Pre-stressed double tee capacity check

[Torres_Structural]

I'm working on a warehouse project renovation which was done back in the 60s-70s. The main level floor has a pre-cast double tee system that will be later used for a trash enclosure with a trash compactor. The existing drawings of the project include a typical detail for a prestressed double tee that is 5'7" wide by 22 1/2" deep, and 4" flanges. I've looked at all the PCI manuals to see if this is a typical section provided on their with load tables, but no luck. I'm trying to get the ultimate capacity and run checks on the actual double tee, but i cant get a solid example to walk me through it. Does anyone have any further information on this subject, or resources that i can review? TIA

 

[Ingenuity]

So you are looking to calculate the ulitmate flexural moment capacity, and probaly shear capacity too? Go back to first principles.

The sketch states 92 kips of final prestressing force (assuming they refer to effective force), so that is only 3 or maybe 4 x 0.5" strands (seems small). It appears they have depressed some strands OR they have slipped (debonded) some at the ends, becuase the CG at the ends of the DT differs from the CG at the center.

For an approximate midspan Mult capacity check, assume 3 or 4 x 0.5" diameter strands, assume a strand pattern at midspan (that results in a cG of 6.1"), and go through the usually ultimate flexural moment capacity calculations, i.e. assume max concrete compression strain of 0.003, etc. PCI Design Handbook 6th Edition has a part-worked exmaple of a DT for Mult with some debonded strands, that may be of assistance.

If you don't have the original precast DT shop draiwngs, and you need more accurate info, then you are going to have to confirm the as-builts strand #, dia and spacing, possibly via exploratory probing.

 

[WARose]

I'm trying to get the ultimate capacity and run checks on the actual double tee, but i cant get a solid example to walk me through it. Does anyone have any further information on this subject, or resources that i can review? TIA

I personally think the best reference on precast concrete (besides the PCI handbook) is: 'Prestressed Concrete: A Fundamental Approach', by Edward G. Nawy. I don't know what edition he is up to now.....but in the edition I have, he walks through the design process (step by step) with a number of section types.