1,720,974 research outputs found
Application of solid phase microextraction for the determination of stimulants, narcotics and other doping agents excreted free in urine
No full textExperimental behavior of prestressed concrete beams under simultaneous sustained loading and corrosion
No full textThe paper presents an experimental study for the evaluation of the flexural response and failure mode of a prestressed concrete (PC) beam subjected to simultaneous sustained loads and corrosion. The obtained results are judged and discussed also through a comparison with the experimental outcomes on a reference sound PC beam, and a companion specimen subjected to artificial corrosion first, and then tested in bending. The three specimens are characterized by a 200 x 300 mm rectangular cross section, a total length of 3700 mm, and a clear span of 2700 mm. The value of the sustained load, applied with a simultaneous accelerated corrosion process of the strands, was chosen, based on the result of the uncorroded reference beam, to achieve a scenario that can occur in a real structure in situ. The flexural response of the tested element was monitored over a period of 70 days, up to failure, and showed to be highly dependent on the localization of the corrosion phenomena affecting the strands, especially when coinciding with the maximum bending moment position. The obtained results are finally compared with the ones obtained on a PC beam with the same geometry and material properties, first subjected to corrosion and then tested in bending. The differences in corrosion morphology and location and in the failure mode of the strand confirm the importance of accounting for the combined effect of reinforcement corrosion and loading when assessing the structural performance of PC beams
Experimental evaluation of the corrosion influence on the structural response of Gerber half-joints
No full textThe assessment of the Gerber half-joints (or saddles), widespread in the infrastructure heritage of different countries, is nowadays a topical problem since they are often affected by chloride corrosion phenomena due to their positioning under the deck joint. In this paper, the influence of steel rebar corrosion on the experimental response of Gerber half-joints is experimentally analysed and discussed. In particular, four elements were cast in Laboratory of University of Rome “Tor Vergata” two of which subjected to accelerated corrosion, and then tested up to failure. The specimens were designed with typical strut and tie models, with the aim of achieving different failure modes governed by the concrete crush or by the tensile rebar breaking. Particular care was devoted to the corrosion process, in order to simulate decay scenarios typical of these structures. The experimental outcomes, expressed in terms of load–displacement curves, crack patterns and failure mechanisms show that also medium-slight degree of pitting corrosion can cause great reductions in capacity and ductility of the saddles, modifying, in addition, their failure mechanism. Finally, from the experimental outcomes, the sensitivity of these peculiar structures, not only to the corrosion amount, but also to its spatial distribution among the different steel rebars, and its morphology (pitting or uniform corrosion) is clearly underlined. As a consequence, the necessity to accurately and properly account for the corrosion phenomenon in the structural assessment is remarked
Analysis of failure mechanisms of Gerber half-joint specimens through digital image correlation technique
No full textReinforced concrete Gerber half-joints are characterized by D-Regions in which the de Saint Venant theory is not valid. Therefore, in the capacity assessment of existing Gerber half-joints, the correct assumptions about the stress fields and the strut-and-tie models play a crucial role. Digital Image Correlation (DIC) is an optical technique for the determination of displacements and strains of specimens subjected to mechanical actions. In this work, the DIC technique is applied within an experimental campaign aimed at identifying the nonlinear behavior of Gerber half-joints according to different construction details. The results obtained using the DIC technique allow to identify the shape of the compression fields (struts) and to predict the development of the crack patterns. Therefore, the outcomes are compared with the expected shapes of the strut-and-tie models and interpreted to analyze the different failure mechanisms oh the half-joints
Structural behaviour of Gerber half-joints subjected to steel corrosion
No full textThe Gerber half-joints assessment is today a topical problem since they are widespread in the infrastructure heritage of different countries. These structural elements are often affected by chloride corrosion phenomena due to their positioning under the deck joint. The paper presents some of the results of a wide research survey, developed at the Laboratory of the University of Rome Tor Vergata, aimed at evaluating their behavior when subjected to corrosion decay, up to failure, through experimental tests and analytical models. The experimental behavior of the specimens, designed with different criteria, and subjected to different degree of accelerated corrosion, is discussed. An accurate design phase of the specimens was followed, based on typical Strut and Tie models, to obtain peculiar and different failure mechanisms, involving both brittle and “ductile” crises. Particular care was devoted to the corrosion process, suitably calibrated for providing different degradation scenarios. The obtained results are analyzed and discussed in terms of load-displacement curves and cracking pattern, underlying the influence of corrosion on the failure mechanism. The experimental outcomes show that both design details and reinforcement corrosion could compromise the strength and ductility requirements of the elements and need to be accounted for in analytical and numerical structural assessment of existing corroded Gerber half-joints
Energy refurbishment planning of Italian school buildings using data-driven predictive models
