[TheForge] J Bolts

[Gareth McNeil White]

J Bolts are used to secure steel fabrication to concrete because they fail by 
"unbending" . This can usually be detected before a catastrophic failure occurs 
and thus are massive head injuries avoided.
It is really important in the case of a jib crane where there is alot of pull 
on one side of bolt pattern. 

If you want to use bolts,  bolt grade 5 or A325 structural bolts of sufficient 
length to a pattern (jig) that matches what you are bolting down and embed them 
(thread end up) in the concrete.  It is best if you have a basket of #10 or 
smaller mesh embedded above the level of the bolt heads extending 15-20 cm 
deeper than the bolt heads.  If you need adjustment, place one set of nuts 
between your concrete and what you are bolting down.  Adjust to level. Place 
enough grout to fill the void then place your device before the grout sets.  
Bolt down with another set of nuts after the grout is dried.  Use non-shrinking 
grout.

We use this method on a lot of structural work that gets done after the 
building is finished.

Yours

Gareth White P.Eng.