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Steel Connection Design

Steel Connection Design

Steel Connection Design

(OP)
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?

RE: Steel Connection Design

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.

RE: Steel Connection Design

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.

RE: Steel Connection Design

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.
 

RE: Steel Connection Design

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

Mike McCann
McCann Engineering

RE: Steel Connection Design

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.

RE: Steel Connection Design

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.

RE: Steel Connection Design

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.

RE: Steel Connection Design

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.

RE: Steel Connection Design

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.

RE: Steel Connection Design

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?

RE: Steel Connection Design

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.

RE: Steel Connection Design

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.

RE: Steel Connection Design

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

RE: Steel Connection Design

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 show the complete design of the Connections in the structural Design Drawings or allow the Fabricator to select or complete the Connection details while preparing the Shop and Erection Drawings. 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:
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.

RE: Steel Connection Design

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.

RE: Steel Connection Design

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.

RE: Steel Connection Design

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.  

RE: Steel Connection Design

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.

RE: Steel Connection Design

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.

RE: Steel Connection Design

This is interesting. As an EOR, I think you own the building and are responsible for everything. However, that is only my feeling. I don't know how the law sees it.

Say for example, you had all your connections to be provided by the fabricator and he submits signed and sealed calcs for you to review, and you skim through it and APPROVE it. God forbid a connection fails, does it absolve you? I think as a person who approved it, you are as guilty (or negligent) as the person who designed it. Like I said, I don't know how the law (or lawyer) will look at it.

I personally think simple shear connections take more time to review (and I mean thoroughly review) than to design yourself. I work in an East coast firm and our firm has a policy that we design all our connections.

RE: Steel Connection Design

Slickdeals, I had no idea that anybody on the East Coast used this approach.  3 for 3 of the firms I worked for didn't do that and (I thought) had solid reasons for letting the fabricators do it.  

Is your firm able to get a higher fee for doing the connections also?

Do you not ever run into a fabricator who is better set up for some other type of connection? (For example, you showed double angles all over the place, but they like shear tabs.)

How do you pick what type of shear connection?  Angles versus shear tabs, for example?

RE: Steel Connection Design

I think our firm is probably an exception. The views in my previous post are from our "steel guru", who has done dozens of stadiums in his lifetime and is very well respected.

We have created standard tables with angles/ shear tabs for beam to girder connections and publish both in our drawings. The steel fab can choose one. Lately the choice has been single angles over shear tabs (all bolted single angles, with eccentricity accounted for in the girder).

Most of our heavier connections are double angles (girder to columns). But again, we discuss these early on in a project and come to a consensus within the office based on previous experience.

On a related note, we have always had problems with delegated engineers. Lately delegated engineers have been doing a very shoddy job of designing and detailing stairs. Most of these designs might work but are worrying. Like providing a single bolted connection, providing questionable weld sizes, providing plate stringers to which the pans are welded close the NA of the plate etc. The amount of time we spend in CA before getting it right is probably as much or even more than what it might have taken us to design it in the first place.

As for fee, I don't think we charge extra fees just because we do our connections, but I am sure we account for it.

RE: Steel Connection Design

slickdeals-
I agree that the EOR owns the connections and if one fails it is on your plate.  That is the reason for the submission of the signed and sealed calcs and shop drawings (probably not signed and sealed).  You have to verify that the connection they are providing has adequate capacity per your reactions on the drawings (or a reaction table- which we use).  I have sent many shop drawings back "Revise and Resubmit" for inadequate connection capacity.  
Just because you are allowing them to pick the connections they want doesn't absolve you of checking the capacity.  Additionally, you rarely have to check more than a couple of connections - they will most likely use one kind for all beam to girder connections, one for beam to column flange connections, and a third for beam to column web connections.  Also, because most firms do this, the calcs have been reviewed by MANY engineers before it gets to you, so there have been many sets of eyes on it already.  They don't redo their calcs for every job - these are, after all, standard shear connections, nothing more.
What do you do when the fabricators prefer double angle connections to the shear tabs that you designed and documented in your drawings?  Do you just say, "No"?  If so, I don't think that is the right approach.  I have taken a pretty good amount of time to design and detail a thru-plate moment connection at a HSS tube beam to a HSS tube column and ended up getting a request for a different type of moment connection that would be easier for them to fabricate.  I reviewed their calcs and allowed them to change the detail.  That was a bit of a pain and a little more annoying - If that happened to every shear connection in the building.........

