1,721,086 research outputs found
Analisi strutturale di serre e tunnel mediante la teoria del II ordine: criteri e metodi progettuali secondo le norme UNI e i nuovi standard europei CEN.
No full textTesi di Dottorato XII Cicl
LOADS INTERACTION DOMAINS METHODOLOGY FOR THE DESIGN OF STEEL GREENHOUSE STRUCTURES
No full textAim of this research is to develop a design methodology which correlates main structural design parameters, whose production is characterised by high levels of standardization, such as the height of gutter or the distance between frames, with actions on the greenhouse. The methodology, based on the use of charts and abacus, permits a clear and a direct interpretation of the structural response to design load combinations and allows the design of structural improvements with the aim of the optimization of the ratio benefits (structural strength)/costs. The study of structural interaction domains allowed a clear and a direct interpretation of the structural response to design load combinations. The diagrams highlight not only if the structure fulfils the standard requirements but also the safety levels with respect to design load combinations and allow the structural designer how to operate in order to optimize the structural response with standard requirements achieving the best ratio benefits (structural safety)/ costs. The methodology was developed basing on criteria assigned by EN13031 on two different kinds of greenhouse structures: an arched greenhouse with a film plastic covering and a duo pitched roof greenhouse cover with rigid plastic membranes. Structural interaction domains for arched greenhouse showed a better capability of the structure to resist to vertical loads then to horizontal one. Moreover, the climatic load distribution on the structure assigned by EN13031 is such that the combination of climatic actions is less dangerous for the structure then their individual application. Whilst, duo pitched roof steel greenhouse interaction domains, showed a better capability of the structure to resist to vertical loads then to horizontal one and that, in any case, the serviceability limit states analysis is more strict then the ULS one. The shape of structural domains highlighted that the combination of actions is more dangerous for the structure then the application of single loads. Charts and abacus very easy to interpret and can be used also by non technicians in order to arrange a quick and reliable estimate of the costs of the structure. For instance, it is sufficient to know characteristic values of snow loads and wind speed to evaluate what is the distance of frame of the arched greenhouse to fulfil EN13031 requirements
Photovoltaic greenhouses: evaluation of shading effect and its influence on agricultural performances
No full textDuring the last years, European government remuneration polices promoted the realisation of photovoltaic systems integrated with the structures instead of on ground photovoltaic (PV) plants. In this context, in rural areas, greenhouses covered with PV modules have been developed. In order to interdict the building of greenhouses with an amount of opaque panels on covering not coherent with the plant production, local laws assigned a threshold value, usually between 25% and 50%, of the projection on the soil of the roof. These ranges seem not to be based on scientific evaluation about the agricultural performances required to the building but only on empirical assessments. Purpose of this paper is to contribute to better understand the effect of different configurations of PV panels on the covering of a monospan duo-pitched roof greenhouse in terms of shading effect and energy efficiency during different periods of the year. At this aim, daylighting and insolation analysis were performed by means of the software Autodesk® Ecotect® Analysis (Autodesk, Inc., San Rafael, CA, USA) on greenhouse model with different covering ratio of polycrystalline photovoltaic panels on the roof
Il condizionamento delle serre in floricoltura: le problematiche in ambiente mediterraneo
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Air flow through net covered arched structures
No full textPermeable coverings facilitate indoor ventilation due to their porosity, the characteristics of the air flow passing through a net depends on the Reynolds number of the system. So far, only the permeability of nets used in application involving low Reynolds numbers have been studied, while the behaviour of nets at high Reynolds numbers, has been poorly studied. The ventilation of a net covered tunnel was numerically and experimentally studied analysing the airflow around and through the structure. The airflow through a two-dimensional tunnel structure (8.0 m wide and 2.5 m high) covered with various nets was numerically calculated by Computational Fluid Dynamics (CFD) simulations. A full scale tunnel structure, of the same geometry, covered with four different nets, characterised by different porosity, was built in order to validate the numerical CFD results. Wind velocity was measured outside and inside the structure by means of two handheld rotary cup anemometers. Data were gathered in the middle of each sector in order to avoid edge effects. The estimation of the indoor/outdoor air velocity reduction ratio shows a good agreement between measured and calculated values, especially for nets with a medium-low solidity ratio. For low solidity ratios the numerical results overestimate the indoor air velocity. Moreover the full scale measurements confirm the dependence of the “a” factor in the Forchheimer equation with the characteristics of the net
Analisi e progetto agli stati limite delle strutture portanti per serre alla luce dei nuovi standard europei
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