Nemetschek Engineering User Contest 2009 • Category 5: CAE Special Projects 189 5 Traffic noise reducing barrier, Eindhoven Characteristics The perforations in the tubes exist of 5.0 mm holes c.t.c. 12.7 mm (alternated). This means a reduction of the surface of: 100x (1- (π/4x52)/(12.72)) = 12%. This reduction has an immediate relation to the stiffness of the perforated tubes (tSLS: rep = 0.88t). The influence of the perforation to the strength of the tube, is determined in accordance with NEN 6710; art. 11.4: • A1 = 18-5 = 13 mm; • A2 = 2x18/√2-2x5 = 15.5 mm; • Anet/A = 13/18 = 0.72. Above mentioned means a reduction of 28% of the strength (tULS;fictive = 0.72t). The thickness of the tubes is 3.0 mm. The thickness which will be imported is such that the FEM program will determine the stresses in a correct way. The preceding gives following input: • Tfi ctive = 0.72x3 = 2.16 mm; • Efi ctive = 0.88/0.72x70000 = 85556 N/mm2. Dimensioning of the Acoustic Screen The loads acting on the acoustic screen are the dead weight of the tubes, which are generated by the FEM program, and the variable wind load. The wind load is 0.95 kN/m2. The input of this load acts on the projection of the tube. This means that the input will be 0.95/2 kN/m2. The accuracy will be seen in the results of the calculations. The load combinations will be generated by the FEM program in accordance to NEN 6702. For the completeness, the model with the wind load is represented in figure 03. Dimensioning of the Box Construction The following thicknesses are taken into account: • Top plate: 5 mm; • Side plate: 5 mm; • Under plate: 5 mm; At the anchors, strengthened with a 25 mm plate (200x200 mm); • Front and back plate/ • Stiffener plates: 4 mm (2+ 3 pieces) Note: The stiffener plates are placed that there is never a conflict with the tubes. The loads exist of the own weight of the box construction, this is generated by the FEM program, the own weight of the tubes and the variable wind load. The 6.0 m height acoustic screen has a dead weight of 1.34 kN/m. In front and in the back of the screen, are some individual tubes, with a load of: • D = 200 mm: Fv;rep = 0.28 kN; • D = 150 mm: Fv;rep = 0.24 kN. The wind load is 0.95 kN/m2. The horizontal load due to the wind load on the top plate is: • qrep = 0.95x6x(6/2+0.4)/0.4 = 48.5 kN/m. The horizontal load due to the wind load on the under plate is: • qrep = 0.95x6x(6/2)/0.4 = 42.8 kN/m. Note: The input of the loads on the top plate is such that the load works on the compressive side of the tube (as in the real situation). As the FEM program cannot make a projection load, the input is adapted so that the result gives the correct load. The load combinations will be generated by the FEM program in accordance to NEN 6702. For the completeness, the model with the wind load is represented in figure 04. figure 01 figure 04 figure 03 figure 02
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