What about Expansion bolts,,, do they,,, expand???
Thank you, thank you, you are a great audience. But seriously folks, other than expansion, what are the pros/cons of them? The only thing I see is the J type would be hook the rebar and maybe take more up lift, but once the conc. cures I don't see how the L type would be any different from the J type.
The difference is in the pullout failure mechanism. For that reason, the J bolt is more appealing to engineers who are faced with a small volume in order to properly anchor a bolt.
I've never understood the advantage of using these hooked anchors. Why not just specify a nut at the end of the anchor and get the capacity of a shear cone?
J-bolts and L-bolts can pull out before concrete failure occurs. This is a disadvantage.
Using a straight bolt with a plate on the end develops a good shear cone and high strength, provided they are placed such that the reinforcing steel intersects the stress development area.
Expansion bolts are designed so that when loaded (pre-load is required for seating during installation), a sleeve or wedge device will be pushed outward against the concrete as the bolt is being pulled upward by the load. The bolts don't actually expand, the design of the bolt device just re-orients the load. Works opposite the "Chinese Finger Puzzle".
Check the new ACI-318-03 Appendix D. Headed bolts are the way to go with anchor bolts. J and L bolts never actually acted the way it was assumed in design.
I have not yet seen ACI-318-03 as it is not applicable to my area. But I would practice following checks before I use headed bolts.
1. Shear Cone as haynewp has said.
2. Threaded/ welded connection between the head and the bolt, if any.
3. Bearing stress directly under the head of bolt (or plate in Ron's post)as this stress will probably govern the design.
Providing the bond length is simpler and more easy in contrast. No?
