Capacities of steel columns with excessive crookedness

This paper explores a number of situations where columns with out-of-tolerance crookedness may still be designed and used without compromising the general levels of structural safety intended by common codes of practice.
The case of a column whose crookedness is out-of-tolerance is first examined, and two design methods are suggested. In the first method, the column is treated in a similar way to that used for the basis of the BS 5950 column design method by allowing for the excess crookednesses.
In the second method, the column is designed as a straight beam-column with design moments equal to those resulting from the first-order analysis of an imperfect structure whose geometry includes the excess crookednesses.
Following this, the case is considered of a column damaged by unexpected bending which leaves an out-of-tolerance permanent set. It is concluded that the damaged column can be designed for its increased crookedness by using either of the methods proposed for columns with out-of-tolerance crookedness. The straightening of the damaged column is also considered.
Finally, the case is analysed of a force-fitted column which has excessive crookedness locked in during its connection to other members of a structure. It is found that the force-fitting deflection can be regarded as an initial crookedness, so that the column can be designed as an out-of-tolerance column.

N. S. Trahair, BSc, BE, MEngSc, PhD, DEng
Emeritus Professor of Civil Engineering, The University of Sydney

K. Kayvani, BSc, MEngSc, PhD
Principal, Connell Mott MacDonald