Set Modifiers In ETABS

[djzzz]

Dear All,
In ETABS while assigning the frame section we give certain values in SET Modifiers option. Especially for torsional constant, Moment of inertia abt 2 axis, Moment of inertia abt 3 axis.
On what basis do we give these values. For eg if am using a Column of size 200x600mm what will be the Set modifiers that I have to give? please help me guys...

 

[asixth]

I generally apply 0.7 to M2, M3 and T (M1). A 200x600 column probably would only attract a small torsional moment which would not be critical to the design.

 

[djzzz]

thank you asixth.... But can you tell me why do u take that value or how did u get at that value... Its for my knowledge

 

[asixth]

Codes normally suggest 0.7 modifier for compression elements and 0.35 for flexural elements. I have not found too many suggestions for torsional multipliers except in the Australian bridge code which suggests as low as 0.1. Depends on how everything is meshed. I only use ETAB's for lateral analysis in which I keep the mesh for the floor slab very coarse (2-3 meters) using shell elements so there is never much torsion which get's put into the column.

I have found that unless it is an equilibrium torsion than the column element will not be too sensitive to variations in the torsion modifier.

 

[johnbridge231]

That fact gets interesting when it's about shell elements (walls).

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html