On the Design of Damaged Steel Columns (No. R846)

Abstract

This paper explores a number of situations where columns with out-of-tolerance crookedness or which have been damaged may still be designed, despite the implications of many codes that they must be replaced, and suggests rules for their design. 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 BS5950 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 residual stresses caused by the damaging bending moments may often be ignored, in which case 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. It is found that the residual stresses which follow relaxation after straightening may also be ignored and the column designed in the usual way. 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.