釘側面抵抗性能および面材張り耐カ壁の面内せん断性能に対する水掛かりの影響

摘要

Lateral nail resistance test (LNR) and racking test of panel sheathed shear wall were conducted for various wood-based structural panels. Seven different types of plywood, three different types of oriented strand board (OSB) ， one type of particleboard (PB) and one type of medium density fiberboard (MDF) were prepared for each test. Half of the lateral nail resistance test specimens and one of the shear wall test specimens were immersed into room-temperature water for 72 hours continuously. The test results were compared with that of the non-treated specimens. In addition, the characteristic values of the lateral nail resistance were compared with that of the shear wall. The test results are summarized as follows ； The strength values (P_y, P_(max), P_u) of LNR were approximately same between the non-treated test specimens and the treated test specimens. Treated test specimens showed greater deformation values (δ_y, δ_(max), δ_u) than non-treated test specimens. However, the stiffness (K) and the ductility factor (μ) of the treated specimens were almost half of that of the non-treated test specimens. In addition, the tendency of the characteristic values of the racking test was almost same as that of the LNR. In the durability evaluation of the panel sheathed shear wall, the reduction of the stiffness should also be considered as well as the reduction of the maximum load.%一般的な木造軸組構法住宅に用いられる面材張り耐カ壁の仕様規定は，幾つかの実験データを基に当時の性能評価法に則ってバラツキを考慮した性能評価を行っており，耐久性や施工性等による低減を考慮しているか否かについては明記されていない。一方で，枠組壁工法住宅の仕様規定では，釘側面抵抗性能と耐カ壁の性能の関係などを参考にして，面材料ごとの耐久性等による低減を考慮している。これら仕様規定とは別に，壁倍率の大臣認定を取得する場合には指定性能評価機関において試験・評価を受ける必要があるが，許容せん断耐力の算定にあたっては耐カ壁の"用途"や"施工性"などを考慮した低減係数(a)を評価することになっている。しかし，各種構造用面材料の低減係数評価に関する技術的知見は少なく，特に構造用面材料を張った耐カ壁の場合には，"用途に伴う影響(水分に曝される危険性を考慮した低減係数)"に関しては，促進劣化処理を施した釘接合部の側面抵抗試験等によって評価することが可能であるため，実験データの蓄積が望まれている。