Truss Moment of Inertia

[slickdeals]

Folks,
Do you have any formulae for truss moment of inertia / deflection etc.

I have been using I = Area of chord * 2 * (dist. to NA)^2. and once I get the I, I use it in beam formulae for deflection.

Thanks

 

[csd72]

Jike interpreted the meaning of my comment exactly.

I used the term shear to continue with the beam analogy.

If you think of the truss as a single beam member then it has a shear and a bending moment (overall).

If you think of it as a series of members then the shear becomes axial load in the diagonals and verticals and the bending becomes axial load in the chords.

 

[civeng80]

I may be seeing this simplistically but if you use virtual work, no moment of inertia would need to be worked out and no reduction of it to account for shear deformation would be necessary.

Now if you have a structural analysis program you would analyse for member actions and also obtain node diplacements right? No need to use reductions for shear defs or moment of inertia right.

Slickdeals are you trying to do a quick and conservative calculation?

If you are it would be interesting to compare this to the more accurate one done by a full structural analysis.

Ciao!

 

[slickdeals]

Guys,
I have done a few test runs with trusses of different L/D ratios and I find that a 14-18% reduction will need to be applied for a truss to account for web deformations.

The reason I started this exercise was to account for composite action of the top chord of the truss. Hence, to account for amplification factors, I started studying the truss MOI.

Thanks for all your responses.