Effective Lengths of Columns in Multi-storey Buildings. Part 3: Features which increase the Stiffnes

The author's experience on several codes-of-practice committees has led him to the conclusion that one of the greatest fields of uncertainty lies in the specifying of effective lengths of continuous columns. This is coincidental with the difficulty of calculating elastic critical load factors and dealing with frame instability. Comprehensive design charts are given for effective lengths of columns with any local
degree of end restraint, both for sway and no sway conditions. To design for the limit-state of collapse it is essential to discover new 'desk' methods of dealing with overall frame instability when effective lengths based on local restraints are not accurate enough. A new technique of 'stiffness distribution', akin to moment distribution, will be acceptable in a drawing office, both for steel and reinforced concrete frames, at the same time providing rapid estimates of the other limit-state of permissible sidesway. Important modifications for strain hardening and composite panel stiffening are included, indicating the urgent need for more full-scale tests on composite action with cladding. The emphasis throughout has been on simplicity of theory and of the many worked examples.

R.H. Wood