International audienceThe mechanical and physical properties of wood structural elements and of wood structures are strongly affected by the combination of humidity, temperature variation and biological attack. The aim of this study is to develop a design model able to estimate timber elements decay function of the exploitation climatic conditions (temperature and humidity). The deterioration program may be applied on any type of wood element and is indicating the necessity of increasing the cross section dimensions if and when the specific humidity and temperature become of significant influence. The results of this study are of great importance as the behavior of a non-treated timber element can be surveyed when directly influenced by changes in climatic conditions (relative humidity and temperature)

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The presence of water in wooden elements is an important factor in the understanding of the evolution of this material used for a structure. This happens because wood has the ability to change its volume due to climate variations; it can shrink or it can double its size depending on the season. This can influence the mechanical properties of the wooden piece and introduce in the structure deformations and changes in sectional efforts that can be very dangerous. For this study, environmental conditions have been tampered with so that wood that has moisture content of 12% will intake or output water, in order to arrive at a moisture content of 8% respectively 16%. In this way, the moisture content of untreated Spruce (Picea abies) and Chestnut (Castanea Sativa) has been modified in a climatic chamber at certain conditions of temperature and relative humidity. The wooden pieces have been verified for their moisture content in an oven with a temperature of 105°C after a complete dry. The purpose of the study is to follow the behaviour of wooden pieces when found in other environments.

Increased interest in wood as construction material has led to the development of research on improving physical and mechanical characteristics of different wood species or various types of processed wood. Since wood construction materials are combustible, it is necessary to improve their fire behavior. This is achieved by treating the surface or the mass of materials using flame retardant substances, which can delay the ignition and can reduce the speed of propagation of fire. Although its benefits: specific weight, thermal conductivity, chemical stability, good vibration and shock absorption, good dimensional stability against temperature, ease of processing, etc., wood has the great disadvantage that it will ignite easily, being a cellulosic material.

Anaerobic sludge fermentation is one of the main technological steps for treating the wastewater resulting from urban consumption in the food industry. Anaerobic fermentation ensures the sludge mineralization treatment and the fermentation gas (biogas) resulting from the process can be used for the production of thermal or electric energy. The fermentation process can take place in closed reinforced concrete tanks (digesters) having different structural forms: cylinder, tapering, ovoid depending on the type of fermentation: mesophilic or thermophilic and on the performance of sludge mixing and homogenization equipment. Fermentation tanks with a capacity of 1000-4000 m3 were designed in Romania so far, the most important being those of Bucharest wastewater treatment plant made of prestressed reinforced concrete having an ovoid shape. The present paper aims at presenting the issues related to designing the fermentation tanks of the water waste plants from urban consumption in the food industry and zoo-technical farms in a new concept in which the main fermentation tank is coupled with the fermenter for the fermentation gas storage. Consequently, hereinafter structural and functional requirements for this kind of structures are presented, together with design principles and methods that must be applied in order to fulfil the performance exigencies related to strength, stability, tightness and durability.