Cheap stud rails 1

[milkshakelake]

I calculated 12 different stud rails on a 9 story concrete project where almost every floor is different and floor openings are moving all over the place. Is it cheaper to reduce the amount of designs (such as number of shear studs and spacing, and maybe minimize it to 1-4 different worst case conditions) or have these 12 different designs?

 

[KootK]

I think that it's wise to condense although 12 isn't terrible for a larger building. I like to be in the six to eight range for most projects. But, then, sometimes drastic times call for drastic measures. Sometimes, if there's an opening near to a column, I'll treat it as truly three sided punching shear even if it isn't just to condense the stud rail designs. Dealing with a bunch of different slab depths also complicates matters and adds more designs unless you're willing to let one pattern apply to multiple depths.

 

[hokie66]

Has there been further research on stud rails, or are designers just blindly plowing ahead?

thread507-306324

 

[KootK]

In North America, I believe that codes have been updated to ensure that a compatible amount of flexural slab steel gets installed into these joints such that shear behavior is more reliable. I'd have to go googling for the exact details of the research findings etc.

 

[milkshakelake]

@KootK Thanks! Will do and reduce the number of designs. The problems did mostly occur near large openings, which I treat as 2 or 3 sided, and most slabs are the same depth.

@hokie66 I'm not sure. Hopefully someone else can chime in. I have talked to two engineers about it. One said to add (2)#5 hooks in columns in all corners and the other said to overdesign the top reinforcement where there could be a problem, so I'm doing both in addition to stud rails. This isn't specifically related to stud rails but I read a case study a while ago where there was a parking garage collapse due to punching shear failure. One of the points raised was that the 90 degrees hooked dowels were present but didn't have enough embedment. So they weren't able to hang onto the slab in the sudden failure. I believe it was the report below, but I'm not sure because the case study costs money and somehow I didn't bother to save it onto my computer.

https://ascelibrary.org/doi/10.1061..., the,slab (composite) concrete construction.

 

[bookowski]

Studrails in ny are only about $75 - $100 per column (assuming 9 rails), refining the number of studs and rails is microscopic savings. Reduce it to a few types or as few as reasonable. It will be much easier to keep track of and inspect. Make sure you get shop drawings for them, and yes it's ok for them to go in upside down.

The tropicana collapse had nothing to do with punching. Note that nyc has integrity requirements beyond aci, in theory those should help if things go south. As to the top steel, there are some provisions for adjusting the gamma f and v proportions based on adjustments in your flexural steel, but that's starting to push the boundaries a bit if you need to use that to make it work.

 

[milkshakelake]

@bookowski That's very helpful and thank you for giving realistic prices. This will help the design. I will just overdesign in this case and look into the NYC adjustment provisions.

 

[structuralCADspecialist]

In North America, I believe that codes have been updated to ensure that a compatible amount of flexural slab steel gets installed into these joints such that shear behavior is more reliable. I'd have to go googling for the exact details of the research findings etc.

Rebar congestion is becoming a problem. And I see what seems to be highly varying amounts of integrity steel even with the same loads/spans/etc... I've seen some pretty gnarly looking designs lately. I only know of one punching shear failure however. But interested to see what the deal is with a building in my province that has had it's occupancy permit revoked.