Timber elements, which are different from other structural elements, have a characteristic problem in that the load bearing capacity decreases due to self-burning in the case of a fire, and this self-burning may continue after other fuel in the room has been exhausted. Therefore, the structural fire performance of timber elements should be clarified during not only the heating phase, but also the ... [Show full abstract] cooling phase. In the present paper, deflection behaviour and failure mode of larch glued laminated timber beams exposed to fire heating and natural cooling is discussed based on load-bearing fire tests in which load level is the test parameter.
The present paper described the fire performance, including the cooling phase, of structural glued laminated timber beams whose section was 210mm (width) x 420mm (height). The main conclusions were:
(1) Failure time was 79 minutes, for the long-term allowable load was loading. It was satisfied the Quasi-fire resistance of 1 hour.
(2) In the cooling phase, it may continue to support the load, when loaded below 0.4 times of long-term allowable load.
(3) On the other hand, in the cooling phase after 1 hour heating, it was confirmed that the deflection is increased. Compared with the deflection just after heating for 1 hour. LF-0.4 (1) in the cooling after 7 hours, deflection than during the just after 1 hour heating was about 6.7 times. LF-0.2 In the cooling After 24 hours, deflection than during the just after 1 hour heating was about 7.2 times.
(4) In the case of bending failure, strength of cooling 7 hours and 24 hours was about the same as the strength of the cooling 3 hours of previous report.
(5) The failure mode, bending failure and due to the laminar layer tensile breaking of the beam bottom, the shear failure due to the slip in the growth ring centroid axis near of the beam cross section was observed. Shear failure was seen in up to 1 to 3 hours from after heating.
(6) Bending strength in the cooling phase of the residual cross-sectional area, calculated value that gave the strength reduction rate due to Eurocode 5 is roughly agreement with the experimental value. On the other hand, the calculated value for the shear strength was significantly higher than the experimental values.
In the future, investigate the relationship between the strength of evaporation and the timber of water from the high-temperature material testing, it is expected to further consider the strength reduction in the cooling phase.