# Studies on Seismic Performance of Precast Concrete Columns with Ground Splice Sleeve
## 3 Test Results and Discussion
### Test Phenomenon
#### 3.1.4 Phenomena of Column 6#  
Column 6# is a cast-in-situ specimen with no strain gauges. In the low cyclic repeated loading stage, after 20 cyclic loads were applied, the specimen began to crack slightly. In the second stage, a crack appeared when the specimen suffered the 3 rd cycle load, and at the 10 th load cycle, this crack was interconnected at both sides of the column. In the static load stage, the second obvious crack appeared at 200 mm above the lower end of the column when the stress of the specimen increased to its yield value. When the load was up to 51.40 kN, the third obvious crack appeared. Finally, the concrete at the compressive zone was crushed to failure while the cracks at the tensile zone developed obviously. The detailed crack distribution and failure mode of column 6# are shown in Figure 8.  
Figure 8: \(Cont\).  
Figure 7: Cracks and failure mode of column 5#.  
According to the test phenomena presented above, the prefabricated columns have fundamentally the same failure mode as that of the cast-in-situ columns, indicating that both of them completely lose the ultimate load-carrying capability due to bending failure. Under this mode of failure, the cracks widened visibly at the tensile edge of the concrete, and the columns failed by crushing of the concrete in the compressive zone and by tensile yielding of the vertical reinforcement bars in the tensile zone.  
However, differences exist in the crack distribution between these two types of columns. For the cast-in-situ columns, the first crack appeared at the bottom of the column, and then it moved toward the opposite side, and finally the interconnected crack almost overlapped with the interface between the column body and the pedestal, as shown in Figure 9a. However, for the prefabricated columns, the width of the horizontal cracks at the column foot were not large, whereas the horizontal cracks above the sleeve were wide, and they propagated downward and became diagonal cracks with a large width, as shown in Figure 9b. The differences in the crack distribution between these two types of columns may be attributed to the following reasons. First, at the connection part of the prefabricated columns, the stress existing in the steel bars is transferred to the sleeve via mortar, and thus the sleeve whose tensile strength is higher than that of the steel bars replaces the steel bars to bear the loads. Furthermore, the compressive strength of grout filled in the sleeve is higher than that of concrete. Consequently, the strength of precast columns at the connection part is enhanced, making the plastic hinge move upward, as illustrated in Figure 9c; Second, for the prefabricated columns, the compressive strength of the two-centimeter-thick mortar layer is low, and thus the bonding strength between the column foot and pedestal is weak, which can possibly lead to the column body separating from the pedestal before failure, as illustrated in Figure 9d.  
Figure 8: Crack and failure mode of column 6\(\#\).  
Figure 9: _Cont._  
It should be noted that although inclination appeared in some columns resulting from the low compressive strength of the two-centimeter-thick mortar layer between the column foot and pedestal, this problem can be avoided in practical engineering if high-strength mortar is utilized.