Strength of concrete cantilever
Strength of concrete cantilever
(OP)
A new truck maintenance building has a 183' long fiberglass trench drain with variable depth of 6" to 13" below fin. floor. The top of the trench drain is a attached to steel angles w/ Nelson studs that were cast into the thickened concrete floor. Due to improper bracing & over-vibration of the concrete during installation, the trench body is twisted out of vertical alignment by varying amounts along its length. In the worst instance, there is now a 1 1/2"H x 7"V triangular "lip" of concrete (rather than a vertical face) supporting the trench frame. The contractor won't warrantee the installation for more than 1 year & the owner wants it replaced because he expects this lip to crack off in the future (as do I). Besides finite element analysis programs (our company doesn't have that capability), what design procedures/standards/formulas are applicable to produce hard data (rather than empirical knowledge) that this installation will fail after repeated loadings? I've asked other engineers I know & they're stumped as well. Any advice would be appreciated.






RE: Strength of concrete cantilever
I'd say, if it looks screwed up and both you and the owner agree...then fix it.
All the FEA in the world can't justify botched workmanship.
RE: Strength of concrete cantilever
RE: Strength of concrete cantilever
The crack will most likely develop at floor level, parallel with the trench. The thickened slab extends below the trench & encases it. How do you propose modeling this for beam depth, length & load application, as well as fatigue?
RE: Strength of concrete cantilever
Also, I'd agree with ToadJones - the contractor screwed up and didn't construct the drain properly. There isn't (or shouldn't be) any cost to the Owner for this.
"Being Stupid should hurt"
RE: Strength of concrete cantilever
BA
RE: Strength of concrete cantilever
RE: Strength of concrete cantilever
RE: Strength of concrete cantilever
RE: Strength of concrete cantilever
If there is rebar in there and the cover is correct I doubt it will crack. But I guess you need proof. Although the contractor's contractual warranty is only for 12 months I expect he is legally liable for a longer period for defective work.
You have to check the contract but it is possible that at the end of the 12 month warranty the warranty period can be extended for the defects picked up in the final inspection.
RE: Strength of concrete cantilever
I don't believe that strength is affected by the twist during pouring. If the drain functions properly, the only issue is whether or not the work is deemed acceptable. The contractor did not conform to the intended geometry shown on the drawings, so he did not meet normal criteria for acceptance.
Perhaps a financial adjustment could be made which would be accepted by all parties. This would be based on the unarguable fact that the contractor did not deliver what was specified.
BA
RE: Strength of concrete cantilever
What is the lengthand spacing of the Nelson stud?
Is there any other rebar which would intersect the failure plane?
I think that the Nelson studs should prevent the 'cantilever' from breaking off, depending on length and spacing.
RE: Strength of concrete cantilever
BA
RE: Strength of concrete cantilever
I believe this is what's is meant by 'cantilever'. That is using a broad definition of the word.
RE: Strength of concrete cantilever
BA
RE: Strength of concrete cantilever
I also don't see this failing unless there are further workmanship issues that cannot be seen on a sketch.
RE: Strength of concrete cantilever
If it was at 80deg to the vertical say, cantilever would be a correct term.
The risk of failure increases as the deviation from vertical increases.
The question is whether the risk has increased significantly at 12deg. I would say no, if the potential failure plane is crossed by studs/rebar. I don't know if that's not the case.
RE: Strength of concrete cantilever
RE: Strength of concrete cantilever
It is just a bad installation job.
...it reminds me of when I build my house and install my sump well in the basement, but left the lid off. The concrete finishers I hired to do the basement slab poured the concrete around the sump well and "smooshed" it out-of-round and the lid would not sit afterwards. The floor looks absolutely beautiful though
RE: Strength of concrete cantilever
Your specification should have a Quality Assurance section that puts a tolerance on formed surfaces, and some verbiage about rejecting out of tolerance work.
RE: Strength of concrete cantilever
The probable failure planes are shown in red on the attached sketch. The failure plane on the left is not significantly narrower on the left side of the trench than on the right side, nor is it significantly narrower than it would be if the trench had been constructed properly.
BA