Behavior of fire-retardant treated bolted timber–steel composites (TSCs) and effective charring depth based on experiment

ABSTRACTThe bolted joints make timber–steel composites (TSCs) easily to be assembled; however, seams exist between the timber components for bolted TSC components resulting in the risk of fire spreading into the joint seam when the component is under fire. The efficient charring depth provided by timber needs to be clarified; furthermore, the raising temperature potentially affects the strength of steel component. In this study, TSCs were tested in fire for 1 hour, and the following issues were examined, including the experimental charring depth of timber components, the influence of fire-retardant finish in order to provide the efficient charring depth, and additionally the suggested charring depth are proposed for the design of TSCs. In conclusion, the charring depth in the seams was greater than the regulation values, and evaluation methods for the charring depth at seams should be reconsidered. Although the fire-retardant finish reduced the formation rate of the char layer, the flames still breached the seams. The results reveal that Douglas fir TSCs with fire retardant are the most efficient specimen, with effective charring depth 52 mm. While the effective charring depth of Douglas fir TSCs without fire retardant and Japanese Cedar TSCs with fire retardant are increased, at least 64 mm and 65 mm needed, respectively.CO EDITOR-IN-CHIEF: Ou, Yu-ChenASSOCIATE EDITOR: Ou, Yu-ChenKEYWORDS: Timber–steel compositeseffective charring depthfire-retardantjoint seams Nomenclature b=original width of TSC componentd0=a constant of 7 mmdchar=charring depthdchar,eff=effective charring depthdchar,x=charring depth along x-axisdchar,y=charring depth along y-axish=original height of TSC componentk0d0=pyrolysis layer thicknessT=Average furnace temperature (°C)t=Elapsed time of experiment (min)β=charring rateAcknowledgmentsThis research was financially supported by National Taiwan University of Science and Technology under grant number II-2-2, Forestry Bureau, Council of Agriculture under grant number 110Linfa-04.1-Zao-24(2), and Ministry of Science and Technology under grant number MOST 110-2221-E-011-055 -.Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was supported by the Ministry of Science and Technology, Taiwan [MOST 110-2221-E-011-055 -]; National Taiwan University of Science and Technology [II-2-2]; Forestry Bureau, Council of Agriculture [110Linfa-04.1-Zao-24(2)].