EXPERIMENTAL AND ANALYTICAL STUDIES OF THE BEARING CAPACITY LONG-SPAN REINFORCED CONCRETE DURING FIRE EXPOSURE

The paper presents the results of experimental and theoretical studies of bendable concrete structures reinforced with post-tensioning tendons placed into steel ducts, and regular unstressed rebars. The behavior of concrete beam prototypes under standard temperature regimes was investigated. The actual limits of fire resistance of these prototypes for the loss of bearing capacity of the structure were determined. On the basis of experimental data, it is shown that concrete structures reinforced with posttensioning tendons placed into steel ducts, which provide traction reinforcement with concrete, have sufficiently high fire resistance limits. This behavior can be explained by tendon placement on structure cross-section, which provides sufficient protective layers of concrete on the lower (stretched) zone, as well as endurance of poststressed structures in stress-strain state, which excludes or minimizes development of cracks in the tension zone. The experimental and analytical studies confirm the assumption that the calculation of the fire resistance of bendable post-tensioned concrete structures can be performed as for conventional ones, without taking into account pre-stress in the reinforcement, provided the limit state is formed at midspan of the beam due to formation of a plastic hinge.