The Influence of Holes and Beam Sleeves on the Compressive Mechanical Properties of Reinforced Concrete Beam Segments

In the newly developed hybrid prefabricated RC-steel structure (SS) foundation pit bracing system, the main braces are the main load-carrying components, which are assembled from standardized prefabricated reinforced concrete beam segments (referred to as beam segments). To facilitate assembly, beam segments are equipped with beam sleeves and beam-end connection holes. The holes at the end of the beam can cause stress concentration problems, while the beam sleeve has a reinforcing effect on the end of the beam segment. To investigate the influence of beam-end holes and beam sleeves on the compressive mechanical properties of beam segments, a numerical simulation study was conducted. Taking the beam segment (specification: 4500 mm × 700 mm × 800 mm) used in a certain foundation pit support project as the research object (i.e., specimen), Abacus software was first used to build parameterized models of beam segments with holes and beam sleeves using the concrete damaged plasticity model (CDP) and the steel double-line strengthening model. Then the influence of three factors, namely end face friction coefficient, beam-end holes diameter, and beam sleeve thickness, on the axial compression performance of the beam segment specimens was studied. The results indicated that the axial compressive capacity of specimens without a beam sleeve decreased with increasing hole diameter; the axial compressive bearing capacities of specimens with hole diameters of 35 mm, 40 mm, and 45 mm were 13,300 kN, 12,500 kN, and 12,300 kN, respectively, which are 11.3%, 16.7%, and 18% lower than the compressive bearing capacity of specimens without holes (15,000 kN). When both a beam sleeve and holes were present, the holes had a negligible influence on the compressive capacity, while the beam sleeve played a decisive role. The compressive bearing capacity increased with greater beam sleeve thickness; the peak bearing capacities of the specimens with beam sleeves 5 mm, 10 mm, and 15 mm thick were 16,200 kN, 16,500 kN, and 17,600 kN, respectively. As the end face friction coefficient decreased from 0.6 to 0.1, the location of maximum compressive damage shifted toward the end face of the beam segment, and the area of maximum concrete damage gradually migrated toward the hole locations. The study demonstrates that the confinement effect of the beam sleeve can compensate for the weakening effect caused by the holes and confirms that the designs of holes in beam segment ends and in the beam sleeve can meet safety requirements.