Live load reduction on double-tee section

[Prestressed Guy]

On a precast 10' wide double-tee with two 24" tall x (2) 5" wide stems at 5' o.c. would you use the trib area to each stem for loaded area or the totoal of both stems.
In other words, for a 10' x 60' DT
1. Would you use 600Sf and assume that that the two stems 5' appart were both effective and working together
2. Would you look at them as two 5' x 60' single stem members with 300Sf and assume that that each stem constitued a member.

 

[dik]

I would not be using LL reduction on single elements and if considered it should be on the tributary area of the single T.

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

-Dik

 

[Settingsun]

Worst case might be 3/4 or less width pattern loading. For these dimensions, that would mean little to no reduction.

 

[JLNJ]

I probably would not specify live load reduction on a single element, even one 600 sq ft, for a new installation, but if I were checking an existing member for some specific, known loads I would probably consider it and use the full 600 sq ft.

 

[MIStructE_IRE]

Would you take a blanket reduction on a flat slab? Of course not, so its not applicable here in my view.

 

[Prestressed Guy]

MIStructE_IRE (Structural)4 Jul 21 22:12
Would you take a blanket reduction on a flat slab? Of course not, so its not applicable here in my view.
The answer to this question according to ASCE 7-10 is YES.
"Section 4.7.6 Limitaions on One-Way Slabs The tributary area, At, of one-way slabs shall not exceed the area defineed by the slab span times a width normal to the span of 1.5 times the slab span"
So if the one-way slab spans 20' you can use a value of 20' x (1.5x20) = 600sq-ft.

 

[MIStructE_IRE]

What I mean is, you can take a live load reduction on a slab to design the member which supports it. However you can’t reduce the load on the slab to design the slab itself - as far as I understand it.

 

[dik]

and for each beam stem, you can only use half the width... I still wouldn't do it...

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

-Dik

 

[KootK]

I feel like you could make a pretty good ASCE7 argument for the full 10' width based on the concept below. Whether or not that adds up to anything meaningful is OP's purview.

 

[dik]

I suspect that if the topping were continuous and the beam stems were at 5' centres, that you could use a trib width of 5' for the beam design, not 10'... just my take... has nothing to do with the shear connection. If they were a series of floor joists at 5' centres and you had 50 of them... you could not count on a trib area of 50x5' x span.

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

-Dik

 

[Prestressed Guy]

Just a bit more info to fill in gaps that have been speculated on.
These will be topped double-tees with 2½" flange and 4" composite topping. My thoughts were that the topping is not sufficently stiff to provide any lateral redistribution so area would be only one stem with 5" width.

 

[dik]

I think you treat it based on trib area, and not 'load sharing' as you do with wood construction.

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

-Dik

 

[BAretired]

Forget about live load reduction, unless you are checking an existing double tee.

BA