# Effects of Grout Compactness on the Tensile Behavior of Ground Splice Sleeve Connectors
## 2 Tensile Tests on GSS Connectors with Different Compactness
### Results and Analysis  
#### 2.3.1 Failure Modes of GSS  
The tensile test results and failure modes for GSS connectors are listed in Table 4 and shown in Figure 6, respectively. In the table, \(P_{u,avg}\) is the tensile load-bearing capacity, \(s_{1}\) is the standard derivation of tensile load-bearing capacity, \(\delta_{u}\) is the failure displacement, \(s_{2}\) is the standard derivation of displacement, I is the rebar rupture failure mode, while II is the bond-slip failure mode of rebar-grout. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Grout Material**} & \multicolumn{3}{c}{**Strength(MPa)**} & \multicolumn{3}{c}{**Fluidity**} \\ \cline{2-6}  & **1 d** & **3 d** & **28 d** & **Initial** & **30 min** \\ \hline M80 & 43.5 & 71.6 & 88.5 & 320 & 290 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mechanical properties of grout material. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \(d_{b}\)/mm & \(f_{y}\)/MPa & \(f_{u}\)/MPa & \(\varepsilon_{y}\)/\(\times\) 10\({}^{-6}\) & \(E_{s}\)/ MPa & \(\
u\) & _A/\%_ \\ \hline
18 & 375 & 620 & 2206 & 210,000 & 0.3 & 12.871 \\
20 & 355 & 590 & 2008 & 210,00 There are two failure modes for GSS connectors, namely the rebar rupture (shown in Figure 6a) and the bond-slip failure of rebar-grout (shown in Figure 6b). Figure 7 shows the load-displacement curves for all four types of fully compact GSS connectors. It can be seen that (1) the load-bearing capacity increases with the rise in the nominal diameter of sleeve and (2) the load-displacement curves are very similar to those of the rebar rupture mode. More specifically, the GSS connector shows elasticity at the initial loading stage in the load-displacement curves. As the loads increase, the grout materials crack. Following the cracks' expansion, the grout materials begin to split, internal cracks develop, and the stiffness gradually decreases, as shown in Figure 8. Obvious rebar elongation and necking deformation are observed after the yielding of rebars. The rebars rupture when the loads \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Types** & \(P_{\textbf{u},avg}\)**/**kN** & \(s_{1}\)**/mm** & \(\delta_{u}\)**/mm** & \(s_{2}\)**/mm** &
\begin{tabular}{c} **Failure** \\ **Modes** \\ \end{tabular} \\ \hline D18-100\% & 143.69 & 3.55 & 72.182 & 0.786 & I \\ D18-90\% & 132.88 & 0.65 & 70.520 & 0.869 & I \\ D18-70\% & 102.2 & 3.70 & 15.832 & 0.241 & II \\ D18-50\% & 79.33 & 2.52 & 13.559 & 0.379 & II \\ D20-100\% & 179.79 & 0.67 & 70.588 & 0.442 & I \\ D22-100\% & 226.40 & 5.24 & 69.326 & 0.336 & I \\ D25-100\% & 288.24 & 0.20 & 76.528 & 0.772 & I \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Tensile results and failure modes. Figure 5: Test setup. (**a**) Loading device. (**b**) Measurement program. Figure 6: Typical failure modes of the GSS connectors. (**a**) Rebar rupture failure. (**b**) Bond-slip failure of rebar-grout. reach the tensile bearing capacity. These indicate that the curves of fully compact GSS connectors are similar to the rebar constitutive relationship curves. Figure 9 shows the curves of D18 GSS connector at different compactness. It is shown that as the compactness decreases, the connector tensile load-bearing capacity gradually decreases as well. It can be observed at the site that the failure mode changes from the rebar rupture failure mode to the bond-slip failure mode of rebar-grout. Note that the failure mode is the bond-slip failure of rebar-grout for the GSS connector with lower compactness (D18-70% and D18-50%). It can be seen in Figure 9, for connectors with bond-slip failure of rebar-grout (D18-70% and D18-50%), that the load-displacement curves of the connectors are very similar to those of the connectors with rebar rupture failure mode before rebars yield. The load-displacement curve indicated that the specimens of D18-70% and D18-50% had no reinforcing stage and showed a rapid decline in bearing capacity.