Does bolting an angle to a C channel form a built up section

[McCarJ]

How an angle bolted staggered each 3' back to back to a C channel will act..
Knowing that
=============
the C Chacnnel is historic 1932 12"x25#
The Angle is a new angle that could be 6" x 4" x 3/8"
The C channel is simply supported with a span of 35'
The C Channel is lateraly unbrace except at the ends
The bottom of the C Channel is lateraly braced
The level of the bottom angle leg is only 3/8" higher than the level of the bottom flange of the C CHannel

Questions:
==========
How bolting the angle will affect the unbraced length of the C Channel?
Does both of them ( C & L ) will act as one unit (built up sec.) for resisting the moment, or what ?
Should i put stiffeners for the C channel to brace the torsional buckling, and what about the lateral buckling of the top compression Flange

Thanks in advance

 

[JAE]

Bolting them together can be done in such a way as to change the properties into a copmosite section where the angle and the channel work together.

It doesn't affect the unbraced length. It may affect how resistant the combined shape is to lateral torsional buckling. If you don't understand these concepts, you should find a structural engineer who does.

 

[desertfox]

Hi McCarj

Bolting on the angle will possibly affect how the channel acts under its normal loading 2 questions

1/ what is the loading?

2/ why have you bolted the angle on?

regards

desertfox

 

[StephenA]

If the moment is increasing, it is likely that the shear force will as well.

The bolting will cause the two to act together if the horizontal shear can be taken through the bolting arrangement, but for that you may well need HSFG bolts.

Stephen Argles
Land & Marine

http://www.landandmarine.com

 

[miecz]

How is the bottom (tension flange?) of the channel braced?

A C12x25 with an unbraced length of 35 feet won't carry much force before it buckles, unless it is stiffening a large rectangular duct for internal pressure. Is this a duct stiffener?

 

[Zhuge]

It won't change the unbraced length. To reduce the unbraced lenght, you need to restraint the compression flange frome any rotation.

 

[McCarJ]

The bottom (tension Flange) of the C channel is braced each 8’ by nodel angles (from one side only)

I thought adding transverse stiffener to the C channel (from one side only )will increase the resistance to tensional buckling

 

[JAE]

Stiffners will only help resist lateral torsional buckling if they are also attached to something else (besides the member itself) where the stiffner can act to resist the lateral translation of the compression flange.

 

[miecz]

Adding an angle near the tension flange will move the neutral axis away from the compression flange, making the composite section more susceptible to bucking than the channel acting alone. You would be better to add material near the compression flange. In either case, you need to recalculate buckling properties. I assume your statement about "tensional buckling" was a typo.