# The Mechanical Properties of Reinforced Concrete Columns with Longitudinal Pre-Embedded Holes
## 3 Results and Discussion  
### Failure Mode and Phenomenon  
Figures 5 and 6 illustrate the distribution of concrete plastic strain and the stress contours of reinforcement, respectively, for a reinforced concrete column without longitudinal pre-embedded holes during the failure process. The figures reveal typical failure characteristics under axial compression. In the initial loading stage, the specimen operates \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Number**} & **Pre-Embedded Hole** & **Concrete** & **Length** & **Sledemess** & **Stirup** & **Ultimate** & **Bearing** & **Damage Pattern** \\  & **(mm)** & **Strength** & **(mm)** & **Ratio** & **(\%)** & **(\%)** & **(kN)** & **Axi compression** \\ \hline D50-C30-S1-L10.2 & 50 & C30 & 5200 & 10.2 & 1.04\% & 7251.75 & Axial compression & damage \\ D50-C30-S1-L12.2 & 50 & C30 & 6200 & 12.2 & 1.04\% & 7262.09 & Axial compression & damage \\ D50-C30-S2-L8.2 & 50 & C30 & 4200 & 8.2 & 1.63\% & 7541.62 & Axial compression & damage \\ D50-C50-S2-L8.2 & 50 & C50 & 4200 & 8.2 & 1.63\% & 10,459.50 & Axial compression & damage \\ D75-C30-S1-L8.2 & 75 & C30 & 4200 & 8.2 & 1.04\% & 7239.18 & Axial compression & damage \\ D75-C25-S1-L8.2 & 75 & C25 & 4200 & 8.2 & 1.04\% & 6415.63 & Axial compression & damage \\ D75-C35-S1-L8.2 & 75 & C35 & 4200 & 8.2 & 1.04\% & 7910.02 & Shear failure \\ D75-C40-S1-L8.2 & 75 & C40 & 4200 & 8.2 & 1.04\% & 8639.91 & Shear failure \\ D75-C50-S1-L8.2 & 75 & C50 & 4200 & 8.2 & 1.04\% & 9883.73 & Shear failure \\ D75-C30-S2-L8.2 & 75 & C30 & 4200 & 8.2 & 1.63\% & 7492.84 & Axial compression & damage \\ D75-C35-S2-L8.2 & 75 & C35 & 4200 & 8.2 & 1.63\% & 8198.16 & Axial compression & damage \\ D90-C30-S1-L8.2 & 90 & C30 & 4200 & 8.2 & 1.04\% & 7163.81 & Axial compression & damage \\ D90-C25-S1-L8.2 & 90 & C25 & 4200 & 8.2 & 1.04\% & 6361.33 & Axial compression & damage \\ D90-C35-S1-L8.2 & 90 & C35 & 4200 & 8.2 & 1.04\% & 7737.69 & Shear failure \\ D90-C40-S1-L8.2 & 90 & C40 & 4200 & 8.2 & 1.04\% & 8441.39 & Shear failure \\ D90-C50-S1-L8.2 & 90 & C50 & 4200 & 8.2 & 1.04\% & 9593.85 & Shear failure & damage \\ D90-C30-S2-L8.2 & 90 & C30 & 4200 & 8.2 & 1.63\% & 7432.91 & Axial compression & damage \\ D90-C35-S2-L8.2 & 90 & C35 & 4200 & 8.2 & 1.63\% & 8116.65 & Axial compression & damage \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._  
Figure 4: Specimen model. in the elastic phase, with the reinforcement and concrete working in unison to bear the load. The overall deformation is minimal, and the material strain levels are low, with no noticeable changes on the specimen's surface. As the load continues to increase, the specimen enters the elastoplastic phase, and noticeable bulging deformation begins to appear in the mid-region. With further deformation, the local bulging becomes more pronounced, the concrete cover gradually crushes and spalls, and the longitudinal reinforcement reaches its yield strength, ultimately leading to the failure of the specimen. This failure process vividly reflects the progressive failure characteristics of reinforced concrete columns under axial compression. Figures 7 and 8 present the stress distribution of a reinforced concrete column with longitudinal pre-embedded holes during the loading process. From the figures, it can be observed that in the initial loading stage, the reinforcement on the side near the hole bears the load first, while the stress in the concrete adjacent to the hole increases significantly faster than in other regions. As the load gradually increases, the stress concentration phenomenon becomes more pronounced, causing the concrete around the hole to exceed its ultimate bearing capacity and fail first. At this stage, the reinforcement surrounding the hole has not yet reached its yield strength. Subsequently, as the load continues to increase, the damaged area of the concrete expands and gradually extends toward the  
Figure 5: Equivalent plastic strain cloud image of specimen D0-C30-S1-L8.2.