Available online at www.CivileJournal.org Civil Engineering Journal (E-ISSN: 2476-3055; ISSN: 2676-6957) Vol. 10, No. 01, January, 2024 189 Behavior of Fire-damaged RC Beams After Strengthening with Various Techniques Asser Elsheikh 1, 2* , Hadeal H. Alzamili 1 1 Department of Civil Engineering, Peoples' Friendship University of Russia (RUDN), Moscow, Russian Federation. 2 Structural Engineering Department, Mansoura University, Mansoura, Egypt. Received 14 September 2023; Revised 15 December 2023; Accepted 20 December 2023; Published 01 January 2024 Abstract High temperatures during a fire can significantly degrade the structural capacity of concrete. However, in many cases, it is possible to restore and strengthen fire-damaged concrete rather than completely rebuild damaged structures. The study considered two types of concrete (normal 25 MPa and high-strength 65 MPa) with two types of strengthening techniques: carbon-fiber-reinforced polymers (CFRP) sheets with different thicknesses of 1.5 and 2.5 mm and slurry-infiltrated fibrous concrete (SIFCON) jacketing with different fiber sizes of 20 and 30 mm. The numerical simulations and analyses were conducted to capture the complex behavior of fire-damaged concrete members (beams). A fire-damaged concrete beam subjected to an extreme or critical fire Exposure time (2 hours) was evaluated and modified using a finite element simulation approach. The simulation process included three stages: the first, subjecting the concrete beam to thermal loading; the second, reflecting the fire distribution map to another model of applying mechanical loading; and the third, involving the application of strengthening to the damaged model. The results showed that the strengthening using CFRP with a thickness of 2.5 improved the load-carrying capacity compared with SIFCON in both types of concrete. 200% improvement for the normal-strength concrete beam and a 136% improvement for the high-strength concrete beam, compared to the damaged beams. Keywords: RC Beam; CFRP; SIFCON; Fire. 1. Introduction After a fire, it is important to conduct a thorough assessment of the damaged structural organs to determine the extent of the damage. Such an assessment may include visual inspections, non-destructive tests, and material sampling to assess the residual strength and integrity of structural elements. In most cases, repair versus replacement is an optimal option, as the decision on the repair or replacement of the affected structural members is made depending on the severity of the damage. In less severe cases, such repair methods as patching, strengthening with the use of additional materials, or applying protective coatings may be sufficient. However, if the damage is extensive, a complete replacement of the damaged organ may be necessary [1]. High temperatures can cause profound changes in the properties of concrete, leading to a potential loss of strength, stiffness, and durability. Understanding the post-fire behavior of concrete is essential for evaluating the residual structural capacity and implementing effective repair and strengthening strategies. The behavior of steel reinforcement in a fire depends on several factors, including the temperature reached, the duration of exposure, and the size and condition of the concrete element, which can lead to deformation, loss of bond with the surrounding concrete, and even * Corresponding author: assermfee@mans.edu.eg http://dx.doi.org/10.28991/CEJ-2024-010-01-012 © 2024 by the authors. Licensee C.E.J, Tehran, Iran. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).