RE: Steel Connection Design

StructuralEIT,
We never reject any drawing/calculation because it deviated from what we intended. If a fabricator can substantiate it with necessary calcs and details, we approve it. After all it is in the best interest of the job.

However, I have been part of peer review teams for many stadium jobs (designed by notable firms) where the moment connections are provided in a table. That table is a standard table that has moment connections for all the W shapes available. Most of these connections are designed for the full capacity of the member (and remember these are in projects in the East coast with little or no seismic demands). No wonder the contractor wants a peer review team because the shoddy engineer just decided to save time and effort of designing the connections. It is just being lazy and irresponsible.

Again I am not debating as to why some firms design their connections and some don't. I am just trying to present the other side.

RE: Steel Connection Design

Our firm designs all connections, shear, moment, baseplates, etc.  We feel it is our job to.  We've got spreadsheets and standard details that handle 99% of the connections.  It's really not that hard, and some of them are actually enjoyable.  And if the fabricator wants something different, he submits alternate designs AT HIS COST.

We were hired once to design connections for a fabricator.  The EOR (from a large, nationwide firm) spec'd 100% shear and moment capacity for all connections (IMO, lazy & irresponsible behavior).  The fabricator knew what this was going to mean, especially at the moment connections.  We had full pen welds, web doubler plates, and stiffeners everywhere.  The fabricator estimated tens of thousand of dollars in extra cost just by requiring 100% capacity.  We argued with the EOR in meeting after meeting to change his design to the actual forces, not 100%.  Finally it took a meeting that included the owner.  The owner looked at us and said "Why are you even here, I thought I hired [EOR] to design the building".  After we explained the cost savings to the owner, the EOR gave in.

Long story short, if it had been our job from day one, the connections would have been on the drawing, and the drawings would actually be constructible as is (imagine that!!).

RE: Steel Connection Design

Oh, and I have also seen a design where instead of thinking of alternative solutions, the EOR provided 3/4" by 24" deep plates welded on either side of a W24 to provide torsional capacity. This was also on a stadium which would have involved around 2000 linear feet of welding per concourse :)

RE: Steel Connection Design

PMR06, are you in an East Coast firm?

RE: Steel Connection Design

After reading all of this so far, I still like the way I used to do it (surprise, surprise, LOL--of course I'm biased!).  All design forces were specified and the fabricator had to hire a connection design engineer who would provide calcs and seal their drawings.  

Other engineers in the firm didn't require calcs and a seal and I do believe that is at least questionable.  They would argue that the designs are in the AISC Manual and it's been done this way for decades.

The approach of providing a table of standard connections is what a connection design engineer usually does anyway.  They have some standard conns in a big table and give those to the detailer and then go work on the harder ones.  It seems to me that either way, a detailer is yanking standard designs from tables and some engineer is taking responsibility at some step in the process.  The big difference IMO is that a connection designer does nothing but connections, so is a lot better at it.  Like I typed before, most every EOR I've known has so little interest in connections that they really know only the bare minimum (what's that U factor for?!).

Obviously several different approaches that seem OK.

RE: Steel Connection Design

271828, no midwest.

RE: Steel Connection Design

I do see some benefit in specifying full-pen welds at all moment connections - but the stiffener/doubler plate requirements should be checked for the actual forces, not 100% capacity.
It is my understanding that if you provide something less than full moment capacity at the connection that it will be a partially restrained connection.  That will allow greater rotation at smaller moments.  Maybe I am overanalyzing, but that seems to me to translate into greater tip deflections, greater frame sway, higher second order effects....  am sure there are a couple others I am leaving out.
Am I wrong in my understanding?

RE: Steel Connection Design

Also, if you are likely to get requests to change the connections, why waste your time designing and documenting them?  Just leave it to the fabricator and check them when they come in - that is what you will do anyway if you get a request to change them?

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