Structural Connection Design 1

[JAE]

To what extent do other engineers typically go in detailing connections on their drawings? In years past, the standard was to let the fabricator do the connection design (either based on given end reactions or based on the maximum reaction the beam could take).

We have typically shown full connection details on our plans to maintain control of the design. In a recent review of our plans, by another engineer, he seemed surprised that we did that. What do you do, typically?

 

[Ron]

JAE,
In my experience, your approach is unusual. Most designers do not want the "fit-up" liability of producing enough detail that it could be construed as a "shop drawing". Granted, we don't absolve ourselves of responsibility by delegation, it just spreads the liability around a bit. In Florida, there is specific language in the engineering law that covers delegated responsibility. It places a more significant responsibility on the delegate sub-specialty engineer, yet still maintains the ultimate responsibility on the Engineer of Record, though slightly softening the EoR's liability position.

Ron

 

[suqlainUK]

In the UK the fabricator ends up designing and detailing the connections. These are then checked by the member designer to ensure that his requirements have been interpreted correctly, and the frame behaves as per his analysis.
I spent 10 years with a steelwork fabricator, and there were standard details set up for simple and rigid connections, complete with holes, endplates, stiffeners, and the fabricator's designer ended up "filling in the blanks".
The office believed that connection design is steel design. Picking steel member sizes is easy. Further, steel fabricators prefer certain steel beam sections which they keep in stock, and therefore prefer to redeisgn in many instances, to achieve economy.

 

[Ginger]

JAE

I undersand what Suqulain is saying but this is only the case for regular pattern / large volume steelwork of a simple nature, say portal frames or standard beam and column design.

I design all of my own connections because usually the space available in tunnels or as a part of temporary works schemes is limited and the connections tend to rely on a particular beam size being used and are often reliant on site welding. To change the beam size to suit a fabricator's stock is not necessarily the best thing to do.

I think that to design your own connections has two benefits: a) this is an integral part of the design for which you as a professional engineer are responsible, and b) as invariably happens, the site team may need to change the detail, and in order to advise them you need the benefit of having designed the connection in the first place.
Regards

Andy Machon
Andy@machona.freeserve.co.uk

 

[JAE]

Good comments everyone....

I was "raised" as an engineer to let the fabricator do the work. This made sense on typical connections. We always designed any connection that was unique.

However, over the last 10 years or so, the nature of liability cases in the U.S. has directed the "blame" back at the EOR as the ultimate source of responsibility for the entire structure. This was especially hit hard on me when I sat at a structural conference and listened to the experiences of Jack Gillum who was the EOR of the Hyatt-Regency in Kansas City. The walkway that collapsed did so through a comedy of errors and oversights. He was depending upon a fabricator to design a connection. It didn't happen. What did happen was:

1. His draftsman failed to place the required load on the detail.
2. The fabricator began the connection design, but, getting a bigger project, farmed the Hyatt out to another fabricator.
3. Fabricator No. 2 "thought" that the partially detailed connection was designed and simply completed the detail.
4. Gillum's firm quickly reviewed the shop drawings, thinking that the connection, as detailed, was designed.
5. The connection was built and one year later collapsed, killing 114.

This drives home the thought that if we depend upon a fabricator to design "our" connection, then we'd better have the discipline to review these connections. That moves me to think that I just ought to design the connection in the first place. Most of the repetitive, basic connections are fairly standardized already (AISC single plate shear connections and AISC double angle connections). The judge in the Hyatt case told Mr. Gillum that he could delegate tasks, but he could not delegate responsibility.

Which takes longer, designing the connections, or spending the time to review someone else's design?

 

[Taro]

In the high seismic zones of the western United States, it is standard practice for the EOR to design all the connections. The EOR would design the unusual connections anyway, and typical connections are standardized so that there is not much extra design effort. It is much simpler to review shop drawings to ensure that they conform to your own design than to review someone else's design to see if they did it correctly. Also, taking on liability for someone else's connection design is unacceptable for many engineers.

 

[flamby]

In India, the person designing the structure is supposed to detail the joints to full details and I believe this is a good practice. Structures like Steel bridges, towers and trestles are designed keeping the support and joint conditions in mind (fixed, pinned, fixed with releases etc) and these conditions are best understood by the engineer himself. Design of sections without connection details can not be said to be a design.

 

[ishvaaag]

In Spain it is usual for the architects and engineers to design enough as to leave no doubt of what the design is, except prefabricated parts. However, it must be said that here a lot of detail is in part of the cases, mainly buildings, made by reference to standard details in mandatory or non compulsive codes, or even good construction practices.

Detailing connections enough -or even rebar, sometimes in engineering works to extensive detail- does not avoid the fabricator use a -normally in house- detailer producing drawings for structural steel structures and 3d party (architect, engineer, owner, authority) review. Prefabrication houses also serve drawings for every purpose.