CMU FLOORS POST TENSION
CMU FLOORS POST TENSION
(OP)
Good morning. About a week ago we were contact to go look at some apartments. The apartments are a two story cmu walls. The floors are also cmu, they use some kind of post tension system, I am posting a picture. Well, the problem is, at the end of the cantilever the rods and anchor plates are corroded. I was trying to tell the owner that we do not know how far the steel rods are corroded, that it is dangerous. He came back and told us that he had removed some of the grout near the wall and it appears the steel is not corroded at the face of the wall. He wants to remove the cantilever and reattach the tension rods to and anchor plate. Have any of you guys have done something similar. I do not want to touch this job, but is something interesting to know, how where they designed, if any ones has knowledge of this type of construction please provide some input.
Thanks
Thanks






RE: CMU FLOORS POST TENSION
I can't say there's never been any prestressed CMU floors, but I've never run into them.
RE: CMU FLOORS POST TENSION
Looks to me that Jed may be correct.
Ralph
Structures Consulting
Northeast USA
RE: CMU FLOORS POST TENSION
RE: CMU FLOORS POST TENSION
What a unique way to construct a floor system!
I'd find the engineer who devised this method and ask him/her how they anticipated the means to repair/alter the floor structure.
We always learn from methods that do not work well. Perhaps this engineer needs a crash course in repair methods.
Ralph
Structures Consulting
Northeast USA
RE: CMU FLOORS POST TENSION
RE: CMU FLOORS POST TENSION
I am not sure when was designed, and sure do not know who was the EOR, the owner does not have any drawings. I do not know how old is the building.
RE: CMU FLOORS POST TENSION
RE: CMU FLOORS POST TENSION
See below... Also see the ICBO archive for ICBO Report 2692 from December of 1974.
Mike McCann
MMC Engineering
RE: CMU FLOORS POST TENSION
RE: CMU FLOORS POST TENSION
Now where have I heard that logic before?
Mike McCann
MMC Engineering
RE: CMU FLOORS POST TENSION
The rods in the bottom (at the sides) must be just to pull it together but any tension in them would be counterproductive to say the least. If that is their purpose, it looks like an over complication use to attach the handrailing system to them.
We are seeing the cantilever, not the slab itself, I wonder what that looks like.
Where is this job?
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: CMU FLOORS POST TENSION
I have only looked at a couple of buildings using this structural system. Both were built in the mid to late 1970's.
RE: CMU FLOORS POST TENSION
In the second photo, there is a rusted bolt end and bearing plate implying that the bolt could extend into the top portion of the center rib of a CMU unit.
Mike McCann
MMC Engineering
RE: CMU FLOORS POST TENSION
RE: CMU FLOORS POST TENSION
Nevertheless, the Devil's in the details...
Mike McCann
MMC Engineering
RE: CMU FLOORS POST TENSION
RE: CMU FLOORS POST TENSION
RE: CMU FLOORS POST TENSION
I doubt the system was "post-tensioned" in the sense of active pre-compression given that the threaded rod would have to be of high-strength to overcome concrete creep losses, and the magnitude of any prestress would be negligible given the very small rod sectional area and the small end-bearing "anchorage" plates.
What is the magnitude of the main span?
Is there any significant deflection in the main span?
In the topping slab non bonded to the blocks? because there appears to be a layer of some material at the exposed edge under the topping.
RE: CMU FLOORS POST TENSION
Some are just floor filler systems that use either small prestressed beams or bar joists at about 16" o.c. because of the size of the filler elements (concrete block or clay tile)
Some of the DOX block systems (and varients) used block that were precision ground on 2 faces for complete bearing as part of the concrete unit manufacturing process. The DOX block were delivered to the site or block were stressed into a 16" wide beam and delivered and erected with a crane.
As you see there are any variations with different block, details and methods of construction. Most were prestressed.
How about the one and two story homes in some of Europe that had interior floors using a floor filler section with a 2" topping. Some even used small prestressed beams (made on 400' long beds, and cut to the desired lengths to achieve a sloped roof with clay or block infill. - The frown on wood for housing in many areas. In MI in about 1950, there was a store built using roof block trusses for longer spans. There seems to be no end of the "unique" systems around the world.
The project shown in the OP is probably some sort of a hybrid that was used by a local engineer working with a local supplier.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.