# The Mechanical Properties of Reinforced Concrete Columns with Longitudinal Pre-Embedded Holes
## 3 Results and Discussion
### Bearing Capacity Analysis  
2.1 Impact of Pre-Embedded Hole Diameter on the Bearing Capacity of Reinforced Concrete Columns with Embedded Pipes  
The load-displacement curves of all specimens are shown in Figure 17. The load-displacement behaviors of all specimens are almost identical. Compared with the reinforced concrete columns without embedded holes, the ultimate bearing capacity of the reinforced concrete columns with embedded holes decreases to varying degrees. As the embedded hole diameter increases, both the peak ultimate bearing capacity and peak displacement of the curves decrease. Specifically, for embedded hole diameters of 50 mm, 75 mm, and 90 mm, the ultimate bearing capacity decreases by 1.76%, 2.22%, and 3.47%, respectively, compared to the corresponding columns without embedded holes. This is primarily because the presence of the embedded pipes reduces the effective load-bearing area of the frame column cross-section. As a result, the reinforced concrete columns with embedded holes are more prone to entering failure conditions under axial loads, leading to a decrease in bearing capacity. 2.2 Impact of Concrete Strength on the Bearing Capacity of Reinforced Concrete Columns with Pre-Embedded Holes  
As shown in Figure 18, when the aperture of the longitudinal pre-embedded holes is smaller (50 mm), with the increase in concrete strength of the specimen, the curve slope of the elastic stage becomes larger, the stiffness of the specimen increases, and the ultimate bearing capacity of the specimen also increases with the increase in the concrete strength. Compared with the specimen D50-C30-S1-L8.2, the axial ultimate bearing capacity of specimens D50-C35-S1-L8.2, D50-C40-S1-L8.2, and D50-C50-S1-L8.2 increased by 10.16%, 21.49% and 39.83%, respectively, while that of specimen D50-C25-S1-L8.2 decreased by 11.40%. However, the ultimate displacement of the specimen column decreases with the increase in concrete strength. This is mainly due to the increase in concrete strength, alongside the increase in the elastic modulus and compressive strength of concrete, and, at the same time, the stress concentration phenomenon at the opening of the pre-embedded hole becomes more significant, resulting in the test column entering the ultimate bearing capacity state in advance, and then the ultimate displacement of the test column reaching the ultimate bearing capacity decreases. Figure 17: Impact of hole diameter on load–displacement curve of columns with longitudinal pre-embedded holes. 3.2.3. Impact of Stirrup Ratio on the Bearing Capacity of Reinforced Concrete Columns with Pre-Embedded Holes  
As shown in Figure 19, the bearing capacity of the longitudinal pre-embedded hole reinforced concrete columns increases with an increase in the stirrup ratio. For specimens with opening diameters of 50 mm, 75 mm, and 90 mm, when the stirrup ratio increased from 1.04% to 1.63%, the ultimate bearing capacities rose from 7291.99 kN, 7239.18 kN, and 7163.81 kN to 7541.62 kN, 7492.84 kN, and 7432.91 kN, respectively. This corresponds to respective increases of 3.42%, 3.50%, and 3.76%. This phenomenon can primarily be attributed to the enhanced confinement effect provided by the stirrup as their ratio increases, which delays the propagation of shear cracks. Consequently, this improves the shear-bearing capacity around the opening, strengthens the confinement of the core concrete, alleviates stress concentration at the opening edges, and effectively enhances the overall bearing capacity of the column. Furthermore, the larger the diameter of the embedded hole, the greater the improvement in ultimate bearing capacity achieved by increasing the stirrup ratio. This is mainly because a larger embedded hole diameter leads to more pronounced section weakening and stress concentration effects, which are mitigated more effectively by an increased stirrup ratio. Additionally, as the opening hole diameter increases, the redistribution of internal forces becomes more significant.