11:15 AM - 11:30 AM
[SVC27-03] Experimental Study on Safety of Wooden Building Roofs Against Impact of Ballistic Ejecta
Keywords:Ballistic ejecta, Wooden buildings roof , Artificial pumice
Damages and destruction of the wooden buildings caused by volcanic activities are due to various factors. Especially, at the phreatic eruption of Mt. Ontake on September 27, 2014, most of the damages were caused by the impact of the ballistic ejecta.
In order to mitigation this damage, it is suggested that evacuation to a mountain hut is effective. Thus, evaluation of safety for wooden buildings (e.g. mountain huts) against ballistic ejecta impact is necessary. Previously, we reported the penetration boundary energy for the unreinforced 15 mm and 18 mm thick wooden building roof. In addition, it was found that by superimposing the cedar boards, impact absorption properties can be improved simply. In this study, we focused on the effect of pumice that are often installed on roofs in many mountain huts and investigated their impact absorption characteristics.
An impact test was carried out at the velocity of 10 to 90 m/s using a large-scale launching system. In this system, a projectile was accelerated by compressed air and then collided with the target. The projectile velocity was measured using two lasers and light receiving parts.
In case of normal phreatic eruptions, the ballistic ejecta with a diameter of approximately φ100 mm are scattered. Therefore, cylindrical abrasive materials similar to the common ballistic ejecta (density: 2400 kg/m3, diameter: 90 mm, length: 170 mm, mass: 2.66 kg) was used as the projectile. A typical wooden roof structure (e.g., cedar boards, waterproof sheet, galvalume steel plate and cedar rafter) was used for the target. The thickness of the cedar board, waterproof sheet and galvalume steel plate were 18 mm, 1 mm and 0.4 mm, respectively. The components were fixed with nails and its spacing was approximately 150 mm. The dimensions of the specimen were 600 mm × 600 mm.
For the impact experiment, artificial pumice (hereafter referred to as pumice) in sandbags was placed in front of the specimen. The pumice with composition and specific gravity similar to natural pumice were used. The sandbag bag containing pumice is approximately 180 mm thick. The pumice used in this study was an inorganic porous material made from 96 % waste glass. Its particle size was approximately 2 to 75 mm and its shape was irregular. The density in oven-dry conditions was between 300 and 600 kg/m3.
In previous study, it was known that the boundary between penetrating and non-penetrating impact energy was taken to be near 1.2 kJ in the unreinforced 15 mm thick wooden building roof.
As a result of the impact test, due to the installation of pumice on the roof structure, the boundary between penetrating and non-penetrating impact energy was taken to be near 3.7 kJ. Therefore, the impact absorption energy of pumice used in this study can be calculated as approximately 2.5 kJ.
In order to mitigation this damage, it is suggested that evacuation to a mountain hut is effective. Thus, evaluation of safety for wooden buildings (e.g. mountain huts) against ballistic ejecta impact is necessary. Previously, we reported the penetration boundary energy for the unreinforced 15 mm and 18 mm thick wooden building roof. In addition, it was found that by superimposing the cedar boards, impact absorption properties can be improved simply. In this study, we focused on the effect of pumice that are often installed on roofs in many mountain huts and investigated their impact absorption characteristics.
An impact test was carried out at the velocity of 10 to 90 m/s using a large-scale launching system. In this system, a projectile was accelerated by compressed air and then collided with the target. The projectile velocity was measured using two lasers and light receiving parts.
In case of normal phreatic eruptions, the ballistic ejecta with a diameter of approximately φ100 mm are scattered. Therefore, cylindrical abrasive materials similar to the common ballistic ejecta (density: 2400 kg/m3, diameter: 90 mm, length: 170 mm, mass: 2.66 kg) was used as the projectile. A typical wooden roof structure (e.g., cedar boards, waterproof sheet, galvalume steel plate and cedar rafter) was used for the target. The thickness of the cedar board, waterproof sheet and galvalume steel plate were 18 mm, 1 mm and 0.4 mm, respectively. The components were fixed with nails and its spacing was approximately 150 mm. The dimensions of the specimen were 600 mm × 600 mm.
For the impact experiment, artificial pumice (hereafter referred to as pumice) in sandbags was placed in front of the specimen. The pumice with composition and specific gravity similar to natural pumice were used. The sandbag bag containing pumice is approximately 180 mm thick. The pumice used in this study was an inorganic porous material made from 96 % waste glass. Its particle size was approximately 2 to 75 mm and its shape was irregular. The density in oven-dry conditions was between 300 and 600 kg/m3.
In previous study, it was known that the boundary between penetrating and non-penetrating impact energy was taken to be near 1.2 kJ in the unreinforced 15 mm thick wooden building roof.
As a result of the impact test, due to the installation of pumice on the roof structure, the boundary between penetrating and non-penetrating impact energy was taken to be near 3.7 kJ. Therefore, the impact absorption energy of pumice used in this study can be calculated as approximately 2.5 kJ.