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Concrete is subjected to elevated temperature for short duration, long duration and cyclic heating on many occasions. The dramatic fire accidents/incidents have renewed the interest in the area of research on concrete subjected to elevated temperature. From the literature review it is found that the experimental data which simulate the conditions of structural elements in stressed conditions when exposed to fire are scarce. The work presents a study on the residual characteristics of R.C. beams subjected to elevated temperature under unstressed and stressed conditions. The R.C beams were of size 120mm×120mm×1500mm and designed with single and double reinforcement and referenced as Type I and Type II respectively. M20 grade of concrete was used in casting the beams. The temperatures were kept as 100°C, 200°C, 300°C, 400°C and 500°C and the duration of exposure was 4 hours. The specimens were cooled in air and the residual properties were tested by conducting two point bending test on R.C. beams and their behavioral parameters were studied in comparison with beams tested under normal (room) temperature conditions. The extent of damage suffered measured by the damage factor was about 32 % for Type I beams and about 48% for the Type II beams tested under unstressed test condition when exposed to 500°C; whereas it is to an extent of 33% for Type I beams and 49% for Type II beams in stressed test condition for the same exposed temperature. The degradation in initial stiffness was nearly 57% and 49% for Type I and Type II beams in unstressed test and 54% and 73% respectively for stressed test when exposed to 500°C. The degradation in stiffness at 50% of ultimate load was nearly 36% and 35% for Type I and Type II beams in unstressed test and 49% and 76.6% respectively for stressed test when exposed to 500°C. The ultimate load of R.C. beams tested in stressed condition were marginally 5% lower than the beams under unstressed test condition.

This review paper seeks to enhance knowledge of how pre-loading affects reinforced concrete (RC) beams under fire. It investigates key factors like deflection and load capacity to understand pre-loading's role in replicating RC beams' actual responses to fire, aiming to improve fire testing protocols and structural fire engineering design.

This review systematically aggregates data from existing literature on the fire response of RC beams, comparing scenarios with (WP) and without pre-loading (WOP). Through statistical tools like the two-tailed t-test and Mann–Whitney U-test, it assesses deflection extremes. The study further examines structural responses, including flexural and shear behavior, ultimate load capacity, post-yield behavior, stiffness degradation and failure modes. The approach concludes with a statistical forecast of ideal pre-load levels to elevate experimental precision and enhance fire safety standards.

The review concludes that pre-loading profoundly affects the fire response of RC beams, suggesting a 35%–65% structural capacity range for realistic simulations. The review also recommended the initial crack load as an alternative metric for determining the pre-loading impact. Crucially, it highlights that pre-loading not only influences the fire response but also significantly alters the overall structural behavior of the RC beams.

The review advances structural fire engineering with an in-depth analysis of pre-loading's impact on RC beams during fire exposure, establishing a validated pre-load range through thorough statistical analysis and examination of previous research. It refines experimental methodologies and structural design accuracy, ultimately bolstering fire safety protocols.

The Reinforced Concrete(RC) elements are known to perform well during exposure to elevated temperatures. Hence, RC elements are widely used to resist the extreme heat developing from accidental fires and other industrial processes. In both of the scenarios, the RC element is exposed to elevated temperatures. However, the primary differences between the fire and processed temperatures are the rate of temperature increase, mode of exposure and exposure durations. In order to determine the effect of two heating modalities, RC beams were exposed to processed temperatures with slow heating rates and fire with fast heating rates.

In the present study, RC beam specimens were exposed to 200 °C, to 800 °C temperature at 200 °C intervals for 2 h' duration by adopting two heating modes; Fire and processed temperatures. An electrical furnace with low-temperature increment and a fire furnace with standard time-temperature increment is adapted to expose the RC elements to elevated temperatures.

It is observed from test results that, the reduction in load-carrying capacity, first crack load, and thermal crack widths of RC beams exposed to 200 °C, and 600 °C temperature at fire is significantly high from the RC beams exposed to the processed temperature having the same maximum temperature. As the exposure temperature increases to 800 °C, the performance of RC beams at all heating modes becomes approximately equal.

In this work, residual performance, and failure modes of RC beams exposed to elevated temperatures were achieved through two different heating modes are presented.