# The Resistance of Welded Joints of GAlvanized RHS Trusses with Different Vent Hole Geometries
## 3 Validation of Finite Element Modeling  
Experimental test results from a pair of CIDECT projects developed at the University of Delft [40, 41] were used to validate the model. These experiments included six tests carried out on RHS K-joint configurations with brace angles of 45\({}^{\circ}\). The reports published force-indentation curves for one of the selected tests (named as Test 1) [40], but they were not published for the other five [41]. The braces did not include any holes for ventilation, and there was always a gap between the braces on the chord face. The gap between the braces was designed to avoid joint eccentricity and the corresponding moment caused by this. The only available data with respect to the weld throat of the specimens indicated that it was equal to the brace thickness, which is in accordance with the previously mentioned rule for modeling the welds. Figure 5 shows the joint configuration used in the tests with the global dimensions of the connected members. In the numerical model, the actual stresses and strains (\(\sigma_{act}\), \(\varepsilon_{act}\)) of the steel were taken, rather than the engineering values (\(\sigma_{mg}\), \(\varepsilon_{mg}\)) from the standard tests. The equations for transforming the values from engineering values to actual values are presented as Equations (3) and (4), below. \[\varepsilon_{act}=Ln\Big{(}\varepsilon_{mg}+1\Big{)} \tag{3}\]  
Figure 4: Global boundary conditions in FE Models. Figure 5: Tested K-joint configuration. \[\sigma_{act}=\sigma_{eng}\Big{(}\varepsilon_{eng}+1\Big{)} \tag{4}\]  
The nominal steel grade was S275, with hot-finished tubes for tests 1, 2, 5 and 6, but cold-formed tubes for tests 3 and 4. To simulate the material behavior, isotropic bilinear hardening was assumed [42]. In the case of tests 3 and 4, a proportionality limit of 85% of the elastic limit was adopted, in accordance with [43]. The material properties (\(f_{y}\) and \(f_{u}\)) of the cold-formed RHS were obtained in Delft from stub column tests. Therefore, the average strain hardening, which primarily affects the corner area, is already considered, and it is not necessary to use additional procedures such as those presented in [44]. Table 1 presents the dimensions of the joint members, the relative gap regarding the chord width (\(gb_{0}\)), the yield limit \(f_{y}\) and the ultimate strength \(f_{u}\), and the tangent modulus (the slope of the strengthening stage) for the six tests. For weld modeling, the same material properties as those of the corresponding welded brace member were adopted. Some previous research [24; 38] carried out in similar situations has confirmed that differences when the base material properties of the steel are also used to model the welds are not noticeable. Although some gaps were smaller than those in EN-1993-1-8 [4], the tests were carried out prior to the formulation of the code, and they were used in this research only for validation of the numerical model. When validating the model, it is important to take into account the joint stiffness and not only the joint resistance. Therefore, complete force-displacement curves were recorded from the simulation of Test 1 and were compared with those available from the experiment [40]. Figures 6 and 7 plot these curves, showing very good agreement in terms of initial stiffness and maximum load between the test and the FE models. Both Figures 6 and 7 present the force applied on the compression brace member vs. the displacement as an indentation measured at points 1 and 2 in accordance with Figure 5. Figures 6 and 7 show the complete force-indentation curves obtained with the FE model (blue curves), but the curves available from the report for the tests carried out in Delft (red curves) are only plotted for indentations of between 8 and 10 mm. As the maximum load achieved during the tests is known from the report, these values were also plotted as a horizontal line in order to compare them with the maximum load predicted by the model, and a good agreement can be observed.