Temporary Shoring for Brick Masonry Facade 2

[nycstructural]

Hello all. I'm working on a 4 story brownstone renovation project where the architect wants to open up the lowest level of the rear facade (leading out to the rear garden). I have designed steel moment frame to support the wall above and resist lateral forces. The contractor has now hired us to design the means and methods to carry out the work. The facade is 16' wide and consists of 3 wythes of brick. The rough opening will be 13' (finished opening is 11' after the moment frame is installed). I'm suggesting clamping the wall just above the proposed opening using two stiff MC's with through bolts. The channels would be supported by perpendicular beams through the windows (rather than needle through the brick piers). I'm at a loss as to what capacity to assume for the bolts. Should I specify a torque to develop a clamping capacity? Can anyone provide some guidance?

 

[dik]

Can you provide a sketch/drawing and a x-section? If a nice old brownstone, you may not want to use through bolts... unless I misunderstand the application.

Dik

 

[MiketheEngineer]

Check out needle beams and shoring??

 

[nycstructural]

Attached is a rough elevation of the proposed arrangement. Note, the architectural background is the new elevation, not the existing condition.

 

[dik]

What are the W12's braced back to? You have a bit of a 'house of cards' from the sketch. The C12 could be replaced by a beam on the flat and anchored to the wall... might reduce the number of fasteners. If historic, you might consider using stainless steel 'spiral' anchors or an epoxy type anchor and not through bolts to provide less damage to the exterior of the masonry wall.

Dik

 

[JAE]

I don't think there's necessarily a house of cards here. If the W12's are adequately clamped/connected to the MC12's they won't go anywhere - presuming the web buckling is OK without stiffeners.

One thing we've done is to attached a series of small clip angles - perhaps 3x3x1/4 on the back side of the channels and then sawcut out (in the mortar joints) slots to receive these angle legs, which serve as ledges for the brick - at least the two outer wythes. The inner wythe is presumed to be adequately interlocked to the outer wythes so that no vertical support is necessary. You might loose a little brick from the inner wythe right at the opening though. The through bolts would still be used - but more to stabilize the channels and less to carry the brick as the clip angles would do that.

This way, once removed, you have fewer holes in the brick and only mortar-repointing to do to "heal" the facade.

 

[nycstructural]

Thanks dik, JAE and Mike for your input. The sketch was only a rough concept. I hadn't gone so far as to figure lateral stability, but I don't think we have a house of cards. This is a rear facade facing a rear yard (not exposed to public) and the masonry is painted brick(not brownstone). On the construction documents I call for interior bolted bent plates (two per floor) to help reinforce the connection between the lot line walls and rear facade. The walls were constructed toothed into each other but I want to reinforce the interface as a precaution. I also call for the floor diaphragms to be tied to the rear facade before structural demolition. The overall intent is to lock the remaining upper wall in place before removing the lower portion. There is no issue with beam buckling as the loads are not large. However, I may want to consider somehow tieing the shoring to the 2nd floor diaphragm. That should alleviate any concerns about the shoring lateral stability. I do like the idea of recessing the clips into the into the wall as I am finding the vertical reaction on the bolts excessive. Also, I don't know what torque to specify for the bolts if I'm to rely on clamping/friction between the masonry and channels.

With all that said, I'm in two minds about whether to use this scheme over simply using needle beams..... There isn't much wall to work with between the windows.

 

[JAE]

I would worry about inducing too much clamping force on the walls.
Let the angle clips do the work.

 

[nycstructural]

I agree. Will incorporate the clips. Thank you all.