Early / Partial Loading on Recently Placed Concrete Foundations
Early / Partial Loading on Recently Placed Concrete Foundations
(OP)
A discussion in our office has come up regarding placement of structural steel columns & overhead crane runway beams on recently placed foundations. We recognize that concrete reaches published strength in the 28 day time frame. But if we simply want to erect the steel say 5 to 7 days after the pour, are there any downsides?
The current example is 8" tube columns with 18x18 base plates. When the crane is operational, the axial column load will be 26 kips. But, the column load due to weight of cranes & structure is only 6 kips.
Note also the anchors will be drilled & epoxy set in the new concrete
For many years we have erected crane systems quite soon after foundations are poured; with no apparent problems...but, someone has brought up the concern, and we want to understand this a better.
We have thought about "high-early" concrete... but we're not sure if this really resolves the potential problems.
If any of you have thoughts or experience on this topic, we would greatly appreciate your insight.
Regards;
The current example is 8" tube columns with 18x18 base plates. When the crane is operational, the axial column load will be 26 kips. But, the column load due to weight of cranes & structure is only 6 kips.
Note also the anchors will be drilled & epoxy set in the new concrete
For many years we have erected crane systems quite soon after foundations are poured; with no apparent problems...but, someone has brought up the concern, and we want to understand this a better.
We have thought about "high-early" concrete... but we're not sure if this really resolves the potential problems.
If any of you have thoughts or experience on this topic, we would greatly appreciate your insight.
Regards;






RE: Early / Partial Loading on Recently Placed Concrete Foundations
Compression would not normally be an issue.
Dik
RE: Early / Partial Loading on Recently Placed Concrete Foundations
RE: Early / Partial Loading on Recently Placed Concrete Foundations
Dik
RE: Early / Partial Loading on Recently Placed Concrete Foundations
RE: Early / Partial Loading on Recently Placed Concrete Foundations
If you allow steel erection to occur, say, at 7 days, then determine your current f'c value from 7 day breaks (or 5 day or 3 day - whatever) and then simply check the footing shear, moments, bearing, anchors, etc. for the anticipated loads between that early point in time and the 28 day mark.
This takes more work for you but if you already have your system analyzed, modeled, etc. then usually it is no trick to quickly check the lighter loads at the lower f'c.
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RE: Early / Partial Loading on Recently Placed Concrete Foundations
For the anchors, you have to get a Hilti judgement. Hilti will either tell you not to torque the anchors (tighten the nut) or to expect time-of-install strength. Other manufacturer's such as Simpson and Powers will not give a judgement.
RE: Early / Partial Loading on Recently Placed Concrete Foundations
Note... We ALWAYS epoxy set our own anchors because the cast-in-place guys cant get them right... No matter how hard they try... Crane runways must be set to very tight straightness tolerances
RE: Early / Partial Loading on Recently Placed Concrete Foundations
Otherwise, I agree with the others. But, the bottom line comes from the FlCraneEngineer responsible for the design.
RE: Early / Partial Loading on Recently Placed Concrete Foundations
I normally spec 28 day strength for legal/spec reasons... and sometimes stipulate a minimum concrete strength for things such as form stripping, anchor rods, etc.
Dik
RE: Early / Partial Loading on Recently Placed Concrete Foundations
dik: 28-day is the standard, absolutely. But you can specify 7-day, and the mix designer will meet it.