Seismic Behavior of Perimeter Moment Resisting Steel Frames

Abstract eng:
The seismic responses of steel buildings with perimeter moment resisting steel frames (MRSF) and interior gravity frames (IGF) are estimated and some aspects related with the building structural idealization are studied. The contribution of IGF to the lateral resistance is evaluated. The seismic responses of the buildings with perfectly pinned (PP) connections are compared to those of the buildings with semi-rigid (SR) connections. The relative importance of the P-δ effect in gravity columns is also studied. The study indicates that the contribution of IGF to the lateral structural resistance may be significant. This contribution is larger for lower stories for the buildings with PP connections. The contribution increases when the stiffness of the beam-to-column connection of the IGF is considered, particularly for upper stories. It is observed that the interstory shears are significantly reduced when the connections stiffness is taken into account. By the other hand, the interstory displacements are similar for the models with PP and SR connections. Resultant stresses also decrease but to a lesser degree. Results also indicate that the second order moments produced in gravity columns are comparable and even larger than those used to design these columns. It is concluded that, if the abovementioned structural system is used, IGF should be considered as part of the lateral resistance system, and that the stiffness of the connections and the P-δ effect should be included in the design of the IGF. Otherwise, the capacity of gravity frames may be overestimated while that of MRSF may be underestimated.

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