Large openings in masonry wall

[rittz]

Hi All

Attached is a sketch showing part of an existing masonry building 60 ft x 60 ft.
At some point an addition was built on the left side of line “A”. The Architect
wishes to open up the entire concrete block wall between the pilasters to create a large room. We would then obviously lose the shear wall “The openings are to drive cars though making the space between line A and B into a show room

One solution we are considering is to build rigid frames with WF beams and cols between the pilasters as indicated on the sketch. The frames would be attached to the pilasters with thru’ bolts

Does this make sense? To anyone

 

[hokie66]

Makes sense to me, but the frames won't be as stiff as the shear wall. May not matter.

 

[demayeng]

Makes sense.

A couple of things that stand out to me:

- you could check whether 1 or 2 frames is enough, the other bay(s) can then just be struts

- The way it is drawn there will be more load transferred via the purlins- you would need check the beam to pilaster connection for transferring the bracing loads down into the frames.

- You could also install diagonal square section struts in the cavity above your frames to prevent the pilasters/end walls from having to cantilever.

- if line A is staying as is, you could also look at roof bracing (instead of frames) to transfer the loads to the side walls.. however the end walls would need to be able to span vertically

 

[csd72]

I have carried out similar modifications in the past though I have a few concerns about your proposal.

1. are the connections between the end of beams and the pilasters of sufficient strength to resist buckling.
2. Resistance against sliding of the masonry along the top of the frames. Particularly if this is a seismic zone.
3. deflection is critcal on this and you may need to use fixed bases in order to keep it to a level that will prevent excessive cracking.

No matter what you do, there will be some cracking in that masonry wall and I would suggest you send a cya letter to the client before designing this.

 

[SAIL3]

For lateral deflection the moment frame would be an order of magnitude more flexible than the remaining 2-bay shear wall and would require the remaining 2-bay shear wall to experience excessive lateral deflection inorder for the moment frame to pick up any significant lateral load leading to cracks etc. in the shear wall.
Therefore:
1. Check remaining 2-bay shear wall to carry all of lateral load
and just use the moment frame for local loads.
2. In any case there will be a redistribution of lateral loads
to the other col. lines due to torsional effects.

 

[rittz]

demayeng
Line “A” is not staying as it is …. The intention is to remove all CB (even above the frames) and install light gage steel studs and metal siding above the frames. With CB removed from line “A” and if no frames were added it seems roof bracing wouldn’t cut it?

Ccsd72
Regarding your comment on cracking.. there would be no concrete block involved in Line “A” …. See above. The frames would be required to take the roof reaction at “A”

Sail3
I may have mislead you …There would be no shear wall left … just frames as described above.

I am attaching the sketch with further “clarifications”

 

[rittz]

Woops here is the intended sketch

 

[csd72]

As others have queried, are thos pilasters sufficient to transfer the load from roof level via cantilever action?

 

[rittz]

Thank you csd72 very good point. I appreciate your response.

To add cross braces as shown on the attached sketch should eliminate the bending in the pilaster aye? Also the connection between the pilaster and the existing upper beams must be adequate.

Wot say?

J

 

[BAretired]

I doubt that there are any upper beams. You probably need to add an upper beam in each of the three bays.

Rather than an "X" brace, you could use a "V" brace. Probably best to brace all three bays.

BA

 

[hokie66]

Maybe it's just a start, but the moment connection in your detail 1/S2 needs some work.