Significance of Concrete Cover to Reinforcement in Structural Element at Varying Temperatures

摘要

This paper evaluated the significance of concrete cover for reinforcement in structural elements at varying temperatures. Sixty samples of 320 mm x 150 mm x 100 mm concrete beams reinforced with 10 mm main bars and 6 mm nominal reinforcement were cast in the laboratory in four batches. Each batch contains fifteen samples with concrete cover for reinforcement varied at 10 mm, 15 mm, 20 mm and 25 mm respectively. After 28 days of curing, the beam samples were subjected to simulated fire in the laboratory furnace at temperatures ranging from 50 oC (122 ºF) – 700 oC (1292 ºF) in steps of 50 oC. Thereafter, the samples were allowed to cool to room temperature. Subsequently, samples of reinforcement were removed from the beam samples and tested with the universal material testing machine. Results of tensile tests on reinforcements showed that ultimate tensile strength of steel decreased with increasing temperatures. The greatest loss in strengths of steel reinforcements was recorded for beams with 10 mm concrete cov-er, which reduced from a value of 592.0 N/mm2 at room temperature to 224.50 N/mm2 at a terminal temperature of 700oC (1292 ºF), which represented a 62% reduction in strength.