Available online at www.CivileJournal.org Civil Engineering Journal (E-ISSN: 2476-3055; ISSN: 2676-6957) Vol. 8, No. 09, September, 2022 2001 Influence of Macro Synthetic Fibers on the Flexural Behavior of Reinforced Concrete Slabs with Opening Rajai Z. Al-Rousan 1* 1 Department of Civil Engineering, Jordan University of Science and Technology, Irbid, Jordan. Received 14 June 2022; Revised 19 August 2022; Accepted 26 August 2022; Published 01 September 2022 Abstract In this study, the flexural behavior of one-way RC slabs after adding the macro discontinuous structural synthetic fiber (DSSF) under different opening sizes is investigated. Based on the previously conducted research, the 0.55 DSSF percentage was utilized since it was reported as the optimum value for enhancing the slab's performance. Moreover, further increases in the DSSF percentages proved to have the same improvement obtained by the 0.55%. Experimental testing was carried out on sixty-four one-way slabs under the effects of square opening existence (with or without), heat levels of 20, 200, 400, and 600 °C, and opening sizes of 100, 150, and 200 mm. The opening was created at the maximum bending moment region at the slab's center between the two loading points. For comparison purposes, the tested slabs were divided into main groups based on the DSSF existence. It was found that the resulted improvement by adding the DSSF material is affected by the size of the created opening. Furthermore, results revealed an increasing linear relationship between the applied load and the deflection and between the longitudinal concrete strain and the steel reinforcement. Besides, duplicating the opening size enhances the ductility index value by a maximum improvement percentage of 13% under an opening size ratio of less than 4.5%, while the improvement percentage becomes less under a further increase in the opening size ratio. Moreover, initial stiffness is more affected by increasing the temperature values twice those recorded for the yielding stiffness. Keywords: Macro; Discontinuous Structural Synthetic Fiber; Flexural Behavior; Reinforced Concrete; Slab Opening. 1. Introduction Structural stability and durability, including toughness and load-carrying capacity, are major concerns, especially after cracking, and many materials are used to improve these properties, such as steel, ceramics, glass, and synthetic fibers [1, 2]. Moreover, adding an appropriate quantity of fibers into concrete mixes reduces its brittle behavior, controls the onset of microcracking, and improves the concrete's tensile strength [3, 4]. Generally, the flexural concrete toughness and ductility are considerably affected by the fiber type, aspect ratio, and volume fraction. Literature has proved that a good performance could be obtained by adding steel fibers into the concrete mixture [5-7]. Therefore, researchers in the past ten years have focused on investigating the behavior of different fiber types other than steel [8-10], aiming to improve the slab's behavior through a feasible and applicable alternative that improves the concrete tensile strength and toughness, besides being chemically resistant to compensate for the corrosion problem [11-13]. DSSF fibers can be further used as a substitute for steel reinforcement. It has been proved that adding a 0.55% of DSSF improves the overall performance of the tested structural element, and this is related to its role in internal cracks stabilization [14]. Safety is a major concern during the design stage, which is affected by creating an opening within the structural element to accommodate different passing installations. Hanging slabs are commonly used for RC structures with * Corresponding author: rzalrousan@just.edu.jo http://dx.doi.org/10.28991/CEJ-2022-08-09-016 © 2022 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/).