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uch comparisons is the fact that, for the future, there is not necessary to spend money on experimental tests (unless necessary). For the simulated analysis, the models were created as solids like in Fig.4. Fig.4 Modeled connection The finite elements were chosen to be arranged in the mesh as structured elements, but, at the intersection of an element’s web with the flange, there cannot be discretized only with tetrahedron elements. This happened because the cross-section of the profile was modeled with the profile’s radius between the web and the flange and not by plate joining. Because the part between the straight flange and the straight web was limited by three surfaces the meshing resulted with much more distorted elements. For this reason the entire profile was meshed using tetrahedron elements. The boundary conditions were defined on surfaces, reducing first the translations on the vertical direction. The analysis did not reach a final analysis so the boundary conditions were changed. The displacement was reduced on both horizontal directions. The error might have occurred because this non structural mesh is not symmetrically with respect to all three axes. The bond between the elements was considered to be “tie”. The application of force was similar to the one applied in reality, a circular surface of 15cm diameter. Fig.5 Deformed shape for initial connection In Fig.5, the deformed shape of the first model (un-strengthened) also shows the stresses in longitudinal direction of the column. Red represents the tension and blue means compression.
Fig.6 shows the same stress at the same force applied on the plate. Also the color representation is the same as mentioned before. Fig.6 Deformed shape for the strengthened elements From the two figures it can be seen that the models have the same behavior but the areas where the stress was maximum, are now smaller or gone, meaning that the connection can still be loaded until it reaches the yielding point. Another thing that can result from the analysis is the fact that, although the strengthening parts on the upper flange of the column are not continuous, there is no stress concentration in the nearby of the welding between the column and the beam. In the first situation, the location where the stresses have high values, are represented by small areas. These locations are: the supports of the model, the corresponding zones but on the other flange, the vicinity of stiffeners. In the second case, the areas, with close values for the stress, are larger meaning that the distribution of stress is more uniform and the location of yielding stress can be seen only in the support surfaces. The circular surface has also yielding points because the bending of the column had an influence on the bending of the plate welded to the beam. The same print could be seen on the experimental specimen, where the force was distributed finally through two areas apart from each other due to the detachment of the center of the plate from the pressure cylinder. Gauge 80204060801001201401601802000 500 1000 1500 2000P [kN]σ [N/mm2]Initial Strengthened Fig.7 Results for gauge 8
Mainly, the stresses in the strengthened elements are less than for the first case, as it can be seen in the charts in Fig.7 and Fig.8. The rhombic filled line represents the values for the un-strengthened model and the triangle filled line represents the model with consolidation plates. Fig.7 and Fig.8 show the stress of gauges 8 and 9 which are positioned on the lower flange of the column. Here, the stresses are reduced by 25-40%. Gauge 90501001502002500 500 1000 1500 2000P [kN]σ [N/mm2]Initial Strengthened Fig.8 Results for gauge 9 Most of the gauges present the same behavior but as the stresses needed to be distributed to the supports, there are locations where the stresses exceeded the values obtained in the first analysis model. A special attention should be paid to these zones as they can reach the yielding point before other main parts of the element.