Rotated Embed Plates w/ Nelson Studs In Masonry Wall

[THERR]

Greetings all,

I am deadling with sloppy contractor work on a small one story masonry administration building. The masonry embed plates in question are spaced approximately 4' o.c. and welded to a continuous L 4x4x1/2 on which the joists are supported. Each 4 X 8 plate contains two fy=51ksi 1/2" diam. studs spaced 4" apart in the vertical direction. Because they were not fully secured the plates rotated away from the wall approximately 1/4" to 3/4" during grouting of the bond beam! Looking down from the roof deck it is actually possible to see the studs entering the wall which is actually pretty scary to me. Anyway, we have noticed large grout voids behind the studs and in some cases can stick our fingers all the way into the masonry cut-outs and find no grout around the studs (talk about a nightmare). My question for the group is - Can anyone think of a good epoxy fix for this situation. In some cases we have very limited access into the masonry cut-outs (less than 1/4&quot. The joists are already in place and construction is continuing as usual. We were thinking along the lines of a Sika injection process but we are not sure we can get the epoxy injection nozzle into such a tight space. Does anyone know of a small almost needle like applicator? The contractor does not want to drill in the masonry wall due to his fears that we might disturb the existing bond beam...kinda tells you something. Thanks in advance for your help.

 

[ishvaaag]

There are superfluid mortars used in rehabilitation of monuments that can be set even by gravity, for your case, closing 3 sides. Sika must have something of the kind. This however won't go upwards not will fill any bubbles formed within. These products are injectable through drilled holes as well, with what the entry problem disappears. Since every support seems to be critical you might even duplicate them under the existing ones, or link them to redistribute any failure. This means new connections and supports.

 

[JAE]

So the studs are embedded into the SIDE of the wall?
And this is a masonry concrete block wall?

At first I thought I was understanding you to describe horizontal plates on the top of the wall, with a continuous angle on top as well. So the joists would be bearing directly on the top of the wall.

But it sounds like you have tried to embed plates flat to the inside veritcal face of the masonry and then welded a shelf-type angle as a ledger to support the joists. Is this correct?

If so, I guess I'm not keen on your design. I don't know of any design criteria to use to calculate the vertical shear and lateral tensile strength of studs embedded in masonry (concrete - yes, but not masonry). How were they embedded? In the mortar joints? Was the eccentricity of the joist load included in the calcs for the studs, the angle, the wall?

For a fix - I guess I'd be very wary of depending on a couple of closely spaced 1/2" dia. studs in hollow block and 2000 psi grout. Even with epoxy injection, I wouldn't have a lot of confidence in what was there.

I would probably come in with a temporary shore under the joists, and then install a continuous channel (C8 maybe) running under your ledge angle. I would use adhesive anchors, through the channel, and into the face of the wall.

HILTI, Inc has their HIT HY20 anchors that work with hollow block. Other manufacturers have similar products.

 

[jheidt2543]

Years ago we were doing an epoxy injection job in a tight spot with barely enough room to get our hands into the area. We went to the local grocery store and bought a case of new, plastic picnic ketchup bottles (the kind you have to pour the ketchup into yourself). We premixed the two part epoxy and poured it into the ketchup bottles and used them to squeeze/inject the epoxy into the cracks. It worked great and for clean up we just through the ketchup bottles away!

Just a thought!

 

[CWIC]

THERR:
I don't think you'll be able to pull off trying to squeez epoxy through the limited access you have to the holes. Epoxy anchors require a specific gap or space around trhe anchor for the epoxy to set and cure properly.

Small diameter anchors such as yours (1/2&quot typically require a 5/8" hole to begin with. The cleanliness and quality of the hole are also very important to ensure proper bonding of the anchor to the substrate. Dust remaining in the holes will further minimize bonding of the epoxy. The mixing tubes used to inject these epoxies are of specific sizes or diameters to ensure proper epoxy component ratios. Modifying mixing tubes may not be a good idea.

I highly recommend contacting the good people at Covert, Sika, Simpson, Hilti (as noted by JAE), Ramset, Anchor-It or Drillco for advice on a fix if you intend to pursue chemical or mechanical anchoring.

 

[southard]

Couple of responses here.

First to Jae...there is code for studs under combined tension and shear in ACI 530.

If it were my building I would try a fix before having them pull out the stud. If you are bearing joist on top of an angle which is improperly anchored into the side of the CMU perhaps you could try this. Try placing another angle (stiffened and continuous) across the tops of the joist seats. Then bolt that anchor into wall with epoxy or wedge anchors. Of course downpours or bond beams may have to be added. Then weld the angle to the top side of the joist seat. Essentially you are now hanging the joist. You could try something similiar from the bottom side in the form a stiffener connecting to the bad angle from the bottom side. Then the stiffener could be connected to the wall with angles placed on each side of the stiffener and wedge anchored into the wall. Again you have to have good concrete in the walls

 

[JAE]

soutard - thanks for the reference - ACI 530 - section 2.1.4.

I would still rather bear the joists on TOP of the wall though.