Connection Design
Connection Design
(OP)
Hello,
I have what seems like a simple question, but it has been bothering me for sometime.
The question, is it a always a safe approach, if I design a beam assuming it is simply supported on both ends, but then provide an end connection which is stronger(thicker plate/larger weld size/weld the flange) then what is required per AISC calculation for simple supports. I understand that the end connection will try to prevent rotation and develop moments. Can that end connection fail because of this additional moment loading which it was not specifically designed for ?
Thanks,
Vick Nand
I have what seems like a simple question, but it has been bothering me for sometime.
The question, is it a always a safe approach, if I design a beam assuming it is simply supported on both ends, but then provide an end connection which is stronger(thicker plate/larger weld size/weld the flange) then what is required per AISC calculation for simple supports. I understand that the end connection will try to prevent rotation and develop moments. Can that end connection fail because of this additional moment loading which it was not specifically designed for ?
Thanks,
Vick Nand






RE: Connection Design
A beam is usually a section made to support moments. It has flanges which have the majority of its cross sectional area. A connection is typically two thin plates (angles) oriented in a way that their moment stiffness and capacity are limited. They're made to be stiff in shear. Now you still have to worry about a small moment if the beam is coped excessively, but in a normal simple supported beam, the moment at the connection is ignored.
RE: Connection Design
RE: Connection Design
In Table - II Pg 21, they have summarized the results. What is worrisome is the fact that the shear carrying capacity in the connection fall below their design values in presence of the additional bending moments.
In light of these results, what are your thoughts on beam connection design? Does is it mean that making the joints stronger (by adding more weld) on the simply supported beam ends is not safe ? This just sounds so counter-intuitive.
Thanks
Vick Nand
PS : @ukengineer: Just read the paper, it is interesting, but he makes everything sound so simple.
RE: Connection Design
Not very likely to produce a true simple connection, but I wouldn't want to provide excessive rotational restraint when it wasn't designed for that.
RE: Connection Design
I haven't read the paper, but does the shear capacity fall below its design value, or is it just inadequate to develop the moments that the connection could attract? That is, fixity at the beam end could result in higher shear at that end, and while the connection might have the bending capacity it might not have the shear capacity. But I'm having a hard time understanding how the shear capacity could actually drop below the intended, simple-span load that it was designed for. If you feel the need to create fixity at a beam end, you should analyze it with that fixity to see what it does to your reactions. I'm guessing that's what the report means, but I have been wrong before.
RE: Connection Design
I agree with grant. Are these problems with real life capacities or when tested to limits, do the moments start to contribute to failure?
I don't think we've been lucky all these years. Connections are recognized as the "weak link" in steel design and are conservatively designed.
RE: Connection Design
RE: Connection Design
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Providing fabrication and erection efficient structural design of connections. Consulting services for structural welding and bolting.
RE: Connection Design
In some cases, when I design my beams (typically a structural angle, or square tubing) as fixed beams, I get very high end moments and it requires lot of welding hours to weld the end connection. Steel being cheaper, I thought, would it possible, to design my beams as simple supported, calculate the end reaction loads, and then find out the minimum weld size required to carry those loads and then add some extra, just for conservatism. The flexibility of end connection for the beams that I deal with, is not documented in AISC. So, I do not know, how to provide flexibility at the end connection, so as not to overly constrain it and result in an end connection failure.
Thanks
Vick Nand