Civil Engineering Association

TOWARD ADVANCED ANALYSIS IN STEEL FRAME DESIGN

The trends for analysis and design of steel frames are indicated in this dissertation. The current practice consists of applying the first-order elastic analysis with amplification factors or second-order elastic analysis in combination with the AISC-LRFD interaction ·
equations. Determination of the effective length factors and individual member capacity checks are necessary to select adequate structural member sizes. The direct analysis method is a second-order elastic analysis approach that eliminates the determination of effective length factors from the current AISC-LRFD method. Unsupported member length is used to calculate the axial strength of a member. Equivalent notional loads
and/or modified stiffuess are applied together with the external loads to account for the effects of initial out-of-plumbness and inelastic softening. For both AISC-LRFD and direct analysis methods, a structure is analyzed as a whole, but the axial and flexural strength of each member is examined individually. Inelastic redistribution of internal forces in the structural system cannot be considered. As a result, determined member forces are not correct and more conservative member sizes will be obtained. Moreover, member-based approaches cannot predict structural behaviors such as failure mode and overstength factor.