Structural Performance of Hybrid Reinforced Concrete T- Beams Combining High Strength Concrete and Lightweight Concrete

Abstract

This paper investigates the structural performance of reinforced concrete hybrid beams, focusing on the effects of the flexural reinforcement ratio and concrete strength on key parameters such as ultimate load, first cracking load, deflection, and crack patterns. An extensive experimental study was conducted on ten simply supported reinforced concrete beams, including nine hybrid concrete reinforced beams and one conventional beam. All beams featured a T-shaped cross-section with dimensions of 200 mm flange width, 60 mm flange depth, 190 mm web depth, and 100 mm web width. For the hybrid beams, lightweight concrete (19 MPa) was used in the web, while high-strength concrete was used in the flange. The conventional beam was constructed entirely of high-strength concrete (46 MPa). The beams were designed with varying flexural reinforcement diameters (8, 10, and 12 mm) and web concrete strengths (46, 62, and 84 MPa). The results demonstrate that increasing the reinforcement ratio (from 0.00217 to 0.00341 and 0.00493) significantly enhances load capacity. Similarly, increasing the compressive strength of the web concrete (from 46 to 62 and 84 MPa) effectively raises the failure load. However, early cracking load values remained consistent across all hybrid specimens due to the uniform use of lightweight concrete in the web. The first cracking load was found to be more influenced by the quality of the concrete within the web, than by the reinforcement ratio. The reference beam, constructed with a web concrete strength of 46 MPa, exhibited superior crack control, with a 21.7%–47% improvement in the first cracking load compared to the hybrid beams. Optimal performance was achieved by combining a higher flexural reinforcement ratio with increased flange concrete strength. The hybrid beam with 84 MPa web concrete strength and 12 mm flexural reinforcement diameter demonstrated the best structural performance, achieving lowest deflection (17.60 mm) at failure and a maximum load capacity of 176.17 kN. This beam exhibited excellent load capacity, stiffness, and crack resistance. In Addition, all beams showed negligible slip between concrete layers, further confirming the effectiveness of the hybrid design. These findings provide valuable insights into designing robust and efficient structural elements with enhanced strength and crack resistance, offering potential applications in various structural contexts.