Bolts thru grouted masonry wall 1

[MAeng]

Referring to the attached drawing, I have several questions. The situation is as follows:

The client desires to remove a section of bearing wall which is around 18' high and supports approx. 35' of steel bar joist/deck roof system. Although I've done this before, I've wondered what others think of certain aspects:

1. Would you take the grout bearing as 0.7(0.85f'c)?

2. Being that it is 12 wide block I feel I should consider bolt bending. What would you use for that value? 0.6Fy?

3. It occurs to me that the amount of grout in the cells above (where there is a bolt) needs to "grip" the masonry, which I know it does assuming an 8-10" slump but what kind of friction value would you use here. To take it to the ridiculous, if I covered the bolt with 1" of grout, it might not hold.

4. Lastly (sorry), I'm curious what you guys think about the order of bolt installation relative to grouting. Grout around an installed bolt or grout first, then drill in to install bolt?

Anyway, I'd appreciate any and thoughts on this matter.

Thanks!

 

[shobroco]

I agree with your grout bearing value, but I don't think bolt bending is significant because the weight of the blocks is mainly in the faces so the force on the bolts is mostly shear. If you want to know the amount of grout above the bolt, you have to calculate the shear in the grout and the block face from the force of the bolt. In this sequence, I would bolt first then grout to get the best bearing of grout on the bolt. That said, I wouldn't do the job this way. Continuous angles or plates welded to your channels & cut into the mortar joint on each side provide continuous bearing for the remaining masonry with no grouting and easy installation. The webs of the blocks provide enough temporary support while the joints are cut to insert the angles, the bolts hold everything together, & removal is easy. Assuming you can size the steel, the bearing on the ends is the biggest concern and would have to be steel columns on new footings with the size of opening that you are looking at.

 

[ron9876]

I never trusted adding grout in that manner. Seems to me that it is very dependent on the quality of the workmanship.

With that condition I would check to see if bearing on the width of the masonry face shell works. If so then I would check bending in the bolt.

If it doesn't work then, similar to shobroco, I would add plates thru the masonry, grouted tight to the underside of the masonry and welded to steel channels. Then add bolts to hold everything together and keep loose block from falling out the bottom of the opening. This is much more predictable and easy to build.

 

[JAE]

I would suggest also something along the lines of what ron9876 is suggesting. We typically use your detail, MAeng, but then only remove the masonry below the opening sequentially, adding cross plates underneath as we go to provide a "U" shaped beam. We only depend on the two channels (not the plate) as part of the beam since the plates are in pieces and we don't want to take the time to but weld them all together for strength.

So the order of installation would be:
1. Drill two holes - one at each end the the channels - through the wall.
2. Install the two channels with two bolts (again - one at each end).
3. If necessary - install vertical jamb channels on each side to serve as columns to the floor if necessary.
4. Through previously pre-drilled holes in the channels - drill through the masonry and install through bolts. (sometimes we've used Hilti HY20's).
5. Sequentially remove 24" wide sections of wall under the channels. The masonry is held up temporarily by the wall through-bolts.
6. For each section removed, install and weld on a cross plate.
7. Alternatively - use pre-welded clip angles with legs installed into mortar joint slots cut in the wall.

Cover plates on the vertical channel jambs can be installed as well to provide a complete steel opening edge surface.