INFLUENCE OF FLANGE STIFFNESS ON DUCTILITY BEHAVIOUR OF PLATE GIRDER: RESULTS AND DISCUSSION(1)

The girder was initially analyzed without considering the web imperfection and noticed that the webs reached to a yielding mode of failure rather than reaching the buckling mode as expected in tension field theory. Further analysis was made with assumed initial imperfection in the web panels and noticed the expected tension field action in the web panels. Modelling the initial imperfection plays a major role in achieving the post yield behaviour of the girder. Out of various available methods, the mode shape superposition was employed to simulate the web imperfection. A buckling analysis was carried out at the first stage and the deformed shape from the first mode of buckling analysis was imported as the imperfection of web panels. In the second stage, the nonlinear analysis was carried out.

The mid-span deflections under various load steps were monitored and retrieved from the FE analysis. A graph was plotted between load and the midspan deflection and was compared with the experimental prediction. The FE model was able to predict the ultimate failure load and the behaviour of girder to an acceptable accuracy. The same modelling technique was adapted to model the previously tested girder SPG2 and the numerically predicted results were compared with experimental results as shown in Fig.2. From these comparisons of experimental vs numerical results of previously tested girders, SPG1 and SPG2, it is concluded that the FE model can predict the ultimate load and its behaviour to an acceptable accuracy and thus the FE model was validated.

Further to the validation of model, the parametric study was carried out. The flange thickness alone varied keeping the other parameters constant. The girders were investigated from the minimum flange thickness which is required from the beam theory to a maximum limit of 30mm. The minimum thickness shown in Table 1 may be sufficient if the girder webs also designed by beam theory. Since, the present girder webs are designed using tension field theory, the web start buckles and further leads to lateral torsional buckling mode of failure under lower flange thicknesses. The FE model predicted a premature failure of girders without reaching the ultimate load. Therefore, further increase in flange thickness was considered.

Fig2Influence Of Flange Stiffness_decrypted

Fig.2.

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