Prestressed Double Tee with Tension Rebar

[bswartz]

I'm looking for some direction on how to approach analyzing an exisiting precast prestressed double tee circa 1960's mfr. by Concrete Masonry Corporation, Inc. (CMC) in Elyria Ohio (out of business). We exposed the rib reinforcing and there is (1) #5 deformed bar 1-1/4" from the bottom, and (1) 7/32" wire strand 1-3/4" above that. The tee is 12" overall deep with 1-1/2" flange/slab thickness (10 1/2" exposed rib/web which tapers 5-1/2" down to 2-1/2". 4'-0" wide, 2'-0" c/c ribs. They span 41 feet and are for roof load in Ohio. Should be around 25 psf LL + 20 psf DL minimum. I found a salesman from that company who thought the prestress was .7ultimate with most strands being 250k yield.

 

[slickdeals]

You will need to calculate the moment capacity of this section based on geometry and reinforcing, compare to the moment induced due to loading. You can use the PCI Design Manual to go over the steps in case you haven't done one before.

We are Virginia Tech
Go HOKIES

 

[slickdeals]

You can look at Example 4.2.1.4 on Page 4-15 for guidance.

We are Virginia Tech
Go HOKIES

 

[bswartz]

I have the PCI 6th - have not done a prestress before -- how to I analyize the non-prestressed #5 bar along with the prestressed strand? I can do each seperately, but have never seen them together...thanks!

 

[bswartz]

OK - Using PCI Ex. 4.2.1.4 I get such a low Mn...12" deep double tee spanning 41 feet is troublesome....

 

[hokie66]

Yes, that sounds flimsy.

 

[jenofstructures]

use can use the examples on the PCI

in our case, when designing the rebars for double tee, we only used the topping then. but not we are using the topping plus the concrete cover of double tee in design, so making our total depth of 4.5 (if your topping is 3" and the concrete cover is 1.5").

for example, a 10DT24 has a total width of 120 inches,but the inner part of it (excluding the overhang) only measures 5ft. your loading wu=1.6*25psf + 1.2*20psf = 64psf.
Get the moment in the inner part of the double tee, Mu=wu*5ft^2/12. from that moment design the reinforcing bar needed.




Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds