How far to stay away from criticial welds

[PEN1460]

When we fabricate our buildings we drill weep holes near the base plates and cap plates. I drill 1/4" weep holes and keep my holes 1" from all welds. I have not found any rule stating how far I have to stay away from welds, but I was just told to stay away from critical welds. I work with built up members so I consider the web to flange weld to be a critical weld. I feel like this should have been an easy subject to research but I'm not finding anything. I've looked in the AISC 16, and D1.1 but I must be looking over something.

 

[phamENG]

I'm not sure of a hard and fast rule either, but you may be able to do a modified yield line analysis to help envision the stress in the plate at failure - put your hole in the lowest stress region you can. There are a couple threads here with some example calcs - this is just an idea and I haven't thought through it far enough to know how useful it may be. Or, you could do a FEM and determine the actual impact of the hole on stress in the plate and see if it causes any problems. Run a handful of scenarios for your typical building(s) and develop a set of rules for yourself - with clear definition of what may change those rules so you don't inadvertently put a hole in the wrong spot on a unique job.

From the sound of it, you may be a PEMB designer - is that true? If so, you may be able to bring some balance to a few on-going conversations about standard practices from Metal Building groups out there...

 

[JStructsteel]

If you are 1" away from welds, doe that mean you allow 1" water at bottom of all columns?

 

[PEN1460]

phamENG:
Yes I am a PEMB designer. I'm fairly new to all this so I don't know how much knowledge I can bring to the table. I work at a firm that doesn't have a licensed engineer, so all my stuff has to be outsourced (Yes I called my state engineering board to ask them if what I am doing is legal and they said it was, I just have to jump through a BUNCH of loops). I have 2 engineers that review my material and give me feedback to improve my designs. However, I've noticed that they sometimes contradict one another, so I'm just trying to get more exposure on what other engineers do. I was thinking about doing a FEM analysis on it to see how it impacts the welds, I just wanted to see if maybe someone did some research on hole size to hole location.

jrisebo:

I've attached an image showing what I mean. We're stacking the columns/rafters on top of each other so if I have a 6" flange and a 14" deep column, that is a lot of water weight that only evaporation can take care of.

 

[phamENG]

For that application, I'd take a look at "Protected Zones" for Special and Intermediate moment frames in AISC 341. They're intended to protect critical connections in a Seismic Force Resisting System from exactly what you're doing. Meet those, and you're not likely to have issues.

 

[KootK]

I'd be inclined not to worry about hole proximity for most applications where you've got:

- low ductility requirements.
- weld capacity well above requirements.
- no particularly demanding fatigue requirements.

 

[kingnero]

To add to KootK's remarks:
if you have the possibility to access the holes from both sides, consider adding a small chamfer to both ends of the hole. Cracks often emerge from sharp edges.
Doesn't really help when working with low quality steel (235 MPa), but is often beneficial when steel grades go up (355 and higher).

 

[dhengr]

PEN1460:
Given your sketch and the assumption that storage or transit are the primary concerns as regards water intake and drainage, why isn’t the hole at mid face width, top and bot., and at mid column length where the deflected low spot will likely be? The column stresses probably aren’t too bad there either. And, .25” dia. is pretty small as the face pl. gets to be any thickness at all. They fill with junk and surface tension prevents them from acting. Then, I’d put another weep hole down near the base pl. too, for when the column is standing in place. Yes, you should stay away from ‘critical welds,’ but exactly what does that mean? Put the drain hole where you need it, but preferably at/near the least stressed weld of that joint. I wouldn’t drill right through the weld, or its root, or right at the toe of the weld, but unless you have some fatigue or fracture issue to consider, I wouldn’t worry much beyond that. It probably is a good idea to debur the drill hole edges a bit. Many times we see stitch welding, and all those starts and stops can’t be less critical than your drill hole. It seems to me that I’ve even seen the drain hole at the base plate made with a ‘mouse hole,’ an upside down “U” shape in the column face pl., with the base pl. weld stopping short of the hole on both sides, placed in the least stressed location, of course. That hole is a bit of a stress raiser, so pay some attention to the direction and magnitude of the stresses around the hole.

 

[PEN1460]

dhengr:
I don't have to have holes in the middle of my columns. I'd rather have them off to the side and in the corner so they're not really visible when they're set in place. These weep holes are only for the contractor benefit when they leave the frames laying on their sides on the job site. Only benefit these holes provide is draining the columns/rafters if it rains the night before so they don't have water splashing everywhere when they start erecting the building. It's a pretty useless concept but we have a fiber laser that cuts this stuff pretty quickly so anything we can do to make the contractors happy is a plus.

When I use to erect buildings, I'd place the columns/rafters in a way where water doesn't pile up, but my boss wants this cause he saw another building manufacture do this, so here I am!!!