Small beam splice

[BigBakwas77]

thread507-51453
I have to design a splice for a C6 purlin which was cut to accommodate the installation of a new equipment and now has to be replaced. The cut was at 0.2L distance from both supports. I am getting moment of 4.7 kN.m and shear of 4.7 kN. The splice shall be a 3/8" thk x 4" plate welded to the web of the new C6 and bolted with 2-3/4" A325 bolts to the C6 left on the structure. How do I go about checking this as a moment connection?

 

[KootK]

I'd be inclined to treat that as a shear only splice as I suspect that its behavior will tend towards that. As a moment connection, you'd analyze the bolts as an eccentric bolt group. Whatever you do, keep any eye on lateral & torsional stability at the joint.

 

[BridgeSmith]

Is this purlin continuous over the adjacent supports, or is it a simple span between the supports? If the purlin is not continuous over both of the adjacent supports, the connections will have to carry the moment at the splice, which will produce a force couple on the bolts, or possibly between the bolts and the top flange, if the ends of the top flanges are close enough to bear against each other before the bolts reach their extreme positions in the holes. You may need to sketch the splice with the channels rotated to see whether the top flanges come together before the top bolt comes up against the side of its hole. That will tell you whether your moment arm is from the bottom bolt to the top flange or only center to center of the bolts.

If it doesn't interfere with its function, you'll get a much better moment connection (stronger w/ less deflection) if you splice the flanges instead of the web.



Rod Smith, P.E., The artist formerly known as HotRod10

 

[BigBakwas77]

KootK/BridgeSmith,
Thank you for your response. I have already asked the contractor to make sure that the new member is fitted tight to the existing ones. I have done beam splice connection before but with two flange plates (top and bottom) to resist moment and two on the web to resist shear. But this one is so lightly loaded that I thought single web plate should be adequate.
BTW, this is a single span, simply supported ridge purlin. (they are actually two of them at the ridge.)