09-11-2012, 03:38 PM
DSM Design Guide
4_DSM Design Guide.ppt (Size: 4.79 MB / Downloads: 63)
DSM Advantages
Practical advantages of DSM:
no effective width calculations,
no iterations required, and
uses gross cross-sectional properties.
Theoretical advantages of the DSM approach:
explicit design method for distortional buckling,
includes interaction of elements (i.e., equilibrium and compatibility between the flange and web is maintained in the elastic buckling prediction), and
explores and includes all stability limit states.
Philosophical advantages to the DSM approach:
encourages cross-section optimization,
provides a solid basis for rational analysis extensions,
potential for much wider applicability and scope, and
engineering focus is on correct determination of elastic buckling behavior, instead of on correct determination of empirical effective widths.
DSM Limitations
Limitations of DSM (as implemented in AISI 2004)
No shear provisions
No web crippling provisions
No provisions for members with holes
Limited number/geometry of pre-qualified members
No provisions for strength increase due to cold-work of forming
Practical Limitations of DSM approach
Overly conservative if very slender elements are used
Shift in the neutral axis is ignored
Limitations of finite strip method
Cross-section cannot vary along the length
Loads cannot vary along the length (i.e., no moment gradient)
Global boundary conditions at the member ends are pinned (i.e., simply-supported)
Assignment of modes sometimes difficult, particularly for distortional buckling
Overcoming FSM difficulties
The discussions in the following section are intended to provide the design professional with a means to apply “engineering judgment” to an elastic buckling analyses. When in doubt of how to identify a mode, or what to do with modes that seem to be interacting, or other problems; remember, it is easy to be conservative. Select the lowest bucking value (i.e., Pcr, Mcr) of all mode shapes which includes some characteristics of the mode of interest. This ensures a lowerbound elastic buckling response. However, this may be too conservative in some cases, and the challenge, often, is to do better than this and use judgment to determine a more appropriate (and typically higher) approximation.