Hooked Bar Anchorage
Hooked Bar Anchorage
(OP)
Is there any reason that the attached connection cannot develop the full capacity (ACI) of the deformed bar anchors located at the edge of the slab?
I have met the hook development length and spacing requirements. My slab has the flexural and shear capacity from a slab analysis standpoint.
I will be adding hair pin ties around the hooks in accordance with 12.5.3.
Could there be something I am not thinking of that would limit the capacity of the DBA's to take the full tension?
Thanks ahead of time.






RE: Hooked Bar Anchorage
RE: Hooked Bar Anchorage
Im thinking I should cantilever a wide flange out from the bottom of the slab such that the load is set back a distance d from the slab edge.
RE: Hooked Bar Anchorage
RE: Hooked Bar Anchorage
I cant help but feel like i am leaving a check out of the analysis, to account for the local effects. Is a punching check appropriate here?
The wide flange, say 4-5 ft long, would act as a propped cantilever, and run perpendicular to the slab edge, underneath. Connected in two locations, one near the slab edge and one further back. The connection nearest the opening would be set in, say 18", but allow the hanger to be connected near the slab edge.
RE: Hooked Bar Anchorage
Could you use a larger and longer plate on the underside of the slab, for the HSS hanger, and a like top plate on the slab; with through bolts btwn. them. This would distribute the hanger load to more of the slab edge, as you wished and need.
RE: Hooked Bar Anchorage
RE: Hooked Bar Anchorage
I immediately thought top plate also, like Dhengr and Hokie. Then you can use punching shear values of the concrete rather than connection pull-out values. Then it becomes a concrete shear and bending problem and not a connection problem.
RE: Hooked Bar Anchorage
The top plate sounds good, but now you are venturing into Appendix D territory and relying on that shear cone. There are no pullout values beyond meeting the requirements of ACI 12.5 (?) for standard hooks, including development length.
This is the part that has me confused. If I develop the hook into the slab, why isnt that enough? Haven't I avoided the App D requirements?
Thoughts?
RE: Hooked Bar Anchorage
RE: Hooked Bar Anchorage
Your current detail is an Appendix D detail, in a cracked conc. region, a pretty difficult detail. There is another thread here right now, thread507-359891: Bent Bar Reinforcement, and TXStructural pretty well covers the current thinking on the issue. The rebar bearing forces on the inside radius of the hooked rebar crush the conc. and actually allow some relaxation of the bar length, rather than development of its tensile strength. Furthermore, your welded studs and the forces associated with them and their failure cone, tend to weaken the slab right where you would like max. slab moment cap’y. to support your hooked bars. At the least, the hooked bar may not be fully developed right where you need it, it’s not well supported because of the stud cones, and the total cap’y. is not the sum of the rebars and the studs under normal conditions. The top pl. detail causes a punching shear problem like that btwn. a slab and an exterior conc. column, a three sided truncated cone.
RE: Hooked Bar Anchorage
RE: Hooked Bar Anchorage
In a similar situation before, I provided some stud rails (upside down) butt up against top plate. Analyze it for punching shear like a 12" x 12" column with a 50 kip load (edge condition).
RE: Hooked Bar Anchorage
I think that what you've shown probably would work if you can deal with the shear in a convincing manner. This is a pretty high stakes connection though so I can see why you're concerned. For some reason, I feel bothered by how close the DBA is to the slab edge in your connection.
I've attached a suggestion to this post. It should be doable if your sketch was approximately to scale. My preference would be for a connection that possesses some ductility. If desired, you could also run an RC beam perpendicular to the slab edge. Then, it would basically be punching shear but handled with stirrups rather than diagonal concrete tension.
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RE: Hooked Bar Anchorage