Clay wall on bamboo lathing is a traditional Japanese method of constructing walls using a timber framework, bamboo lathing, and plaster produced by mixing clay and straw. Although the use of clay walls is environmentally friendly, it is necessary to evaluate the performance of the walls, especially their structural resistance, so that they can be used widely and safely.
This paper aims to clarify the influence of the behaviors of plastering layers of clay walls upon their mechanical characteristics and fracture behaviors. Two experiments were conducted, that included diagonal loading onto small element specimens, referred to element experiments, and the loading of horizontal force onto structural specimens, referred to structural experiments.
First, the element experiments were conducted to clarify the influence on the mechanical properties of three factors; (1) degree of looseness around the end of “bamboo furring”, that is inserted into holes in the sides of neighboring framework members, (2) composition of wall clay mixture for each plastering layers, base-coat layer and middle-coat layer, and (3) ratios of thickness between the base-coat and middle-coat layer. As a result, we clarified the followings;
(1) In case of without looseness around bamboo furring, the load tends to small because larger delamination between the face and back of the base-coat layer is created.
(2) The initial stiffness was high with the specimens using mixture had large elastic modulus and compressive strength for the middle-coat layer, so that this layer started to resist at an early stage of loading. Then around the maximum load point, after the corners of the base-coat layer started to resist, the load was large with the specimens using mixture had large absorbed energy for the base-coat layer.
(3) The initial stiffness was higher when the middle-coat layer was thicker, so that this layer started to resist at an early stage of loading.
Secondly, the structural experiments were conducted to confirm the results of the element experiments. The specimens employed had the same cross-sectional dimensions of framework members as those used in real buildings. However, the specimens were proportionally smaller in height. The specimens had different factors based on the result of element experiments. Horizontal force was loaded to the positive and negative sides, alternating every three cycles until the prescribed deformation angle was reached. As a result, we clarified the followings;
(1) From the observation of the destructions, we confirmed four elements contributed to resistance to the horizontal forces. These resistance elements exist different layers, two base-coat and two middle-coat layers. Therefore, resistance of those elements cause the different behaviors of each layers and cause the delamination at the interface of layers that are difficult to repair.
(2) Clay walls of high initial stiffness can be achieved by avoiding gaps around the resistance elements. However, such walls tend to develop the delamination at the interface of layers.