Structural Behaviour of Plastered Straw Bale Panels Under Non-Uniform Loading
Rakowski, Michael Robert
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The search for more sustainable construction methods has created a renewed interest in straw bales technology. Straw bales are a composite material that is energy efficient and durable. Rectangular straw bales stacked in a running bond and plastered on the interior and exterior faces have adequate strength to resist typical loads found in two-storey structures. The structural behaviour of a load-bearing plastered straw bale wall subject to uniform loading is well researched. However, door and window voids in the wall redistribute vertical load paths and produce areas of concentrated stress. This thesis describes experiments on small-scale plastered straw bale panels subjected to loading conditions that simulate the loading conditions experienced in areas around door and window voids. Twenty-one specimens were tested under two main types of loading conditions. The specimens were rendered with lime-cement plaster, were one to three bales (0.33 m to 0.99 m) in height, and were either unreinforced, or contained metal diamond lath or chicken wire embedded within the plaster. The specimens were pin-supported at various centre-to-centre distances ranging from 200 mm to 500 mm and were loaded either uniformly or by a point load. Two distinct types of failure were observed. Strut-and-tie models were developed to describe the structural behaviour of panels undergoing vertical cracking of the plaster skin at failure. Bearing models were developed to describe the structural behaviour of panels undergoing crushing of the plaster skin beneath the point of applied load. The models predicted the correct failure mode of 92% of the specimens and had an average ratio of experimental strength to theoretical strength of 0.95 with a standard deviation of 0.17. The results show that the behaviour of plastered straw bale walls can be predicted using common methods of structural analysis. A parametric analysis of door and window voids within plastered straw bale walls is presented.