The use of 'Dog-Bone' for the Seismic Improvement of Steel MRFs

摘要

This work is devoted to the strengthening of steel moment resisting frame designed in order to bear vertical loads only. In particular, the idea is based on the attainment of improvement of seismic performance by simply trimming the flanges of the beam ends. This strategy can be applied by considering both the results of the theory of plastic mechanism control and the rules assuring the yielding of reduced beam sections (RBS) when seismic loads are applied to the structure. It is important to underline that the results of such strategy is not always effective. In fact, there are several condition that are to be satisfied in order to obtain an actual seismic improvement. Notwithstanding, when these conditions are satisfied, the cost of intervention can be considered as negligible. For this reason this strategy can be very interesting and the rules applied in this work can clarify which is the effect of RBS taking into account all the parameters playing a role in the final design:, i.e. existing column sections, resistance and ductility of existing connections, vertical loads acting in seismic load combination, amount of the reduction of beam section and its distance from the connection. By means of a worked example the effectiveness of the proposed procedure is shown.