Studio teorico e verifiche sperimentali di barriere in legno insonorizzanti per il territorio rurale

TIMBER NOISE ABSORBING BARRIERS FOR RURAL LANDSCAPES: PRELIMINARY ACOUSTIC TESTS, DESIGN AND EXPERIMENTAL EVALUATION P. Pellegrini, M. Monti SUMMARY This study arises from the concurrence and the convergence of several needs: – the growing awareness of noise damping problems in rural landscapes, regarding both settlements (dwellings or farmhouses, where people live and work) and recreational or ecological activities, such as the ones in protected areas, bird nesting areas, and so on; – the need to build noise reducing devices that harmonise well with these environments; – the choice to employ wood in technologically advanced uses as the main building material of the noise barriers; in fact it is not only a renewable resource, but its production cycle brings about favourable results for the territory, first of all it controls depopulation. In order to pursue environmental safety, materials must be chosen so as to minimize the environmental impact during every phase of the life cycle of the barrier: from raw material production, to transport, workmanship, operation and final disposal. After examining the characteristics of the local types of wood which can be used to build outdoors structures, chestnut wood has been chosen. This species has a high durability even if subjected to severe conditions of use. Sound absorbing capacity of several loose materials and vegetable fibrous fabrics has been tested according to Kundt’s tube technique. Following these tests, expanded clay aggregate has been chosen. Its absorption capacity turned out to be suitable for the project requirements; moreover it is inert, cheap and can easily be supplied and disposed of. Owing to the absence of compulsory italian national rules regarding the acoustic performances of noise reducing devices we have referred to the UNI (Italian National Standards Body) standards, and to several technical documents issued by Italian Roads and Highways Corporate Bodies or Companies. Four diverse prototypes have been designed based on the sound absorbing capacity of expanded clay aggregate or of resonant panels; each prototype has been reproduced in five 0.75 by 1.5 m samples and tested in a reverberating chamber. A specimen built according to the properties of Helmholtz resonators has been tested with a modified Kundt’s tube. Taking into account all these results, a final prototype element has been designed and produced. It uses loose expanded clay filling as sound absorbing material, without either any adhesives for timber gluing or any synthetic substances. After it has passed the tests in the reverberating chamber, it has been built in the 16 0.75 by 3.00 m samples needed to make the experimental barrier. The load-bearing capacity has been designed in accordance with Eurocode. The noise barrier has been built fastening the elements to posts of galvanized HE beams anchored to prefabricated reinforced concrete foundations. To sum up, the developed study helps to show how a design process based on performance requirements may lead to innovative outcome within timber noise absorbing barriers.