INFLUENCE OF FLANGE STIFFNESS ON DUCTILITY BEHAVIOUR OF PLATE GIRDER: RESULTS AND DISCUSSION(2)

The girder SPG1 with a flange thickness of 10mm reached the desired load of 420kN and showed reduction in load carrying capacity after reaching the ultimate load. It is proved that the minimum thickness of flanges could reach the ultimate load but no ductility would be obtained.

Further increase in flange thickness increased the ultimate to certain extent and the ductility to a greater extent. The uniform increase in the load-deflection profiles can be clearly seen from Fig-3. It is observed that the yield load as well as the ultimate load increases with the flange stiffness. It can also be noted that the increase in flange stiffness widens the curve and becomes more flatten with considerable increase in the deflection range. It reveals that the ductility factor increases i.e. it undergoes large deformations without decrease in the load. The ductility factor and ultimate load of the plate girders with various flange thicknesses were calculated and listed below in Table 2.

Similar behavior was observed in Girder SPG2. The minimum flange thickness required for SPG2 is 10mm as shown in Table-1. Referring to the Fig-4, though the 10mm thickness flange reached the required ultimate load, it loses its load carrying capacity immediately after the yield load which indicate the lower thickness flange is not able to provide any ductile behavior. The same behavior is observed in SPG2 up to a flange thickness of 18mm. A lateral torsional buckling mode of failure was observed for the flange thicknesses varies from 10mm to 18mm. On the other hand the ductility behavior is observed only when the flanges are provided such that the Mp/M ratio more than 2.5. The ductility factor increases with increase in Mp/M ratio and shows a direct proportion. This can be noticed from T able-3

Results obtained from SPG3 and SPG4 indicated a different behavior from SPG1 and SPG2. The girders SPG3 and SPG4 are not reached the expected ultimate loads which were calculated through the tension field theory. A sudden decrease in load capacity is noticed after the yield load. No ductile behavior was observed for SPG3 and SPG4. These can be revealed from Fig-5 and Fig-6. No increase in ultimate load also noticed for smaller d/t girders.

From the Table-2 it can be seen that the ultimate load capacity increases even up to 41.5% with the increase in flange stiffness for the girder SPG1 with a d/t ratio of 250. But Table -3 to Table -5 indicate that the increase in ultimate load w.r.t. flange thickness is decreasing with decreasing d/t ratios.

From the present study the following conclusions are drawn.

• The ductility factor is less for the girders with Mp/M ratio less than 2.5, and it increases drastically with increase in Mp/M ratio more than 2.5. This observation is made only for girders with d/t ratios equal to or greater than 150. For girders with d/t ratio 125 and 94, no ductility behaviour is observed.
• Girders with larger d/t ratio (i.e for 250 and 150) are sensitive to the flange stiffness. These types of girders provide more ductile behaviour for the increasing flange thickness. Also, showed up to 41% increase in ultimate load for the increased flange thickness.
• For girders with smaller d/t ratios, not much difference is observed between Mp and M.
• Consideration of small increase in flange thickness provides better ductility behaviour and therefore well suited for seismic regions.

Fig3Influence Of Flange Stiffness_decrypted
Fig. 3 Typical Stress-Strain Curve for Steel

Fig4Influence Of Flange Stiffness_decrypted
Fig. 4: Load rc Deflection Behaviour of Girders SPG1 to SPG4 (Ansys vs

Fig5Influence Of Flange Stiffness_decrypted
Fig.5. Typical View of the Girder SPG1 at Ultimate Load [Shanmugam, N.E. and Baskar, K., 2003]

Fig6Influence Of Flange Stiffness_decrypted
Fig.6. Deformed Shape of the Girder SPG1 Predicted through FE Model

Fig7Influence Of Flange Stiffness_decrypted
Figure 7: Load-deflection Behaviour of SPG1 with Various Flange

Fig8Influence Of Flange Stiffness_decrypted
Figure 8: Load-deflection Behaviour of SPG2 with Various Flange

Fig9Influence Of Flange Stiffness_decrypted
Figure 9: Load-deflection Behaviour of SPG3 with Various Flange

Fig10Influence Of Flange Stiffness_decrypted

Figure 10:Load-deflection Behaviour of SPG4 with Various Flange Thickness


Table 2: Ductility Factor and Increase in Ultimate Load of SPG1

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1 10 .57 5 422.77 0.00
2 14 2.20 5 440.47 4.20
3 16 2.51 5 453.31 7.20
4 18 2.83 5 45 9.0 467.57 10.6
5 20 3.14 5 81 16.2 483.68 14.4
6 22 3.46 5 11 22.2 502.28 18.8
7 24 3.77 5 >126 >25.2 523.36 23.8
8 26 4.08 5 >126 >25.2 546.86 29.4

9 28 4.40 5 >126 >25.2 572.28 35.4
10 30 4.71 5 >126 >25.2 598.40 41.5

Table 3: Ductility Factor and Increase in Ultimate Load of SPG2

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1 10 1.13 5 754.66 0.00
2 14 1.58 5 766.09 1.51
3 16 1.80 5 767.47 1.69
4 18 2.03 5 780.68 3.41
5 20 2.25 5 34 6.8 788.79 4.45
6 22 2.48 5 59 11.8 806.31 6.67
7 24 2.70 5 88 17.6 825.04 8.99
8 26 2.93 5 >88 >17.6 846.39 11.58
9 28 3.15 5 >88 >17.6 871.38 14.53
10 30 3.38 5 >88 >17.6 900.32 17.86

Table 4: Ductility Factor and Increase in Ultimate Load of SPG3

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Ductilityfactor Ultimate load, kN ■    s 

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1 4 1.13 4 1006.79 0.00
2 6 1.29 4 1009.35 0.25
3 8 1.45 4 1023.26 1.63
4 0 1.61 4 1027.43 2.04
5 2 1.77 4 1034.76 2.75
6 4 1.93 4 1041.09 3.37

7 6 2.10 4 1046.72 3.91
8 28 2.26 4 1052.79 4.49
9 30 2.42 4 1070.40 6.16

Table 5: Ductility Factor and Increase in Ultimate Load of SPG4

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% increase in ultimate load w.r.t first girder
1 24 1.10 5 1591.42 0.00
2 26 1.19 5 1603.20 0.74
3 28 1.28 5 1614.16 1.42
4 30 1.37 5 1622.90 1.97

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