ABSTRACT
Lu et al. (2009) developed a simple extension to Direct Analysis called Extended Direct Analysis. It considers section plasticity in the analysis and increases the realism of the model/analysis. This can be implemented with many computer packages, but residual stress effects have been included directly in the computer software MASTAN2 (Ziemian and McGuire, 2008) for each of the five Australian/NZ column design curves. Because the analysis and model consider all the major parameters needed for design, acceptance criteria are relatively simple. If the frame collapses under the applied loads in the analysis, then the frame does not satisfy the limit state criteria and a different configuration, or larger member sizes are required. However, if the frame resists the applied loads, then the frame is satisfactory for that load case. This methodology is being used for non-seismic
1 INTRODUCTION
In non-seismic plastic design of steel structures, methods to design frames have generally relied on an elastic first-order analysis with a number of empirical corrections accounting for geometric nonlinearity for braced and sway components of member actions, residual stress effects, etc. Out-of-plumb effects may be taken into account by notional loads applied to frames. A methodology to consider these effects directly in the analysis has been developed by AISC (2005) called Direct Analysis. Here, notional loads may applied to the frame to consider outof-plumb, the member stiffness is calculated as a function of the axial force and residual stresses (as well as other member properties), and second-order frame analysis is conducted to capture the geometry. Also, the effect of the statistical variation in the member properties are considered by modifying the material properties by the
steel frame design in NZ and has the potential to simplify and the design of non-seismic steel frames around the world and to reduce the time required for analysis.
