Steve Firth wrote:
Peter Percival wrote:
Rick Hughes wrote:
[snip]

you could use resin fixings, no risk of cracking concrete and hole is
fully filled

Excuse my ignorance, but I've never heard of resin fixings.

You drill a hole, inject a liquid resin and hardener then insert a threaded
rod and wait for the resin to harden before using the rod to bolt down the
attachment.

That sounds like a good idea. Let's suppose I fix the wood to the
concrete thus, there will be a gap. It there something like the stuff
one puts round the edge of baths (silicone something-or-other) that I
can fill that gap with, but suitable for out-door use?

Another method is to use non-expanding masonry screws. These need an exact
hole drilling so you need an SDS drill and the appropriate bit.

Otoh "exact" is a bit worrying.

http://www.toolstation.com/shop/Scre.../sd1950/p82307

Also available as "Multi-Monti" from Screwfix and other places.

--
I think I am an Elephant,
Behind another Elephant
Behind /another/ Elephant who isn't really there....
A.A. Milne