Back to back embeds 1

[vvaccare]

Good morning everyone,

Hoping to get some insight on an issue that I am having on a project. I have a scenario where I have two wide flange beams framing to the same 4000 PSI 8" concrete beam, back to back (see attached detail). The loads carried by the beams and embeds is controlled by my wind uplift (building to be designed for 220 MPH...). I've used a spreadsheet and the Hilti Profis program to help design the embeds. Here is my issue. I can only get the embeds to pass by checking that the reinforcement from the concrete beam will help the anchorage resist the loads seen. I have included a detail in our drawings to add stirrups in areas near the embeds. I have read through ACI318-11 to try and justify this assumption, and based on what I am reading in section D5.2.9 & D6.2.9 I believe the extra stirrups/ties will help me out. If i interpreted D5.2.9 correctly, stirrups spaced within 1/2" my effective emebedment depth may be used as anchor reinforcement.

Another reason I am concerned, is I have not been able to find any literature on how to handle a situation such as mine. Will the concrete beam reinforcement act in a way to prevent concrete breakout and blowout from both beams in such a narrow beam? I believe that the additional stirrups should help, but I am not having any luck finding anything to support this thought..I know the obvious answer would to add a concrete column or thicken the beam, however the architect is adamant on sticking with 8" walls.

I apologize if these issues have been addressed previously and I missed it.

Thank you all.

 

[vvaccare]

Attached is the stirrup detail I hope will help.

 

[JedClampett]

I don't know the beam sizes, but my initial observation is that you have a lot of stuff happening in an 7 5/8 inch thick wall. Two curtains of reinforcing, stirrups, embed plates and studs. The odds of getting well consolidated concrete in there is pretty slim.
I'd go back to the drawing board on this. Maybe you could embed a short 8 inch square tube with plates on each side and studs around the perimeter. Or reorient you beams so they don't line up.

 

[vvaccare]

I agreed with reorienting the beams to avoid such a conflict. However, I am kind of forced to leave them where they are at because they are my ridge line beams for a gabled roof. I agree with that there is a lot going on in this little area, which is exactly why I am concerned with there not being enough concrete keep everything in place; too much steel reinforcing to properly allow the concrete to fill in. I like the tube embed idea, I'd have to do a little research to figure out how to get a proper calc on that. To better inform everyone, the beams being used are a W18 & W24.

 

[hokie66]

Why not cast in through bolts. You could either double nut them to your flush plates, or bolt the plates to the face.

 

[RHTPE]

Sleeve the wall, don't embed the plates, then through-bolt the plates to the wall once the formwork is gone.

If tolerances are a concern, use oversize corrugated sleeves and provide for pressure grouting after the plates are installed.

Embed plates with shear stud on opposite wall faces will be drastically affected by Murphy's Law.

KISS works in this situation.

Ralph
Structures Consulting
Northeast USA

 

[BUGGAR]

The beautiful part of through-bolting is that ACI Appendix D does not apply.

Ding dong, the witch is dead.

 

[structSU10]

Can you just put a beam pocket/hole in the wall? if you can resolve the forces around the hole you can have one beam go through the wall to the other side, then do a shear connection to the end of the other beam. You could then grout the hole solid after installation of the beams.

 

[MrHershey]

Not sure I agree that Appendix D doesn't apply. Pryout wouldn't, but I would still check shear breakout in this case. The stirrups being close by should address it, as long as they've been sized to take the whole load.

Agree on the throughbolt idea though. I believe that's what we did in a similar situation on a recent project (though that was a wall, not a beam). Either that or we had one continuous steel piece with an embed place on either face and welded rods connecting the two plates.