Precast Double Tee Dapped End

[KimWT]

Hi!

This picture shows some reinforcements around dapped end of typical double tee like 12DT30.
Is there any test data available with PLAIN concrete, no reinforcement?
In this case, which failure mode happens first? Bearing? Shear?

Thanks in advance!

KimWT

 

[MIStructE_IRE]

It doesn’t seem like a great idea not to have rebar there. My guess would be shear failure before bearing - but it depends on your load/span/bearing width/tee depth etc.

Without bars there, how are you dealing with shear?

 

[TehMightyEngineer]

Almost certainly shear failure first, without rebar there is nothing to take the horizontal tension. You could potentially make this work but I'd be extremely skeptical of it's long-term success. I use plain concrete shiplap joints all the time in precast but for non-critical connections like joints between panels and such.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[Agent666]

I doubt you will find any research on no reinforcement, because its just a terrible idea and certainly probably not worthy of any research effort for practical uses of double tees.

Usually as well there is a high degree of restraint due to shrinkage due to the prestressing and incompatibility once locked in with any topping, and wheres it going to crack to relieve these stresses/strains, most likely right where you don't want it to at the dapped end which you are reliant on for the gravity support of the unit.

Usually you need shear reinforcement at the ends as well to cover the case of the strands developing their strength and hence the shear strength developing any shear reinforcement further into the span.

 

[KimWT]

Thanks for your input!

This question sometimes happens.
For example, if you need to repair 10ft long DT with cutting stem,
do you want to increase/supplement concrete volume
or add additional plate/reinforcement?
If you have to cut stem by 4" or 6", do you have to add Av or Ash?
...
So, this test data will help me decide repair decision more confidently.

 

[BridgeSmith]

Double Tees are typically a precast section, which are also typically prestressed. That looks fairly normal for a prestressed beam, where the compression of the strands increases the shear capacity of the concrete (except at the ends, where the strands aren't fully developed). Are you sure what you're looking at isn't just the mild reinforcing layout of a prestressed beam, with the strand layout shown elsewhere?