Shear Studs Welding enquire 1

[tristan861]

Hello Guys…
I’m using shear studs for an embedded plates (Steel to pre cast concrete connections) but it happens that the beams have high moments end forces. So I have to use large diameter shear studs (up to 1’’ or more).

The problem here is they told me that the welding gun available in the shop can weld up to ¾’’ only. So for larger stud diameters they will use normal welding (maybe fillet I’m not sure).

So my question is: Is it ok to use other kinds of welding the diameter of studs other than the Nelson gun? Or is it like the gun guarantees full bonding between the plate and the studs?

And in case if it is not OK. What is my alternative option? I checked the capacity of the regular anchor rods in tension and its way less than the shear studs capacity. So it is not an option in my opinion.

Your help would be so much appreciated.

 

[KootK]

Normal welding is fine I think but some, appropriate AWS welding procedure and possibly testing should be followed.

I checked the capacity of the regular anchor rods in tension and its way less than the shear studs capacity. So it is not an option in my opinion.

In tension, you're almost always governed by the breakout capacity of the concrete rather the tension capacity of the anchor. Keep an eye on that.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Ron]

Shear studs are often welded by conventional welding. Some engineers actually prefer and specify it.

 

[SlideRuleEra]

Agree with Ron.
AISC "Modern Steel Construction" magazine has an article on how to properly specify weld studs for use with the drawn arc stud welding process in structural applications.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[hokie66]

No issue with welding the studs, but as KootK pointed out, the weak link will be the concrete. We haven't been given any information about the precast element involved, but prying forces are not something which concrete likes.

 

[tristan861]

Slide thanks for the article.
I know the anchorage checks (Breakout and Pullout) will govern but in my case the concrete failure is out of the company's scope. So my concern is only the Anchors capacity and the embedded plate of course. They are telling me to use regular bolts like (A325 or G8.8) as anchor rods instead of shear studs since they have higher tension capacity. Is that Okay?

As far as I know these bolts are intended for steel to steel connections only.. what's your thoughts guys?

 

[Ron]

Use shear studs. A325 bolts shouldn't be welded to plate for these applications. Since the concrete will fail first, you will not develop the full tensile strength of either a shear stud or an A325 bolt, so that argument is moot.

 

[hokie66]

Separating the responsibility for the tensile capacity of connectors from the ability of the concrete to accept that capacity is foolhardy.

If you have to use 1" shear studs to get the tensile capacity required, I can guarantee that the concrete will fail first.

You gave neither the thickness of the concrete or the length of the studs, so we are guessing at your detail.

There is a reason that shear studs are called "shear studs". They are for shear, and not for making moment connections of steel to concrete.

 

[tristan861]

Here is the detail; All notes are welcome

The concrete breakout fails at this detail but it will be sent to the concrete designer to make a special reinforcement since the concrete elements are not our scope.

Note: concrete column dimensions are (300x1000) mm and not (300x400) mm

 

[hokie66]

That is a ridiculous detail. You have to realize that steel and concrete are two very different materials. Expect the "concrete designer" to send this right back to you.

 

[Ron]

Agree with hokie66. The detail is absurd. This is an interaction failure waiting to happen.

 

[tristan861]

Well, calling this detail " ridiculous'' is disrespectful and will not help.

I thought this forum is about spreading the knowledge and helping each other!!

 

[dmoench01]

Tristan,

The forces are obviously substantial to warrant this many shear studs in your design. I guess my first concern is what are the forces that are going to this connection? At first blush, it seems impossible the concrete designer will be able to take these forces.

 

[chicopee]

My question is when DOT reviewed the detailed drawing, what were their comments? Also it is possible that upon acceptance by DOT for whatever reason, the life expectancy of the bridge might have been reduced.

 

[dik]

OP:

Insensitive stuff removed...

Sure hope you can get concrete and ties into the column; for the moment developed you will have a lot of reinforcing for the relatively small column.

Without compromising the strength of the wall column, you should be looking at a pinned end connection and design only for shear, or something of that ilk.

Dik

 

[JLNJ]

How did you determine the forces in the studs?

Just looking at it, I imagine the only studs which will activate (before the entire thing zips apart) are the rows of studs either side of the top and bottom flanges. I can't imagine that the other eight rows of studs do much at all, except to carry the small shear reaction.

Also, if you start sketching in the bars in the column (to scale) you will find things very, very congested. Taking 324 foot kips into that small column will require some pretty heavy reinforcement, leaving no room for your studs. For example, 1/2 the column width is 150mm. Subtract 80mm for the first stud spacing and 50mm for rebar cover leaves you 20mm. Subtract 1/2 the stud width leaves you 300/2-80-50-12= 8mm to place a rebar which probably wants to be a #10bar (32mm) or larger. It violates the time-space continuum.

The studs are too close together to fully activate each stud. Your grouping of studs 3 across will hardly have more capacity than a double row of studs, and placing the studs so close together vertically reduces the capacity of the individual studs significantly as well.

Depending on the seismic zone, you have other issues to consider, such whether the code even permits such a home-grown detail.

The welds appear to be just partial penetration - I would be tempted to provide full-pen welds no matter what the force.

It just doesn't look right. It looks like something someone drafted rather than engineered and designed.

 

[tristan861]

First, thanks for all the replies guys.

dmoench01:
I did not do neither the member Design nor the Concrete column design for this project. My responsibility is the steel to concrete connection only. And Yes the loads are huge on the member ends (Up to +1100 K.ft).


chicopee:
Nobody reviewed the details yet.

dik:
As far as I know, the columns are reinforced and have ties. but I don't know if a supplementary reinforcement will be adequate to this huge tensile loads on the concrete.

JLNJ:
I did the analysis using PROFIS (a software from Hilti), and all studs take some tension except for the bottom row, Check attached.
Yes. The studs are very close to each other but I had to use 3 studs per row to cover the tensile load that comes from the moment ( with minimum spacing vertically and horizontally). I know this will reduce the concrete capacity in Breakout but I'm restricted by the col. geometry. Another reason for putting the studs too close to each other is that the bearing capacity of the embedded plate reduces significantly when the cantilever length increases (Per Design Guide 1).

After all, it seems that I have to change the whole concept. this is not working!!
Maybe changing the columns to encased columns or just steel columns ? I don't know if its can be done.

 

[sandman21]

For such a large moment and connection your studs are way to short. ~6.25". Hilti assumes a rigid plate to distribute loads to anchors, with the thickness of the plate you have, ~1.18", that assumption should be called into question.

 

[tristan861]

Sansldman, you're definetly right the embedment length is too short.but thats the length available in the stock.
Like everybody said earlier, this detail will not work.:/

 

[JLNJ]

sandman is spot on.

Be careful when using Profis. A rigid base plate is not necessarily a conservative assumption for a case such as this.

I believe Profis just determines the resultant tension force location and proportions the bolt force based on distance from the resultant. Your forces might be double or triple those "calculated" by Profis.