Boxing/punching bag weight & live load

[WWTEng]

Working on a gym where they intend to hang three punching bags from a bar joist. I know that typically the weights of bags are 80#, 100# & 120# but should I consider some live loads associated with each bag?

I was going to assume 120# worst case and use an impact factor of 1.5. But during the few classes of MMA I took sometime ago, I have also seen guys sort of hugging the bags but not really hanging from them. I was wondering if anyone had to design for these bags before and had some info that I am missing.

 

[1gibson]

I'd at least consider a 200# guy hanging on them. You've not seen the exercise where they straddle with their legs, lean back (now hanging upside down) and do crunches? I vaguely remember seeing it in some montage in an action movie.

Or, put a sign up that says "no hanging from bags." Fitness junkies get creative.

 

[PicoStruc]

... If you put a sign... for sure they will hang from the bag !

 

[CANPRO]

Agree with gibson, add 200lbs. There probably won't be much of a difference in the end if you ran the numbers with 120lbs or 400lbs, once you consider the much larger live or snow load from above. If its in a gym and the ceilings are open then the minimal reinforcing will be an easy add on anyway

 

[MiketheEngineer]

Agree w/Gibson - but might use 250-300 lbs. Guys are getting pretty big these days!!

 

[SLTA]

CANEIT, there's a big difference in distributed snow load and point heavy guy load, in the way bar joists are designed. Those suckers are great for distributed loads and usually stinky for point loads.

 

[CANPRO]

slta, not to say the 400 lbs is insigificant...but my experience has been that designing for a 200lbs point load and 400lbs point load won't make a difference in the required reinforcing. For example, around here, the OWSJ is typically spaced 5' c/c and the joints (webs interceting with top/bottom chords) within the truss are about 2' c/c...minimum snow load around here is about 50psf...so thats 500lbs of snow just for that small section of joist...my main point was that the OP shouldn't waste time splitting hairs about 200lbs...just add the 200lbs and move on.

 

[MiketheEngineer]

Canett -

I might tend to disagree with you... esp in the winter.

I have reverse engineered many of these and they are right at the nat's A$$. Very little room for ANY extra weight.

When I see spacing say at 5'-3 3/4'' I KNOW they were squeezed. Yep - they probably saved 1 or 2 joists but no room for later mods.

 

[MrHershey]

I'd probably go with a 300 point live load. Dudes are huge now. ASCE 7 uses 300 pounds for point loads due to people in many instances as well (see roof surfaces subject to maintenance workers).

 

[Ron]

Look at the attachment hardware for the punching bag. They are usually hung from a cast plate with a relatively heavy chain. If you work backward from the capacity of the fasteners used to attach the cast plate, you'll have your point load answer.

 

[a2mfk]

Also, I believe most joist manufacturers recommend specifying KCS joists rather than placing point loads on the plans. Easier for you to design and coordinate too. This also allows some flexibility in the field for future renovations, additions, or plain mess-ups....

 

[ChipB]

I agree with Mike. I have yet to come across one that wasn't designed to the gnat's butt. Much like the pre-engineered metal buildings.

Ron: You are usually pretty serious with your answers. I can only imagine the smirk on your face when you wrote the response. WWTEng, your bar joist will be WAY overstressed if you do that. The companies that manufacture these bags don't have an engineer designing the attachment. They just go with the age ole rule of "When In Doubt, Make It Stout!" The customer is paying for it anyway. They don't care.

If it were me, I'd locate the bags between two bar joist, and place a member perpendicular to the bar joists to support the bag from. That way it's shared between two joists. I would place 500#s on each of the bags(250/joist).

Just my 2 cents.