Investigating the Impact of Temperature Variations on the Load-Carrying Capacity of Plain Concrete Beams

Fires are among the most common and devastating accidents that unexpectedly impact service structures, often starting with little effort but requiring substantial time, resources, and expense to control. In Ethiopia, fire accidents have frequently caused severe damage to buildings, emphasizing a critical issue. While concrete behavior under normal conditions is well understood and applied in design, its performance under extreme heat remains less explored, posing challenges in creating structures with sufficient fire resistance. The repeated occurrence of destructive fires, resulting in both loss of life and structural failures, highlights the urgency of designing buildings that can withstand high temperatures. This paper examines how elevated temperatures affect the load-carrying capacity of plain concrete beams, focusing on their performance after exposure to intense heat. Factors such as compressive strength, vertical displacement, and load-carrying capacity were analyzed using load-displacement curves under varying temperature levels and exposure durations. Key variables, including concrete grade, temperature, and exposure time, were considered to assess concrete strength in extreme conditions. An experimental study on plain concrete beams with grades C-15, C-25, C-30, and C-40 was conducted under temperatures of 100°C, 200°C, and 300°C for four and eight hours. The results revealed that as temperature and exposure time increased, load-carrying capacity significantly declined, with lower-grade concrete suffering more strength loss while higher-grade concrete exhibited better fire resistance. This study underscores the importance of incorporating fire performance into building codes to enhance structural adaptability in fire-prone regions.