## 3 Test Results
### Energy Dissipation Analysis  
In order to quantitatively evaluate the energy dissipation capacity of the joints, the energy dissipation ratio \(\eta\), accumulative energy dissipation \(U_{sum}\) and maximum hysteretic loop energy dissipation \(U\) were introduced, which were defined in Equations (1)-(3). Among them, \(U_{i}\) represented the area enveloped by each hysteretic loop of the joint. \(U_{sum}\) indicated the total area of all hysteretic loops. Energy dissipation ratio \(\eta\) was based on accumulative energy dissipation \(U_{sum}\) and hysteretic loop energy dissipation \(U_{i}\), considered the elastic potential energy of each hysteretic loop, which could more accurately reflect the energy dissipation capacity of the joints. Additionally, \(P_{y}^{+}\), \(\delta_{y}^{+}\), \(P_{y}^{-}\) and \(\delta_{y}^{-}\) represented the yield load and yield displacement of the joints under positive and negative loading, respectively. The energy dissipation evaluation parameters for the joints are shown in Table 4.  
\[U_{sum}\,=\,\sum_{i}^{n}U_{i} \tag{1}\]  
\[\eta\,=\,\sum_{i}^{n}\frac{U_{i}}{U_{ij}} \tag{2}\]  
\[U_{iy}\,=\,\frac{1}{2}\,(P_{y}^{+}\,\times\,\delta_{y}^{+}\,+\,P_{y}^{-}\, \times\,\delta_{y}^{-}) \tag{3}\]  
As can be seen from Table 4, the maximum hysteretic loop energy dissipation of K-CCC1 and K-CCC2 was 6.8% and 74.0% higher than that of the corresponding K-CC joint. Compared with the K-RC joint, the maximum hysteretic loop energy dissipation of K-RCC1 and K-RCC2 increased by 6.3% and 54.5%. In terms of \(U_{sum}\), the accumulative energy dissipation of the strengthened joints was obviously higher than those of unstrengthened joints. The strengthening measure of grouting concrete in the chord could effectively improve the bearing capacity of joints, which contributes to the increase of accumulative energy dissipation \(U_{sum}\) and maximum hysteretic loop energy dissipation \(U\). On the contrary, the energy dissipation ratios of strengthened joints were obviously smaller than those of unstrengthened joints. For example, the energy dissipation ratios of K-CCC1 and K-CCC2 was 132.3% and 81.2% smaller than that of the K-CC joint, and the energy dissipation ratio of K-RC was approximately three times and two times that of K-RCC1 and K-RCC2. The changing trend of the energy dissipation parameters of the above joints showed that grouting concrete in the chord improved the radial stiffness of the chord, restrained the plastic deformation of the chord and weakened the  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Specimens** & \(\mathbf{U}\) (kN-m) & \(\mathbf{U_{sum}}\) (kN-m) & \(\mathbf{\eta}\) \\ \hline K-CC & 2.08 & 9.95 & 13.68 \\ K-CCC1 & 2.22 & 15.54 & 5.89 \\ K-CCC2 & 3.62 & 23.22 & 7.55 \\ K-RC & 2.24 & 9.66 & 13.46 \\ K-RCC1 & 2.38 & 18.02 & 4.48 \\ K-RCC2 & 3.46 & 26.71 & 6.58 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Evaluation of energy dissipation.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Specimens** & \(\mathbf{\delta_{u}}\) (mm) & \(\mathbf{\delta_{y}}\) (mm) & \(\mathbf{\mu}\) \\ \hline K-CC & 6.20 & 1.68 & 3.68 \\ K-CCC1 & 11.89 & 3.56 & 3.34 \\ K-CCC2 & 12.52 & 3.62 & 3.46 \\ K-RC & 6.73 & 1.74 & 3.87 \\ K-RCC1 & 12.47 & 3.61 & 3.45 \\ K-RCC2 & 13.06 & 3.66 & 3.57 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Ductility coefficient of joints.  
plastic energy dissipation capacity of the joint to a certain extent, so that the energy dissipation ratio of the unstrengthened joints relying on plastic deformation was larger than the strengthened joints. What's more, the energy dissipation ratio, accumulative energy dissipation and maximum hysteretic loop energy dissipation of the joint strengthened with grouting fly ash concrete in a chord were all higher than those of the joint strengthened with grouting ordinary concrete in the chord.