Assessment and modelisation of the mechanical performance of straw bales for use in construction

The advantages of straw bale construction techniques over conventional ones in terms of environmental impact, thermal insulation and breathability are well known. Straw bale buildings can also perform well against earthquakes thanks to the reduced weight of the constructions and the dissipation properties of the straw bales. Usually, straw bale walls are composite structures constituted by a stack of straw bales plus an inner and an outer plaster skins. The plaster skins are the stiffer element in the composite and, in load-bearing straw bales buildings, they carry almost all the mechanical load of the building. However, in case of failure of the plaster (due to natural disasters, for instance), straw bales are required to sustain mechanical load. In order to understand the post-calamity behaviour of a straw bale building, the mechanical properties of unplastered straw bales have to be known; in addition, reliable models are needed to assist designers in the prediction of the behaviour of the buildings in such scenarios. This paper presents the results of an extensive experimental campaign in which the elastic and inelastic mechanical properties of straw bales have been determined. The influence of bales material, density, bales orientation, baling process and loading rate on the mechanical properties of straw bales is highlighted. A theoretical model is also described which is able to predict the performance of straw bales under compression starting from the dimension and the density of the bales.