Demolition engineering - Determination of the axial load capacity of steel columns weakened by horizontal and diagonal cuts

Author(s): T. Dunn, R.S. Walls

Abstracts

There is no proven theoretical framework regarding the structural design for the demolition of steel structures. Current demolition methods require a structure to be strategically weakened by cutting and removing certain columns or beams. This paper initially gives an overview of the current, limited research on the subject matter and introduces the “flange-cut”, “horizontal cut” and “angled cut” weakening techniques used by demolition contractors. Experimental setups are developed and utilised to determine the extent to which these cuts, and combinations of these cuts, weaken columns such that engineers can determine whether structures are safe prior to demolition, whilst still allowing the minimum effort possible to cause collapse. Experimental results show that even when columns are fully cut through they can maintain up to 90% of their axial load capacity, even when 10° diagonal cuts are used. However, if a combination of weakening techniques is applied, axial load capacity may be reduced up to 50%, with an average reduction of around 30%. It is observed that global, weak-axis buckling dominates the failure mechanism and that the weakening combinations ensure a relatively similar reduction in capacity for different sized columns. However, the type of weakening techniques used on a single column can have a significant effect on the type of failure. A horizontal cut setup results in explosive, sudden failure which would be unsafe due to the lack of warning prior to collapse. In contrast an angled cut results in a gradual reduction of axial load capacity. A simplified design method is proposed.