Full text linkIn the current practice, the design of energy refurbishment interventions for existing buildings is typically addressed by performing time-consuming software-based numerical simulations. However, this approach may be not suitable for preliminary assessment studies, especially when large building portfolios are involved. Therefore, this research work aims at developing simplified data-driven predictive models to estimate the energy consumption of existing school buildings in Italy and support the decision-making process in energy refurbishment intervention planning at a large scale. To accomplish this, an extensive database is assembled through comprehensive on-site surveys of school buildings in Southern Italy. For each school, a Building Information Modelling (BIM) model is developed and validated considering real energy consumption data. These BIM models serve in the design of suitable energy refurbishment interventions. Moreover, a comprehensive parametric investigation based on refined energy analyses is carried out to significantly improve and integrate the dataset. To derive the predictive models, firstly the most relevant parameters for energy consumption are identified by performing sensitivity analyses. Based on these findings, predictive models are generated through a multiple linear regression method. The suggested models provide an estimation of the energy consumption of the “as-built” configuration, as well as the costs and benefits of alternative energy refurbishment scenarios. The reliability of the proposed simplified relationships is substantiated through a statistical analysis of the main error indices. Results highlight that the building's shape factor (i.e., the ratio between the building's envelope area and its volume) and the area-weighted average of the thermal properties of the building envelope significantly affect both the energy consumption of school buildings and the achievable savings through retrofitting interventions. Finally, a framework for the preliminary design of energy refurbishment of buildings, based on the implementation of the herein developed predictive model, is proposed and illustrated through a worked example application. Worth noting that, while the proposed approach is currently limited to school buildings, the methodology can conceptually be extended to any building typology, provided that suitable data on energy consumption are available
Application of solid-phase microextraction to antidoping analysis: Determination of stimulants, narcotics, and other classes of substances excreted free in urine
No full textThis paper describes the application of solid-phase microextraction
(SPME) with subsequent injection in a gas chromatograph–mass
spectrometer (GC–MS) (electron impact, full scan) for the
screening analysis of stimulants and narcotics in urine. Several
d i fferent kinds of fibers were preliminarily tested and
comparatively evaluated considering the influence on the overall
analytical performance of the method; other experimental
parameters; and, primarily among them, the volume of urine, the
pH value, and the time of adsorbtion. The optimal experimental
conditions have been recorded using 0.5 mL of urine with the pH
value adjusted to 10 with carbonate buffer, and in which is
immersed a polydimethylsiloxane/divinylbenzene fiber, with a
sampling time of 30 min; the fiber is then directly desorbed in the
injection port of the GC–MS equipment. All the analytes show a
good linearity (R2 > 0.99 for most substances) and a good
reproducibility at the concentration corresponding to the minimum
performance requirement limit or at the cut-off value fixed by the
World AntiDoping Agency (CV% < 11). The limit of detection of
the method is 50 ng/mL for the majority of the substances
investigated. Imidazole-based drugs (e.g., naphazoline) and local
anesthetics can also be included in this screening method.
Whenever necessary, confirmation analyses may also be performed
by following the same pre-chromatographic procedure. Integrating
the SPME process and the GC–MS analysis with a dedicated
autosampler that combines the microextraction and injection
capacities maximizes the overall analytical capacity of a single
GC–MS system and reduces the human labor necessary for and the
environmental impact of screening for stimulants and narcotics
excreted free in urine
Modelling Strategies for the Numerical Simulation of the Behaviour of Corroded RC Columns under Cyclic Loads
Full text linkRebars corrosion phenomena can modify the structural behaviour of reinforced concrete (RC) members and consequently the seismic performance of RC structures. Since many existing RC structures are affected by this phenomenon, the influence of the reinforcement corrosion on the seismic performance is still under examination, especially when the corrosive attack is localized in the dissipative areas of the plastic hinges. In this work, the effect of localized corrosion is numerically investigated, through the adoption of a suitable finite element model, object of validation with the outcomes of an experimental campaign carried out in the Laboratory of the University of Rome “Tor Vergata”, on un-corroded and corroded RC columns subjected to axial load and cyclic horizontal actions. Particular attention has been paid to the definition of the three-dimensional model and to the modelling of the corroded rebars and their corrosion morphology. Indeed, different modelling strategies are proposed with the aim to properly simulate the cyclic behaviour of the corroded columns. The main results show how more refined strategies taking into account the morphological aspects of the corrosion phenomenon produce a better fit with the experimental results for both Damage Control and Life Safety limit states performance
Detection of 5α-reductase inhibitors by UPLC–MS/MS: Application to the definition of the excretion profile of dutasteride in urine
No full textAn analytical procedure based on ultra-performance liquid chromatography-mass spectrometry was developed to screen and to confirm dutasteride and its metabolites in human urine. Sample preparation included an enzymatic hydrolysis followed by solid-phase extraction using the strong cation exchange cartridges OASIS® MCX. The chromatographic separation was carried out on C18 column, employing as mobile phases ultra purified water and acetonitrile, both containing 0.1% formic acid. Detection was achieved using a triple quadrupole as a mass spectrometric analyzer, with positive ion electrospray ionization and multiple reaction monitoring as acquisition mode. The analytical procedure developed was validated according to ISO 17025 and World Anti-Doping Agency guidelines. The extraction efficiency was estimated to be greater than 75% for both dutasteride and its hydroxylated metabolites. Detection capability was determined in the range of 0.1–0.4 ng/mL. Specificity and repeatability of the relative retention times (CV% < 0.5) and of the relative abundances of the characteristic ion transitions selected (CV% < 10) were confirmed to be fit for purpose to ensure the unambiguous identification of dutasteride and its metabolites in human urine. The developed method was used to characterize the urinary excretion profile of dutasteride after both chronic and acute administration of therapeutic doses. After chronic administration, dutasteride and its hydroxylated metabolites were easily detected and confirmed. After acute administration, instead, only the two hydroxylated metabolites were detected for 3–4 days
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