Reduction in gross area for bolted flange plates in moment splice of channels

[EngDM]

Hello,

I am being asked to design a connection to splice a channel at midspan so that they can get the channel into the space (for a reno). They are requesting bolted connections to avoid welding in a combustible space.

By adding a row of bolts to develop the full strength of the channel, I am essentially reducing the gross area in tension and compression of the channel. In compression I don't see any real issue since it will transfer thru the bolt, but the tension flange is losing quite a bit of area. Not to mention the shear lag reducing my bolts even more, and requiring more bolts.

By adding this connection it seems to me that I am reducing the capacity of the channel by a lot.

I really would prefer to do welded flanges and a shear web bolted plate.

Has anyone here dreamed up a full capacity splice for channels before? My Tf/Cf for full strength is like 365kN...

 

[human909]

Under the code I use (AS4100) and there is reasonable chance that your code is similar, bolt holes (unless they reduce the flange area quite significantly) don't reduce capacity. The AS code below allows for the local area around the holes to under go some yielding and relies on ultimate tensile strength of the small are of flange around holes.

But a full strength bolt splice is can be difficult and there are other issues like deflection. Unless you design the bolts as slip critical you should expect a certain amount of movement in your joint before it engages the bolts in bearing and then further rotation as that bolted bearing is properly engaged.

Has anyone here dreamed up a full capacity splice for channels before? My Tf/Cf for full strength is like 365kN...

Keep you plates thick and long, your bolts many (and small if necessary to minimise flange reduction) and you should be able to get there.**


**Depends on your approach to the connection design. A quick check of the design guide that I use assumes all the moment resistance is found within the flange. Whereas at full member capacity some moment resistance is actually performed by the web. Thus using THAT specific connection design you are never going to reach full member capacity due to an conservative assumption that differs from the assumptions made in calculating member capacity.

 

[271828]

How are you commuting the strength? Seems like flexural rupture per F13 applies. Rupture might not apply especially if the channels are A36.