EXISTING BUILDING RENOVATION WITHOUT DEMOLISHING THE EXISTING BEARING WALL 1

[sea2003]

Hi,

We are renovating an existing building, the structural system consists of a solid slab supported by a concrete beam and bearing stone wall (as shown in the sketch) and the foundation type is stone strip footing.
the client wants to avoid any demolishing to the existing wall during renovation work

I have three questions?

First question :

The concrete strength of the existing beam located along with the stone wall is very low (8 MPA).
How can we replace this beam on-site?
Do you recommend any alternative option to renovate this beam?

Second question :

the foundation will be widening as shown in the sketch and we will connect the new footing steel bar to the existing footing using chemical material
Is this connection enough to consider the new and old footing will work together as one footing?

Third question :
How we can determine the stone masonry compressive strength if the contractor is not able to take a prsime sample from the existing wall?

 

[Enable]

You'll likely want steel beams running perpendicular to the wall just above the concrete replacement locations (keep 1" above for deflection and finishing) and support them on 10 kip frames either side to grade. Typical spacing is 16" c/c depending on loads. I'm currently removing 10 LF out of a basement level shear wall on a 5 story building using the same shoring system. Though, since you are above grade and subject to wind loads you will also want to think about in-plane loads to be transferred as well and might need to add steel by-pass at those locations. Kick plates can be added on top of the steel beams for perpendicular lateral loads (i.e. wind, minor seismic).


Depends on site-conditions but typical removal techniques involve chipping with pneumatic hammers. Depending on the condition of the wall you may be concerned about vibrations into the existing structure in which case you'd switch to coring or something of the sort.


What's your concern with the beam as it stands right now? Is it simply the compressive strength or is it spawling, cracking, etc? Why are we repairing this in the first place?


The sketch indicates that the existing footing is of stone construction. I would not assume doweling + epoxying into the existing is sufficient to cause adjacent concrete to act as one unit with existing. You'd be better off coring through every so often and creating transfer beams through the wall to independent footings on either side.


Is there not a single piece of stone that can be removed? You will have to demo some of the stone to install the shoring. You really need to tell the owner some of their wall is going to have to go. At which point just get a sample for compressive strength. You can also definitely take a sample from below grade.

 

[sea2003]

Thank you very much for your valuable response.



my concerns are
1-The beam compressive strength is very low and it does not achieve the Durability requirements
2- We will replace the existing slab with a new slab and we will connect the new slab bars to the existing beam using chemical material. So, I am afraid if the connection between the beam and the new steel bar to be failed as well.
Is there a way to improve the concrete beam compressive strength without replacement?



Do you think the compressive strength for pieces of stone is enough to give you a proper compressive value for the whole wall?
my concern is the compressive strength value for stone pieces will be higher than the actual even if we used a lower value than the test resultant.

 

[Enable]

Unfortunately not that I am aware of. However, I have abandoned existing structural elements (well, in effect done so) by creating an entirely different structure around / through the abandoned element. In this case that might look like a steel truss either side of the beam that is connected via struts that go through the beam (you'd core for these and grout afterwards). It could be concealed by recessing it into the cover of the concrete and building the beam out a little bit either side.

TBH I would suspect it would be a lot of work and perhaps not even feasible in this case but I threw it out there just to get your creative juices flowing.


You have to be careful with this. Chemical anchoring does not replace development length or typical anchorage requirements. So if you simply replace the slab and dowel in new bars those bars should be treated as pinned only. This is not necessarily a problem but you must make sure the way you analyze the new slab / beam connection takes this into account. If you rely on that connection to transfer moment you may not be able to do so.

You will also want to consider where the effective face of the shear support is given the new cold joint location. In restoration we would typically chip a 1" key to have a "shoulder" for the slab to rest on, and install an angle iron below which effectively extends the face of the shear support. The angle is then encased in a concrete haunch as fireproofing during the slab pour.


Not a single stone, no. But several stones combined with a T-test would do just fine (you can code one up in the free R software easy as pie). The T-distribution was designed for small sample sizes of this kind and will give you a distribution of the mean compressive strength. I'd probably take the compressive strength to be the 5th percentile of whatever distribution you get, but to be sure, I am not aware of any code that tells you exactly what probability is the correct mark. You'll have to use your engineering judgement on that one.

Of course don't just look at the T-distribution. Compare that to known compressive strength of stones of a similar era and see if it makes sense.