UKC

Situation summary.

About to be locked down. Live in an apartment block, great balcony. I want to install gymnastic rings suspended from the ceiling of the balcony. Needs to take a load of ~70kg. 
 

I can think of two options, try and drill and install bolts (but straight pull, length? Expansion, glue in?) or bond a piece of wood that I can the screw into... thoughts? 

Always drill. And well. I know of someone paralysed when a pull-up bar failed. 

Plenty of people could say the same drilling overhead. Make sure you know what is above and how it’s supported (and who owns it).

Not sure about practicality/legality/effect on structure of holes of holes in ceiling of balcony (it may be floor of another balcony). 

How about using ceiling as part of stability of a structure...if you were building a garden one from timber you'd probably have horizontal and diagonal support elements eg like garden swing. In your case additional horizontal elements hard against the ceiling might add stability. 

Dan Arkles's comment about danger if it collapses is really important. My easiest option  for pull ups etc would a huge oak (neighbour's garden, preservation order) but I hesitate to attach a rope to the big branch 30ft up, it should be OK but if it did break I'd be directly underneath. In your case I'd probably have a strong backup beam which would take the weight almost immediately the main one started breaking.

As above;

I would move towards having something in the wall with the the ceiling acting as part of the support structure, not relying on fixings necessarily directly in tension.

Make sure the ceiling is yours before you do anything to it. If using fixings acting only in tension, never use adhesive, rely on mechanical action (i.e. check out Hilti HUS or better yet HSA series). Also factor up by a good amount. If you need it to take 70kg, that's a static load. If you're doing anything remotely dynamic which even pull-ups would be you'll be increasing the load way beyond a simple 70kg.

Wooden bar with 2 uprights wedged between your balcony and upper one would be my preference.

That's how I put kayak racks into a previous garage without drilling into the ceiling.

Doubt your upstairs neighbour would want you drilling into his balcony.

I think you'll need to design for at least 200 kg load.  You might weigh 70 kg but you'll exert more than 1g when you swing, pull-up or drop down.  So make that 70x1.5g = 105 kg.  And you'd want a margin for safety, say a factor of 2, so 105 becomes 210 kg.

If you drill horizontal fixings for your (mostly) vertical load, small bolts should be strong enough (say two M5 bolts).

However, if you drill vertically, your load will try and pull the bolts out, so the only thing stopping that is friction.  You'll exert much more load on the bolts (and the surrounding structure) in order to achieve that level of friction. Horizontal fixings is the way to go.

Actually, another method that might be better, if your upstairs neighbour is in agreement, would be to put a wooden beam across the balcony and use some brackets to hook the ends onto the upper balcony. If they have railings, you might be able to lash to that.

Even better, another beam across their floor and bolt the ends together, basically sandwiching the upper balcony.

Depends if you can get around the ends of the balcony, obviously.