Engineers-Bolt load capacity question

[NPloysa]

All, we (museum) have large laminated beams in our great hall meeting/conference room often used to hang catwalks and girder stuff to hang audio equipment, lights, speakers, etc.



Each beam, 5 of them, has 5 equally spaced bolts.



They are a lag type eye bolt with "Chicago" stamped on the eye.



I was wondering if you could tell me the capacity of them.



The threads are 3. 5" long



From the top of threads to the point is 4"



The diameter of the bolt is 7/8" overall, including bolt diameter outside of threads.



The diameter of the inner shaft area where the threads start is 11/16"



That leaves it with 3/32" of thread all the way around, 3/32" to actually grab the wood.



The wood they are screwed into is laminated structural, the lag bolts are screwed in all the way to the eye, utilizing all 3. 5" of thread.



Any ideas appreciated!!!!



We gave the info to our engineer who designed the building, but the bolts were added after the fact and can find no paperwork on them.



THANKS!!!!



Nick

 

[fest3er]

Seat-of-the-pants, if the bolts are 7/8" and they are screwed in horizontally (that is, the hanging weight is on the shank, not the threads or heads of the bolts), they should hold any reasonable load for a maintenance catwalk or collection of lights; 7/8" of steel has an adequate sheer strength. If they are screwed in vertically, *I* would be looking for another method of fastening the equipment up there. I would want any single bolt to be able to support the entire weight of whatever is up there if there is anything of value (or anyone) underneath.



N

 

[NPloysa]

Yeah, forgot to say, they are screwed in vertically. We were giving the events people a rough guess of 600 pounds each.

 

[DaveN]

If the bolts are made of junk steel, they should be able to easily carry 3700 pounds each. This is assuming about a 2. 5 safety factor. I would not worry about the bolts themselves. 600 pounds per bolt on a 7/8" steel bolt is fine, assuming the load is static (i. e. not moving), the bolt is loaded axially (along it's length) and the bolt is tightened.



I would be more worried about the wood stripping out where it's threaded in. If you are hanging 600 pounds per bolt - I would be concerned.



The thread strength of wood is difficult to calculate. It depends on a variety of factors, wood type, density, moisture content, does it have a knot in there, etc etc etc.



Typically in that situation I would prefer to see the bolt drilled through the wood, and have a nut on the back side with a washer. This allows the load to be distributed to the beam, not to the wood fibers.



If you estimate the total weight hung to be 600 pounds, and you are EVENLY distributing that to 25 bolts, then I would say you are fine. That's only 24 pounds per bolt. But if you are hanging 600 pounds per bolt, then in my opinion you need to do something different.



Credentials - BSME, I work in a bolt factory.

 

[NPloysa]

Thanks guys. I know the bolts are plenty strong, it's the wood and how much of the wood the bolt threads can actually take. I just called the engineer back and am waiting on an answer from him so I will let you know what I find out.



Also, when I first started working here I thought the bolts were drilled through the beams and nutted and/or nutted in countersunk holes. Then, when I learned they were lag style I thought they would be at least as long as the beam is thick, about 18 inches, not the 4 inches that they are.



I know as of yet, no one has hung 600 pounds on any single bolt, the most that has been hung on one is probably around 300.



Thanks again, Nick