## 3 Test Program  
### Specimen Details  
To investigate the behavior and failure mode of plate-to-RHS K-connections, cyclic loading tests of three truss specimens (N00-150, S15-150, and S25-200) were performed. Table 3 and Figure 4 show the test variables and connection details of the specimens. In the specimen names, the first letters N and S indicate the plate-to-RHS connections without and with chord face stiffener, respectively; the following numbers \"15\" and \"25\" indicate the thickness of the stiffeners (\(t_{s}=\)15 and 25 mm, respectively); and '150' and '200' indicate the width of the connecting chord face (\(b=\) 150 and 200 mm, respectively). As shown in Figure 4a, the plate-to-RHS K-connections were fabricated as follows. First, the longitudinal plate of thickness \(t_{p}=\) 15 mm and length \(l_{p}=\) 700 mm was welded to the connecting chord face. Then, two concrete-filled composite branch members were connected to the longitudinal plate by bolting (i.e., slip-critical joint). For the bolted joint, a T-stub including the gusset plate PL-100 \(\times\) 310 of thickness 15 mm was used at the end of the branch members. To mitigate stress concentration at the weld joint, the gusset plate was extended by 90 mm inside and welded to the steel section (B-100 \(\times\) 100 \(\times\) 4.0) and embedded D10 bars; in addition, 4M8 bolts were installed to tie the gusset plate and steel section. The inclination angle between the chord and branch members was \(\theta=\) 45\({}^{\circ}\). The geometrical parameters of the chord and branch members, longitudinal plate, and chord face stiffener are summarized in Table 3.  
Figure 4: Configuration and connection details of truss specimens with plate-to-RHS K-connection (unit: mm): (**a**) Configuration of RHS truss connection specimens; (**b**) Composite branch member and bolted joint; (**c**) Details of plate-to-RHS K-connections with or without chord face stiffener.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimen** & **Type** & **Chord Member** & **Longitudinal Plate** & **Chord Face Stiffener** \\ \hline N00-150 & Unstiffened & \(b=\) 150 mm; \(b/t=\) 33.3 & \(l_{p}=\) 700 mm & \(l_{p}/b=\) 4.67 & - \\ \hline S15-150 & Stiffened & \(b=\) 150 mm; \(b/t=\) 33.3 & \(l_{p}=\) 15 mm & \(l_{p}/b=\) 4.67 & \(b_{s}=\) 120 mm; \(t_{s}=\) 15 mm; \(bs/b=\) 0.8 \\ \hline S25-200 & Stiffened & \(b=\) 200 mm; \(b/t=\) 44.4 & \(l_{p}/b=\) 3.5 & \(b_{s}=\) 170 mm; \(t_{s}=\) 25 mm; \(b_{s}/b=\) 0.85 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Geometric parameters of plate-to-RHS truss connections.  
A square hollow structural section of B-150 \(\times\) 150 \(\times\) 4.5 (\(h\) = \(b\) = 150 mm and \(t\) = 4.5 mm) was used for the chord member in N00-150 and S15-150, while a rectangular hollow structural section of B-150 \(\times\) 200 \(\times\) 4.5 (\(h\) = 150 mm, \(b\) = 200 mm, and \(t\) = 4.5 mm) was used in S25-200. For N00-150, the longitudinal plate (\(t_{p}\) = 15 mm and \(l_{p}\) = 700 mm) was welded to the connecting chord face (\(t\) = 4.5 mm) without stiffener; for S15-150 and S25-200, on the other hand, the same longitudinal plate was used along with the chord face stiffener of thickness 15 and 25 mm, respectively.  
For N00-150, weld size was \(w\) = 1.41 = 6.5 mm at the joint between the longitudinal plate and chord face. For S15-150 and S25-200, \(w\) = 6.5 mm at the weld joint between the chord face and stiffener and \(w\) = 10 mm at the weld joint between the longitudinal plate and stiffener.