Parking Deck LFRS 1

[WARose]

I am looking at a existing parking deck to check a variety of things. This thing was built in about 1998.....and I (of course) have no drawings. One thing I cannot figure with this thing is: what is the diaphragm? It appears to be just a bunch of double Tees spanning between girders (with no topping slab). And the girders sit on a corbel that is part of the column. So is the lateral force transferring by friction? I see no connection (other than bearing) between the Tees & girders and the girders & columns.

I ask here because I figure there is a design philosophy with these things......and I have never done one.

 

[dik]

Do the DTs have weld plates to connect eachother?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[WARose]

Do the DTs have weld plates to connect eachother?

Nope.

 

[KootK]

What?!? Are you sure about the absence of the TT flange connectors? They're typically something like the vector connectors shown below and can be a bit difficult to spot if you don't know what to look for. If there really is no connection between tee flanges then you're likely either looking at something that was done incorrectly or, at the least, unconventionally. Usually you've got shear connections of some stripe around all of the perimeter edges of these kinds of structures to the beams & walls at the perimeter that perform the boundary element function.

 

[WARose]

What?!? Are you sure about the absence of the TT flange connectors?

About as sure as I can be: they are not visible from the top or bottoms of the Tee.

 

[KootK]

It is normal for these things to be covered with grout from the top and only very marginally visible from the bottom. That said, I will of course take you at your word if you say that there's nothing there. Unfortunately, in the absence of any kind of flange to flange shear connection, your diaphragm really becomes your beams acting in weak axis.

 

[WARose]

So what you are saying is: for something made in '98....it is highly unlikely it doesn't have this right? (It's just not visible)

 

[KootK]

Yes, exactly.

 

[WARose]

Thanks Kootk

 

[KootK]

No sweat, hopefully the connectors are actually there to be found. As a more pedestrian matter, the same connection is usually relied upon to keep differential movement and camber from creating an elevation step at the flange junction. Having no connection at all strikes me as a bit risky in this respect.

 

[dik]

Can you use a metal detector? or GPR? I would have thought they would be there... we can save a buck if we don't put them in... they're common even with a concrete topping... I haven't seen a DT floor without topping, come to think of it.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[spaseur]

I worked for a firm in the 80s that did audits for the PCI certification program. I cannot remember seeing a double tee that did not have weld plates at the sides of the flanges to connect the tees together. Particularly if it was an untopped tee. It not only provided for some diaphragm action it also help to control the relative deflection between the tees. You do not want on tee deflection as you drive up the ramps and the adjacent tee be up.