wideflange beam over wideflange beam - lateral restraint

[bhiggins]

Howdy Engineers!

I currently have a project where I am designing a steel frame to support punching bags at a fitness center. The main wideflange beam supporting the punching bags is supported by an HSS column on one end, and on the other end rests on top of a wideflange beam and is bolted at the flanges. For analysis purposes, what is a reasonable value the unbraced length for LTB (Lby)? If the beam length is 25 feet, would it be prudent to increase the Lby because it isn't really fixed at one end? I would assume the true unbraced length is somewhere between L and 2L. Possibly take Lby as 1.5L?

Does this connection simply not meet code requirements for beam bracing at supports? It is just supporting punching bags so I don't want to be overly conservative with the design.

 

[SlideRuleEra]

I would design the beam for deflection. Deflection itself is not the problem but the "springy", trampoline type action that comes with would be an issue. For a 25' span, IMHO, no W6 would work. A modest W8 with a wide flange... maybe. A light W10 with a wide flange, probably.
When a proper beam is selected for deflection, LTB will take care of itself for light loads. The material cost of an undersized W6 compared with a suitable W8 or W10 will be "peanuts".

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[bhiggins]

I was actually designing the beam as a W12x. I placed a 500 LB load on each punching bag which required a W12x22. The beam is at 90% capacity and would fail in LTB which made me think about lateral restraint, deflection is fine with the W12x. I also see this situation from time to time so I'm curious about how to design this beam where lateral restraint is in question.

 

[SlideRuleEra]

A wider flange is the easiest fix, increased Y-axis properties. Check a W12x26, then W12x40.

You most likely have an advantage, I assume the load is applied to lugs on the bottom of the bottom flange. If so, a beam's problems with LTB are much reduced. The load provides a stabilizing moment.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Lomarandil]

First, why not provide nominal stiffeners at the support locations? There are reasons not to, but let's not reinvent the wheel if a stiffener will solve the problem nicely.

The old BS standards treated this situation by adding 2*d (presumably, 1*d at each end) to the unbraced length of the beam to account for an unstiffened web supporting the top flange. I'd be a little conservative with this for a slim beam like you're proposing -- I typically used this rule with WF shapes.

----
The name is a long story -- just call me Lo.

 

[jayrod12]

I'm with SRE, take your required moment of inertia and choose a shorter, more robust beam and your LTB issues "magically" disappear.

 

[Thulz]

Hi Sir (Bhiggins)


Actually I have seen your previous thread "Curved Stair Sanity Check" -

https://www.eng-tips.com/viewthread.cfm?qid=430210

.
I couldn't able to reply since its been closed.
So am replying here.
Am also designing similar curved steel staircase.
I have some doubts in it.
Kindly see below link and if you can clarify, pls comment it,

https://www.eng-tips.com/viewthread.cfm?qid=439014&action=updated

and the stair which you have posted is working good???
have you checked the stiffness of the stringer beam?..