Steel Connection Design

[PG35]

In ontario & michigan, we specify that connection design is to be carried out by the steel fabricator and/or engineer retained by the steel fabricator. This is common practise here.

Is this common everywhere in the US? Why don't the design engineers always do the connection design?

 

[Lion06]

It is common for us. We publish a reaction table showing the highest reaction for each depth beam, then let the fabricator pick his own connections. Part of the reason for this is to allow the shop the flexibility to use what works best for them. Different shops like different connections for different reasons. You won't know this during design and will likely get a request to change your connections.
We do require signed and sealed calculations for the connections.
It should be noted that this is only for simple shear connections. We design and document all unique connections.

 

[JKW05]

If it is a really basic steel frame with only a couple of different connection conditions, I tend to detail them. Otherwise, for the reasons StructuralEIT listed, I specify the fabricator is to produce the designs for shear connections. The only difference being that I list the reactions on the plan at each end of the beam.

 

[lkjh345]

We, as the EOR, show all connections on the design drawings. This is more the norm in our area of the country (Nebraska).

For basic shear connections, we have standard connection details with tables for how many bolts to use, tab plate lengths (or double angles), weld sizes and lengths, etc.

For non-standard connections, we provide full, unique, details as required.

A fabricator is free to propose different connections if they chose. We then require calculations to show that the proposed connection(s) meet or exceed the capacity of the connections we show on the design drawings.

FWIW, most of the projects in our area are either design-build or 'directed contractor'. So, for I would guess 80% of our work, we know who the steel fabricator will be when we start the deign. For most of the fabricators around here, we know what works best for their shop (becasue they have told us) so we design around their preferred connections if we can. If we have not worked with the fabricator before, we ask them what they prefer. For these reasons, we do not see many requests for connection changes.

Just our way of doing things that seems to work well for us.

 

[msquared48]

Not commom with me - leaves too much to chance. Plus, I am responsible for the connections too.

Mike McCann
McCann Engineering

 

[JAE]

We usually detail the connections - even the simple shear ones.

The argument that the fabricators have their "own" way of doing connections has some merit - but not much anymore. Most fabricators use the same bolt-to-bolt spacing (3") and same bolt-cover distance (1 1/2") and can provide single shear plate or double angle connections that don't really deviate from AISC's connection tables all that much.

Plus, most fabricators are getting more and more automated so they can many times plug in the bolt hole locations, clips, etc. without relying on some "standard" connection method.

Plus Plus: many fabricators don't have licensed engineers on staff anyway.

 

[Taro]

In the U.S., the west coast standard is for the Engineer of Record to design and detail all connections. East coast practice is to delegate some or all of the connections to the fabricator.

The west coast practice was dictated by the regional Uniform Building Code which mandated that all "connections which resist seismic forces shall be designed and detailed on the drawings". That leaves only the gravity connections which are fairly standard and can be handled with a few typical details and schedules. So all connections in the west were designed and detailed by the EOR and that practice continues today.

 

[Lion06]

I didn't mean that the fabricator's have their own way of doing things in terms of bolt spacings, etc. I meant that some prefer single shear tabs at columns, others prefer unstiffened seats.
On beam to girder connections it varies even more - some like double angles all bolted, some like double angles welded to supported beam and bolted to supporting beam, some like shear tabs, some like end plates.
Some of their preference has to do with complying with OSHA regulations during erection.

 

[JAE]

But I guess why would you delegate the most critical part of any structure (the connections) to someone else?

Jack Gilliam did that back in the 70's on the Hyatt Regency and look what happened.

 

[Lion06]

It is common practice on the east coast. Additionally, we get calcs submitted and each connection is verified during the shop drawing phase to ensure that it has adequate capacity.

 

[nutte]

JAE, I would disagree with your point that all fabricators do it the same way (not your exact words, just paraphrased). I perform connection design for fabricators, and they often have preferences over connection types. Some shops prefer all bolted connections, while some shops prefer shop welding when possible.

Your point about the most critical component being subbed out has merit, but our services are most often required on large, complex projects. As I've mentioned before, I also think most engineers performing overall building design have little experience, if any at all, designing complex connections.

