Limit states design of beam-columns in CSA SI 6.1-94

The different modes of failure of beam-columns are assessed independently by checking interaction equations for cross-sectional strength, in-plane bending strength and out-of-plane behaviour. The analyses to determine the stress resultants on the ends of members must include the second-order geometric (PA) effects. Effective lengths of members that fail by excessive bending are taken as the actual lengths avoiding the need to assess effective lengths at the expense only of the approximations inherent in the interaction equations used. A minimum notional horizontal load at each storey level of 0.005 times the sum of the vertical loads applied there is used to account for the potential mode of failure of sides way buckling, but only when the structure is subject to gravity loading. Areas of non-conservatism and conservatism of the current approach are discussed. Arguments are presented to apply the notional load in conjunction with other lateral loads and to reassess its value.