低輻射加熱を受けた木材の燃焼性能および強度性能

Abstract

The purpose of this study was to obtain the fundamental values which were required to establish the decisions for the fire resistance verification method in case of localized fire scenario. The species of wood samples tested in this study was limited to Sugi (Cryptomeria japonica) controlled at the moisture content of less than 15%. In Chapter 1, the present circumstances of the fire resistance verification method since 2000 when Building Standard Law of Japan had been revised was explained. And the definitions for fire resistive buildings and what kind of values needed for this method were put in order. Then previous studies regarding the ignition, burning and the charring behavior are reviewed and the content of experiments carried out in this study was introduced In Chapter 2, the ignitability tests and cone calorimeter tests (CCM) at the incident heat fluxes of less than 20 kW/m2 from 20 to 30 minutes were conducted. The lowest radiant heat flux to cause ignition within 30 minutes was found to be from 13 to 15 kW/m2 because neither glowing nor flaming was observed at the incident heat fluxes of less than 13 kW/m2. And the linear function, which could lead to the time to ignition (tig), based on the date by plotting 1/√tig against incident heat fluxes was proposed. On the other hand, the temperature, which had been quoted as one of the determinants for ignition typically, was not suitable to the criterion to ignite because even if the temperature reached to 260°C or more on the surface of the test samples, ignition didn't occurred or delayed because of the lack of the amount of enough vaporized fuel to cause ignition below 20 kW/m2. Then even if ignition occurred, each test sample was extinguished automatically at the incident heat fluxes of 15~20 kW/m2. And it was found that the char depth could be obtained by the linear regression that were made through the char depth to the product of the given incident heat fluxes by the difference between the experimental period and the time to ignition. But the darkening was observed on the surface of the samples even if not ignited, and the temperature at the depth of 5mm from the bottom of the char layer was also measured more than 180°C. These phenomena could influence to the strength and the toughness of the wood. Therefore, in Chapter 3, the static bending test and impact test of small pieces of wood exposed to heating at 120°C, 150°C or 180°C for 20 minutes and stored later in the desiccator at 20°C for several days were performed. And the date from the experiments was compared with the date from the test samples not to be exposed to heating in order to investigate the possibility of deterioration of the structural performance of wood by heating. And by the comparison using statistics, it was not seemed that the strength and the toughness of wood would fall. In addition, the effect of the thermal degradation characteristics of wood on the duration of load was considered by the previous study and the date from the tests conducted in this report. And the heating at below 150°C was unlikely to degrade the structural performance of wood. Consequently, we propose the equation for the time to ignition, the equation for the char depth and the effective section size of the beams to check the structural performance as the decision for the fire resistance verification method in case of localized fire scenario for 20 minutes.