Vibration mode vs. collapse mechanism control for steel frames

The problem of controlling the plastic collapse mechanism of steel frames is discussed focusing on the strict relationship existing with vibration modes. General considerations are first made, which are applicable to every structural type. Specific analytical formulations are then presented with reference to moment resisting and braced steel frames. The proposed approach is derived starting from elementary kinematics of frames and can be considered one step of a direct displacement-based designed methodology. When first-mode response is dominant, as is the case for low- to medium-rise buildings, the design approach satisfactorily predicts the structure behaviour.