# The Resistance of Welded Joints of GAlvanized RHS Trusses with Different Vent Hole Geometries
## 4 Parametric Study of K- and N-joints Results and Discussion  
After validation, the model was extended by means of a parametric study to take into account other K-joints and some N-joint configurations. All the new joints, initially without the vent holes, were combined with the three above described vent hole geometry. The complete program included eight K-joints plus three N-joints involving different sizes of rectangular hollow sections as chord members and square hollow sections as brace members. The K-joints were symmetrical, with brace angles of 45\({}^{\circ}\), 55\({}^{\circ}\) and 60\({}^{\circ}\). The diagonal brace in the N-joints had an angle of 45\({}^{\circ}\). The purpose of this was to be able to analyze the influence of several variables linked to the geometry on the joint strength, together with the presence of the hole in the braces and its shape and position. Table 3 presents the member dimensions, gap, angles and some other relative geometrical variables considered in the extended models. The joint reference indicates the type and number of joints, along with the expected failure mode, as described below. For every joint, a set of four options, including the three types of vent hole as well as the same joint without any holes, were studied. That means that 44 joints were analyzed. All these joints avoided eccentricities due to the coincidence of the chord and brace axes. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Joint** & **2** & **3** & **4** & **5** & **6** \\ \hline Test [kN] & 102 & 215 & 172 & 198 & 193 \\ Model [kN] & 105.9 & 232.1 & 185.3 & 204.3 & 198.6 \\ \hline Deviation \% & 3.8 & 7.9 & 7.7 & 3.2 & 2.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Maximum load from tests and simulation. Figure 9: Model vs. tests for 2 nd validation. Table 4 shows the main dimensions of the three vent holes considered in the extended model according to Figure 2. In this part of the research, a nominal S275 was chosen, assuming bilinear behavior of the steel with a tangent modulus (the slope of the hardening stage) of 1330 N/mm\({}^{2}\). In these kinds of joints, it is common to establish as a limit the load at which the indentation in the chord face reaches 3% of the chord width (\(b_{0}\)) [45]. Therefore, both the maximum load supported by the joint and the load corresponding to the indentation criterion of 3% were registered. These data are presented in Table 5 for the 44 configurations corresponding to the combinations of the type of joint and the shape of the vent hole. The criterion of 3% indentation always presented a lower result than the maximum load in the joint. Table 5 also includes the predicted failure mode according to formulation in EN-1993-1-8 [4]. These failure modes are: BF (brace failure), CF (chord plastification), and PS (punching shear). However, this was not conclusive for joints 1 to 5, because the values for the ultimate loads based on 3% indentation and those based on the maximum load supported by the joint were very close to one another, with differences of less than 5%. Table 6 presents the deviations of maximum loads achieved using both criteria when joints with different vent holes are compared to joints without any holes. The results from Tables 5 and 6 indicate that joint resistance hardly changes with different shapes or positions of the vent holes, or when compared with the same joint without any holes. If the 3%\(b_{0}\) criterion is applied, deviations of mean values for different geometries when compared with joints without vent holes are lower than 1% in the case of circular holes, 2.2% for semi-circular holes, and only 3.4% when using V-notched holes.