Mortar finishing external wall is one of a typical external wall for wooden houses in Japan. It is constructed using sophisticated plasterer's technics, which is able to be given various textures on the surface. The mortar finishing external wall shows good fire resistant performance, however, not a few mortar of the external walls fell off under earthquake in the past. The reasons of the falling off of the mortar were use of inadequate materials and execution method, decay of timber, corrosion of metal materials, etc. To improve its durability and prevent falling off of the mortar, ventilation method for the mortar finishing external wall has been introduced. With the ventilation space, since moisture is vented out of a wall, it is able to be kept dry.
To investigate the failure mode and the seismic performance of mortar finishing external wall with the opening which was built by ventilation method, static shear loading tests of specimens with 4550mm of wall length which had various openings were conducted. There are two kinds of opening, namely, door type opening and window type opening. Each type has three opening widths, 910mm, 1820mm and 2730mm. In addition to these six specimens with the one opening, three specimens with no opening were also prepared. The repeated static shear load was applied to the beam of the specimen until 3.3% of story drift and after that one directional loading followed.
Average maximum shear strength of the specimens with no opening was 42.8kN at around 2% of story drift. The maximum shear strength of the specimens with door type opening decreased with the opening width. The shear force ratio (Fr) with 910mm, 1820mm and 2730mm opening were 85%, 63% and 40%, respectively. Where, the shear force ratio (Fr) is defined as a ratio of the maximum shear strength of the specimen with opening to the one with no opening. Each maximum shear strength was at about 2% of story drift. Maximum shear strength of the specimens with window type opening were remarkably higher than the ones with door type opening. The maximum shear strength decreased with the opening width except for the specimen whose opening width was 910mm. The shear force ratio (Fr) with 910mm, 1820mm and 2730mm opening were 104%, 87% and 67%, respectively. During the loadings, the mortar layer did not fall off. From the relationship between shear force ratio (Fr) and the ratio of the mortar area to the area of whole wall area(β), the regression line Fr =1.8β-0.7 was derived. Especially at 0.5% and 2% of story drift, the good agreement between the two values was shown.
Moreover, to understand the shear stress and displacement distribution of connectors, FEM analysis of mortar finishing external walls with and without the one opening was conducted. Finally, considering the shear displacement distribution of connectors, the simple equations to evaluate shear strength of mortar finishing external wall were proposed. While the calculated shear strength by the proposed equation at 0.5% of story drift is conservative compared to the experimental value, it is close to the value by FEM. The calculated value at 2% of story drift, on the other hand, is slightly higher than the experimental value. However, it is considered that the proposed equations are usable to evaluate shear strength of mortar finishing external wall.
From these experimental and analytical studies, the failure mode and the shear strength of this type of mortar finishing external wall came to be clear. It is expected that the number of mortar finishing external wall increases and the sophisticated plasterers' technique is transmitted to the younger generation.