Performance of Reinforced Concrete Beam after Exposed to Fire

Abstract

Reinforced concrete beams play a crucial role in structural systems, but their strength and durability can be severely affected when exposed to fire. This study explores what happens to these beams after fire damage and how we can effectively bring them back to life through retrofitting. After exposing concrete beam specimens to high temperatures, different retrofitting methods—such as fibre-reinforced polymer (FRP) wrapping and cement-based jacketing—were applied to assess their ability to restore structural performance. We then tested the beams to understand how much of their strength, stiffness, and load-bearing capacity could be recovered. The findings showed that retrofitting significantly improved the condition of fire-damaged beams, with FRP techniques standing out for their efficiency and simplicity. This research highlights how timely intervention and the right repair techniques can extend the life of fire-affected concrete structures, ensuring safety and stability.

Introduction

Overview

Reinforced Concrete (RC) is a fundamental material in infrastructure due to its strength, adaptability, and cost-efficiency. However, fire exposure severely compromises its integrity, particularly in beams. High temperatures can:

• Weaken concrete (spalling, cracking, reduced compressive strength)

• Degrade steel reinforcement (loss of yield strength, bond failure)

This significantly reduces the load-bearing capacity and poses safety risks.

Need for Retrofitting

Instead of demolishing and rebuilding, which is costly and unsustainable, retrofitting offers a practical solution to restore or enhance structural performance after fire damage. Common retrofitting methods include:

• Fibre-Reinforced Polymer (FRP) wrapping

• Cementitious jacketing

These are evaluated for their effectiveness in strength recovery, failure mode improvement, and real-world applicability.

Literature Review Highlights

1. GFRP Effectiveness: Experiments using Glass Fiber Reinforced Polymer (GFRP) after ISO-standard fire exposure (100°C–700°C) showed significant improvements in load-deflection behavior.

2. Environmental Benefits: Natural Fiber Reinforced Polymer (NFRP) offers sustainability advantages, though it has slightly lower mechanical strength.

3. Thermal Impact Studies: Fire-induced thermal stress alters concrete and steel properties—key factors in structural degradation.

Experimental Study

10 RC beam specimens (600×100×150 mm) made of M20 grade concrete were:

• Cured for 21 days

• Exposed to fire (300°C–700°C) for 2 hours

• Reinforced with 12 mm bars (main) and 8 mm stirrups

Testing methods included:

• Two-point flexural loading to evaluate deflection and ductility

• Non-Destructive Testing (NDT): Rebound Hammer and Ultrasonic Pulse Velocity

Key Results

Rebound Hammer Test:

• Compressive strength decreased sharply with temperature rise

• At 700°C, concrete retained only 20% of its original strength

• Concrete quality transitioned from Good → Fair → Poor

Ultrasonic Pulse Velocity Test:

• Quality remained Good up to 400°C

• Dropped to “Doubtful” beyond 500°C

• At 700°C, only 3% of original pulse velocity remained—indicating severe internal damage

Conclusion

1) As the temperature rises, loss of strength is observed. 2) From the performance of above test on the beams it concludes that there is no major temperature effect up to 300? to 400??. From the performance of above test on the beams it conclude that there is no major temperature effect up to 300 to 400 ?.? 3) Rebound number and compressive strength decreases with increase in temperature. 4) Range from 300 to 400 the compressive strength decreases 20 to 80 with the increase in temperature. 5) Maximum compressive strength decreases 80 at 700 C. 6) From the UPV test it can be concluded that there is significant degradation of concrete with rise in temperature.

References

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Copyright

Copyright © 2025 Prof. S. V. Dhoke, Sayali Umale, Prachi Kale, Prajwal Wakte, Kartik Kavitkar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.