## 5 Conclusions  
This paper investigated the seismic behavior and failure mechanism of a peculiar hybrid structure consisting of steel truss and RC pipe columns with steel diagonal braces through a series of PDTs and QSTs on a scaled specimen. The main findings can be summarized as follows:  
1. Due to the special structural composition, resulting in the lower torsional stiffness, the first vibration mode was torsion and the corresponding fundamental period was 0.319 s. Besides, the periods of first three vibration modes are close with each other. The equivalent base shear method is not suitable to calculate the earthquake action. And the translation-torsion coupling earthquake action calculation method was recommended. In addition, in order to consider the adverse influence of the torsion, the calculated earthquake actions were suggested to be enlarged.
2. The lateral deformation mode of the steel truss-RC column hybrid structure with steel diagonal braces belongs to shear-type and the lateral displacement curve was divided into two significant part at the corbel because of the rigid-upper-flexible-bottom characteristics of vertical stiffness distribution condition that the stiffness of the upper part above the corbel is much larger than that of the pipe columns. The drift concentration mainly occurred on the column, where the peak of maximum drift ratio occurred at the height of corbel after PGA came up to 0.30 g.
3. Analysis of the stiffness deterioration demonstrated that the steel truss-RC column hybrid structure with steel diagonal braces had a rather good stiffness performance. When the PGA came up 0.40 g which referred to the major earthquake having 2% probability in 50 years, the stiffness was about 60% of the initial stiffness. After PGA equaled to 0.80 g, the stiffness was about 41% of the initial stiffness.
4. Damage observation showed that cracks mainly occurred two parts of columns including the bottom of column and the lower part of corbel. This was due to the setting of diagonal braces, resulting in the change of bending moment distribution pattern along the height of column. Overall, the new supporting structure consists of steel truss, RC pipes column with steel diagonal braces can satisfy the seismic demand under severe earthquakes.  
Support for this research from the National Natural Science Foundation of China (NSFC, Grant No. 51708037), China Postdoctoral Science Foundation (Grant No. 2017M610616) and Shanxi Province Postdoctoral Science Foundation (Grant No. 2017 BSHEDZZ111) is gratefully acknowledged.  
[PERSON] contributed to the study design, analysis of data and writing; [PERSON] contributed to the fabrication of specimen and acquisition of data; [PERSON] contributed to the design of experimental program; [PERSON] contributed to the conception of this paper; [PERSON] contributed to literature search and revision of this paper.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Location** & **Encryption Height** & **Stirrup Diameter** & **Stirrup Spacing** \\ \hline Base of column & 3.0\(d\) & & \\ Lower part of corbel & 1.0\(d\) & \(\geq\)12 mm & \(\leq\)150 mm \\ Upper part of corbel & 1.0\(d\) & & \\ \hline \hline \end{tabular} Note: \(d\) is the external diameter of pipe column.  
\end{table}
Table 6: Stirrup densification recommendation.