As the engineer of record, we also design buildings, and on these projects, we don't have the budget to perform connection design. Lkjh345, how does your compeny account for this? Do you increase your fee to include connection design, or do you provide the same fee and assume design of the connections for nothing extra?

 

[rday]

My experience has been the same as Taro. The first structural office I worked in had senior guys from Cali and from Mass.

The Cali guy said detail all your own connections the Mass guy said schedule the loads and let the shop provide details for review.

I detail all my connections; it's my seal. The shop can submit revisions for review if they want something different.

 

[JKW05]

I should amend my previous post. As I said, on larger steel frames, I specify the fabricator is to handle the connections (yeah, I'm East Coast). What I didn't mention is that during the shop drawing review, I do verify the connection capacities against the reactions I show on the plans. On a very rare occasion, I have sent it back asking for an extra bolt or longer weld, requiring a resubmission of that detail. If there is resistance to change it, then I require sealed calculations for it. I guess my logic is that, I think in the end, the EOR is responsible.

I also do write in that the shops are to be prepared under the "supervision of a PE". I don't require them to be sealed, and I'm sure that 90% of the time this isn't done. But it does give me something to fall back on if there is resistance to changing a detail.

It saves me the detailing time, which would often be changed anyway, while still recognizing it's my call in the end.

 

[271828]

This is an interesting topic for me. Coming from the East Coast also, all the firms I worked for left simple shear connections up to the fabricator. I know for a fact that some of them we worked for liked shear tabs better while some liked single and double angles better. Like some here, however, I never really understood why non-engineers could be trusted with these designs. Near the end of my design career, I still made the fabricators do this, but I required that they provide sealed connection design calcs. The fabricator or detailer would then hire a connection design specialist to do these. My personal opinion is that's the best way to go. Most EOR types I know (but definitely not all) know about as much about connections as the detailers, so I don't see how it's an improvement for most of them to do it instead.

Just my $0.015

 

[JAE]

Here's the snippet out of AISC's Code of Standard practice. (emphasis by me):

3.1.2. The Owner’s Designated Representative for Design shall either [red]show the complete design of the Connections in the structural Design Drawings[/red] or [green]allow the Fabricator to select or complete the Connection details while preparing the Shop and Erection Drawings.[/green] When the Fabricator is allowed to select or complete the Connection details, the following information shall be provided in the structural Design Drawings:

(a) Any restrictions on the types of Connections that
are permitted;
(b) Data concerning the loads, including shears, moments, axial forces and transfer forces, that are to be resisted by the individual members and their Connections, sufficient to allow the Fabricator to select or complete the Connection details while preparing the Shop and Erection Drawings;
(c) Whether the data required in (b) is given at the service-load level or the
factored-load level; and,
(d) Whether LRFD or ASD is to be used in the selection or completion of Connection details.

When the Fabricator selects or completes the Connection details, the Fabricator shall utilize the requirements in the AISC Specification and the Contract Documents and submit the Connection details to the Owner’s Designated Representative for Design for approval.

Commentary:
[blue]When the Owner’s Designated Representative for Design shows the complete design of the Connections in the structural Design Drawings, the following information is included:

(a) All weld sizes and lengths;
(b) All bolt sizes, locations, quantities and grades;
(c) All plate and angle sizes, thicknesses and dimensions; and,
(d) All work point locations and related information.

The intent of this approach is that complete information necessary for Connection detailing, fabrication and erection is shown in the structural Design Drawings. The Steel Detailer will then be able to transfer this information to the Shop and Erection Drawings, applying it to the individual pieces being detailed.

