为解决现有组合式顶管技术和三圆盾构施工大断面地下空间技术中永久结构因纵梁尺寸过大，极大地压缩梁下可使用空间的问题，提出一种新型组合结构——预应力管片-型钢混凝土组合梁，并针对是否设置预应力筋和施加预应力大小等6种工况，开展四点弯曲试验，研究其破坏模式、受力性能、变形能力及应变规律。研究结果表明： 1）正、负弯矩下，该组合梁试件均表现为延性破坏。2）正、负弯矩下，设置预应力筋可以显著提高组合梁的承载能力；其中，负弯矩下极限承载力最高可提高69.3%，正弯矩下最高可提高12.1%。3）正弯矩下，预应力筋的存在使组合梁的抗裂性能有所降低，主要表现为设置预应力筋后组合梁开裂荷载有所降低，但设置预应力筋可以显著提高组合梁抗变形能力；负弯矩下，预应力筋使组合梁的抗裂性能和抗变形能力均有显著提高。4）随着预应力的增大，组合梁极限承载力、抗裂性能和抗变形能力在正弯矩下的提升效果不明显，而在负弯矩下的提升效果显著。5）跨中截面应变沿梁高方向基本呈线性分布，整体符合平截面假定。
The longitudinal beam dimensions in permanent structures within large cross-sectional underground spaces constructed by the combined pipe-jacking and three-circle shield method are too large, leading to compressed spaces under the beam. To address this problem, a novel type of combined structure—prestressed segment-steel reinforced concrete composite beam—is proposed. Six working conditions are set with and without prestressed reinforcement and prestress to conduct flexural tests on the failure mode, stress performance, deformation capacity, and strain patterns. The primary conclusions are as follows: (1) Under positive and negative bending moments, prestressed composite beams exhibit ductile damage. (2) Under positive and negative bending moments, prestressed reinforcement significantly improves the ultimate bearing capacity of such combined beams, increasing it by 69.3% and 12.1%, respectively. (3) Under positive bending moments, prestressed reinforcement slightly reduces the cracking load but significantly improves the deformation resistance of such combined beams. Under negative bending moments, prestressed reinforcement significantly improves the crack and deformation resistance of such combined beams. (4) Increasing prestress slightly improves the ultimate bearing capacity, crack resistance, and deformation capacity of the combined beams under positive bending moments while substantially enhancing these properties under negative bending moments. (5) The strain in the mid-span section is linearly distributed along the height direction of the beam, consistent with the assumption of flat section.
