This paper proposes a new hybrid composite tubular beam system that consists of an exterior high-density polyethylene (HDPE) tube with interior steel tube and self-compacting geopolymer concrete (SCGC). The flexural behavior of composite tubular beams with SCGC encased in HDPE tubes was investigated experimentally and theoretically. A total of twenty-two specimens was tested, including twelve confined and ten unconfined specimens. The test variables include the presence of confinement (confined or unconfined), HDPE tube thickness and interior diameter, presence of inner steel tube, cross section of inner layer (circular or square), and presence of SCGC filling in inner layer. The failure mode, flexural strength and fracture energy are examined based on measured load–deflection data by four point bending test. Results indicated that the HDPE confinement provided significant enhancement in flexural response and especially the ductility of specimens, demonstrating considerably large plastic deformations before failure. A theoretical methodology was developed to predict the ultimate flexural load capacity. The analysis was conducted based on the combination of classical beam theory and the modification of a previously proposed methodology. Results of the analysis confirmed the high accuracy of proposed methodology in predicting ultimate flexural capacity of HDPE tube-confined beams.

本文提出了一种新的混合复合管梁系统，该系统由外部高密度聚乙烯 (HDPE) 管和内部钢管和自密实地质聚合物混凝土 (SCGC) 组成。通过实验和理论研究了在 HDPE 管中包裹 SCGC 的复合管梁的弯曲行为。共测试了 22 个试件，包括 12 个受限和 10 个非受限试件。测试变量包括有无约束（有约束或无约束）、HDPE 管厚度和内径、有无内钢管、内层横截面（圆形或方形）以及内层是否存在 SCGC 填充物。基于通过四点弯曲试验测得的载荷-挠度数据来检查失效模式、弯曲强度和断裂能。结果表明，HDPE 限制在弯曲响应方面提供了显着增强，尤其是试样的延展性，在破坏前表现出相当大的塑性变形。开发了一种理论方法来预测极限弯曲载荷能力。该分析是基于经典梁理论和先前提出的方法的修改相结合进行的。分析结果证实了所提出的方法在预测 HDPE 管约束梁的极限抗弯能力方面的高精度。该分析是基于经典梁理论和先前提出的方法的修改相结合进行的。分析结果证实了所提出的方法在预测 HDPE 管约束梁的极限抗弯能力方面的高精度。该分析是基于经典梁理论和先前提出的方法的修改相结合进行的。分析结果证实了所提出的方法在预测 HDPE 管约束梁的极限抗弯能力方面的高精度。