When the Owner’s Designated Representative for Design allows the Fabricator to select or complete the Connections, this is commonly done by referring to tables in the Contract Documents or in the AISC Manual of Steel Construction, or by schematically showing the types of Connections required in the structural Design Drawings. The Steel Detailer will then configure the Connections based upon the design loads and other information given in the structural Design Drawings. If the desired Connection is not covered in those tables, a detail of the “special” Connection should be contained in the structural Design Drawings. This detail should provide such information as weld sizes, plate thicknesses and quantities of bolts. However, there may be some geometry and dimensional information that the Steel Detailer must develop. The intent of this method is that the Steel Detailer will select the Connection materials and configuration from the referenced tables or complete the specific Connection configuration (i.e. dimensions, edge distances and bolt spacing) based upon the Connection details that are shown in the structural Design Drawings.

This method will require the skill of an experienced Steel Detailer, who is familiar with the AISC requirements for Connection configurations, capable and experienced in the use of the Connection tables in the AISC Manual of Steel Construction and capable of calculating dimensions and adapting a typical Connection detail to similar situations. Notations of loadings in the structural Design Drawings are only to facilitate selection of the Connections from the referenced tables. It is not the intent of this method that the Steel Detailer practice engineering.

If there are any restrictions as to the types of Connections to be used, particularly as it relates to simple shear Connections, it is required that these limitations be set forth in the structural Design Drawings and Specifications. There are a variety of Connections available in the AISC Manual of Steel Construction for a given situation. Preference for a particular type will vary between Fabricators and Erectors. Stating these limitations, if any, in the structural Design Drawings and Specifications will help to avoid repeated changes to the Shop and Erection Drawings due to the selection of a Connection that is not acceptable to the Owner’s Designated Representative for Design, thereby avoiding additional cost and/or delay for the redrawing of the Shop and Erection Drawings.

The structural Design Drawings must indicate the method of design used as LRFD or ASD. In order to conform to the spirit of the AISC Specification, the Connections must be selected using the same method and the corresponding references.[/blue]

 

[271828]

Hey guys, sorry for the way my next-to-last sentence reads. Didn't mean for it to sound so harsh.

The reality is, though, that almost all of the folks I know (EORs in reputable east coast firms) know how to figure out the kips/ 3/4" bolt and kips/in./1/16th of fillet weld, but that's about it -- simply NO interest in the subject. I'm sure they could figure it out if they tried. It's just not their thing...and they like it that way, LOL. They check the shop drawings to see if anything *looks* crazy and that seems to avoid nutty connections getting through.

 

[abusementpark]

This is how all simple shear connections are done in our office: We show typical details of the connections (beam to column, beam over column, splice, etc.), however the only requirement is in our General Notes where there is the note "Steel Fabricator to provide maximum number of A325-N bolts for Simple Connections", that isn't verbatim, but it is something to that effect. So, essentially we rely on the fabricator to design the connection, yet we do not even provide load data

Now, I am just an EI, and this is not my policy. When I questioned my boss about the safety and economy of this he basically said that for any beam we designed for flexure with a uniform distributed load and point load in center span, adherence to the aforementioned note will yield a conservative connection 99% of the time. Well, what about the other 1% of the time? He said that we can recognize situations where it might be an issue, for instance beams with low height to weight ratios (ie, W12x96), or a beam with a point load close a support. I also questioned the loss in economy, and said simply that connections are generally cheap and that the additional material cost will be canceled by cheaper labor bids from fabricators, since this requires less effort on their part.

This does seem to be a practice among many in our area. To me, it doesn't seem like much effort to provide a max reaction table for the fabricators to design for.

 

[strguy11]

If the connections are left up to the fabricator to design, the EOR still must review and approve the connections, so I think they are taking some responsibility for the design.

 

[Lion06]

strguy-
That is correct. We let the fabricator detail it how they want, but we check their connections against our reactions to make sure adequate capacity is provided.

 

[hokie66]

Just to add a bit of international flavour to this discussion, in Australia we don't depend on the detailer for any design. The detailers here have to contend with having very few dimensions on the structural drawings, instead having to get all their dimensional data from the architectural drawings. They are good with geometry, but don't do design. We show them on our drawings how to make all the connections. Most are typical, shown in details and tables. Special connections are drawn individually. Single cleat plate shear connections are typical here, with angle connections rare.

We never get into an argument with a fabricator about telling him how to do something. It is only when we don't give him all the information that the fabricator complains.