Bending stiffness, yield moment, and bending capacity of steel bar-timber composite beam under high-temperature environment with uncontrolled humidity were revealed by heating and loading tests, and methods for estimating those were proposed. Internal stresses of rebar and glulam timber within the beam, derived from temperature rising, did not affect the stiffness and capacity, but only the yield moment. The stiffness and capacity could be estimated by considering only deterioration of wood and rebar owing to temperature rising. The internal stresses were appropriately estimated using the previously proposed equations, and the yield moment could be estimated using values of the stress.
