Brace connection using clevis and pin

[Nitesh Sadashiva]

Hello,

In one of the project for which I am doing connection engineering, there was a brace with Clevis detail at the end connection as shown in the below sketch.

The specified design force was 20 kips. After discussion with the fabricator, We changed the connection to use end plate and two fork plates as shown in the below sketch.

In approval return of shop drawing, EOR has commented as shown in below sketch. I am not understanding the EOR comment. Can anyone help me on this?

 

[human909]

That comment seems pretty crystal clear to me. And I'd expect it to be pretty clear to structural engineer especially somebody involved in designing and modifying previously designed connections.

If it isn't clear to you and you can not follow that design process I suggest you listen to to EOR and PROVIDE CONNECTION AS DETAILED IN STRUCTURAL DRAWINGS.

 

[Nitesh Sadashiva]

@Human909: Do you mind elaborating what is the intent of this? So, that I can take care in future. Here the brace is an axial member specified with the axial force and I believe it as Tie member. Why the gusset has to be designed for the max plastic moment of the member?

 

[DrZoidberWoop]

I don't like it when EORs give circuitous responses like these. They are obviously trying to make you conform to their original connection concept. Maybe give the EOR a phone call to discuss their design intent and squash the matter quickly and cheaply, without additional back-and-forth paperwork?

 

[WinelandV]

I use double bolt connections on angle to gussets all the time, only checking the assembly for the axial load from the brace. But... there is not much appreciable rotation at the joint (my joints are in a trussed tower scenario).

If this strut needs to be able to rotate a few degrees, then the (2) bolt connection will generate some not so fun forces as the strut tries to rotate.

Why are you unable to provide the clevis and padeye?

Please note that is a "v" (as in Violin) not a "y".

 

[phamENG]

We're not mind readers any more than you are - to know the EOR's intent, call the EOR.

 

[JLNJ]

Sounds like the EOR intended to allow for some rotation of the tension member about the clevis attachment. The proposed two-bolt connection does not allow for any rotation.

 

[Enable]

I agree with human909 that this is pretty clear but I also agree with phamENG & DrZoid that a phone call might help smooth things over in terms of allowing for alternative configurations. Seems like they'd like to allow for rotation and a two bolt connection limits that ability; may not be enough to matter but you'd need to get that out of the EOR. To me their response indicates they don't want to think that hard about it and just wanted to ensure that somehow this thing would work (hence matching plastic moment capacity of brace). If they're not being paid a considerable sum I don't blame them, to be honest.

As an aside, I dislike what is happening here for another reason and that is that the connection was pretty much specified on the original drawings. They give you gusset sizes, dimensions, specific interface welds, etc. Most of the pertinent connection information is there (other than loads) and I absolutely hate it when an EOR gives me a connection to "design" or stamp where they've already given me the configuration; that's basically asking you to plan stamp their design, and what's worse is when they do this (in my experience) they usually dont include loads so you cant even do a proper double check! If they do this they should take responsibility for the connection. EDIT - Of course you can back-calculate the design based on the configuration and then put that on your drawings, but man is this ever a waste of time (since the EOR should already have computed a capacity by stipulating such and such configuration with such and such welds / details). Though they actually gave the design force in this case, which was nice of them.

 

[271828]

Seems pretty clear to me. The EOR thinks their connection would have concentrically loaded welds and no moment at the gusset-to-beam interface. They think you changed the connection so the welds will be eccentrically loaded and there will be a moment at the gusset-to-beam interface.

The plastic moment of the HSS3x0.203 should be small, so I'd just modify the calcs to show that the gusset and welds still work.

The EOR must know that this is silly. My paranoid hunch is you're being spanked for not using their detail. LOL

 

[Brad805]

Where did the web stiffener go? You annoyed the EOR. One or two changes, ok, but you basically did your own thing. Did anyone ask about making the change before hand or sending an RFI?

 

[BridgeSmith]

Without seeing the bigger picture, there's no way for us to know how much rotation of the joint is required or may occur, so we don't know whether the EOR's request is frivolous or necessary.

In any case, if you don't know why the EOR is asking for this, a call to him or her may be in order. If you don't understand how to do what the EOR is asking, you're in over your head. If you don't understand what the EOR is asking you to do, you're in way over your head.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[271828]

Regarding sending an RFI to ask for permission to change the connection:

As Enable mentioned above, these almost designed connections are problematic.

I spent a couple of days this week on one of these. The EOR showed a configuration that's intended to be the "general concept," but it won't work. I changed the configuration to something that will work, and we're going to ask for permission in an RFI. It's pretty likely the response will take so long that the fabricator will roll the dice and tell the detailer to model what I came up with. Then we cross our fingers the EOR won't reject it.

The timeframe for this kind of work is very short, often in days, not weeks or months. To ask permission would only work if we could get the RFI answer back very quickly.

 

[Nitesh Sadashiva]

Hello all,

Thanks for your responses. I am checking with EOR and changing the connection to clevis arrangement shown in the design drawings. Initially we RFI'd this modification. However, due to the time frame, fabricator confirmed this modification and asked as to place verify note in the shop drawing. Unfortunately, this is how the system works. Also, connection is delegated to us. When the forces are given in design drawing, we may have to change couple of connections to fabricator friendly connections which will be economical. For example, in the EOR given detail, stiffener has been shown in the beam web. But for the specified force, stiffener is not required. Beam has adequate capacity locally without the stiffener. If we are to confirm these modifications in an RFI, we will not get a quick response from EOR. But to keep the project moving, we need to proceed with verify notes in shop drawing. This is what happened in this project. However, I will consider it as lesson learnt.