Creating new flying points in concrete ceiling

[andylouder]

One of the nightclub gigs I do , is hoping to contract a company to install a new speaker system , some of which will need to be flown.

 

We currently have 4, 15 inch speaker cabs flown from chains suspended by eyebolts (?) fixed into the concrete ceiling / concrete ceiling beams.

 

We may look for an alternative placement point for the speakers and may need to create new flying points in the ceiling.

 

I will not be doing this myself.

 

I assume a hole is drilled in the ceiling and this eyebolt is secured with an industrial raw plug and some sort of product.

 

One of the 'sales reps ' said ' yes that's all fine we use 'chem lock' to secure the bolt.

 

The club is in a basement , I am unsure of the depth available in the ceiling , one of my colleagues said he drilled up into the ceiling and came out in the shop above , so securing the bolt with a backing plate may not be an option .

 

A quick look at some of the specs for speaker boxes we may look at , I would expect the weight to be approximately 71kg / 156.5 lbs

 

Questions:

Would one flying point per box be sufficient or would it be better to have two.

 

Does this reference to 'chem lock ' seem feasible , what is the product.

 

Assuming this is done by a 'competent person' what sort of load testing might they do.

 

I realize it may not be possible to have a definitive answer on the forum , just looking for some opinions.

[ianl]

yes, a fairly standard method is to chem-fix or similar an eyebolt (or piece of studding and eyenut) into the concrete

 

drill hole

brush out hole

blow dust out of hole

apply chem-fix (a 2 part "glue" that mixes in the nozle. can either be look just like a tube of sealant or be a double cartridge that loads in a double "sealant gun")

whack in piece of high tensile studding

pop on an eyenut

touch dry in minutes

structural in hours

load test the point to 6 or 8 times your required swl (hang a cradle and slowly fill with weights )

 

as long as youve got 3 or 4 inches of concrete to drill into you should be fine

 

done properly its the studding that is the week point not the chem-fix. given the right eyebolts and a strong enough concrete slab you can hang tons

 

I would always tend to use a minimum of 2 points, usually 3 , not just for safety and redundancy but also to make it easier to angle your boxes and make them stay there.

[Piers Shepperd]

...as long as youve got 3 or 4 inches of concrete to drill into you should be fine

 

There is a significant difference between a pre / post -tensioned concrete slab / beam or cast in-situ slab / beam, particularly with regard to how it will react if you happen to drill though the reinforcement bar (rebar). I would strongly recommend asking a structural engineer to calculate what loading is available to allow for these loads.

This is not a difficult service to procure, and also not an expensive one, but it is a critical part of the design process.

[Nick S]

done properly its the studding that is the week point not the chem-fix. given the right eyebolts and a strong enough concrete slab you can hang tons

 

...although I'm reminded of a fatal accident about three years ago in the Boston Big Dig, where a number of rigging points holding up a ceiling failed due to the contractors using an incorrect glue mix. As Piers says, worth making sure the company you're contracting is planning on getting an engineer in to briefly survey.

[andylouder]

Ian thanks for your prompt and straightfoward explanation , confirming the vague infomation I had and for the tip suggesting 3 points would be handy for adjusting boxes to desired angle. Piers and Nick thanks for the sensible safety advice.

 

 

Also , sound hire , sales and install companies within or near M25 area please see my wanted ad.

[s buckley-jones]

One of the nightclub gigs I do , is hoping to contract a company to install a new speaker system , some of which will need to be flown.

answer

 

the safest method for this type of instalation would be the use the following. unistrut pre formed steel bolted and glued . the "front" load point secured with 3 no fixings and 2 no fixings for the "rear" fixing point this has the effect of spreading the load and also has less effect on the slab when drilled. you would also require a safety point Also all conponents used would require to be rated

[DSA]

Piers offers good advice. In addition to it being sensible safety advice, employing a qualified structural engineer will give you the backing of their own liability insurance. If the slab is prestressed, then drilling through a tendon could result in a significant reduction of its load carrying capacity. To locate any reinforcement, a covermeter survey may prove useful. Even if the slab is cast in-situ, the effect of the point loads should be considered by a professional.

 

There are several suitable fixings available: Resin anchors are certainly a possibility - however exapanding and tapcon style fixings may also be worth considering. Rawl/Hilti/Spit etc. all supply suitable products. Your engineer will happily specify the right fixing for you as part of their service.

 

If you do use chemical anchors then IT IS ESSENTIAL that the drilled hole is free from dust. You must install the fixing in accordance with the manufacturers instructions and recommendations, which is generally to brush and blow twice after drilling the hole. You do not want to bond to dust!

 

David

[TimmyP1955]

I would have large plates made (at least 18", square or round). These would attach to the ceiling, and the points would be attached to the plates. This would give you multiple bolts into the ceiling instead of just one. This would all have to be certified of course.