International Journal of Mechanical, Electrical and Civil Engineering E-ISSN: 3047-4531 P-ISSN: 3047-4523 DOI : https://doi.org/10.61132/ijmecie.v2i2.245 https://international.aritekin.or.id/index.php/IJMECIE (Research/Review) Article Impact of Concrete Grade and Stirrups Spacing on Performance Enhancement of Hybrid T-Beams Using Lightweight Concrete and High Compressive Strength Combinations Ibrahim Idrees Ezzulddin 1* , Hammad D. Merie 2 1,2 Civil Engineering Department, College of Engineering, University of Kirkuk, Iraq. ; e-mail : hammad1974@uokirkuk.edu.iq * Corresponding Author : Ibrahim Idrees Ezzulddin; Abstract: This study examines the performance of a total of ten reinforced concrete T-beams, nine of which were made as hybrid beams by casting the web with LW concrete and the flange with HS concrete; the last beam was cast as a normal beam (entirely cast with HS concrete). All beams underwent testing under two-point loads following a 28-day period. The variables of the experimental program include the concrete grade within the web (46, 62, and 82 MPa) and stirrup distribution distances (100, 200, and 300 mm). The experimental program includes load-deflection curves and failure modes for hybrid and normal beams. The results showed that all the beams failed in shear- flexural mode. Also, increasing flange compressive strength increased shear. strength. Increasing stirrup distribution distance from 100 to 200 and 300 mm reduced the ultimate load capacity; specimens with stirrup spacing of 300 mm failed directly after yielding of steel due to crushing the concrete over the support and spalling concrete cover within the shear zone. The study also determined that reducing stirrup spacing to 100 mm did not alter the failure mode, as shear failure was dictated by the compressive strength of the lower layer of the hybrid beams (19 MPa compressive strength of LW concrete). Keywords: Hybrid Beams; Shear Strength; Lightweight Beam; Stirrup Spacing; Deflection 1. Introduction Efficiency and dependability are crucial factors in construction. Regarding RC beams in civil engineering, these elements serve as primary load-bearing components in many constructions, including buildings, bridges, and numerous other infrastructure projects. Design considerations and structural integrity are closely associated with safety, serviceability, and durability issues related to reinforced concrete beams. In that respect, the engineers and designers' understanding of influencing parameters regarding performance becomes vital. The benefits of interaction between LWC and HSC in hybrid sections are numerous. To begin, LWC reduces overall weight without affecting the strength of the structure, while HSC increases load-bearing capacity, especially when compressive stresses are present, Ezzulddin and Merie [1]. This hybrid strategy offers several advantages in enhancing energy efficiency within a building, as lighter buildings necessitate reduced energy for heating and cooling. Lightweight Concrete (LWC) is an environmentally sustainable material characterized by low density, which decreases building expenses by lowering the dead load. A variety of lightweight aggregates with diverse characteristics is presently accessible. Lightweight aggregates may originate from natural sources such as tuff, diatomite, scoria, and pumice, or Received: 12 January, 2025 Revised: 15 February, 2025 Accepted: 08 March, 2025 Online Available : 11 March, 2025 Curr. Ver.: 11 March, 2025 Copyright: © 2025 by the authors. Submitted for possible open access publication under the terms and conditions of the Creative Commons Attribution (CC BY SA) license (https://creativecommons.org/li censes/by-sa/4.0/)