Non-linear analysis of structural steel frames

Abstract

Material, geometrical and connection non-linearities could have a significant influence on the forces and moments in a steel structure, especially in sway frames at ultimate load levels. Some structural steel design codes (such as CAN3-S16·1-M89) require that a designer consider second-order moments (i.e. the geometric non-linearities). If the steel members are able to redistribute moments through plastic hinge formation, it makes economic sense to do a plastic design. Certain so-called ‘hinge’-connections do in fact transfer significant moments. It would thus also make the structure more economical if one can take this moment transfer into account. All the above effects could be built into a steel frame analysis program. In this paper, ways of including geometrical, material and connection non-linearities into the matrix stiffness method in a relatively uncomplicated manner will be discussed. A computer program developed by the authors, for design-office use, where the matrix stiffness method has been adjusted to incorporate all these non-linearities is described. The use of the computer program is illustrated by means of an example.