Connecting a New Foundation to an Existing
Connecting a New Foundation to an Existing
(OP)
I have been asked by a client to design a foundation for a building which will cover an existing structure (a concrete aggregate bin). The bin sits on a large mat foundation and the dimensions of this new building are very tight to the existing structure.
Before I had known that the existing foundation was so large I had sized footings which apparently will now interfere with the corners of the existing matt. The new building only has four columns. The contractor thinks this is a simple issue and wants me to simply put a large notch in my footing and tie into the existing matt.
I was going to resort to building a model in RISA to see how my new irregular footing and the existing mat footing would interact if knitted together. Is this overcomplicating the issue? I am interested to hear how others would approach this problem.
I also have a question about how they plan to tie the two foundations together. The contractor says that they just drill holes in the existing foundation and hammer in rebar that fits tight in the hole and then pour the new foundations around the bar. They claim that have done this for years and they do not use epoxy, grout or any other kind of bonding agent. Is this common? I plan to specify Hilti expoxy and whatever size rebar is required to meet the shear load.
Any thoughts or comments are greatly appreciated.
Thanks!
Before I had known that the existing foundation was so large I had sized footings which apparently will now interfere with the corners of the existing matt. The new building only has four columns. The contractor thinks this is a simple issue and wants me to simply put a large notch in my footing and tie into the existing matt.
I was going to resort to building a model in RISA to see how my new irregular footing and the existing mat footing would interact if knitted together. Is this overcomplicating the issue? I am interested to hear how others would approach this problem.
I also have a question about how they plan to tie the two foundations together. The contractor says that they just drill holes in the existing foundation and hammer in rebar that fits tight in the hole and then pour the new foundations around the bar. They claim that have done this for years and they do not use epoxy, grout or any other kind of bonding agent. Is this common? I plan to specify Hilti expoxy and whatever size rebar is required to meet the shear load.
Any thoughts or comments are greatly appreciated.
Thanks!






RE: Connecting a New Foundation to an Existing
I have a feeling that the large mat foundation for the aggregate bin is large enough and a chip out should not create any problem? If this is the case, why to tie the new foundation with the old one? Chip out existing foundation as needed, place some bond breaker at the interface and pour the new foundation. This bond breaker should make the new foundation work as per design.
RE: Connecting a New Foundation to an Existing
I would guess the contractor has little appreciation for your work.
RE: Connecting a New Foundation to an Existing
Mike McCann
McCann Engineering
RE: Connecting a New Foundation to an Existing
You are right about the contractor jike. He is used to dealing with a fly by the seat of your pants old timer who had 50 years of experience and would eyeball alot of the stuff right on the spot for him. Unfortunately I do not have all that experience to draw upon so when I need to take a few days to look at something he doesn't understand the delay.
Regardless of whether or not there is interference with the mat foundation I was still planning to tie my new footing into the 12" thick slab which is poured over the whole site. This is to resist some of the large horizontal forces from the PEMB. So this brings me back to my other question regarding the rebar dry driven into holes in the existing concrete. Has anyone else used this method or heard of it being used?
Thanks again!
RE: Connecting a New Foundation to an Existing
Typically the design of the mat for an aggregate bin is controlled by wind or seismic. So the size of the mat is more than likely related to the mass needed to resist the overturning of the bin. This could be checked rather easily from some rough estimations. If the bin foundation is controlled by wind, then once the bin is enclosed, the wind is only acting on the building. Just increase the area of the bin foundation to what ever is required by your design and set the columns. If the bin foundation is controlled by seismic, then the bin foundation would need to be checked a little more closely with the building loads added to it.
In either case, by extending each side of the bin foundation, your essentially creating a larger mat to support both the bin and the building.
The contractor's method of drilling a hole and hammering the rebar tight is probably not something I would want to take responsibility for on a design. If the rebar did end up fitting tight, then friction is the only thing resisting the forces. You're on the right track by specifying Hilti and the bar size required.
RE: Connecting a New Foundation to an Existing
RE: Connecting a New Foundation to an Existing
RE: Connecting a New Foundation to an Existing
RE: Connecting a New Foundation to an Existing