The Behaviour of Axial Compression Timber Elements at Fire

This investigation is intended for an experimental assessment of the fire resistance of the axially loaded timber members aff ected by open flames and for comparing those with design results obtained in accordance with EC5-1-2:2005 provisions. Differently from metal or reinforced concrete structures, the longitudinal strains of timber at elevated temperature are negligible. A decrease in the bearing resistance of the timber member is associated with diminishing the cross section at the later stages of heat exposure. The process of diminishing the cross section leads to buckling an element or the other mode of fracture. The necessity of special equipment and a great quantity of smoke during an experiment are big problems for researching timber members under fire conditions. Therefore, practically it is impossible to use standard test equipment applied for testing steel or reinforced concrete members at elevated temperature. When researching the behaviour of axially loaded timber members under fire conditions, the furnace was specially designed to use a gas burner to provide the heating of specimen. The furnace was constructed from a special devise for loading the specimen and keeping it at required load level during the test. All timber specimens were of the same cross-section (50mm × 50mm) and length (1.2m). The compression specimens were pin-ended using spherical hinges. Fire resistance and the mode of failure were estimated during the test. The failure of axial compression specimens exposed to fire from one side is based upon diminishing the cross-section, a decrease in compression strength and the modulus of elasticity. In this case, the deflection of specimens follows flame direction. Design value fire resistance for timber elements was calculated using (EC 5-1-2:2005) provisions for the reduced cross-section. The calculation of load-bearing capacity was performed for axially loaded timber elements. The data required for design such as cross-sectional reduction due to charring and timber shrinkage was measured after testing fire.