ABSTRACT
This paper presents the results of nonlinear seismic dynamic analyses performed on a 16- and a 24-storey braced frame buildings to evaluate the flexural demand imposed on the columns when subjected to code level earthquake ground motions. Partially-encased composite columns designed for axial loading only were used in the buildings. The columns were continuous over 2 or 3 storeys and were subjected to bending moments due to differential inter-storey drifts that developed in adjacent levels during seismic motions. The flexural demand on gravity columns was found to be limited. Conversely, the columns of the bracing bents experienced considerably larger bending moments and such demand will need to be accounted for in the column design. Higher mode effects resulted in larger column bending moments in the upper part of the buildings. A selection of the braces with the slenderness being constant or reducing towards the base of the structure was found to be beneficial for the buildings studied.
