Shrinkage in Conc and Supporting Precast

[dcarr82775]

I have a project where I need to add some CIP beams below some existing double tees. The beams will support a vehicle loading traveling across the DT's. I estimate the height of the CIP beam will shrink between 1/64" and 1/32". What are people opinions/concerns regarding this gap and possible impact from the vehicle load closing this gap again and again over time?

I have no reasonable way to preload the system to remove this potential shrinkage gap. thanks

 

[paddingtongreen]

Make the gap bigger and dry pack or use a non shrink, flowable grout in the gap

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[hokie66]

Could you not post-tension the new CIP beams to create some preload? But whatever you do, you should keep in mind that precast double tees do not take kindly to being supported in the middle of the span.

 

[dcarr82775]

I could PT the beams, but it would be very difficult. I don't want to get into the specifics as it would take page to explain it all. Grouting could work, designing in a large gap that gets filled in later after most of the shrinkage had occurred is probably the easiest way to go.

Hokie66, I understand what you mean. The new loading is only applied directly over the new CIP beams, the DT stem acts like a short column. As far as the DT knows its span hasn't changed as there is virtually no Live Load other then the vehicle. The DT is already there and supports the DL. I will not be getting negative moments, or substantially reduced positive moments in the DT

 

[hokie66]

Would a physical connection between the precast and the new beam be feasible? Maybe something bolted to the side of the tee webs.

 

[csd72]

paddingtongreens suggestion is the simplest and is exactly how it is done for underpinning under houses.