Sensitivity on Load Carrying Capacity of Frames to Member Disappearance

A sensitivity index of vertical load carrying capacity to member disappearance in a framed structures is proposed: The index is defined as the ratio of the load carrying capacity after a member or a set of a few adjacent members disappears to the original load carrying capacity. The member or the set of members that has the highest index may be regarded as a key element or the Achilles heel in the frame. One of the countermeasures against accidental events or attacks is to prepare a careful multiple protection of this Achilles heel. This paper utilizes an efficient linear-programming technique, which is termed as Compact Procedure, to evaluate the load carrying capacities before and after the member disappearance. Planar and 3D frame models are studied about the sensitivity index on vertical load carrying capacity to member disappearance. From these studies, basic properties can be seen on structural sensitivity to member disappearance: (1) In case of strong floor-beam system, corner columns have higher importance than central columns; (2) Violation of symmetric column layout usually results in high sensitivity; (3) An outrigger truss installed at top stories in a multi-story frame is effective to reduce the sensitivity to the column disappearance.