# Seismic Behavior and Modeling of Ductile Composite Steel-Trussed Concrete Beam to Column Joints
## 2 Experimental Tests
### Experimental Results  
The results of experimental tests carried out on the hinged column model (test specimen 1) at the Materials and Structures Test Facility of the University of Basilicata are shown in Figure 7 in terms of the envelope of local moment-rotation of the connection element (Figure 7a) and the envelope of global force-drift of the specimen (Figure 7b). The force values considered are the values recorded at the actuator located at the top of the column, while the drift is calculated as the ratio between the displacement made by the actuator and the distance between the actuator and the cylindrical base hinge.  
In the same way, the results of experimental tests carried out on the fixed column model (test specimen 2) at the manufacturing facility of Metal-Ri S.r.l. are shown in Figure 8. In this case, a reduction of the experimental drift compared to the theoretical drift in the actuator pull direction is observed due to the different deformability on the two sides of the external steel reaction structure. The fixed-base column responded within its elastic range and contributed to increasing the global force compared with the hinged-base column.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**N\({}^{\circ}\) Test**} & **Drift** & **Hinged Column** & **Fixed Column Displ.** \\  & **[\%]** & **Display. [mm]** & **[mm]** \\ \hline Test 1 & 0.05\% & \(\pm 1.50\) & \(\pm 2.25\) \\ Test 2 & 0.25\% & \(\pm 7.50\) & \(\pm 11.25\) \\ Test 3 & 0.50\%  
In both cases, the plastic hinge deformation can be observed at the end section of the beam, starting from about 1% of drift. Good dissipative and ductile capacities are shown in Figures 7a and 8a. The connections are able to support gravity loads despite the significant reduction of global stiffness and strength related to the damage developed starting from test 9 or test 8, respectively. Figure 8c represents the moment-rotation envelope at the base of the column, which essentially remains in its elastic range.  
Figure 9 shows for both specimens the crack pattern detected at the end of the test. From Figure 9a, referring to the hinged specimen, it can be observed the plasticization of the column beam connection section and a series of moderate cracks across the entire RC joint panel. Figure 9b,c, related to the fixed base column specimen, shows the complete flexural plasticization of the beam-column connection element while the integrity at the base of the CFT column, where a possible plastic zone is expected, is preserved.  
The direct comparison of experimental results is shown in Figure 10. Both specimens are characterized by the same local behavior (Figure 10a) of the joint connection, while the global behavior (Figure 10b) of the fixed column model has a significantly higher strength and displacement capacity due to the influence of different test schemes.  
Figure 8: Experimental results of specimen 2: (**a**) moment-rotation envelope at the end of the beam; (**b**) force-drift envelope; and (**c**) moment-rotation envelope at the base of the column.  
Figure 7: Experimental results of specimen 1: (**a**) moment-rotation envelope and (**b**) force-drift envelope.