Channel splice welded with another channel 1

[PSSC]

I had a bolted beam splice (channel), however due to things moving the bolted connection has to be removed.
My first option would be to simply weld flanges together in the field with a welded splice plate on the web.
For safety and other reasons I do not believe it would be possible to weld the bottom (tension) flange in the field.
My next option is to weld a smaller in height but equally strong channel to the backside of the original channel, basically a MC10 welded to the back of a C12.
The connection has to resist moment and shear but is braced at the center.

My real points of concern are two things
1, with a 1" gap above and below between the two channels flanges does the force transfer well from the C12 to the MC10? I had though of putting end cap plates on the ends of the MC10 that would extend to the edges of the C12. This is maybe overkill.

2, the weld, I have looked at this a few ways, I would rather just design the connection to handle the entire allowable moment for the C12. I have ran the weld calcs a few different ways, as a rectangle with the moment in the center and as two "C" shaped welds, these turn out to be the same thing after ran the numbers and actually looked at it.

Does anyone have any suggestion on the how to look at this weld or any other insight?

I have tried to attach a sketch.

thanks

 

[PSSC]

The end plates were in my mind to help transfer the load from the C12 flanges to the MC10 flanges. It might not really work that way but that was my thought process.

 

[KootK]

Ok this has always confused me, if there was a simply supported beam with a moment at the center, the reaction at each side would be equal and opposite but you wouldn't ignore what the other reaction was doing. You don't just assume the moment is going one direction.

This is how I see the statics of this at the splice ignoring the shear.

 

[PSSC]

That does make sense, but it still seems to go against the reactions at either end.
The reactions then would be M/(L/2) instead of M/L, I am less arguing than trying to align these two thoughts in my head.

 

[KootK]

The reactions then would be M/(L/2) instead of M/L, I am less arguing than trying to align these two thoughts in my head.

Civilized argument is constructive and no cause for offence for anybody with a well adjusted ego. Don't you worry about me.

1) First, we need to understand the applied load that you're considering when doing the M/L thing. You can't do it properly without that piece.

2) I'm going to assume that you mean to suggest a load case where a single, mid-span point load creates [M]. In that case:

P = 4 x M / L

R = 2 x M / L = M / (L/2)

I this case M/L would overestimate your reactions by a factor of two.

 

[PSSC]

No I was thinking about a case of a moment applied at the center of a simply supported beam.
I see what you are describing, then the reactions are force/2, the force equally divided between the two supports.
For "M" as a moment in the center of a simply supported beam then R1 = R2 = M/L, but if I think of the moment as transferring fully to each side then the length to the support would be half of the total length so R1 = R2 = M/(L/2)

 

[PSSC]

As I look at what you are saying it makes sense that the moment is a result of a load, not just a random moment in the center of a beam. if there was a small gap in the weld it would be two "C" shapes of weld on each side,and in order to stay in equilibrium there would have to be equal and opposite moments at that point.
What you are describing initially looked more like a cantilevered beam with a moment on the end to me.

 

[KootK]

No I was thinking about a case of a moment applied at the center of a simply supported beam.

In that case M/L would be correct as would M/2 on the welds. Is that really your load case? If so, I wouldn't actually consider this joint a splice in the conventional sense. Just load sharing on two 1/2 beam segments.

 

[KootK]

Ignore my latest, we simul-posted.

 

[PSSC]

Thanks for taking the time to help me on this.
I can actually brace the C12 at green dots fairly easily.
So I will do that along with extending the MC10 for a weld that handles the full moment on each side.

thanks again.

 

[KootK]

You're most welcome PSSC. Best of luck with your project.