Within the Ph.D course in "design of structure" one of the authors is working on the design of tension roofs with medium to large span, with particular attention to their cable structure. This kind of structures are light and characterized by innovative construction materials and technical elements such as conditioning, lighting, etc. The design of tension roofs is always striving towards technological and structure innovation in order to build lighter and lighter structures to cover ever larger spans. Tension structures are in line with the new contemporary architectural concept of space, allowing for the construction of a large free space where the flexibility and the modifiability of structures are the most important prerequisites.[1] Tension structures meet the demand for structures that only need basic planned maintenance and have a good seismic performance, too. In Italy, this constructive typology has been neglected so far and even ignored by building regulations; in fact no mandatory standards have been set for the design and construction of these structures, except for temporary constructions. The shape selected for a parameterization leading to an optimized design of this kind of structures is the hyperbolic paraboloid. This research work followed two consecutive steps: the first was aimed at developing an optimized procedure of preliminary design for the cable structure [3]; the second was focussed on the study of the wind action on these structures. The procedure of preliminary design consists in evaluating prefixed cable spans and sags, the minimum values of pretensions and areas of the two series of cables (load bearing and stabilizing) so as to maintain the cable stress within the limit value under the two opposite load configurations: maximum snow load and maximum depression of wind. By using the procedure for a set of values of span and sags, a statistical sample of different roof shapes has been produced. Having in mind the design of sport palaces, swimming-pools, meeting rooms, we have taken into account another geometrical parameter (in the following Hb) measuring the distance between the roof and the ground floor. This parameter has been added to the span/sag ratio in the experimental tests in the wind tunnel. In fact, the model is built in two different heights. In the second phase of the work, experimental tests were performed in the CRIACIV's wind tunnel in Prato, in order to assess the wind action on tension roofs with a hyperbolic paraboloid shape. While there are precise indications for shells, slopes and domes, in Italy there are no wind regulations for this shape. No prescriptions are provided in the new CNR-2008 for the calculation of the wind action, either.

a b s t r a c tSheltering efficiency of wind barriers on viaducts was experimentally studied in a boundary layer wind tunnel. Effects of wind incidence angle on flow field characteristics in the wake of a wind barrier were reported. Mean velocity fields and vorticity fields were determined using the Particle Image Velocimetry (PIV) technique. Freestream velocities were measured using hot-wire and Pitot tube. Results indicate a possibility of wind-induced instability of high-sided vehicles at larger vertical incidence angles, especially in the traffic lane close to trailing edge of the bridge, as velocity fluctuations and mean freestream velocities approach the road surface when increasing the vertical incidence angle. Removing elements from the wind barrier causes very large local velocities immediately downstream from a barrier and strong vorticity in the entire area in the wake of a wind barrier. Variations in horizontal incidence angle do not seem to affect flow field characteristics significantly. Without a wind barrier, wind velocities on bridges reach 80% of the freestream velocity at height as low as 1 m full-scale along with very strong vorticity in the immediate vicinity of the road surface.

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This research work presents a modelling strategy to analyse thermal conversion rates of two thermal wood modification processes based on time-temperature superposition method. It gathers in a single study different original and bibliographic experimental works analysing the dry mass variation that occurs during thermal and hydro-thermal wood modification processes. The mass loss kinetic was successfully modelled using a modified Arrhenius approach. The time-temperature superposition method allowed to define for each wood modification process a master curve and its time shift depending on the treatment temperature. The analysis of ventilated oven and saturated steam treatments pointed out the existence of a continuous single kinetic for the ventilated oven which became more complex for saturated steam since a second kinetic stage appeared. This kinetic difference was sustained by infrared spectra chemical analysis which showed that hemicelluloses degraded much faster in presence of steam while lignin degradation occurred in both conditions.