Section Modulus

[lotoo123]

All things being equal, for dynamic loaded beams, which is stronger-larger section modulus- steel I beam or seel C section, as it applies to steel frames on over the road heavy duty trailers.

 

[rb1957]

i think the I-beam has the advantage of being symmetrical, but the C-channel is easier to work with (having a flat face to join with other structure.

 

[GBor]

For the strong axis, the properties are identical, but locally, you would have flange bending in the C section before you would have it in the I beam. For the weak axis, the centroid is still located at the center of the section, but for the C section, it moves to the side of the web. Depending on your loading, one may be more useful than the other...

Garland E. Borowski, PE
Engineering Manager
Star Aviation

 

[tstanley]

Usually in a heavy duty trailer application weight is an issue, so the I beam is a more effecient section. That is, for equivalent section modulus, the I beam is lighter.

The attachment of the cross-members isn't usually an issue because they are set down for the decking and are welded to the web of the mainrail I beams.

The analysis of trailer frames is why I became interested in FEA many years ago.

Tom Stanley

 

[GregLocock]

Is torsional stiffness at all important?

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[tstanley]

Actually, it needs to be torsionally flexible to accomodate the variations in the road surface. If it's too stiff, then the welds between the crossmembers and the web of the mail rail will start to crack.

Tom Stanley