656 research outputs found
Thermo-mechanical compatibility of CFRP versus steel reinforcement for concrete at high temperature
Optimization of the design of concrete structures has become a driver for the use of nonconventional reinforcing materials. One example of this is the emerging use of non-corrosive, highstrength, and lightweight carbon fibre reinforced polymer (CFRP) prestressing tendons. It is widely known that the bond between FRP reinforcing tendons and concrete deteriorates at elevated temperature due to a combination of factors. Lateral thermal expansion of FRP reinforcing tendons at elevated temperature has been shown to have consequences for the bond performance of these systems. This paper presents the results of an experimental study carried out to assess the occurrence of heat-induced longitudinal splitting cracks in concrete specimens reinforced with CFRP or steel prestressing tendons. A novel testing methodology, namely a Heat-Transfer Rate Inducing System (H-TRIS), is used to subject specimens to thermal loading which replicates that experienced by equivalent specimens in a standard fire resistance test. A comparison between CFRP and steel tendons is made, and the occurrence of longitudinal splitting cracks is evaluated in terms of the time to occurrence and thermal gradient within the concrete. Results are compared against an available analytical model
Influence of Temperature on the Mechanical Performance of Unidirectional Carbon Fibre Reinforced Polymer Straps
Influence of interface potential on the effective mass in Ge nanostructures
The role of the interface potential on the effective mass of charge carriers
is elucidated in this work. We develop a new theoretical formalism using a
spatially dependent effective mass that is related to the magnitude of the
interface potential. Using this formalism we studied Ge quantum dots (QDs)
formed by plasma enhanced chemical vapour deposition (PECVD) and co-sputtering
(sputter). These samples allowed us to isolate important consequences arising
from differences in the interface potential. We found that for a higher
interface potential, as in the case of PECVD QDs, there is a larger reduction
in the effective mass, which increases the confinement energy with respect to
the sputter sample. We further understood the action of O interface states by
comparing our results with Ge QDs grown by molecular beam epitaxy. It is found
that the O states can suppress the influence of the interface potential. From
our theoretical formalism we determine the length scale over which the
interface potential influences the effective mass
Assessment of the radiological impact of a decommissioning nuclear power plant in Italy
The assessment of the radiological impact of a decommissioning Nuclear Power
Plant is presented here through the results of an environmental monitoring
survey carried out in the area surrounding the Garigliano Power Plant. The
levels of radioactivity in soil, water, air and other environmental matrices
are shown, in which {\alpha}, {\beta} and {\gamma} activity and {\gamma}
equivalent dose rate are measured. Radioactivity levels of the samples from the
Garigliano area are analyzed and then compared to those from a control zone
situated more than 100 km away. Moreover, a comparison is made with a previous
survey held in 2001. The analyses and comparisons show no significant
alteration in the radiological characteristics of the area surroundings the
plant, with an overall radioactivity depending mainly from the global fallout
and natural sources
Assessment of the radiological impact of a decommissioning nuclear power plant in Italy
The assessment of the radiological impact of a decommissioning Nuclear Power
Plant is presented here through the results of an environmental monitoring
survey carried out in the area surrounding the Garigliano Power Plant. The
levels of radioactivity in soil, water, air and other environmental matrices
are shown, in which {\alpha}, {\beta} and {\gamma} activity and {\gamma}
equivalent dose rate are measured. Radioactivity levels of the samples from the
Garigliano area are analyzed and then compared to those from a control zone
situated more than 100 km away. Moreover, a comparison is made with a previous
survey held in 2001. The analyses and comparisons show no significant
alteration in the radiological characteristics of the area surroundings the
plant, with an overall radioactivity depending mainly from the global fallout
and natural sources.Comment: 13 pages, 6 figures, 2 table
Fretting Fatigue Performance of Unidirectional, Laminated Carbon Fibre Reinforced Polymer Straps at Elevated Service Temperature
The fretting fatigue performance of laminated, unidirectional (UD), pin-loaded, carbon fibre-reinforced polymer (CFRP) straps that can be used as bridge hanger cables was investigated at a sustained service temperature of 60 °C. The aim of this paper is to elucidate the influence of the slightly elevated service temperature on the tensile fatigue performance of CFRP straps. First, steady state thermal tests at ambient temperature and at 60 °C are presented, in order to establish the behaviour of the straps at these temperatures. These results indicated that the static tensile performance of the straps is not affected by the increase in temperature. Subsequently, nine upper stress levels (USLs) between 650 and 1400 MPa were chosen in order to establish the S–N curve at 60 °C (frequency 10 Hz; R = 0.1) and a comparison with an existing S–N curve at ambient temperature was made. In general, the straps fatigue limit was slightly decreased by temperature, up to 750 MPa USL, while, for the higher USLs, the straps performed slightly better as compared with the S–N curve at ambient temperature
The influence of feedback and convection on imposed heating conditions when using gas-fired radiant panels in fire testing
Study of 236U/238U ratio at CIRCE using a 16-strip silicon detector with a TOF system
Accelerator Mass Spectrometry (AMS) is presently the most sensitive technique for the measurement of long-lived actinides, e.g. 236 U and x Pu isotopes. A new actinide AMS system, based on a 3-MV pelletron tandem accelerator, is operated at the Center for Isotopic Research on Cultural and Environmental Heritage (CIRCE) in Caserta, Italy. In this paper we report on the procedure adopted to increase the 236 U abundance sensitivity as low as possible. The energy and position determinations of the 236 U ions, using a 16-strip silicon detector have been obtained. A 236 U/ 238 U isotopic ratio background level of about 2.9×10 −11 was obtained, summing over all the strips, using a Time of Flight-Energy (TOF-E) system with a 16-strip silicon detector (4.9×10 −12 just with one strip)
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