水平加力後に延焼抑止効果を保持できる木造土壁仕様の開発研究

 Influence of horizontal loading on the fire resistance of traditional wood/soil wall qualified as Quasi-fireproof Construction is verified against loaded fire tests after racking tests for the survey of the feasibility of large-scale public buildings based on traditional timber structure harmonized with historic landscape. The specimen, 150mm square Cryptomeria Japonica (Japanese Cedar) columns and 90mm thick soil walls with bamboo mesh at the center of the wall, was designed to achieve 45 minutes loadbearing capacity, integrity and thermal insulation under the vertical loading to each column, 80.9kN, reproducing that on the ground floor of a three-story historic townhouse at the conservative side. The thickness of the wall panels was chosen to secure at least 40mm thick clay layer even if the clay layer on either side of the bamboo mesh partly fall for seismic effect or for fire exposure. Maximum deformation angles of the racking tests were chosen as 1/100 and 1/50 radians, to reproduce a typical condition assumed for the seismic design of low-rise wooden buildings and to reproduce a more plastic damage that could be caused by severer seismic effect. Red clay from North Kanto district was used for the wall panels, and the seismic effect on the fire resistance was verified through the comparison against the test without preceding racking test. The fire test with the deformation angle 1/100 radians was also conducted on the wall with Fukakusa clay, normally used for traditional buildings in Kyoto, of identical specifications except for the use of local materials for partial reinforcement. Previous fire tests showed Fukakusa clay wall weaker thermally insulating than Red clay wall. All tests were terminated by the acceleration of the deformation of the columns. The tests yielded the following conclusions.<br><br> (1) Maximum deformation angle of 1/100 radians caused gaps between the wall panel and the timber frame and cracks on the wall panel surfaces. These damages do not cause noticeable reduction of fire resistance, which is confirmed as 47.5 minutes at the fire test without racking test.<br> (2) Maximum deformation angle of 1/100 radians caused larger cracks to the Red clay wall than to the Fukakusa clay wall, yet not resulting in noticeable difference of the fire resistance.<br> (3) Deformation angle larger than 1/100 radians caused noticeable plastic damage to the wall panel surface and edge between the wall panel and the timber frame. The test with maximum deformation angle 1/50 radians result in 5% reduction of the fire resistance in terms of the time of the column buckling. However, the fire resistance time is still over 45 minutes.<br> (4) Some parts of the wall panel on the furnace side fell during the fire test after the maximum deformation angle 1/50 radians. However, it does not affect the thermal insulation because of the survival of the clay layers on back surface side.<br> (5) The reduction of the fire resistance by horizontal loading of the present specimens is notably weaker than that of the Quasi-fireproof walls of popular modern wooden constructions.