WT Bracing 1

[CCCCDDDD]

I was wondering which way people orientate the WT bracing.
With stem of WT vertical or horizontal?

https://files.engineering.com/getfi...-472b-42cb-947d-9e57b779f403&file=Capture.JPG

 

[cliff234]

It's not necessarily the orientation of the WT that is an issue, but the means by which the WT is connected at each end. Bolting the WT flange to the gusset plate makes for an easier (less expensive) connection. Also, since most of the area of the WT is in the flange, there is more load in the flange and there is a more direct load path from the WT to the gusset plate if the flange is bolted to the gusset plate. (The load does not have to leave the flange, go into the web, and then go into the gusset plate.)

 

[CCCCDDDD]

Bolting to the flange also makes since to me.
Just that I am seeing the new generation of engineers bolting to the stem which causes them to have to strip flange at the gusset plate.
Even AISC only gives a bolt gage for the flange not the stem.

 

[mtu1972]

If I ever used WT’s as bracing it would have been as X braces, so bolting to the flange would allow a plate to connect the two members at their intersection point.

gjc

 

[cliff234]

Craig D - Many in the "new generation of engineers" are not thinking about the connections. Many are solely focused on modeling - and they are not considering that just because a structure can be modeled, does not mean it can be economically constructed. I refer to these engineers as living in "model world". They are not thinking about the connections because they are not taught connection design in school, and the importance of considering constructability. (It boggles my mind that when we hire new graduates fresh out of school with BS degrees, most don't know what an A325 bolt is, and none of them know how to design a fillet weld.)

 

[phamENG]

As one of the "younger generation," I'll also say that the practice of delegating connection design doesn't help. As an EIT, I would get in trouble if my boss found evidence that I had been considering connection geometry too closely - they'd say that's why we delegate it, there's no fee for that, etc.. Delegated design has always left a bad taste in my mouth, and it always seemed like it took longer for me to review and understand a delegated submittal than it did to do the design from the beginning. It makes sense in some cases - truss design, for example - but connections, stud walls, etc. should be done by the EOR. Sorry - I'll stop ranting.

 

[JLNJ]

I feel your pain phamENG. Knowing which way a brace you specified is oriented should not be "considering the connection geometry too closely".

For example, if it's an X-brace, was the engineer's intent to cut the braces and intersect them or let the braces pass by flange to flange? And a tee connected to the flange might have a 1 1/2" eccentricity while the stem connection has double the amount.

I sit next to some steel detailers and they are forever complaining about connections not thought through and lack of indication of the engineer's intent. When they get a thorough, graceful design, they are thrilled.

 

[cliff234]

phamENG - Welcome to the profession!

Read AISC 303-16, the latest AISC “Code of Standard Practice”. Specifically, read Section 3. (It’s only a few pages.) If you have a 15th Edition AISC Manual of Steel Construction, you have AISC 303-16. If you don’t have the 15th Edition, you can download the COSP for free from the AISC website. You might want to show your boss this document. There have been some huge clarifications to the COSP since earlier editions. Two important points... First, there is more to delegating connection design than just delegating connection design. Second, if an EOR is involved in project where connection design was delegated, and where there was a connection failure, the EOR bears ultimate responsibility for that connection. Like it or not, that’s what it says (indirectly) in the COSP. There are articles and webinars available (at no cost to AISC members) on the AISC website that explain more. As more cities and jurisdictions adopt IBC 2018 (which references the 15th Edition AISC Manual, and AISC 303-16) it will become more and more important for EOR’s to understand the issues related to delegation of connection design, and the responsibilities of the EOR when doing so.

 

[phamENG]

cliff234 - thanks. I have it and I have read it (several times). I haven't been around long by the measure of many of our colleagues here, but I do have my license and have pushed back considerably on the prevailing mindset I've encountered regarding design delegation. My jurisdiction(s) are only just now coming to the 2015 IBC, so I have a ways to go before I have to update my references.

 

[JoshPlumSE]

Bo Dowswell and Allen Brice had an MSC article on WT horizontal bracing a few years ago. I found it to be helpful over the years. For what it's worth, I have always connected to the flange for WT braces. Even for vertical bracing.

https://www.aisc.org/globalassets/modern-steel/steelwise/072010_july10_steelwise_web.pdf

 

[cliff234]

phamENG - Just to clarify, just because your work might now be dictated by AISC 303-10, the fundamentals of AISC 303-10 are the same as those in AISC 303-16. AISC 303-16 added greater clarity to issues around delegation of connection design. COSP Commentary Section 4.4.1 states, "The owner's designated representative for design has thus retained responsibility for the adequacy and safety of the entire structure since at least the 1927 edition of this Code". The bottom line is this: The EOR is ultimately responsible for the safe design of all connections even when delegating connection design to a connection design engineer working for the fabricator.

 

[phamENG]

cliff - I agree wholeheartedly, both in the technical reading of the COSP and in the spirit of it. I am wholly responsible for all aspects of the structural design of a building or non-building structure to which I affix my seal, end of story. If I take advantage of the expertise of a specialist, or direct the contractor to do the same, I don't give that away. I still have to ensure all of the pieces of the puzzle fit together. Thank you for your insights.

 

[canwesteng]

On topic - usually I use WT for horizontal bracing, stem points down, connect to the flange. Very clean connection and easy to construct, which more than offsets the added steel you need to make up for the eccentricity between centre of load and shear centre.

 

[ldeem]

A little off topic but I recently did a design where I had several WT horizontal and vertical braces. During pre-bid meeting a fabricator told me WT's are hard to get and hard to get straight for use in braces. Cost wise they preferred double angles.

 

[canwesteng]

Are you in north America?

 

[CCCCDDDD]

I am in America.
Right now I am dealing with vertical bracing

 

[azcats]

Are WT sections actually made by mills? Or do fabricators end up fabricating them by splitting WF sections?

At my last job we had some one-off uses for WT sections and the fabricator made them by splitting beams. I have a video of one when they made the final cut after stitch cutting the web and the stresses released were significant. And it was nowhere near straight. Had to send out for straightening before getting back to fab the assembly.

 

[KootK]

Or do fabricators end up fabricating them by splitting WF sections?

That one in my experience. I have fabricators tell me that they prefer to just weld them out of plates rather than cut them from I-section. Perhaps it depends on the quantity.

Consider playing chess with me on the Social Chess app at iTunes. Same handle. Fear not, I suck.

 

[ldeem]

I am in southern Ohio and in this area WT's are cut from beams.