## 2 Materials and Methods  
### Experimental Investigation  
Two connections of identical geometry 2B and 3B were tested. For the tests, a 1000 t capacity press was used. Geometry of the joints is presented in Figure 1a. The characteristics of materials used for the tests were obtained experimentally and are presented in Tables 1 and 2. Loading was divided into two steps. In the first step, an initial 50 t compression force in the column was introduced and maintained, then, in the second step, equal and opposite moments were induced by manually controlled hydraulic cylinders (Figure 1). The ends of the column were fixed; in contrast, the ends of the beams were not restrained. Figure 1: Test setup: (**a**) plan view; (**b**) test stand. Vertical displacements of the ends of the beams were measured with two linear variable differential transformers (LVDT) per side to account for plausible torsion. These LVDTs were placed on the bottom flange near the loading gear. Lateral displacements of the beam ends were controlled with one LVDT, which was attached to the middle of the web. In addition to this, horizontal displacements of the endplates were measured by placing LVTDs in the middle of the bolt spacing: both in the compression and in the tension zones. For the redundancy of the measurements, the digital 2d image correlation technique was also tested, which proved to be accurate, but it did not show significant advantages in comparison to the conventional LVTDs. Curved endplates were manufactured from a seamless CHS 219 \(\times\) 10 pipe, which was cut into four equal pieces (the central angle of the endplate is equal to 90 deg.) The average throat thickness of the filled weld joining the endplates with IFE 270 cantilevers was 4.44 mm. The endplates were connected to the cold formed CHS 219 \(\times\) 6 column with four high-strength M12 \(\times\) 35 HV bolts by using a regular wrench, and then the assembled columns were filled with the concrete. Bolts were tightened by applying the full-strength torque to establish firm contact between the column and the endplate; however, no firm contact could be achieved. The bolt tightening force was not measured or controlled by any means. After tightening, the gaps at the ends of the plates were measured with the feeler gauges at three points (two corners and in the middle in accordance with Figure 1). The measurements are presented in Figure 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Index**} & \multicolumn{2}{c}{**Endplate Steel P355N**} & \multicolumn{2}{c}{**Steel of CHS S235**} & \multicolumn{2}{c}{**High-Strength Bolts**} \\  & \multicolumn{2}{c}{**(4 Tests)**} & \multicolumn{2}{c}{**(4 Tests)**} & \multicolumn{2}{c}{**M12 \(\times\) 35 10.9 HV (4 Tests)**} \\ \cline{2-7}  & **Average** & \multicolumn{2}{c}{**Standard**} & \multicolumn{2}{c}{**Average**} & \multicolumn{2}{c}{**Standard**} & \multicolumn{2}{c}{**Average**} & \multicolumn{2}{c}{**Standard**} \\  & & **Deviation** & \multicolumn{2}{c}{**Average**} & \multicolumn{2}{c}{**Deviation**} & \multicolumn{2}{c}{**Average**} & \multicolumn{2}{c}{**Deviation**} \\ \hline Yield strength & 389.8 MPa & 4.30 MPa & 318.8 MPa & 21.52 MPa & — & — \\ Ultimate strength & 551.9 MPa & 2.83 MPa & 419.6 MPa & 11.28 MPa & 1147 MPa & 14.31 MPa \\ Modulus of elasticity & 280.2 GPa & 16.10 GPa & 151.6 GPa & 5.63 GPa & — & — \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The mechanical and physical properties of the steel and fasteners. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**N**} & \multirow{2}{*}{**Specimen**} & \multicolumn{2}{c}{**Compressive Cube Strength, MPa**} & \multicolumn{2}{c}{**Density, kg/m3**} \\ \cline{3-5}  & & **Average** & **Standard Deviation** & **Average** & **Standard Deviation** \\ \hline
1 & 2B (8 tests) & 39.7 & 1.9 & 2318 & 12.9 \\
2 & 3B (8 tests) & 30.6 & 1.2 & 2351 & 17.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mechanical and physical properties of the 10 \(\times\) 10 \(\times\) 10 cm concrete cubes.