Over the weekend, we moved a few pictures around in the house and hung some that had been waiting for us to find a suitable place.
We hung one large oil picture (140cm x 110cm) in a stairwell having run out of wall space in the rest of the house.
At a guess, I’d say it weighs between 15 and 20kg (30 and 70lbs) as I can lift easily it by myself and hold it against a wall without much difficulty.
After I’d hung it using 2 off No. 3 ‘X’ Hooks (with 2 nails) about 80cm apart it seemed secure enough and I moved on to other jobs…
My subconscious had other ideas and prompted me, as a I was waking up this morning, to double-check and figure out whether the picture would stay fixed to the wall!
After some ‘research’ (i.e. Googling for ‘picture hook SWL’ and ‘picture hook pull out’) I found Danny Lipford (there are other references 1) who has done some testing and has found that the pull-out load on a single nail picture hanger is between 60 and 80lbs (27 and 36kgs) with a Safe Working Load (SWL) – or as it is now known Working Load Limit (WLL), of about 10 to 30lbs less (4.5 to 14kgs).
Danny said the “While the fasteners pulled out of the wall at the pounds listed (except for toggles, which remained intact), they started showing signs of failure at 10-30 pounds less…”
Danny didn’t say which hooks the load reductions applied to, but I’m going to assume the 10lb reduction was on the small hook and the 30lb reduction was on the large hook.
This would give a general WLL of 50lbs (23Kgs) for any of the hooks.
If I can remember back to my Strength of Materials classes; the load divides evenly and that although the vertical load of 10kgs will place a side load on the frame and tension in the wire, in this case the hooks act as pin joints and only react the vertical loads.
This would mean that each hook is supporting a maximum of 10Kgs (22lbs) with a safety factor of between 2.3 and 3, which I think is acceptable given the pictures location and likelihood of it receiving extra load (aka children – or adults, fiddling with it!)
Footnotes
1 – I also found the exactly same tests reported here, but neither quote an original source and couldn’t determine who should get the reference.
