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Proceedings of the METNET Seminar 2015 in Budapest
The largest temperature differences within the joints are observed in case of the column base joint, where the concrete foundation has also a significant cooling down effect. The numerical calculations showed, that the temperature of the concrete base reaches 500 °C after 15 sec fire, but under the base plate the temperature will be only 160°C, which can have positive effect on the joint behaviour in fire. On the other side the temperature in the anchor bolts are also significantly smaller than in other steel parts of the joints. The structural behaviour of the ridge joint and the beam-to-column joints showed similar temperature distributions. Thus the web plate in the investigated beam and column belongs to Class 4 cross section, the local plate buckling is a relevant optional failure mode of the girder. Thus the increase in the temperature is the largest in the webs, the elongation will be the largest here also, which results in additional compression stresses coming from the supporting and pushing effect of the flanges. It means that by increasing the temperature in the web, the buckling susceptibility increases as well and after the local buckling the stiffness and the load carrying capacity of the joint decreases rapidly. The final result for all the investigated joints are the moment – rotation curves regarding different time steps and temperature distributions. The typical curves representing the structural behaviour of the beam-to-column joint is presented in Figure 6. The initial stiffness of the joint and the load carrying capacities can be determined for all the analysed joints using the coupled analysis method.
Figure 6. Moment – rotation curves of the beam-to-column joint in different time steps.