overall, our results show that, although being quickly internalized, PS-COOH can be easily eliminated by the coelomocytes but may still be able to trigger an immune response upon long-term exposure scenarios. Taking into account that sediments along Mediterranean coasts are a sink for micro- and nanoplastics, the latter can reach concentrations able to exceed toxicity-thresholds for marine benthic species
Under pressure: Nanoplastics as a further stressor for sub-Antarctic pteropods already tackling ocean acidification [Short communication]
No full textIn the Southern Ocean (SO), plastic debris has already been found in waters and sediments. Nanoplastics (<1 μm) are expected to be as pervasive as their larger counterparts, but more harmful to biological systems, being able to enter cells and provoke toxicity. In the SO, (nano)plastic pollution occurs concomitantly with other environmental threats such as ocean acidification (OA), but the potential cumulative impact of these two challenges on SO marine ecosystems is still overlooked. Here the single and combined effects of nanoplastics and OA on the sub-Antarctic pteropod Limacina retroversa are investigated under laboratory conditions, using two surface charged polystyrene nanoparticles (PS NPs) as a proxy for nanoplastics. Sub-Antarctic pteropods are threatened by OA due to the sensitivity of their shells to changes in seawater carbonate chemistry. Short-term exposure (48 h) to PS NPs compromised the ability of pteropods to counteract OA stress, resulting in a negative effect on their survival. Our results highlights the importance of addressing plastic pollution in the context of climate change to identify realistic critical thresholds of SO pteropods
Experimental tests on existing RC beams strengthened in flexure and retrofitted for shear by C-FRP in presence of negative moments
No full textThe shear strength of reinforced concrete beams extracted from existing buildings often reveals insufficient transversal steel reinforcement, mainly due to design or construction defects or increased design load requirements. FRP wrapping is one of the best solutions to improve beam shear strength as the retrofitting intervention is fast and the cost is modest. Design codes provide clear indication about the retrofitting design of simply supported beams, while the case of a beam with negative moments at the end is not considered, although this is in the case of a beam in a framed structure. One of the main uncertainties lies in the effectiveness of the FRP U sheet anchorage behavior in the area of negative bending moments with cracked concrete. This may limit the shear strength of the retrofitted beam. In this study, two beams extracted from an existing building constructed in the 1930s in Rome and retrofitted by carbon fiber-reinforced polymer (C-FRP) U strips placed at beam ends, where also negative bending moments were present, and have been evaluated with experimental tests at the laboratory of the Department of Architecture of Roma Tre University. Beam steel and concrete characteristics were evaluated by means of different tests. The experimental results are discussed considering the final results in terms of maximum shear resistance in the presence of negative bending moments. Load deflections at different points along the beam, shear-C-FRP deformation along the reinforcement strips and the damage state for different load levels, are presented. The importance of avoiding possible fragile mechanisms in the sections retrofitted with FRP is clearly shown
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