材料物性と下地仕様の観点からみた木摺り漆喰天井部材における基本性能と健全度評価に関する実験的検討

Abstract

In the Great East Japan Earthquake, a large number of buildings collapsed and the strength of ceiling boards using plaster finishing was occurred as serious problems as a possible problem. That is why, since the Great East Japan Earthquake, the owners of old buildings are concerned about the deterioration of the building components. Therefore the number of owners seeking to strengthen their building's components have been increasing day by day. Moreover, in addition to preserving these historical buildings, it is also necessary to secure the safety from the standpoint of cultural and historical values. Therefore, we focused on these wooden lath and plaster ceiling that's used as a target of evaluation for saving the historical building. In this study, an experimental study of inspection of an existing wooden lath and plaster ceilings, we evaluate the strength and other properties of plaster, and finally conduct the objectives to prolong the duration of life with safety conditions. Plaster materials have been frequently used in old building's ceilings and walls. In general, the role of plaster ceilings are to transfer stress buffering between the lath and plaster. Therefore, it is important for the lath and plaster to be strongly adhered. This portion has been called Plaster Key in general and its role is to evaluate the mechanical properties of the plaster ceiling and wall. In Japan, this type of ceiling using plaster and mortar has been used from the early 1900s, and over a century has passed since the lath and plaster ceilings were developed, and at the same time the plaster has been frequently damaged in earthquakes. Stress transmission of lath and plaster are into the four patterns. The shear resistance is a stress. Shear is a stress that caught the lath. The tensile resistance is a stress that support the load of plaster. The bending resistance is a stress against the deformation of the plaster. The adhesive resistance is the stress of the adhesive surface of the plaster and lath. The lath and plaster ceiling specimens could be evaluated to measure the strength conditions of the ceiling member. This specimen was made in suspending conditions of same environment of the ceiling. The tensile testing instrument was attached to the surface of the finishing plaster after curing. The tensile strength test was enforced to pull plaster against the lath and record the peeling resistance in maximum load, the plaster deformation, and destruction pattern of plaster key. The results of strength examination of the plaster containing fiber, the maximum stress of the plaster was increased, and the fracture energy was increased. The case of including small fibers was effective at increasing the shear stress, stress in a similar function as reinforced concrete rebar. Then, as for the plaster containing sand, the maximum stress was not increased. As for the flexural strength, the plaster including the maximum amount of fiber was increased by increasing fiber contents, and the fracture energy of the sand was reduced. The results of strength examination by the lathing plaster specimen, the breaking load was correlated with the width of the wooden lath clearance. As the length between wooden lath and the plaster is closer, the length between the lath and plaster, the plaster key would expect strong mechanical interlocking conditions. However, if the amount of sand is too large, the positive effectiveness was eliminated, the strength would be decreased.