What is the purpose of end plates when connecting beams together?

Question

Quite often this kind of arrangement can be seen when beams are connected together. A rectangular plate is welded into a beam, and the plate is bolted to the other beam. I suppose one purpose would be simply that bolting is easier to do in some cases at the site rather than welding the beams together directly at construction site, but is there any other purpose?
I remember once hearing this kind of plate refered to as a moment plate, but I couldn't really find much information on such a thing. Is there some kind of moment-related purpose for this plate or am I just remembering wrong?

kamran · Accepted Answer

You are right. It is easier to do a weld under the specified heat and approved specs in a shop likely by a robot and get the welds pre approved by the authority in charge as a large batch. As opposed to having to pay a license welder and a authorized weld inspector.
Bolts could be torqued  by automatic torque wrench easily on the job site.
This saves time, money.

Lee Sam · Answer

Welding a beam to a column can deform the column at its bending axis.
The axial load on a steel column is determined by multiplying the moment by a bending factor. The bending factor is the area of the cross section divided by the section modulus.
These factors are tabulated in the AISC Manual for the x and y axis.
When a portion of that cross section is modified by welding, the column is no longer as strong.

What is the purpose of end plates when connecting beams together?

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