Hanger Detail 1

[Gopher13]

I have a simple span beam that I would like to support by hanging from the top chord of an existing steel truss. Please see the attached detail. A quick design would just put half the load on each hanger with both in tension. However, isn't the inside hanger in tension and the outside hanger in compression, or is that ignored?

 

[KootK]

I don't know about "ignored" but perhaps evaluated with a critical eye and deemed to be of little concern. How the forces distribute to the bolt groups will be a function of the interplay of:

1) The flexural stiffness of the beam and;

2) The torsional stiffness of the top chord.

Without knowing the particulars of your truss, I would expect that there would be enough torsionoal flexibility in the truss top chord that it would rotate to match the slope of the supported beam and all would be well. You've got a rather long cope there but that's something that can simply be calc'ed out.

Personally, I'd seek to improve this aspect of the connection. If there's physical space to do so, I'd run a horizontal plate between the two hangers and bolt that to a vertical tab welded to the top of the beam. With the tab located right under the truss, you've got a few more parts and pieces but this issue goes away.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Gopher13]

Thanks for the response and great idea! I think I got it. Is this what you are talking about?

 

[KootK]

You're most welcome Gopher. And yeah, that's just what I had in mind.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BAretired]

Much better detail.

BA

 

[dik]

and design the 'padeye' (attachment plate) using ASME Under the Hook... I think 2014 is the current issue.

Dik

 

[thaidavid40]

@dik -
I am curious about your suggestion to use ASME BTH requirements for this design. If the beam is supporting building loads, then wouldn't the IBC and ASCE 7 cover the design requirements? And if it serves as a monorail beam for a trolley and hoist, wouldn't it thus be designed as a crane runway, and would still be designed according to IBC and ASCE 7 requirements? I've only ever use the BTH requirements for spreader bars, grips and such, which were truly "below the hook". How does it fit in with this particular design question?
Thanks,
Dave

Thaidavid

 

[MotorCity]

From a constructability standpoint, is there a roof deck or roofing on the truss top chord? If so, it may be difficult to re-roof around the beam you propose on the top chord.

 

[Gopher13]

MotorCity: There is no roof deck at this location. It is kind of a weird situation. There was an existing building with bowstring truss roof structure and then they pretty much built a new roof over the original one.