ABSTRACT
Plastered straw bale construction has, in recent years, become an alternative to typical residential construction. Plastered straw bales provide an environmentally friendly alternative to stud-framed walls for the load bearing components of residential, and other single-story buildings. Although the environmental benefits of straw bale construction are well documented, the structural behaviour of plastered straw bale walls is still not well understood beyond sporadic anecdotal information. As a result, a program of testing and modeling has been undertaken to understand the behaviour of plastered straw bale walls subjected to axial compression. Numerous prior experiments on wall panels 0.33 m tall have given light to the structural performance of plastered straw bale walls. This paper notes that walls with larger aspect ratios (ratio of height to plaster thickness) may experience different failure modes than walls only 0.33 m tall. In order to study the effect of increasing wall height on the strength and performance of plastered straw bale walls, panel sections 0.99 and 2.31 m tall have been tested in axial compression. Three specimens, one bale wide with a plaster width of 0.6 m were tested for each height. A testing and construction jig was fabricated to facilitate reproducible panels up to seven bales (2.31 m) in height. The ultimate strength of each wall section is compared to the results for individual plastered bales to determine the effect of increased aspect ratio. Observing cracking patterns and lateral displacements of the plaster skins during testing provides an indication of the failure modes which may exist for plastered straw bale walls loaded in compression. In addition, the stress-strain response for the wall panels is compared to a theoretical non-linear stress-strain curve in an attempt to model the response of the plastered straw bale wall panels as they are loaded in compression to ultimate failure. The conclusions described in this paper indicate that there is likely global buckling of the plastered bale walls at ultimate failure. This is supported by lateral deflection measurements and calculations showing that when buckling is considered, the stresses which exist in the plaster at ultimate failure of the bale walls varies from 0.777 MPa to 1.032 MPa. These values are in a similar range as the values for the compressive cube strength of the plaster itself. Without considering buckling, calculations suggest that the stresses in the plaster at ultimate failure of the wall are only about 80% of the compressive cube strength of the plaster. It was also found that a non-linear stress-strain model could be used as a means of representing the stress-strain behaviour of a plastered straw bale wall panels tested.
