What fabricator wants every structural steel detailer to know about connections 7

[Nitesh Sadashiva]

Hello everyone,

This is something different from what we usually discuss in this forum. I am working on creating a content (powerpoint presentation) on a topic "What fabricator wants every structural steel detailer to know about connections". I am taking a training session to young detailers with minimum experience on this topic. As a engineer, you might have come across many situations where detailer had done blunders and you might have thought detailer should be aware of these basics before proposing some connections to EOR. So, I need your valuable suggestions or input based on your experience, so that I can include in my content which will be helpful for many young structural steel detailers. I am looking for a very basic topics which detailer should be aware regarding the steel connections. Thank you all in advance

 

[human909]

Galvanising holes.

 

[DrZoidberWoop]

Here is a list of some common and widespread mistakes I notice detailers make during my shop drawing reviews, pre fabrication (USA):

1) Incorrect welds for skewed shear tabs. I see this ALL THE TIME. They should review this document.

https://www.aisc.org/globalassets/modern-steel/steelwise/072012_steelwise.pdf

2) Incomplete CJP/PJP weld information on final sheets. For example, only showing the weld symbol and not the AWS prequalified weld code. Another example, not specifying underfill for flare-bevel groove welds. If you have a weld joint that requires a flare-bevel groove weld and you don't specify the required underfill, the guys in the shop are going to fill that joint to the top. Depending on the members being welded, that could result in a LOT of unnecessary material and man-hours per ton of shop output.

3) Lack of awareness of the new nominal hole sizes in AISC Table J3.3, for AISC SCM 15th Ed.

4) How to prescribe the correct bolt lengths and required washers (Section 6 RCSC 2020). My organization had a period where the bolt lengths, specified from AISC SCM Table 7-14, were arriving on site too long, resulting in bolt-jamming, improper thread runout, and other general erection issues. We ended up creating our own bolt-length program, which more closely matched the old document "Specifying Bolt Length for High-Strength Bolts" by Charles J. Carter. Close familiarity with the tolerances and specs in ASME B18.2.6 are important.

5) Do some research into the tools steel erectors use to pretension hex-head and tension-controlled high-strength bolts. Sometimes connections result in tight spaces and the proper tooling must fit. There are Autocad files kicking around that can be imported for verifying clearances and avoid fouling.

6) Bent plates. A lot of EORs like to avoid bent plate connections, but sometimes they are convenient. Their fabrication is a bit of an art form due to press-brake operation and spring-back. Detailers should be aware of AISC SCM Table 10-13, min inside radius for cold-bending.

7) Know the maximum member lengths 1) the mills can provide and 2) the fabricator can ship to the final destination. Otherwise, the advanced bill of materials the detailer submits is going to be unrealistic.

8) Specification of "safety connections" or temporary/erection supports at "double connections." See AISC SCM page 10-5 & 6. It's for erectability and worker safety.

9) "Riding the fillet" or allowable encroachment into the fillet area of a wide flange member, on page 10-7. For shear tabs the encroachment values do NOT apply to the supporting member, only the beam being supported.

10) Coatings and surface preparation. Always have a coatings expert on staff. It's a whole world of its own.

11) Always specify an overly large radius at "reentrant corners" or where something like a steel gusset/plate will have a point of stress concentration.

12) Frequently send your fabricator's engineering team gift baskets of snacks/booze, as a sign of your commitment to a long-term working relationship.

That's all I can think of off the top of my head during morning coffee. Hope it helps.

 

[rowingengineer]

Depending on location the advice can vary, but generally the following are my recommendations:

1. Pick and stick, don't be a Picasso and develop a new connection for the fun of it, select connections that will cover a few locations.

2. Try to pick similar thickness plates and bolts for multiple locations, all main column hold down bolts should be the same size unless it is an architect required detail.

3. Don't try to name every connection individually, you are not judged on how many trees you kill when the details are printed.

4. Flexible connections may need some moment abilities during construction, or base plates, columns are always more stable with 4 instead of 2 bolts.

 

[Nitesh Sadashiva]

@rowingengineer: The location is USA.

 

[human909]

Good post DrZoiderWoop! Must better than my first post which was a quick post before lunch. And good question Nitesh Sadashiva.

I cut my teeth in the engineering world as a young steel detailer in a fabrication workshop. I quickly learnt from the experienced 'boilermakers' aka the welders on the shop floor if some was drawn or detailed poorly. Those 40 year old guys with fists the size of sledge hammers had little issues telling me at my clean white desk if something was poorly detailed. Often using quite blunt and impolite language!

Sometimes getting engineers to understand how things are actually built is sometimes a challenge. On the flipside I've also seen experience steel detailers or fabricators doing some the 'sensible' way but making a subtle but significant engineering mistakes that isn't obvious unless you are an engineer. (Think Hyatt Regency Collapse without the severe outcome.)

A good operator in the construction should be able to grasp the basics of all aspects up and down the chain of design construction. I am trying to get to an 'all encompassing' level of knowledge but there is always so much more to learn and so many gaps in my knowledge. I spent 20minutes today quickly detailing up a connection as I wasn't quite sure it was constructible until I sketched it out. It was a simple engineering design but the clearances were tight so until it was sketched out it wasn't entirely clear what I was asking to be built was at all sensible.

 

[swimfar]

Just a grammar edit. It should be "What fabricators want every structural steel detailer to know about connections".

 

[RangeRock]

@rowingengineer

Hench the OSHA requirement - Section 1926.755 "Column Anchorage"

"(a) General requirements for erection stability. (1) All columns shall be anchored by a minimum of 4 anchor rods (anchor bolts).

(2) Each column anchor rod (anchor bolt) assembly, including the column-to-base plate weld and the column foundation, shall be designed to resist a minimum eccentric gravity load of 300 pounds (136.2 kg) located 18 inches (.46 m) from the extreme outer face of the column in each direction at the top of the column shaft. * * * "