Relocated Building - Slab on Grade becomes Elevated
Relocated Building - Slab on Grade becomes Elevated
(OP)
We are relocating a building in which a slab on grade is going to become and elevated slab. The building mover is proposing a system of masonry piers 24" SQ spaced at 4'-0" OC each way to sit the new slab on. They will grout beneath the bearings at the piers to ensure direct bearing. They said they have done this numerous of times and have had no problems during or after the move nor did they have any problems with the building officials.
We were asked to provide foundation design for the relocated building. When reading ACI 318, Chapter 22, specifically says that structural plain concrete shall be limited to members that are continuously supported by soil or supported by other structural members capable of providing continuous vertical support. Even though the slab may be reinforced with 6x6 W1.4 W1.4 WWF, it is still considered "plain" concrete per definitions section of ACI. I checked the flexural and shear capacities of the 4" SOG for the 4' clear span and they are all within the limits, however the code says you can't do this.
One way is to fill the space underneath the slab with grout or a flowable fill essentially turning it back into a slab on grade, however, this would be very costly. Maybe you could compact the site beneath the building and pump sand under the building since sand doesn't compact. Any other ideas?
Has anyone come across this? This is a commercial building (Dr. Office) and not a house.
Any tips or advice would be appreciated.
Thanks in advance
We were asked to provide foundation design for the relocated building. When reading ACI 318, Chapter 22, specifically says that structural plain concrete shall be limited to members that are continuously supported by soil or supported by other structural members capable of providing continuous vertical support. Even though the slab may be reinforced with 6x6 W1.4 W1.4 WWF, it is still considered "plain" concrete per definitions section of ACI. I checked the flexural and shear capacities of the 4" SOG for the 4' clear span and they are all within the limits, however the code says you can't do this.
One way is to fill the space underneath the slab with grout or a flowable fill essentially turning it back into a slab on grade, however, this would be very costly. Maybe you could compact the site beneath the building and pump sand under the building since sand doesn't compact. Any other ideas?
Has anyone come across this? This is a commercial building (Dr. Office) and not a house.
Any tips or advice would be appreciated.
Thanks in advance






RE: Relocated Building - Slab on Grade becomes Elevated
RE: Relocated Building - Slab on Grade becomes Elevated
RE: Relocated Building - Slab on Grade becomes Elevated
RE: Relocated Building - Slab on Grade becomes Elevated
RE: Relocated Building - Slab on Grade becomes Elevated
If the existing slab is being reused it would be advantageous to place as much fill as possible prior to placing the slab. I doubt that pumped sand will not compact.
RE: Relocated Building - Slab on Grade becomes Elevated
Advice: don't get involved in silly schemes.
RE: Relocated Building - Slab on Grade becomes Elevated
Mike McCann
MMC Engineering
RE: Relocated Building - Slab on Grade becomes Elevated
RE: Relocated Building - Slab on Grade becomes Elevated
I've actually seen this more than once in Florida where houses are built on slabs with thickend edges at the perimeter below a masonry wall, difficult to move without slab. They decided to put in a new road or bridge and had a bunch of reasonably decent homes in the way so they moved them. Then gave me a call to look at cracking slabs and masonry walls where the slab was set on masonry piers 4' o.c. Told them to fill the crawl space with flowable concrete fill.
They didn't like that answer and called another guy.
good luck
RE: Relocated Building - Slab on Grade becomes Elevated
RE: Relocated Building - Slab on Grade becomes Elevated
lkjh345 has a good point. Economics. Perhaps a sit down meeting with the moving contractor to have him show you the cost of shoring and supporting the slab during excavation, lifting, moving and setting back down would be a good place to start. And also ask him what he will do if the slab cracks somewhere in the middle of this process. Will he pay you for it? Or just say "act of God, so give me my $"?
Then call up the local concrete guys, who according to my global economic outlook are pretty slow and will cut you a good deal just to stay competitive.
Your answer will be at the end of those two numbers.
The reason the moving contractor wants to move it is because he knows that he will profit $$ big time.
RE: Relocated Building - Slab on Grade becomes Elevated
Therein lies the innate problem with this idea - the viability of the walls and slab after the move. The slab alone has top be at least 50% of the dead load of the building.
No mention in the original post about CMU walls - I was assuming wood. The CMU would complicate it further, but actually stiffen the edge of the slab, in addition to any thickening of the slab. Any thickened edge of the slab would make it hard to swhore under the slab prior to any lift. I would not want to be the tunnel jockey that had to crawl under the slab next to the shoring/lifting beam to install the shims to the slab...
So...what is the actual existing construction of the foundation here?
Mike McCann
MMC Engineering
RE: Relocated Building - Slab on Grade becomes Elevated
Mike McCann
MMC Engineering
RE: Relocated Building - Slab on Grade becomes Elevated
Extension to my original suggestion to add wood joists on top of the pedestals - how about make it a wood sub-floor to sustain the floor loads including the 4" concrete slab? The house can directly set on the new foundation and sub-floor, the 4" SOG can be left as flooring, or demo later. For 4'x4' spans, wood expert, now is your time to say something.
RE: Relocated Building - Slab on Grade becomes Elevated